Gratings composed of cholesteric liquid crystals as an important optical element for emerging applications such as augmented and virtual reality and are renowned for their characteristic single reflective diffraction band. Heliconical liquid crystal is a newly discovered state where the constituent molecules self-organize into helical structures with a non-90° polar angle between the director and the helical axis. Here, we present a numerical study on the reflective diffraction of gratings made of heliconical liquid crystals. Remarkably, numerical results demonstrate that there exist two diffraction bands at the same diffraction angle, with one peak wavelength being twice the other. We show that the short-wavelength diffraction originates from the Pancharatnam-Berry phase acquired by the reflected light while the long-wavelength diffraction stems from the reflection of the slanted volume grating, and that the wavelengths of these two diffraction bands can be attributed to the first and second band gaps of the slanted volume grating as a one-dimensional photonic crystal. We further show that the polarization of the reflected diffraction light is circular, exhibiting the same handedness as the liquid crystal for the short-wavelength band, whereas it is perfectly linearly polarized along the grating direction for the long-wavelength band.
{"title":"Dual diffraction bands of heliconical liquid crystal gratings","authors":"Sha Liu, Hao Yu, Miao Jiang, Ling-Ling Ma, Yan-Qing Lu, Qi-Huo Wei","doi":"10.1103/physrevmaterials.8.085201","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.085201","url":null,"abstract":"Gratings composed of cholesteric liquid crystals as an important optical element for emerging applications such as augmented and virtual reality and are renowned for their characteristic single reflective diffraction band. Heliconical liquid crystal is a newly discovered state where the constituent molecules self-organize into helical structures with a non-90° polar angle between the director and the helical axis. Here, we present a numerical study on the reflective diffraction of gratings made of heliconical liquid crystals. Remarkably, numerical results demonstrate that there exist two diffraction bands at the same diffraction angle, with one peak wavelength being twice the other. We show that the short-wavelength diffraction originates from the Pancharatnam-Berry phase acquired by the reflected light while the long-wavelength diffraction stems from the reflection of the slanted volume grating, and that the wavelengths of these two diffraction bands can be attributed to the first and second band gaps of the slanted volume grating as a one-dimensional photonic crystal. We further show that the polarization of the reflected diffraction light is circular, exhibiting the same handedness as the liquid crystal for the short-wavelength band, whereas it is perfectly linearly polarized along the grating direction for the long-wavelength band.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-13DOI: 10.1103/physrevmaterials.8.083605
Shehab Shousha, Sourabh Bhagwan Kadambi, Benjamin Beeler, Boopathy Kombaiah
The Nabarro-Herring (NH) diffusional creep theory postulates the vacancy-mediated transport of atoms under a stress gradient as the creep mechanism under low-stress and high-temperature conditions. In multicomponent alloys, we premise that this stress-assisted flow of vacancies to and from grain boundaries will produce elemental segregation. An observation of such segregation, validated with theoretical predictions, can provide the necessary experimental evidence for the occurrence of NH creep. Theoretical calculations of the segregation tendencies via analyzing the dominant solute diffusion mechanisms and the difference in diffusivities of the elements are therefore essential. To this end, this study applies density functional theory calculations of migration barriers and solute-vacancy binding energies as input to the self-consistent mean-field theory to assess the vacancy-mediated diffusion mechanisms, transport coefficients, and segregation tendencies of Co, Cr, Mo, Re, Ta, and W solutes in face-centered-cubic Ni. We find Co, Re, and W to be slow diffusers at high temperatures and Cr, Mo, and Ta to be fast diffusers. Further analysis shows that the slow diffusers tend to always enrich at vacancy sinks over a wide range of temperatures. In contrast, the fast diffusers show a transition from depletion to enrichment as the temperature lowers. Furthermore, our analysis of the segregation tendencies under tensile hydrostatic strains shows that slow diffusers are largely unaffected by the strain and favor enrichment. On the other hand, the fast diffusers exhibit high sensitivity to strain and their segregation tendency can transition from depletion to enrichment at a given temperature. The transport coefficients calculated in this work are expected to serve as input to mesoscale microstructure models to provide a more rigorous assessment of solute segregation under NH creep conditions.
