Hong Hao-Yi, Gao Mei-Qi, Gui Long-Cheng, Hua Jun, Liang Jian, Shi Jun, Zou Jin-Tao
Understanding the statistical fluctuations of lattice observables over the gauge configurations is important both theoretically and practically. It provides physical insights to tackle the famous signal-to-noise problem and the sign problem, and inspires new thoughts in developing methodologies to improve the signal of lattice calculations. Among many efforts, exploring the connections between the real and imaginary parts of lattice numerical results is a novel way to learn about the lattice signal and error, since both the real and imaginary parts originate from the same sampling of gauge fields and their distributions over the gauge samples are in principle related. Specifically, by analyzing the distributions of the real and imaginary parts of quenched lattice two-point functions with high statistics and non-zero momentum, this work proposes a possible quantitative formula connecting these two distributions as R(x) = ∫dyS(y - x) [I(y)K(Uy)], where R(x) stands for the real-part distribution, I(x) the imaginary-part distribution, S(x) the underlying signal distribution and K(Ux) a kernel function of the gauge field. This theoretical assumption is of general validity since the kernel function contains the gauge field information that determines all the distributions. The formula is numerically verified by calculating the non-trivial statistical correlations of the real parts and the kernel-function-modified imaginary parts with further assumptions on the kernel function. It is found that the most naïve guess of K(Ux) = 1 does not work, which leads to no statistically significant correlation. Meanwhile, the assumption that K(Ux) is only a sign function works well, giving rise to ~ 70% correlation. Then, random distortions on the absolute values of the imaginary parts are added with different strength and the results show that even a small distortion, say 1%, would reduce the correlation between the real and imaginary parts down to less than 50%. This essentially proves that the observed ~ 70% correlation is highly non-trivial and the hypothesis of K(Ux) being a sign function captures at least some of the physical mechanisms behind the scenes. Employing this correlation, the variance of lattice results can be improved by around 40%. It is not a significant improvement in practice; however, this study offers an innovative strategy to understand the source of statistical uncertainties in lattice QCD and to improve the signal-to-noise ratios in lattice calculations. Further studies utilizing the power of machine learning on a variety of more precise lattice data will hopefully give better indication and constraint on the form of the kernel function.
{"title":"The Imaginary-Part Distribution of Lattice QCD Data and Signal Improvement","authors":"Hong Hao-Yi, Gao Mei-Qi, Gui Long-Cheng, Hua Jun, Liang Jian, Shi Jun, Zou Jin-Tao","doi":"10.7498/aps.72.20230869","DOIUrl":"https://doi.org/10.7498/aps.72.20230869","url":null,"abstract":"Understanding the statistical fluctuations of lattice observables over the gauge configurations is important both theoretically and practically. It provides physical insights to tackle the famous signal-to-noise problem and the sign problem, and inspires new thoughts in developing methodologies to improve the signal of lattice calculations. Among many efforts, exploring the connections between the real and imaginary parts of lattice numerical results is a novel way to learn about the lattice signal and error, since both the real and imaginary parts originate from the same sampling of gauge fields and their distributions over the gauge samples are in principle related. Specifically, by analyzing the distributions of the real and imaginary parts of quenched lattice two-point functions with high statistics and non-zero momentum, this work proposes a possible quantitative formula connecting these two distributions as R(x) = ∫dyS(y - x) [I(y)K(Uy)], where R(x) stands for the real-part distribution, I(x) the imaginary-part distribution, S(x) the underlying signal distribution and K(Ux) a kernel function of the gauge field. This theoretical assumption is of general validity since the kernel function contains the gauge field information that determines all the distributions. The formula is numerically verified by calculating the non-trivial statistical correlations of the real parts and the kernel-function-modified imaginary parts with further assumptions on the kernel function. It is found that the most naïve guess of K(Ux) = 1 does not work, which leads to no statistically significant correlation. Meanwhile, the assumption that K(Ux) is only a sign function works well, giving rise to ~ 70% correlation. Then, random distortions on the absolute values of the imaginary parts are added with different strength and the results show that even a small distortion, say 1%, would reduce the correlation between the real and imaginary parts down to less than 50%. This essentially proves that the observed ~ 70% correlation is highly non-trivial and the hypothesis of K(Ux) being a sign function captures at least some of the physical mechanisms behind the scenes. Employing this correlation, the variance of lattice results can be improved by around 40%. It is not a significant improvement in practice; however, this study offers an innovative strategy to understand the source of statistical uncertainties in lattice QCD and to improve the signal-to-noise ratios in lattice calculations. Further studies utilizing the power of machine learning on a variety of more precise lattice data will hopefully give better indication and constraint on the form of the kernel function.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85466007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yuan Hong-Rui, Liu Tao, Zhu Tian-Xin, Liu Yun, Li Xiang, Chen Yang, Duan Chuan-Xi
