The stacking order of two-dimensional transition metal dichalcogenides (TMDs) is attracting tremendous interest as an essential component of van der Waals heterostructures. A common and fast approach to distinguish between the AAprime (2H) and AB (3R) configurations uses the relative edge orientation of each triangular layer (theta) from optical images. Here, we highlight that this method alone is not sufficient to fully identify the stacking order. Instead we propose a model and methodology to accurately determine the bilayer configuration of WSe2 using second harmonic generation (SHG) and Raman spectroscopy. We demonstrate that the SHG response of the AB phase (theta = 0) deg layers is more intense than the signal from the single layer structure. However, the SHG totally vanishes in the AAprime and ABprime phases (theta = 60 deg) and 0 deg respectively) of homo-bilayer WSe2. Also, several optical features of homo-bilayer WSe2 are found to depend on the details of the stacking order, with the difference being the clearest in the low frequency (LF) Raman frequencies, as confirmed by DFT simulation. This allows unambiguous, high-throughput, nondestructive identification of stacking order in TMDs, which is not robustly addressed in this emerging research area.
{"title":"Distinguishing different stackings in WSe2 bilayers grown Using Chemical Vapor Deposition","authors":"Aymen Mahmoudi, Meryem Bouaziz, Davide Romani, Marco Pala, Aurelien Thieffry, Thibault Brule, Julien Chaste, Fabrice Oehler, Abdelkarim Ouerghi","doi":"arxiv-2409.08617","DOIUrl":"https://doi.org/arxiv-2409.08617","url":null,"abstract":"The stacking order of two-dimensional transition metal dichalcogenides (TMDs)\u0000is attracting tremendous interest as an essential component of van der Waals\u0000heterostructures. A common and fast approach to distinguish between the AAprime\u0000(2H) and AB (3R) configurations uses the relative edge orientation of each\u0000triangular layer (theta) from optical images. Here, we highlight that this\u0000method alone is not sufficient to fully identify the stacking order. Instead we\u0000propose a model and methodology to accurately determine the bilayer\u0000configuration of WSe2 using second harmonic generation (SHG) and Raman\u0000spectroscopy. We demonstrate that the SHG response of the AB phase (theta = 0)\u0000deg layers is more intense than the signal from the single layer structure.\u0000However, the SHG totally vanishes in the AAprime and ABprime phases (theta = 60\u0000deg) and 0 deg respectively) of homo-bilayer WSe2. Also, several optical\u0000features of homo-bilayer WSe2 are found to depend on the details of the\u0000stacking order, with the difference being the clearest in the low frequency\u0000(LF) Raman frequencies, as confirmed by DFT simulation. This allows\u0000unambiguous, high-throughput, nondestructive identification of stacking order\u0000in TMDs, which is not robustly addressed in this emerging research area.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Raphaëlle Delagrange, Manjari Garg, Gaëlle Le Breton, Aifei Zhang, Quan Dong, Yong Jin, Kenji Watanabe, Takashi Taniguchi, Preden Roulleau, Olivier Maillet, Patrice Roche, François D. Parmentier
Under high perpendicular magnetic field and at low temperatures, graphene develops an insulating state at the charge neutrality point. This state, dubbed $nu=0$, is due to the interplay between electronic interactions and the four-fold spin and valley degeneracies in the flat band formed by the $n=0$ Landau level. Determining the ground state of $nu=0$, including its spin and valley polarization, has been a theoretical and experimental undertaking for almost two decades. Here, we present experiments probing the bulk thermal transport properties of monolayer graphene at $nu=0$, which directly probe its ground state and collective excitations. We observe a vanishing bulk thermal transport, in contradiction with the expected ground state, predicted to have a finite thermal conductance even at very low temperature. Our result highlight the need for further investigations on the nature of $nu=0$.