纳巴罗-赫林（NH）扩散蠕变理论假定，在低应力和高温条件下，原子在应力梯度下的空位迁移是蠕变机制。在多组分合金中，我们假设空位在应力作用下进出晶界会产生元素偏析。观察到这种偏析并与理论预测进行验证，可以为 NH 蠕变的发生提供必要的实验证据。因此，通过分析主要的溶质扩散机制和元素扩散率的差异来对偏析趋势进行理论计算是至关重要的。为此，本研究将迁移障碍和溶质-空位结合能的密度泛函理论计算作为自洽平均场理论的输入，以评估面心立方 Ni 中 Co、Cr、Mo、Re、Ta 和 W 溶质的空位介导扩散机制、迁移系数和偏析倾向。我们发现 Co、Re 和 W 在高温下扩散速度较慢，而 Cr、Mo 和 Ta 扩散速度较快。进一步的分析表明，在很宽的温度范围内，慢速扩散者往往总是在空位汇处富集。与此相反，随着温度的降低，快速扩散体显示出从耗尽到富集的过渡。此外，我们对拉伸静水应变下的偏析趋势进行的分析表明，慢速扩散器基本上不受应变的影响，并倾向于富集。另一方面，快速扩散器表现出对应变的高度敏感性，在给定温度下，它们的偏析趋势会从贫化过渡到富集。这项工作计算出的迁移系数有望作为中尺度微结构模型的输入，从而对 NH 蠕变条件下的溶质偏析进行更严格的评估。
{"title":"Vacancy-mediated transport and segregation tendencies of solutes in fcc nickel under diffusional creep: A density functional theory study","authors":"Shehab Shousha, Sourabh Bhagwan Kadambi, Benjamin Beeler, Boopathy Kombaiah","doi":"10.1103/physrevmaterials.8.083605","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.083605","url":null,"abstract":"The Nabarro-Herring (NH) diffusional creep theory postulates the vacancy-mediated transport of atoms under a stress gradient as the creep mechanism under low-stress and high-temperature conditions. In multicomponent alloys, we premise that this stress-assisted flow of vacancies to and from grain boundaries will produce elemental segregation. An observation of such segregation, validated with theoretical predictions, can provide the necessary experimental evidence for the occurrence of NH creep. Theoretical calculations of the segregation tendencies via analyzing the dominant solute diffusion mechanisms and the difference in diffusivities of the elements are therefore essential. To this end, this study applies density functional theory calculations of migration barriers and solute-vacancy binding energies as input to the self-consistent mean-field theory to assess the vacancy-mediated diffusion mechanisms, transport coefficients, and segregation tendencies of Co, Cr, Mo, Re, Ta, and W solutes in face-centered-cubic Ni. We find Co, Re, and W to be slow diffusers at high temperatures and Cr, Mo, and Ta to be fast diffusers. Further analysis shows that the slow diffusers tend to always enrich at vacancy sinks over a wide range of temperatures. In contrast, the fast diffusers show a transition from depletion to enrichment as the temperature lowers. Furthermore, our analysis of the segregation tendencies under tensile hydrostatic strains shows that slow diffusers are largely unaffected by the strain and favor enrichment. On the other hand, the fast diffusers exhibit high sensitivity to strain and their segregation tendency can transition from depletion to enrichment at a given temperature. The transport coefficients calculated in this work are expected to serve as input to mesoscale microstructure models to provide a more rigorous assessment of solute segregation under NH creep conditions.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"28 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-13DOI: 10.1103/physrevmaterials.8.l082601
Himangsu Bhaumik, Daniel Hexner
Training materials through periodic drive allows us to endow materials and structures with complex elastic functions. As a result of the driving, the system explores the high-dimensional space of structures, ultimately converging to a structure with the desired response. However, increasing the complexity of the desired response results in ultraslow convergence and degradation. Here, we show that by constraining the search space, we are able to increase robustness, extend the maximal capacity, train responses that previously did not converge, and in some cases accelerate convergence by many orders of magnitude. We identify the geometrical constraints that prevent the formation of spurious low-frequency modes, which are responsible for failure. We argue that these constraints are analogous to regularization used in machine learning. We propose a unified relationship between complexity, degradation, convergence, and robustness.