Sulfur hexafluoride (SF６) is a greenhouse gas of very long lifetime. Its infrared absorption spectrum is very important for modeling the atmospheric radiation balances. SF６ is also a prototypical system for studying the principles and techniques of laser isotope separation using powerful infrared lasers. As a very heavy molecule, the infrared spectrum of SF６ at room temperature is very dense, which poses a great challenge for monitoring the relative abundances of different SF６ isotopomers by direct absorption spectroscopy. Supersonic jet expansions have been used widely to simplify gas phase molecular spectra. In this work, astigmatic multi-pass absorption cell and distributed feed-back quantum cascade lasers (QCLs) are used to measure jet-cooled rovibrational absorption spectrum of 32SF６ and 33SF６ at 10.6 μm. The spectrometer works in a segmented rapid-scan mode. The gas mixtures (SF6:Ar:He = 0.12:1:100) are expanded through a 80 mm×300 μm pulsed slit nozzle. Two QCLs running at room temperature are used and each one covers a spectral range of about 3.0 cm-1. The v3 fundamental bands of both 32SF６ and 33SF６ are observed. The rotational temperature of 32SF６ and 33SF６ in the ground state in the supersonic jet is estimated to be about 10 K and the linewidth is about 0.0008 cm-1 by comparing the simulated and observed spectrum with the PGOPHER program. A new weak vibrational band centered around 941.0 cm-1 is observed and tentatively assigned to the v1+v2+v3-(v1+v2)hot band of 32SF６. The effective Hamiltonian used to analyze the rovibrational spectrum of SF６ is briefly introduced. A simplified rotational analysis for this hot band is performed with the XTDS program developed by the Dijon group. The band-origin of this hot band is determined to be 941.1785(21) cm-1. The rotational temperature of this hot band is estimated to be about 50 K. A new scheme by measuring the jet-cooled absorption spectrum of this hot band of 32SF6 and the v3 fundamental band of 33SF６ is proposed for measuring the relative abundance of 33SF６／32SF６.
{"title":"High-resolution jet-cooled laser absorption spectroscopy of SF6 at 10.6 μm","authors":"Yuan Hong-Rui, Liu Tao, Zhu Tian-Xin, Liu Yun, Li Xiang, Chen Yang, Duan Chuan-Xi","doi":"10.7498/aps.72.20222285","DOIUrl":"https://doi.org/10.7498/aps.72.20222285","url":null,"abstract":"Sulfur hexafluoride (SF<sub>６</sub>) is a greenhouse gas of very long lifetime. Its infrared absorption spectrum is very important for modeling the atmospheric radiation balances. SF<sub>６</sub> is also a prototypical system for studying the principles and techniques of laser isotope separation using powerful infrared lasers. As a very heavy molecule, the infrared spectrum of SF<sub>６</sub> at room temperature is very dense, which poses a great challenge for monitoring the relative abundances of different SF<sub>６</sub> isotopomers by direct absorption spectroscopy. Supersonic jet expansions have been used widely to simplify gas phase molecular spectra. In this work, astigmatic multi-pass absorption cell and distributed feed-back quantum cascade lasers (QCLs) are used to measure jet-cooled rovibrational absorption spectrum of <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> at 10.6 μm. The spectrometer works in a segmented rapid-scan mode. The gas mixtures (SF<sub>6</sub>:Ar:He = 0.12:1:100) are expanded through a 80 mm×300 μm pulsed slit nozzle. Two QCLs running at room temperature are used and each one covers a spectral range of about 3.0 cm<sup>-1</sup>. The <i>v</i><sub>3</sub> fundamental bands of both <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> are observed. The rotational temperature of <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> in the ground state in the supersonic jet is estimated to be about 10 K and the linewidth is about 0.0008 cm<sup>-1</sup> by comparing the simulated and observed spectrum with the PGOPHER program. A new weak vibrational band centered around 941.0 cm<sup>-1</sup> is observed and tentatively assigned to the <i>v</i><sub>1</sub>+<i>v</i><sub>2</sub>+<i>v</i><sub>3</sub>-(<i>v</i><sub>1</sub>+<i>v</i><sub>2</sub>)hot band of <sup>32</sup>SF<sub>６</sub>. The effective Hamiltonian used to analyze the rovibrational spectrum of SF<sub>６</sub> is briefly introduced. A simplified rotational analysis for this hot band is performed with the XTDS program developed by the Dijon group. The band-origin of this hot band is determined to be 941.1785(21) cm<sup>-1</sup>. The rotational temperature of this hot band is estimated to be about 50 K. A new scheme by measuring the jet-cooled absorption spectrum of this hot band of <sup>32</sup>SF<sub>6</sub> and the <i>v</i><sub>3</sub> fundamental band of <sup>33</sup>SF<sub>６</sub> is proposed for measuring the relative abundance of <sup>33</sup>SF<sub>６</sub>／<sup>32</sup>SF<sub>６</sub>.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76611261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It is shown that discharges with negative triangularity have lower turbulence induced transport and better energy confinement, so the tokamaks with negative triangularity are recognized as a better choice for future fusion devices. In order to explore the features of the energetic particle driven instabilities with negative triangularity, the kinetic- magnetohydrodynamic hybrid code M3D-K has been applied to investigate the linear instability and nonlinear evolution of the fishbone driven by energetic ions with different triangularity. Based on EAST like parameters, it is found that negative triangularity destabilizes the ideal internal kink mode, but stabilizes the fishbone instability. Nonlinear simulations show that the fishbone instability with negative triangularity is hard to saturate without fluid nonlinearity. The possible explanation is that the orbits of fast ions locate more centrally with negative triagularity, so the energy exchange between energetic ions and the fishbone is more efficient than that with positive triangularity. These simulation results demonstrate that considering the fishbone driven by energetic particles, the negative triangularity does not confer a obvious advantage over the positive triangularity.