{"title":"Vanishing bulk heat flow in the nu=0 quantum Hall ferromagnet in monolayer graphene","authors":"Raphaëlle Delagrange, Manjari Garg, Gaëlle Le Breton, Aifei Zhang, Quan Dong, Yong Jin, Kenji Watanabe, Takashi Taniguchi, Preden Roulleau, Olivier Maillet, Patrice Roche, François D. Parmentier","doi":"arxiv-2409.08878","DOIUrl":"https://doi.org/arxiv-2409.08878","url":null,"abstract":"Under high perpendicular magnetic field and at low temperatures, graphene\u0000develops an insulating state at the charge neutrality point. This state, dubbed\u0000$nu=0$, is due to the interplay between electronic interactions and the\u0000four-fold spin and valley degeneracies in the flat band formed by the $n=0$\u0000Landau level. Determining the ground state of $nu=0$, including its spin and\u0000valley polarization, has been a theoretical and experimental undertaking for\u0000almost two decades. Here, we present experiments probing the bulk thermal\u0000transport properties of monolayer graphene at $nu=0$, which directly probe its\u0000ground state and collective excitations. We observe a vanishing bulk thermal\u0000transport, in contradiction with the expected ground state, predicted to have a\u0000finite thermal conductance even at very low temperature. Our result highlight\u0000the need for further investigations on the nature of $nu=0$.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"192 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observation of filling factor 6/13 is one of the surprising fractional quantum Hall states in the second Landau level because, in contrast to the standard wisdom, the fractions ($nu < 1/2$) with lower numerators, namely 4 and 5, have not yet been observed. We find that a state indeed forms at $nu=6/13$ as an intermittent topological state between two prominent states at $nu =1/2$ and $nu = 2/5$ with lower numerators. Also, we predict that a state forms at $nu=5/13$ as an intermittent to $nu = 2/5$ and $nu =3/8$. Our proposed wave functions for $nu =6/13$ and $5/13$ have excellent overlaps with the corresponding exact ground state wave functions. The Chern-Simons coupling matrices deduced from the form of these wave functions are analyzed to predict the topological properties, which may be experimentally verified.
{"title":"Enigmatic 2+6/13 Filling Factor: A Prototype Intermittent Topological State","authors":"Sudipto Das, Sahana Das, Sudhansu S. Mandal","doi":"arxiv-2409.09002","DOIUrl":"https://doi.org/arxiv-2409.09002","url":null,"abstract":"Observation of filling factor 6/13 is one of the surprising fractional\u0000quantum Hall states in the second Landau level because, in contrast to the\u0000standard wisdom, the fractions ($nu < 1/2$) with lower numerators, namely 4\u0000and 5, have not yet been observed. We find that a state indeed forms at\u0000$nu=6/13$ as an intermittent topological state between two prominent states at\u0000$nu =1/2$ and $nu = 2/5$ with lower numerators. Also, we predict that a state\u0000forms at $nu=5/13$ as an intermittent to $nu = 2/5$ and $nu =3/8$. Our\u0000proposed wave functions for $nu =6/13$ and $5/13$ have excellent overlaps with\u0000the corresponding exact ground state wave functions. The Chern-Simons coupling\u0000matrices deduced from the form of these wave functions are analyzed to predict\u0000the topological properties, which may be experimentally verified.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Franco P. Bonafé, Esra Ilke Albar, Sebastian T. Ohlmann, Valeriia P. Kosheleva, Carlos M. Bustamante, Francesco Troisi, Angel Rubio, Heiko Appel
We report the first ab initio, non-relativistic QED method that couples light and matter self-consistently beyond the electric dipole approximation and without multipolar truncations. This method is based on an extension of the known Maxwell-Pauli-Kohn-Sham approach for the use of a full minimal coupling Hamiltonian, where the space- and time-dependent vector potential is coupled to the matter system, and its back-reaction to the radiated fields is generated by the full current density. The implementation in the open-source Octopus code is designed for massively-parallel multiscale simulations considering different grid spacings for the Maxwell and matter subsystems. Here, we show the first applications of this framework to simulate renormalized Cherenkov radiation of an electronic wavepacket, magnetooptical effects with non-chiral light in non-chiral molecular systems, and renormalized plasmonic modes in a nanoplasmonic dimer. We show that in some cases the beyond-dipole effects can not be captured by a multipolar expansion Hamiltonian in length gauge. Finally, we discuss further opportunities enabled by the framework in the field of twisted light and orbital angular momentum, inelastic light scattering and strong field physics.