{"title":"Mechanical regularization","authors":"Himangsu Bhaumik, Daniel Hexner","doi":"10.1103/physrevmaterials.8.l082601","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.l082601","url":null,"abstract":"Training materials through periodic drive allows us to endow materials and structures with complex elastic functions. As a result of the driving, the system explores the high-dimensional space of structures, ultimately converging to a structure with the desired response. However, increasing the complexity of the desired response results in ultraslow convergence and degradation. Here, we show that by constraining the search space, we are able to increase robustness, extend the maximal capacity, train responses that previously did not converge, and in some cases accelerate convergence by many orders of magnitude. We identify the geometrical constraints that prevent the formation of spurious low-frequency modes, which are responsible for failure. We argue that these constraints are analogous to regularization used in machine learning. We propose a unified relationship between complexity, degradation, convergence, and robustness.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"30 11 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The intrinsic anomalous Hall conductivity (AHC) in a ferromagnetic metal is completely determined by its band structure. Since the spin orientation direction is an important band–structure tuning parameter, it is highly desirable to study the anomalous Hall effect in a system with multiple spin reorientation transitions. We study a layered tetragonal room temperature ferromagnet , which gives us the opportunity to measure magnetotransport properties where the long -axis and the short -axis can both be magnetically easy axes depending on the temperature range we choose. We show a moderately large fully intrinsic AHC up to room temperature when the crystal is magnetized along the -axis. Interestingly, the AHC can be tuned to completely extrinsic with extremely large values when the crystal is magnetized along the -axis, regardless of whether the -axis is magnetically easy or hard axis. First-principles calculations show that nodal line states originate from Mn- orbitals just below the Fermi energy () in the electronic band structure when the spins are oriented along the -axis. Intrinsic AHC originates from the Berry curvature effect of the gapped nodal lines in the presence of spin-orbit coupling. AHC almost disappears when the spins are aligned along the -axis because the nodal line states shift above and become unoccupied. Since the AHC can be tuned from fully extrinsic to intrinsic even at 300 K, becomes a potential candidate for room-temperature spintronics applications.
铁磁金属的本征反常霍尔电导率（AHC）完全由其带状结构决定。由于自旋取向方向是一个重要的带状结构调整参数，因此研究具有多个自旋重新取向跃迁的体系中的反常霍尔效应是非常理想的。我们研究的是一种层状四方室温铁磁体 SmMn2Ge2，它为我们提供了测量磁传输特性的机会，根据我们选择的温度范围，长 c 轴和短 a 轴都可以是易磁轴。我们发现，当晶体沿 c 轴磁化时，在室温下会产生中等大小的完全本征 AHC。有趣的是，当晶体沿 a 轴磁化时，无论 a 轴是磁易轴还是磁硬轴，AHC 都能被调谐到完全外在的极大值。第一原理计算表明，当自旋沿 c 轴定向时，结线态源于电子能带结构中费米能（EF）正下方的 Mn-d 轨道。内在 AHC 源自存在自旋轨道耦合时间隙节点线的贝里曲率效应。当自旋沿 a 轴排列时，AHC 几乎消失，因为结线态转移到 EF 以上，成为空闲态。由于即使在 300 K 时也能将 AHC 从完全外在状态调整为内在状态，SmMn2Ge2 成为室温自旋电子学应用的潜在候选材料。