{"title":"Numerical simulations of fishbones driven by fast ions in negative triangularity tokamak","authors":"Ren Zhen-Zhen, Shen Wei","doi":"10.7498/aps.72.20230650","DOIUrl":"https://doi.org/10.7498/aps.72.20230650","url":null,"abstract":"It is shown that discharges with negative triangularity have lower turbulence induced transport and better energy confinement, so the tokamaks with negative triangularity are recognized as a better choice for future fusion devices. In order to explore the features of the energetic particle driven instabilities with negative triangularity, the kinetic- magnetohydrodynamic hybrid code M3D-K has been applied to investigate the linear instability and nonlinear evolution of the fishbone driven by energetic ions with different triangularity. Based on EAST like parameters, it is found that negative triangularity destabilizes the ideal internal kink mode, but stabilizes the fishbone instability. Nonlinear simulations show that the fishbone instability with negative triangularity is hard to saturate without fluid nonlinearity. The possible explanation is that the orbits of fast ions locate more centrally with negative triagularity, so the energy exchange between energetic ions and the fishbone is more efficient than that with positive triangularity. These simulation results demonstrate that considering the fishbone driven by energetic particles, the negative triangularity does not confer a obvious advantage over the positive triangularity.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76887094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Gao Wei, Yifan Luo, Xing Yu, Ding Peng, Chen Bin-Hui, Han Qing-Yan, Yan Xue-Wen, Zhang Cheng-Yun, Dong Jun
Building core-shell structures have been widely used to enhance and regulate the luminescence properties of rare-earth-doped micro/nano materials. In this work, a variety of different NaErF4 core-shell and core-shell-shell nanocrystals were successfully constructed based on high temperature co-precipitation method by epitaxial growth technology. The upconversion red emission intensity of Er3+ ions in different core-shell structures was effectively enhanced by regulating their structures and doping ions. The experimental structures show that the constructed core-shell nanocrystals are all hexagonal phase structure, and the size of the core-shell structure is about 40 nm. In the near infrared 980 nm laser excitation, the NaErF4 core-shell nanocrystals showed strong single-band red emission. And the single-band red emission intensity of Er3+ ions was enhanced through constructing the NaErF4@NaYbF4:2%Er3+ core-shell structures. The experimental results showed that red emission intensity of Er3+ ions was about 1.4 times higher than that of the NaErF4@NaYbF4 core-shell structures by constructing the NaErF4@NaYbF4:2%Er3+ core-shell structures under 980 nm excitation, and the red/green emission intensity ratio was increased from 5.4 to 6.5. Meanwhile, when NaErF4@NaYbF4:2%Er3+ core-shell structures have recoated the NaYF4 inert shell and introduced trace amounts of Tm3+ ions, the red emission intensity of Er3+ ions was 23.2 and 40.3 times compared with NaErF4@NaYbF4 core-shell structures, and the red/green emission intensity ratio reached 7.5 and 10.2, respectively. The red emssion enhancement of Er3+ ions was mainly caused by bidirectional energy transfer processes of high excitation energy of Yb3+ ions and energy trapping center of Tm3+ ions which effectively changed the densities of population of luminescent energy levels of Er3+ ions. What’s more, the coated NaYF4 inert shell also effectively reduced the surface quenching effect of nanocrystals. The mechanism of red enhancement in different core-shell structures were discussed based on the spectral properties, the processes of interion energy transfer and luminescence kinetics. The constructed NaErF4@NaYbF4:2%Er3+@NaYF4 core-shell structures with high-efficiency red emission in this work has great application potential in the fields of colorful anti-counterfeiting, display and biological imaging.