我们报告了第一种超越电偶极近似且无需多极截断的自洽耦合光与物质的非相对论 QED 方法。该方法基于对已知的 Maxwell-Pauli-Kohn-Sham 方法的扩展，以使用全最小耦合哈密顿，其中与空间和时间相关的矢量势与物质系统耦合，其对辐射场的反作用由全电流密度产生。开源章鱼（Octopus）代码中的实现设计用于大规模并行多尺度模拟，考虑了麦克斯韦和物质子系统的不同网格间距。在此，我们展示了这一框架的首次应用，以模拟电子波包的重正化切伦科夫辐射、非手性光在手性分子系统中的磁光效应，以及二聚体中的重正化质子模式。我们表明，在某些情况下，长度规的多极扩展哈密顿无法捕捉到超越偶极的效应。最后，我们讨论了该框架在扭曲光与轨道角动量、非弹性光散射和强场物理领域带来的更多机遇。
{"title":"Full minimal coupling Maxwell-TDDFT: an ab initio QED framework beyond the dipole approximation","authors":"Franco P. Bonafé, Esra Ilke Albar, Sebastian T. Ohlmann, Valeriia P. Kosheleva, Carlos M. Bustamante, Francesco Troisi, Angel Rubio, Heiko Appel","doi":"arxiv-2409.08959","DOIUrl":"https://doi.org/arxiv-2409.08959","url":null,"abstract":"We report the first ab initio, non-relativistic QED method that couples light\u0000and matter self-consistently beyond the electric dipole approximation and\u0000without multipolar truncations. This method is based on an extension of the\u0000known Maxwell-Pauli-Kohn-Sham approach for the use of a full minimal coupling\u0000Hamiltonian, where the space- and time-dependent vector potential is coupled to\u0000the matter system, and its back-reaction to the radiated fields is generated by\u0000the full current density. The implementation in the open-source Octopus code is\u0000designed for massively-parallel multiscale simulations considering different\u0000grid spacings for the Maxwell and matter subsystems. Here, we show the first\u0000applications of this framework to simulate renormalized Cherenkov radiation of\u0000an electronic wavepacket, magnetooptical effects with non-chiral light in\u0000non-chiral molecular systems, and renormalized plasmonic modes in a\u0000nanoplasmonic dimer. We show that in some cases the beyond-dipole effects can\u0000not be captured by a multipolar expansion Hamiltonian in length gauge. Finally,\u0000we discuss further opportunities enabled by the framework in the field of\u0000twisted light and orbital angular momentum, inelastic light scattering and\u0000strong field physics.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kunyan Zhang, Chuliang Fu, Shelly Kelly, Liangbo Liang, Seoung-Hun Kang, Jing Jiang, Ruifang Zhang, Yixiu Wang, Gang Wan, Phum Siriviboon, Mina Yoon, Peide Ye, Wenzhuo Wu, Mingda Li, Shengxi Huang
Polarons, quasiparticles arising from electron-phonon coupling, are crucial in understanding material properties such as high-temperature superconductivity and colossal magnetoresistance. However, scarce studies have been performed to investigate the formation of polarons in low-dimensional materials with phonon polarity and electronic structure transitions. In this work, we studied polarons of tellurene that are composed of chiral chains of tellurium atoms. The frequency and linewidth of the A1 phonon, which becomes increasingly polar for thinner tellurene, exhibit an abrupt change when the thickness of tellurene is below 10 nm. Meanwhile, the field effect mobility of tellurene drops rapidly as the thickness is smaller than 10 nm. These phonon and transport signatures, combined with the calculated phonon polarity and band structure, suggest a crossover from large polarons for bulk tellurium to small polarons for few-layer tellurene. Effective field theory considers the phonon renormalization in the strong coupling (small polaron) regime, and semi-quantitatively reproduces the observed phonon hardening and broadening effects in few-layer tellurene. This polaron crossover stems from the quasi-1D nature of tellurene where modulation of the interchain distance reduces the dielectric screening and promotes electron-phonon coupling. Our work provides valuable insights into the influence of polarons on phononic, electronic, and structural properties in low-dimensional materials.