{"title":"Tuning intrinsic anomalous Hall effect from large to zero in two ferromagnetic states of SmMn2Ge2","authors":"Mahima Singh, Jyotirmoy Sau, Banik Rai, Arunanshu Panda, Manoranjan Kumar, Nitesh Kumar","doi":"10.1103/physrevmaterials.8.084201","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.084201","url":null,"abstract":"The intrinsic anomalous Hall conductivity (AHC) in a ferromagnetic metal is completely determined by its band structure. Since the spin orientation direction is an important band–structure tuning parameter, it is highly desirable to study the anomalous Hall effect in a system with multiple spin reorientation transitions. We study a layered tetragonal room temperature ferromagnet <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>Sm</mi><msub><mi>Mn</mi><mn>2</mn></msub><msub><mi>Ge</mi><mn>2</mn></msub></mrow></math>, which gives us the opportunity to measure magnetotransport properties where the long <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>c</mi></math>-axis and the short <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>a</mi></math>-axis can both be magnetically easy axes depending on the temperature range we choose. We show a moderately large fully intrinsic AHC up to room temperature when the crystal is magnetized along the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>c</mi></math>-axis. Interestingly, the AHC can be tuned to completely extrinsic with extremely large values when the crystal is magnetized along the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>a</mi></math>-axis, regardless of whether the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>a</mi></math>-axis is magnetically easy or hard axis. First-principles calculations show that nodal line states originate from Mn-<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>d</mi></math> orbitals just below the Fermi energy (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>E</mi><mi mathvariant=\"normal\">F</mi></msub></math>) in the electronic band structure when the spins are oriented along the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>c</mi></math>-axis. Intrinsic AHC originates from the Berry curvature effect of the gapped nodal lines in the presence of spin-orbit coupling. AHC almost disappears when the spins are aligned along the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>a</mi></math>-axis because the nodal line states shift above <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>E</mi><mi mathvariant=\"normal\">F</mi></msub></math> and become unoccupied. Since the AHC can be tuned from fully extrinsic to intrinsic even at 300 K, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>Sm</mi><msub><mi>Mn</mi><mn>2</mn></msub><msub><mi>Ge</mi><mn>2</mn></msub></mrow></math> becomes a potential candidate for room-temperature spintronics applications.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"9 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-13DOI: 10.1103/physrevmaterials.8.084406
M. Waqas Khaliq, Oliver J. Amin, Alberto Hernández-Mínguez, Marc Rovirola, Blai Casals, Khalid Omari, Sandra Ruiz-Gómez, Simone Finizio, Richard P. Campion, Kevin W. Edmonds, Vít Novák, Anna Mandziak, Lucia Aballe, Miguel Angel Niño, Joan Manel Hernàndez, Peter Wadley, Ferran Macià, Michael Foerster
Magnetoelastic effects in antiferromagnetic CuMnAs are investigated by applying dynamic strain in the 0.01% range through surface acoustic waves in the GaAs substrate. The magnetic state of the CuMnAs/GaAs is characterized by a multitude of submicron-sized domains, which we image by x-ray magnetic linear dichroism combined with photoemission electron microscopy. Within the explored strain range, CuMnAs shows magnetoelastic effects in the form of Néel vector waves with micrometer wavelength, which corresponds to an averaged overall spin-axis rotation up to driven by the time-dependent strain from the surface acoustic wave. Measurements at different temperatures indicate a reduction of the wave amplitude when lowering the temperature. However, no domain wall motion has been detected on the nanosecond timescale.