{"title":"Enhancing red upconversion emission of Er3+ by building NaErF4@NaYbF4:2%Er3+ core-shell structure","authors":"Gao Wei, Yifan Luo, Xing Yu, Ding Peng, Chen Bin-Hui, Han Qing-Yan, Yan Xue-Wen, Zhang Cheng-Yun, Dong Jun","doi":"10.7498/aps.72.20230762","DOIUrl":"https://doi.org/10.7498/aps.72.20230762","url":null,"abstract":"Building core-shell structures have been widely used to enhance and regulate the luminescence properties of rare-earth-doped micro/nano materials. In this work, a variety of different NaErF<sub>4</sub> core-shell and core-shell-shell nanocrystals were successfully constructed based on high temperature co-precipitation method by epitaxial growth technology. The upconversion red emission intensity of Er<sup>3+</sup> ions in different core-shell structures was effectively enhanced by regulating their structures and doping ions. The experimental structures show that the constructed core-shell nanocrystals are all hexagonal phase structure, and the size of the core-shell structure is about 40 nm. In the near infrared 980 nm laser excitation, the NaErF<sub>4</sub> core-shell nanocrystals showed strong single-band red emission. And the single-band red emission intensity of Er<sup>3+</sup> ions was enhanced through constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures. The experimental results showed that red emission intensity of Er<sup>3+</sup> ions was about 1.4 times higher than that of the NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structures by constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures under 980 nm excitation, and the red/green emission intensity ratio was increased from 5.4 to 6.5. Meanwhile, when NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures have recoated the NaYF<sub>4</sub> inert shell and introduced trace amounts of Tm<sup>3+</sup> ions, the red emission intensity of Er<sup>3+</sup> ions was 23.2 and 40.3 times compared with NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structures, and the red/green emission intensity ratio reached 7.5 and 10.2, respectively. The red emssion enhancement of Er<sup>3+</sup> ions was mainly caused by bidirectional energy transfer processes of high excitation energy of Yb<sup>3+</sup> ions and energy trapping center of Tm<sup>3+</sup> ions which effectively changed the densities of population of luminescent energy levels of Er<sup>3+</sup> ions. What’s more, the coated NaYF<sub>4</sub> inert shell also effectively reduced the surface quenching effect of nanocrystals. The mechanism of red enhancement in different core-shell structures were discussed based on the spectral properties, the processes of interion energy transfer and luminescence kinetics. The constructed NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYF<sub>4</sub> core-shell structures with high-efficiency red emission in this work has great application potential in the fields of colorful anti-counterfeiting, display and biological imaging.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76909564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
β-Ga2O3 has drawn much attention in the field of power and radio frequency electronics, due to an ultrawide bandgap energy of ∼4.9 eV and a high breakdown field strength of ~8 MV/ cm (Poncé et al, 2020 Physical Review Research.2 033102). The in-plane lattice mismatch of 2.4% between the (-201) plane of β-Ga2O3 and the (0002) plane of wurtzite AlN is beneficial for the formation of an AlN/β-Ga2O3 heterostructure (Sun et al, 2017 Appl. Phys. Lett.111 162105), which is a potential candidate for β-Ga2O3-based high electron mobility transistors (HEMTs). In this study, the Schrödinger-Poisson equations are solved to calculate the AlN/β-Ga2O3 conduction band profile and the 2DEG sheet density, based on the supposition that the 2DEG originates from door-like surface states distributed evenly below the AlN conduction band. The main scattering mechanisms in AlN/β-Ga2O3 heterostructures, i.e. the ionized impurity scattering, interface roughness scattering, acoustic deformation-potential scattering and polar optical phonon scattering are calculated using the Boltzmann transport theory, moreover, the relative importance of different scattering mechanisms is evaluated. The results show that at room temperature, the 2DEG sheet density increases with increasing AlN thickness, and reaches 1.0×1013cm-2 at an AlN thickness of 6 nm. With the increase of the 2DEG sheet density, the ionized impurity scattering limited mobility increases, but other scattering mechanisms limited mobilities decrease. The interface roughness scattering dominates the mobility at low and moderate temperatures (T<148 K), and the polar optical phonon scattering dominates the mobility at temperatures above 148 K. The room-temperature mobility is 368.6 cm2/Vs for the AlN/β-Ga2O3 heterostructure with an AlN thickness of 6 nm.