{"title":"Thickness-Dependent Polaron Crossover in Tellurene","authors":"Kunyan Zhang, Chuliang Fu, Shelly Kelly, Liangbo Liang, Seoung-Hun Kang, Jing Jiang, Ruifang Zhang, Yixiu Wang, Gang Wan, Phum Siriviboon, Mina Yoon, Peide Ye, Wenzhuo Wu, Mingda Li, Shengxi Huang","doi":"arxiv-2409.08458","DOIUrl":"https://doi.org/arxiv-2409.08458","url":null,"abstract":"Polarons, quasiparticles arising from electron-phonon coupling, are crucial\u0000in understanding material properties such as high-temperature superconductivity\u0000and colossal magnetoresistance. However, scarce studies have been performed to\u0000investigate the formation of polarons in low-dimensional materials with phonon\u0000polarity and electronic structure transitions. In this work, we studied\u0000polarons of tellurene that are composed of chiral chains of tellurium atoms.\u0000The frequency and linewidth of the A1 phonon, which becomes increasingly polar\u0000for thinner tellurene, exhibit an abrupt change when the thickness of tellurene\u0000is below 10 nm. Meanwhile, the field effect mobility of tellurene drops rapidly\u0000as the thickness is smaller than 10 nm. These phonon and transport signatures,\u0000combined with the calculated phonon polarity and band structure, suggest a\u0000crossover from large polarons for bulk tellurium to small polarons for\u0000few-layer tellurene. Effective field theory considers the phonon\u0000renormalization in the strong coupling (small polaron) regime, and\u0000semi-quantitatively reproduces the observed phonon hardening and broadening\u0000effects in few-layer tellurene. This polaron crossover stems from the quasi-1D\u0000nature of tellurene where modulation of the interchain distance reduces the\u0000dielectric screening and promotes electron-phonon coupling. Our work provides\u0000valuable insights into the influence of polarons on phononic, electronic, and\u0000structural properties in low-dimensional materials.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142268810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The optimization of physical parameters serves various purposes, such as system identification and efficiency in developing devices. Spin-torque oscillators have been applied to neuromorphic computing experimentally and theoretically, but the optimization of their physical parameters has usually been done by grid search. In this paper, we propose a scheme to optimize the parameters of the dynamics of macrospin-type spin-torque oscillators using the gradient descent method with automatic differentiation. First, we prepared numerically created dynamics as teacher data and successfully tuned the parameters to reproduce the dynamics. This can be applied to obtain the correspondence between the simulation and experiment of the spin-torque oscillators. Next, we successfully solved the image recognition task with high accuracy by connecting the coupled system of spin-torque oscillators to the input and output layers and training all of them through gradient descent. This approach allowed us to estimate how to control the experimental setup and design the physical systems so that the task could be solved with a high accuracy using spin-torque oscillators.
{"title":"Gradient-based optimization of spintronic devices","authors":"Yusuke Imai, Shuhong Liu, Nozomi Akashi, Kohei Nakajima","doi":"arxiv-2409.09105","DOIUrl":"https://doi.org/arxiv-2409.09105","url":null,"abstract":"The optimization of physical parameters serves various purposes, such as\u0000system identification and efficiency in developing devices. Spin-torque\u0000oscillators have been applied to neuromorphic computing experimentally and\u0000theoretically, but the optimization of their physical parameters has usually\u0000been done by grid search. In this paper, we propose a scheme to optimize the\u0000parameters of the dynamics of macrospin-type spin-torque oscillators using the\u0000gradient descent method with automatic differentiation. First, we prepared\u0000numerically created dynamics as teacher data and successfully tuned the\u0000parameters to reproduce the dynamics. This can be applied to obtain the\u0000correspondence between the simulation and experiment of the spin-torque\u0000oscillators. Next, we successfully solved the image recognition task with high\u0000accuracy by connecting the coupled system of spin-torque oscillators to the\u0000input and output layers and training all of them through gradient descent. This\u0000approach allowed us to estimate how to control the experimental setup and\u0000design the physical systems so that the task could be solved with a high\u0000accuracy using spin-torque oscillators.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"54 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The traditional Landau-Lifshitz-Gilbert (LLG) equation has often delineated the linear and nonlinear magnetization dynamics, even at ultrashort timescales e.g., femtoseconds. In contrast, several other non-relativistic and relativistic spin torques have been reported as an extension of the LLG spin dynamics. Here, we explore the contribution of the relativistic field-derivative torque (FDT) in the nonlinear THz magnetization dynamics response applied to ferrimagnets with high Gilbert damping and exchange magnon frequency. Our findings suggest that the FDT plays a significant role in magnetization dynamics in both linear and nonlinear regimes, bridging the gap between the traditional LLG spin dynamics and experimental observations. We find that the coherent THz magnon excitation amplitude is enhanced with the field-derivative torque. Furthermore, a phase shift in the magnon oscillation is induced by the FDT term. This phase shift is almost 90 for the antiferromagnet, while it is almost zero for the ferrimagnet under our investigation. Analyzing the dual THz excitation and their FDT, we find that the nonlinear signals can not be distinctly observed without the FDT terms. However, the inclusion of the FDT terms produces distinct nonlinear signals which matches extremely well with the previously reported experimental results.