通过在砷化镓衬底上施加 0.01% 范围内的表面声波动态应变，研究了反铁磁性铜锰砷化物中的磁弹性效应。CuMnAs/GaAs 的磁性状态以大量亚微米大小的磁畴为特征，我们通过 X 射线磁线性二色性结合光发射电子显微镜对这些磁畴进行了成像。在所探究的应变范围内，CuMnAs 显示出波长为微米的奈尔矢量波形式的磁弹性效应，这相当于在表面声波随时间变化的应变驱动下，平均整体自旋轴旋转达 2.4∘。在不同温度下进行的测量表明，当温度降低时，波幅会减小。然而，在纳秒时间尺度上没有检测到域壁运动。
{"title":"Néel vector waves in antiferromagnetic CuMnAs excited by surface acoustic waves","authors":"M. Waqas Khaliq, Oliver J. Amin, Alberto Hernández-Mínguez, Marc Rovirola, Blai Casals, Khalid Omari, Sandra Ruiz-Gómez, Simone Finizio, Richard P. Campion, Kevin W. Edmonds, Vít Novák, Anna Mandziak, Lucia Aballe, Miguel Angel Niño, Joan Manel Hernàndez, Peter Wadley, Ferran Macià, Michael Foerster","doi":"10.1103/physrevmaterials.8.084406","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.084406","url":null,"abstract":"Magnetoelastic effects in antiferromagnetic CuMnAs are investigated by applying dynamic strain in the 0.01% range through surface acoustic waves in the GaAs substrate. The magnetic state of the CuMnAs/GaAs is characterized by a multitude of submicron-sized domains, which we image by x-ray magnetic linear dichroism combined with photoemission electron microscopy. Within the explored strain range, CuMnAs shows magnetoelastic effects in the form of Néel vector waves with micrometer wavelength, which corresponds to an averaged overall spin-axis rotation up to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>2</mn><mo>.</mo><msup><mn>4</mn><mo>∘</mo></msup></mrow></math> driven by the time-dependent strain from the surface acoustic wave. Measurements at different temperatures indicate a reduction of the wave amplitude when lowering the temperature. However, no domain wall motion has been detected on the nanosecond timescale.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"180 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Understanding the superconductivity in relation to chemical bonding is essential for the development of superconductors. We propose that pressure-reduced ionic bonding strength is beneficial for improving superconductivity in hydrides (negative correlation between bonding strength and critical temperature). We model ionic hydrides using a prototypical ionic lattice (CsCl-type) with simple-valence metal Li/Rb and hydrogen and control the bonding strength via external pressure. First-principles calculations reveal that the ionic bonding strength in LiH increases with pressure while its critical temperature () simultaneously decreases. A higher at lower pressures is attributed to stronger electron-phonon coupling (EPC) induced by weaker ionic bonds and significant EPC contributions from mid-frequency phonons. RbH's pressure dependences of bonding strength and are the reverse of those of LiH, and the EPC primarily results from high-frequency phonons. The distinct interorbital electron transition mechanism and amounts of charge transfer are responsible for the opposite trend of changes in bonding strength and superconductivity in LiH and RbH. The proposed correlation is further validated by the other six ionic hydrides. Substantial change (e.g., 126.2 K at 100 GPa and 5.7 K at 300 GPa in LiH) in response to bonding strength variation reveals a key factor for designing new superconductors.
{"title":"Strong correlation between ionic bonding strength and superconductivity in compressed hydrides","authors":"Xing Li, Zixuan Guo, Yansun Yao, Xiaohua Zhang, Shicong Ding, Guochun Yang","doi":"10.1103/physrevmaterials.8.084805","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.084805","url":null,"abstract":"Understanding the superconductivity in relation to chemical bonding is essential for the development of superconductors. We propose that pressure-reduced ionic bonding strength is beneficial for improving superconductivity in hydrides (negative correlation between bonding strength and critical temperature). We model ionic hydrides using a prototypical ionic lattice (CsCl-type) with simple-valence metal Li/Rb and hydrogen and control the bonding strength via external pressure. First-principles calculations reveal that the ionic bonding strength in LiH increases with pressure while its critical temperature (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>T</mi><mi mathvariant=\"normal\">c</mi></msub></math>) simultaneously decreases. A higher <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>T</mi><mi mathvariant=\"normal\">c</mi></msub></math> at lower pressures is attributed to stronger electron-phonon coupling (EPC) induced by weaker ionic bonds and significant EPC contributions from mid-frequency phonons. RbH's pressure dependences of bonding strength and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>T</mi><mi mathvariant=\"normal\">c</mi></msub></math> are the reverse of those of LiH, and the EPC primarily results from high-frequency phonons. The distinct interorbital electron transition mechanism and amounts of charge transfer are responsible for the opposite trend of changes in bonding strength and superconductivity in LiH and RbH. The proposed correlation is further validated by the other six ionic hydrides. Substantial <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>T</mi><mi mathvariant=\"normal\">c</mi></msub></math> change (e.g., 126.2 K at 100 GPa and 5.7 K at 300 GPa in LiH) in response to bonding strength variation reveals a key factor for designing new superconductors.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"25 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-13DOI: 10.1103/physrevmaterials.8.084407