由于β-Ga2O3具有~ 4.9 eV的超宽带隙能量和~8 MV/ cm的高击穿场强，在功率和射频电子领域引起了广泛的关注(ponc等人，2020物理评论研究，2 033102)。β-Ga2O3的(-201)面与纤锌矿AlN的(0002)面之间存在2.4%的面内晶格失配，有利于形成AlN/β-Ga2O3异质结构(Sun et al .， 2017)。理论物理。Lett. 111 162105)，它是基于β- ga2o3的高电子迁移率晶体管(HEMTs)的潜在候选者。在本研究中，基于假设2DEG来源于均匀分布于AlN导带下方的门状表面态，求解Schrödinger-Poisson方程，计算AlN/β-Ga2O3导带剖面和2DEG片密度。利用玻尔兹曼输运理论计算了AlN/β-Ga2O3异质结构中的主要散射机制，即电离杂质散射、界面粗糙度散射、声变形势散射和极性光学声子散射，并对不同散射机制的相对重要性进行了评价。结果表明:在室温下，随着AlN厚度的增加，2DEG片密度逐渐增大，当AlN厚度为6 nm时达到1.0×1013cm-2;随着2DEG片密度的增加，离子杂质散射限制迁移率增加，而其他散射机制限制迁移率降低。AlN厚度为6 nm的AlN/β-Ga2O3异质结构在低温和中温(T2/Vs)下的迁移率主要由界面粗糙度散射决定。
{"title":"Studies on Mechanism of Electron Transport in AlN/β-Ga2O3 Heterostructures","authors":"Zhou Zhanhui, Li Qun, He Xiaomin","doi":"10.7498/aps.72.20221545","DOIUrl":"https://doi.org/10.7498/aps.72.20221545","url":null,"abstract":"β-Ga<sub>2</sub>O<sub>3</sub> has drawn much attention in the field of power and radio frequency electronics, due to an ultrawide bandgap energy of ∼4.9 eV and a high breakdown field strength of ~8 MV/ cm (Poncé et al, 2020 <i>Physical Review Research.</i> <b>2</b> 033102). The in-plane lattice mismatch of 2.4% between the (-201) plane of β-Ga<sub>2</sub>O<sub>3</sub> and the (0002) plane of wurtzite AlN is beneficial for the formation of an AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructure (Sun et al, 2017<i> Appl. Phys. Lett.</i> <b>111</b> 162105), which is a potential candidate for β-Ga<sub>2</sub>O<sub>3</sub>-based high electron mobility transistors (HEMTs). In this study, the Schrödinger-Poisson equations are solved to calculate the AlN/β-Ga<sub>2</sub>O<sub>3</sub> conduction band profile and the 2DEG sheet density, based on the supposition that the 2DEG originates from door-like surface states distributed evenly below the AlN conduction band. The main scattering mechanisms in AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructures, i.e. the ionized impurity scattering, interface roughness scattering, acoustic deformation-potential scattering and polar optical phonon scattering are calculated using the Boltzmann transport theory, moreover, the relative importance of different scattering mechanisms is evaluated. The results show that at room temperature, the 2DEG sheet density increases with increasing AlN thickness, and reaches 1.0×10<sup>13</sup>cm<sup>-2</sup> at an AlN thickness of 6 nm. With the increase of the 2DEG sheet density, the ionized impurity scattering limited mobility increases, but other scattering mechanisms limited mobilities decrease. The interface roughness scattering dominates the mobility at low and moderate temperatures (T<148 K), and the polar optical phonon scattering dominates the mobility at temperatures above 148 K. The room-temperature mobility is 368.6 cm<sup>2</sup>/Vs for the AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructure with an AlN thickness of 6 nm.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77159046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Huang Zhi-Qiu, Zhang Meng, Peng Zhi-Min, Wang Zhen, Yang Qian-suo
Using numerical simulation and a constructed cavity ring-down spectroscopy device, the influence of the finite coherence of the injected laser on the coupling process between the injected light and the cavity longitudinal mode was studied. The finite coherence of the injected light leads to the randomness of the coupling pulse during frequency scanning. The randomness is mainly reflected in two aspects: Firstly, as the coherence length decreases, the random amplitude range of the coupling pulse increases. Secondly, as the coherence of the injected light deteriorates, the coupling pulse changes from a single pulse with intensity evolution to continuous multiple pulses, and the overall width gradually increases with the decrease of the scanning rate. Moreover, with the deterioration of the coherence, when the light intensity of the cavity is used to turn off the injected light, the decrease in the scanning rate can cause more than one injection shut-off and ring-down event in a frequency coupling process, especially when scanning with the length of the cavity. In addition, a theoretical method is proposed to estimate the ring-down time using the strength integral of different time intervals, and the relevant experimental verification is carried out. The experimental results show that the relative error of the ring-down time obtained by the intensity integration method is smaller than that obtained by the traditional fitting method.