{"title":"Role of material-dependent properties in THz field-derivative-torque-induced nonlinear magnetization dynamics","authors":"Arpita Dutta, Pratyay Mukherjee, Swosti P. Sarangi, Somasree Bhattacharjee, Shovon Pal, Ritwik Mondal","doi":"arxiv-2409.08541","DOIUrl":"https://doi.org/arxiv-2409.08541","url":null,"abstract":"The traditional Landau-Lifshitz-Gilbert (LLG) equation has often delineated\u0000the linear and nonlinear magnetization dynamics, even at ultrashort timescales\u0000e.g., femtoseconds. In contrast, several other non-relativistic and\u0000relativistic spin torques have been reported as an extension of the LLG spin\u0000dynamics. Here, we explore the contribution of the relativistic\u0000field-derivative torque (FDT) in the nonlinear THz magnetization dynamics\u0000response applied to ferrimagnets with high Gilbert damping and exchange magnon\u0000frequency. Our findings suggest that the FDT plays a significant role in\u0000magnetization dynamics in both linear and nonlinear regimes, bridging the gap\u0000between the traditional LLG spin dynamics and experimental observations. We\u0000find that the coherent THz magnon excitation amplitude is enhanced with the\u0000field-derivative torque. Furthermore, a phase shift in the magnon oscillation\u0000is induced by the FDT term. This phase shift is almost 90 for the\u0000antiferromagnet, while it is almost zero for the ferrimagnet under our\u0000investigation. Analyzing the dual THz excitation and their FDT, we find that\u0000the nonlinear signals can not be distinctly observed without the FDT terms.\u0000However, the inclusion of the FDT terms produces distinct nonlinear signals\u0000which matches extremely well with the previously reported experimental results.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"49 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We derive the angular generation density of photoexcited carriers in gapless and gapped Bernal bilayer graphene. Exploiting the strong anisotropy of the band structure of bilayer graphene at low energies due to trigonal warping, we show that charge carriers belonging to different valleys propagate to different sides of the light spot upon photoexcitation. Importantly, in this low-energy regime, inter-valley electron-phonon scattering is suppressed, thereby protecting the valley index. This optically induced valley polarisation can be further enhanced via momentum alignment associated with linearly-polarised light. We then consider gapped bilayer graphene (for example with the gap induced by external top- and back-gates) and show that it exhibits valley-dependent optical selection rules with circularly-polarised light analogous to other gapped Dirac materials, such as transition metal dichalcogenides. Consequently, gapped bilayer graphene can be exploited to optically detect valley polarisation. Thus, we predict an optical valley Hall effect - the emission of two different circular polarisations from different sides of the light spot, upon linearly-polarised excitation. We also propose two realistic experimental setups in gapless and gapped bilayer graphene as a basis for novel optovalleytronic devices operating in the elusive terahertz regime.