Xinyu Tian, Xiao Xie, Jia Li, Xiangru Kong, Wei-Jiang Gong, François M. Peeters, Linyang Li
The combination of auxetic property, ferroelasticity, and ferroelectricity in two-dimensional materials offers new avenues for next-generation multifunctional devices. However, two-dimensional materials that simultaneously exhibit those properties are rarely reported. Here, we present a class of two-dimensional Janus-like structures (, As, and Sb) with a rectangular lattice based on first-principles calculations. We predict that those monolayers are stable semiconductors with both intrinsic in-plane and out-of-plane auxetic properties, showing a bidirectional negative Poisson's ratio effect. The value of the out-of-plane negative Poisson's ratio effect can reach −2.28/−3.06/−3.89. By applying uniaxial strain engineering, two transition paths can be found, including the VA main group element path and the rare-earth metal element path, corresponding to the ferroelastic and the multiferroic (ferroelastic and ferroelectric) phase transition, respectively. For the monolayer, the external force field can not only control the ferroelastic phase transition, but it can also lead to the reversal of the out-of-plane polarization, exhibiting potential multiferroicity. The coupling between the bidirectional negative Poisson's ratio effect and multiferroicity makes the monolayers promising for future device applications.
{"title":"Multiferroic ScLaX2 (X=P, As, and Sb) monolayers: Bidirectional negative Poisson's ratio effects and phase transformations driven by rare-earth (main-group) elements","authors":"Xinyu Tian, Xiao Xie, Jia Li, Xiangru Kong, Wei-Jiang Gong, François M. Peeters, Linyang Li","doi":"10.1103/physrevmaterials.8.084407","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.084407","url":null,"abstract":"The combination of auxetic property, ferroelasticity, and ferroelectricity in two-dimensional materials offers new avenues for next-generation multifunctional devices. However, two-dimensional materials that simultaneously exhibit those properties are rarely reported. Here, we present a class of two-dimensional Janus-like structures <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ScLa</mi><msub><mi>X</mi><mn>2</mn></msub></mrow></math> (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>X</mi><mo>=</mo><mi mathvariant=\"normal\">P</mi></mrow></math>, As, and Sb) with a rectangular lattice based on first-principles calculations. We predict that those <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ScLa</mi><msub><mi>X</mi><mn>2</mn></msub></mrow></math> monolayers are stable semiconductors with both intrinsic in-plane and out-of-plane auxetic properties, showing a bidirectional negative Poisson's ratio effect. The value of the out-of-plane negative Poisson's ratio effect can reach −2.28/−3.06/−3.89. By applying uniaxial strain engineering, two transition paths can be found, including the VA main group element path and the rare-earth metal element path, corresponding to the ferroelastic and the multiferroic (ferroelastic and ferroelectric) phase transition, respectively. For the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ScLaS</mi><msub><mi mathvariant=\"normal\">b</mi><mn>2</mn></msub></mrow></math> monolayer, the external force field can not only control the ferroelastic phase transition, but it can also lead to the reversal of the out-of-plane polarization, exhibiting potential multiferroicity. The coupling between the bidirectional negative Poisson's ratio effect and multiferroicity makes the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ScLa</mi><msub><mi>X</mi><mn>2</mn></msub></mrow></math> monolayers promising for future device applications.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"71 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-12DOI: 10.1103/physrevmaterials.8.084804
M. Gonzalez, A. Ievlev, K. Lee, W. Kim, Y. Yu, J. Fowlie, H. Y. Hwang
The discovery of superconductivity in the infinite layer nickelates introduced a materials system analogous to the cuprates for the study of unconventional superconductivity. The synthesis of infinite layer nickelates, (, R = lanthanide) often uses calcium hydride () to facilitate the deintercalation of apical site oxygen atoms from a precursor perovskite () phase via topotactic reduction. However, it remains uncertain whether the use of results in the insertion of hydrogen into the infinite layer structure, and if it does, what the implications are for superconductivity. To quantify the hydrogen composition of highly crystalline infinite layer nickelates, we synthesized thin films on LSAT substrates and conducted time-of-flight secondary ion mass spectroscopy measurements to generate hydrogen depth profiles. We compare the hydrogen density of nickelates prepared with and without a capping layer. Additionally, we measure the hydrogen content in nickelate samples at various doping levels spanning the superconducting phase space, including the underdoped, optimally doped, and overdoped regime. We report no significant increase in hydrogen density between the perovskite and infinite layer phases in any of the measured samples. Furthermore, we put an upperbound on the hydrogen concentration of our nickelate samples to . Our results imply that hydrogen is not responsible for the emergence of superconductivity in the infinite layer nickelates.