{"title":"The influence of the finite coherence of injected light on the ring-down cavity measurement method and the intensity integral method for the ring-down time determination","authors":"Huang Zhi-Qiu, Zhang Meng, Peng Zhi-Min, Wang Zhen, Yang Qian-suo","doi":"10.7498/aps.72.20230448","DOIUrl":"https://doi.org/10.7498/aps.72.20230448","url":null,"abstract":"Using numerical simulation and a constructed cavity ring-down spectroscopy device, the influence of the finite coherence of the injected laser on the coupling process between the injected light and the cavity longitudinal mode was studied. The finite coherence of the injected light leads to the randomness of the coupling pulse during frequency scanning. The randomness is mainly reflected in two aspects: Firstly, as the coherence length decreases, the random amplitude range of the coupling pulse increases. Secondly, as the coherence of the injected light deteriorates, the coupling pulse changes from a single pulse with intensity evolution to continuous multiple pulses, and the overall width gradually increases with the decrease of the scanning rate. Moreover, with the deterioration of the coherence, when the light intensity of the cavity is used to turn off the injected light, the decrease in the scanning rate can cause more than one injection shut-off and ring-down event in a frequency coupling process, especially when scanning with the length of the cavity. In addition, a theoretical method is proposed to estimate the ring-down time using the strength integral of different time intervals, and the relevant experimental verification is carried out. The experimental results show that the relative error of the ring-down time obtained by the intensity integration method is smaller than that obtained by the traditional fitting method.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77210397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Magnetic topological insulators have been a significant focus in the research of condensed matter physics over the past decade. The intricate interplay between the nontrivial band topology and spin, orbit, charge, and dimensionality degrees of freedom can give rise to a plethora of exotic topological quantum states and topological phase transitions. Measuring the transport properties of magnetic topological insulators is a crucial approach to exploring their exotic properties, which bears significant scientific importance in deepening our understanding of topological quantum states. Simultaneously, it also holds substantial potential for application in the development of novel low-power electronic devices. This article reviews the recent experimental advancements in transport studies of magnetic topological insulators in the past few years, encompassing the quantum anomalous Hall effect and topological quantum phase transitions in magnetically doped topological insulators, the quantum anomalous Hall phase, axion insulator phase and Chern insulator phase in intrinsic antiferromagnetic topological insulator MnBi2Te4, as well as the helical phase emerged from the Chern insulator in pulsed high magnetic fields. Finally, this article analyzes the future direction of development in magnetic topological insulators and the transport phenomena that remain to be understood in these systems, offering insights and perspectives on the potential breakthroughs to be achieved in this area of research.
{"title":"Quantum Transport Phenomena in Magnetic Topological Insulators","authors":"Chang Liu, Yayu Wang","doi":"10.7498/aps.72.20230690","DOIUrl":"https://doi.org/10.7498/aps.72.20230690","url":null,"abstract":"Magnetic topological insulators have been a significant focus in the research of condensed matter physics over the past decade. The intricate interplay between the nontrivial band topology and spin, orbit, charge, and dimensionality degrees of freedom can give rise to a plethora of exotic topological quantum states and topological phase transitions. Measuring the transport properties of magnetic topological insulators is a crucial approach to exploring their exotic properties, which bears significant scientific importance in deepening our understanding of topological quantum states. Simultaneously, it also holds substantial potential for application in the development of novel low-power electronic devices. This article reviews the recent experimental advancements in transport studies of magnetic topological insulators in the past few years, encompassing the quantum anomalous Hall effect and topological quantum phase transitions in magnetically doped topological insulators, the quantum anomalous Hall phase, axion insulator phase and Chern insulator phase in intrinsic antiferromagnetic topological insulator MnBi2Te4, as well as the helical phase emerged from the Chern insulator in pulsed high magnetic fields. Finally, this article analyzes the future direction of development in magnetic topological insulators and the transport phenomena that remain to be understood in these systems, offering insights and perspectives on the potential breakthroughs to be achieved in this area of research.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76282749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nong Jie, Zhang Yi-Yi, Wei Xue-Ling, Jiang Xin-Peng, Li Ning, Wang Dong-Ying, Xiao Si-Yang, Chen Hong-Ting, Zhang Zhen-Rong, Yang Jun-Bo
The "cat's eye effect" in the optical window of all kinds of photoelectric equipment is the main basis of a laser active detection system, which poses a great threat to military equipment and combatants. However, under the condition of ensuring high visible transmittance, the sniper stealth scheme for anti-laser active detection remains to be discussed. In this paper, genetic algorithm was used to reverse design the metasurface anti-reflection film. Si3N4 and Ag were composed of three-layer anti-reflection film, and rectangular array of metal micro-nano structures were added on the top layer to form a wavelength selective absorber, so as to achieve the effect of low reflection and high absorption at laser wavelength. By combining the device design with genetic algorithm, the parameter combination that best meets the target performance of the device is obtained. The average transmittance at 380nm~780nm is 88% meanwhile the maximum transmittance peak of 94%. The reflectance at 1550nm of 10%, and the absorption rate of 80% are achieved. In order to better meet the requirements of practical application, we further designed the cross metal array to obtain polarization insensitive characteristics. The metasurface anti-reflective membrane with improved structure can achieve an average visible transmittance of 82% and a reflectance of 5% at 1550nm. The two metasurface anti-reflection film designed in this paper does not require additional devices, and the imaging quality can be guaranteed. At the same time, it can effectively reduce the laser echo energy, so as to achieve the effect of high quality visible light transmittance and laser stealth compatibility.
{"title":"Research on Dielectric/Metal/Dielectric film system for high transmittance compatible laser stealth","authors":"Nong Jie, Zhang Yi-Yi, Wei Xue-Ling, Jiang Xin-Peng, Li Ning, Wang Dong-Ying, Xiao Si-Yang, Chen Hong-Ting, Zhang Zhen-Rong, Yang Jun-Bo","doi":"10.7498/aps.72.20230855","DOIUrl":"https://doi.org/10.7498/aps.72.20230855","url":null,"abstract":"The \"cat's eye effect\" in the optical window of all kinds of photoelectric equipment is the main basis of a laser active detection system, which poses a great threat to military equipment and combatants. However, under the condition of ensuring high visible transmittance, the sniper stealth scheme for anti-laser active detection remains to be discussed. In this paper, genetic algorithm was used to reverse design the metasurface anti-reflection film. Si3N4 and Ag were composed of three-layer anti-reflection film, and rectangular array of metal micro-nano structures were added on the top layer to form a wavelength selective absorber, so as to achieve the effect of low reflection and high absorption at laser wavelength. By combining the device design with genetic algorithm, the parameter combination that best meets the target performance of the device is obtained. The average transmittance at 380nm~780nm is 88% meanwhile the maximum transmittance peak of 94%. The reflectance at 1550nm of 10%, and the absorption rate of 80% are achieved. In order to better meet the requirements of practical application, we further designed the cross metal array to obtain polarization insensitive characteristics. The metasurface anti-reflective membrane with improved structure can achieve an average visible transmittance of 82% and a reflectance of 5% at 1550nm. The two metasurface anti-reflection film designed in this paper does not require additional devices, and the imaging quality can be guaranteed. At the same time, it can effectively reduce the laser echo energy, so as to achieve the effect of high quality visible light transmittance and laser stealth compatibility.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76259113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mixing between shell material and gas fuel, caused by hydrodynamic instability, isolated defects, or kinetic effects, is the key to understand the degradation of implosion performance in the research of inertial confinement fusion. Understanding the mixing mechanism and reducing its impact is of extreme importance to achieve the ignition and high gain. The impact of mixing morphology on thermonuclear reaction rate in sub grid level has gradually attracted people’s attention in recent years due to its direct influence on burn rate and fusion process, the study on physical model of thermonuclear reaction rate in different mix morphology has important scientific significance and application value.In the paper, the dependence of thermonuclear reaction rate on mass distribution of different fuel concentrations at sub grid scale is derived. Based on thermodynamic equilibrium and ideal gas equation of state, the physical law of the evolution of the thermonuclear reaction rate with mix morphology under the dominance of diffusion mixing is revealed through analytical formula and numerical solution of diffusion equation in one-dimensional spherical geometry. It is convinced that the mixing amount directly affects the thermonuclear reaction rate by mainly affecting the volume fraction of the fuel, and the mixing diffusion time determined by heterogeneous mixing scale and diffusion coefficient directly affects the evolution behavior of the thermonuclear reaction rate. Furthermore, based on mutual diffusion coefficient obtained from direct simulation of diffusion process by Monte Carlo method, the difference of impact to thermonuclear reaction rate for low-Z Carbon and high-Z gold mixing is quantitatively investigated. Heterogeneous mix size with 0.1μm, 0.01μm respectively for the low-Z and high-Z mixing can be treated as atomic mix in burn rate aspect, and heterogeneous mix size with 10μm, 1μm respectively for the low-Z and high-Z mixing can be treated as ideal chunk mix in burn rate aspect, and heterogeneous mix size in the middle state needs to be evaluated by using the heterogeneous mixing model of thermonuclear reaction rate in the paper. Finally, the physical model is compared with 3D simulation results of the heterogeneous mixing effect experiment called "MARBLE Campaign" carried out on OMEGA laser facility, which is designed as a separated reactant experiments and capsules are filled with deuterated foam and HT gas pores of different size, covering typical mix morphology from atomic mix to chunk mix, which validate the reliability of the theoretical evaluation about the evolution of mixing morphology and its impact to thermonuclear reaction rate.This work is significant for the design and improvement of inertial confinement fusion mixing effect experiment in China.