{"title":"Absence of hydrogen insertion into highly crystalline superconducting infinite layer nickelates","authors":"M. Gonzalez, A. Ievlev, K. Lee, W. Kim, Y. Yu, J. Fowlie, H. Y. Hwang","doi":"10.1103/physrevmaterials.8.084804","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.084804","url":null,"abstract":"The discovery of superconductivity in the infinite layer nickelates introduced a materials system analogous to the cuprates for the study of unconventional superconductivity. The synthesis of infinite layer nickelates, (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>RNiO</mi><mn>2</mn></msub></math>, R = lanthanide) often uses calcium hydride (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>CaH</mi><mn>2</mn></msub></math>) to facilitate the deintercalation of apical site oxygen atoms from a precursor perovskite (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>RNiO</mi><mn>3</mn></msub></math>) phase via topotactic reduction. However, it remains uncertain whether the use of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>CaH</mi><mn>2</mn></msub></math> results in the insertion of hydrogen into the infinite layer structure, and if it does, what the implications are for superconductivity. To quantify the hydrogen composition of highly crystalline infinite layer nickelates, we synthesized <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>Nd</mi><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub><msub><mi>Sr</mi><mi>x</mi></msub><msub><mi>NiO</mi><mn>2</mn></msub></mrow></math> thin films on LSAT substrates and conducted time-of-flight secondary ion mass spectroscopy measurements to generate hydrogen depth profiles. We compare the hydrogen density of nickelates prepared with and without a <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>SrTiO</mi><mn>3</mn></msub></math> capping layer. Additionally, we measure the hydrogen content in nickelate samples at various doping levels spanning the superconducting phase space, including the underdoped, optimally doped, and overdoped regime. We report no significant increase in hydrogen density between the perovskite and infinite layer phases in any of the measured samples. Furthermore, we put an upperbound on the hydrogen concentration of our nickelate samples to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>Nd</mi><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub><msub><mi>Sr</mi><mi>x</mi></msub><msub><mi>NiO</mi><mn>2</mn></msub><msub><mi mathvariant=\"normal\">H</mi><mrow><mn>0.05</mn></mrow></msub></mrow></math>. Our results imply that hydrogen is not responsible for the emergence of superconductivity in the infinite layer nickelates.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"4 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-12DOI: 10.1103/physrevmaterials.8.083604
Junyi Miao, Shi He, Kaihua He, Kewei Ding, Wei Dai, Cheng Lu
Ammonia is the most stable compound of nitrogen and hydrogen at ambient pressure. However, the chemical reaction of nitrogen and hydrogen is more complex and difficult to explore at high pressures. Here, we have performed extensively structural searches of ammonia-hydrogen compounds based on particle swarm optimization algorithms and first principles calculations. The calculated results show that the main reaction products of nitrogen and hydrogen under high pressure can be divided into two categories: high-energy density material (HEDM) and hydrogen storage material (HSM). Three different phases of are potential HEDMs, which are found to be stable or metastable at 40 GPa to 300 GPa, and metastable at ambient pressure with energy density of about . The phase of is an outstanding HSM with ultrahigh hydrogen storage (41.7 wt%) and release (29.2 wt%) capacities. These findings offer significant insights into the structural arrangements and chemical bonding patterns of ammonia-hydrogen compounds at high pressure, and suggest potential experimental avenues for elucidating how diverse metastable structures with distinct properties might be existed in planetary interiors.