{"title":"Investigation on the fusion reaction rate of deuterium and tritium under heterogeneous mixing","authors":"Shen Gang, Zhong Bin, Wu Yong, Wang Jian-guo","doi":"10.7498/aps.72.20221197","DOIUrl":"https://doi.org/10.7498/aps.72.20221197","url":null,"abstract":"Mixing between shell material and gas fuel, caused by hydrodynamic instability, isolated defects, or kinetic effects, is the key to understand the degradation of implosion performance in the research of inertial confinement fusion. Understanding the mixing mechanism and reducing its impact is of extreme importance to achieve the ignition and high gain. The impact of mixing morphology on thermonuclear reaction rate in sub grid level has gradually attracted people’s attention in recent years due to its direct influence on burn rate and fusion process, the study on physical model of thermonuclear reaction rate in different mix morphology has important scientific significance and application value.In the paper, the dependence of thermonuclear reaction rate on mass distribution of different fuel concentrations at sub grid scale is derived. Based on thermodynamic equilibrium and ideal gas equation of state, the physical law of the evolution of the thermonuclear reaction rate with mix morphology under the dominance of diffusion mixing is revealed through analytical formula and numerical solution of diffusion equation in one-dimensional spherical geometry. It is convinced that the mixing amount directly affects the thermonuclear reaction rate by mainly affecting the volume fraction of the fuel, and the mixing diffusion time determined by heterogeneous mixing scale and diffusion coefficient directly affects the evolution behavior of the thermonuclear reaction rate. Furthermore, based on mutual diffusion coefficient obtained from direct simulation of diffusion process by Monte Carlo method, the difference of impact to thermonuclear reaction rate for low-Z Carbon and high-Z gold mixing is quantitatively investigated. Heterogeneous mix size with 0.1μm, 0.01μm respectively for the low-Z and high-Z mixing can be treated as atomic mix in burn rate aspect, and heterogeneous mix size with 10μm, 1μm respectively for the low-Z and high-Z mixing can be treated as ideal chunk mix in burn rate aspect, and heterogeneous mix size in the middle state needs to be evaluated by using the heterogeneous mixing model of thermonuclear reaction rate in the paper. Finally, the physical model is compared with 3D simulation results of the heterogeneous mixing effect experiment called \"MARBLE Campaign\" carried out on OMEGA laser facility, which is designed as a separated reactant experiments and capsules are filled with deuterated foam and HT gas pores of different size, covering typical mix morphology from atomic mix to chunk mix, which validate the reliability of the theoretical evaluation about the evolution of mixing morphology and its impact to thermonuclear reaction rate.This work is significant for the design and improvement of inertial confinement fusion mixing effect experiment in China.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85421579","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiong Pei-Yu, Ni Zhuang, Lin Ze-Feng, Bai Xin-Bo, Liu Tian-Xiang, Zhang Xiang-Yu, Yuan Jie, Wang Xu, Shi Jing, Jin Kui
BaxSr1-xTiO3(BST) ferroelectric thin films are widely used in microwave tunable devices due to their high dielectric constant, strong electric field tunability and low microwave loss. However, because of the temperature dependence of dielectric constant in ferroelectric materials, the high-tunability for conventional single component ferroelectric thin films can only be achieved in the vicinity of Curie Temperature (TC) which results in that the ferroelectric thin films are difficult to apply to wide temperature range. To obtain ferroelectric thin films available for temperature stable functional devices, single composition Ba0.2Sr0.8TiO3 thin films, Ba0.5Sr0.5TiO3 thin films and heterostructure ofBa0.2Sr0.8TiO3/Ba0.5Sr0.5TiO3 thin films are deposited by pulsed laser deposition (PLD). By comparing with their dielectric properties in a wide temperature range, it’s found that the temperature sensitivity of BST films can be effectively reduced by introducing a composition gradient along the epitaxial direction. However, the heterostructure engineering may bring extra troubles caused by interfaces, which may limit the quality factor Q. In this paper, we extend our combinatorial film deposition technique to ferroelectric materials, and successfully fabricated in-plane composition-spread Ba1-xSrxTiO3 thin films, which are expected to broaden the phase transition temperature range of BST films while avoiding the problem of interface control.
{"title":"Composition-spread Epitaxial Ferroelectric Thin Films for Temperature Insensitive Functional Devices","authors":"Xiong Pei-Yu, Ni Zhuang, Lin Ze-Feng, Bai Xin-Bo, Liu Tian-Xiang, Zhang Xiang-Yu, Yuan Jie, Wang Xu, Shi Jing, Jin Kui","doi":"10.7498/aps.72.20230154","DOIUrl":"https://doi.org/10.7498/aps.72.20230154","url":null,"abstract":"Ba<sub>x</sub>Sr<sub>1-x</sub>TiO<sub>3</sub>(BST) ferroelectric thin films are widely used in microwave tunable devices due to their high dielectric constant, strong electric field tunability and low microwave loss. However, because of the temperature dependence of dielectric constant in ferroelectric materials, the high-tunability for conventional single component ferroelectric thin films can only be achieved in the vicinity of Curie Temperature (<i>T</i><sub>C</sub>) which results in that the ferroelectric thin films are difficult to apply to wide temperature range. To obtain ferroelectric thin films available for temperature stable functional devices, single composition Ba<sub>0.2</sub>Sr<sub>0.8</sub>TiO<sub>3</sub> thin films, Ba<sub>0.5</sub>Sr<sub>0.5</sub>TiO<sub>3</sub> thin films and heterostructure ofBa<sub>0.2</sub>Sr<sub>0.8</sub>TiO<sub>3</sub>/Ba<sub>0.5</sub>Sr<sub>0.5</sub>TiO<sub>3</sub> thin films are deposited by pulsed laser deposition (PLD). By comparing with their dielectric properties in a wide temperature range, it’s found that the temperature sensitivity of BST films can be effectively reduced by introducing a composition gradient along the epitaxial direction. However, the heterostructure engineering may bring extra troubles caused by interfaces, which may limit the quality factor <i>Q</i>. In this paper, we extend our combinatorial film deposition technique to ferroelectric materials, and successfully fabricated in-plane composition-spread Ba<sub>1-<i>x</i></sub>Sr<i><sub>x</sub></i>TiO<sub>3</sub> thin films, which are expected to broaden the phase transition temperature range of BST films while avoiding the problem of interface control.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85789379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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