{"title":"Chemical reaction mechanisms of solid state ammonia and hydrogen under high pressure","authors":"Junyi Miao, Shi He, Kaihua He, Kewei Ding, Wei Dai, Cheng Lu","doi":"10.1103/physrevmaterials.8.083604","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.083604","url":null,"abstract":"Ammonia is the most stable compound of nitrogen and hydrogen at ambient pressure. However, the chemical reaction of nitrogen and hydrogen is more complex and difficult to explore at high pressures. Here, we have performed extensively structural searches of ammonia-hydrogen compounds based on particle swarm optimization algorithms and first principles calculations. The calculated results show that the main reaction products of nitrogen and hydrogen under high pressure can be divided into two categories: high-energy density material (HEDM) and hydrogen storage material (HSM). Three different phases of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>NH</mi><mn>4</mn></msub></math> are potential HEDMs, which are found to be stable or metastable at 40 GPa to 300 GPa, and metastable at ambient pressure with energy density of about <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>2.15</mn><mspace width=\"0.28em\"></mspace><mi>kJ</mi><mo>/</mo><mi mathvariant=\"normal\">g</mi><mo>∼</mo><mn>3.86</mn><mspace width=\"0.28em\"></mspace><mi>kJ</mi><mo>/</mo><mi mathvariant=\"normal\">g</mi></mrow></math>. The <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>P</mi><mi>m</mi></mrow></math> phase of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>NH</mi><mn>10</mn></msub></math> is an outstanding HSM with ultrahigh hydrogen storage (41.7 wt%) and release (29.2 wt%) capacities. These findings offer significant insights into the structural arrangements and chemical bonding patterns of ammonia-hydrogen compounds at high pressure, and suggest potential experimental avenues for elucidating how diverse metastable structures with distinct properties might be existed in planetary interiors.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"27 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-12DOI: 10.1103/physrevmaterials.8.l081401
Anna L. Ravensburg, Mirosław Werwiński, Justyna Rychły-Gruszecka, Justyn Snarski-Adamski, Anna Elsukova, Per O. Å. Persson, Ján Rusz, Rimantas Brucas, Björgvin Hjörvarsson, Peter Svedlindh, Gunnar K. Pálsson, Vassilios Kapaklis
We report on the discovery of a boundary-induced body-centered tetragonal iron phase in thin films deposited on (001) substrates. We present evidence for this phase using detailed x-ray analysis and ab initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetization direction are observed, as compared with body-centered cubic iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultrathin iron layers.
我们报告了在 MgAl2O4 (001) 基底上沉积的薄膜中发现的边界诱导体心四方铁相。我们利用详细的 X 射线分析和非初始密度泛函理论计算为这一相提供了证据。与体心立方铁相比，我们观察到了较低的磁矩和易磁化方向的旋转。我们的发现扩大了铁的已知晶体和磁性相的范围，为利用超薄铁层开发异质结构器件提供了宝贵的见解。
{"title":"Boundary-induced phase in epitaxial iron layers","authors":"Anna L. Ravensburg, Mirosław Werwiński, Justyna Rychły-Gruszecka, Justyn Snarski-Adamski, Anna Elsukova, Per O. Å. Persson, Ján Rusz, Rimantas Brucas, Björgvin Hjörvarsson, Peter Svedlindh, Gunnar K. Pálsson, Vassilios Kapaklis","doi":"10.1103/physrevmaterials.8.l081401","DOIUrl":"https://doi.org/10.1103/physrevmaterials.8.l081401","url":null,"abstract":"We report on the discovery of a boundary-induced body-centered tetragonal iron phase in thin films deposited on <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>MgAl</mi><mn>2</mn></msub><msub><mi mathvariant=\"normal\">O</mi><mn>4</mn></msub></mrow></math> (001) substrates. We present evidence for this phase using detailed x-ray analysis and <i>ab initio</i> density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetization direction are observed, as compared with body-centered cubic iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultrathin iron layers.","PeriodicalId":20545,"journal":{"name":"Physical Review Materials","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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