{"title":"Valley separation of photoexcited carriers in bilayer graphene","authors":"T. J. Osborne, M. E. Portnoi, E. Mariani","doi":"arxiv-2409.08807","DOIUrl":"https://doi.org/arxiv-2409.08807","url":null,"abstract":"We derive the angular generation density of photoexcited carriers in gapless\u0000and gapped Bernal bilayer graphene. Exploiting the strong anisotropy of the\u0000band structure of bilayer graphene at low energies due to trigonal warping, we\u0000show that charge carriers belonging to different valleys propagate to different\u0000sides of the light spot upon photoexcitation. Importantly, in this low-energy\u0000regime, inter-valley electron-phonon scattering is suppressed, thereby\u0000protecting the valley index. This optically induced valley polarisation can be\u0000further enhanced via momentum alignment associated with linearly-polarised\u0000light. We then consider gapped bilayer graphene (for example with the gap\u0000induced by external top- and back-gates) and show that it exhibits\u0000valley-dependent optical selection rules with circularly-polarised light\u0000analogous to other gapped Dirac materials, such as transition metal\u0000dichalcogenides. Consequently, gapped bilayer graphene can be exploited to\u0000optically detect valley polarisation. Thus, we predict an optical valley Hall\u0000effect - the emission of two different circular polarisations from different\u0000sides of the light spot, upon linearly-polarised excitation. We also propose\u0000two realistic experimental setups in gapless and gapped bilayer graphene as a\u0000basis for novel optovalleytronic devices operating in the elusive terahertz\u0000regime.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We demonstrate that (001) grown Cd3As2 thin films with a superlattice-patterned gate can potentially realize the moir'e Bernevig-Hughes-Zhang (BHZ) model. Our calculations identify the parameterization region necessary to achieve topological flat mini-bands with a C4z symmetric and a C6z symmetric potential. Additionally, we show that a spin-polarized state can serve as the minimal platform for hosting the moir'e induced quantum anomalous Hall effect, supported by Hartree Fock interaction kernel analysis and self-consistent mean field calculations.
{"title":"Artificial moiré engineering for an ideal BHZ model","authors":"Wangqian Miao, Arman Rashidi, Xi Dai","doi":"arxiv-2409.08540","DOIUrl":"https://doi.org/arxiv-2409.08540","url":null,"abstract":"We demonstrate that (001) grown Cd3As2 thin films with a\u0000superlattice-patterned gate can potentially realize the moir'e\u0000Bernevig-Hughes-Zhang (BHZ) model. Our calculations identify the\u0000parameterization region necessary to achieve topological flat mini-bands with a\u0000C4z symmetric and a C6z symmetric potential. Additionally, we show that a\u0000spin-polarized state can serve as the minimal platform for hosting the moir'e\u0000induced quantum anomalous Hall effect, supported by Hartree Fock interaction\u0000kernel analysis and self-consistent mean field calculations.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The quasi-static transverse conductivity of clean Fermi liquids at long wavelengths displays a remarkably universal behaviour: it is determined solely by the radius of curvature of the Fermi surface and does not depend on details such as the quasi-particle mass or their interactions. Here we demonstrate that Berry phases do not alter such universality by directly computing the transverse conductivity of two-dimensional electronic systems with Dirac dispersions, such as those appearing in graphene and its chiral multilayer variants. Interestingly, however, such universality ceases to hold at wave-vectors comparable to the Fermi radius, where Dirac fermions display a vividly distict transverse conductivity relative to parabolic Fermions, with a rich wave-vector dependence that includes divergences, oscillations and zeroes. We discuss how this can be probed by measuring the $T_1$ relaxation time of spin qubits, such as NV centers or nuclear spins, placed near such 2D systems.
{"title":"Berry phase effects on the transverse conductivity of Fermi surfaces and their detection via spin qubit noise magnetometry","authors":"Mark Morgenthaler, Inti Sodemann Villadiego","doi":"arxiv-2409.09117","DOIUrl":"https://doi.org/arxiv-2409.09117","url":null,"abstract":"The quasi-static transverse conductivity of clean Fermi liquids at long\u0000wavelengths displays a remarkably universal behaviour: it is determined solely\u0000by the radius of curvature of the Fermi surface and does not depend on details\u0000such as the quasi-particle mass or their interactions. Here we demonstrate that\u0000Berry phases do not alter such universality by directly computing the\u0000transverse conductivity of two-dimensional electronic systems with Dirac\u0000dispersions, such as those appearing in graphene and its chiral multilayer\u0000variants. Interestingly, however, such universality ceases to hold at\u0000wave-vectors comparable to the Fermi radius, where Dirac fermions display a\u0000vividly distict transverse conductivity relative to parabolic Fermions, with a\u0000rich wave-vector dependence that includes divergences, oscillations and zeroes.\u0000We discuss how this can be probed by measuring the $T_1$ relaxation time of\u0000spin qubits, such as NV centers or nuclear spins, placed near such 2D systems.","PeriodicalId":501137,"journal":{"name":"arXiv - PHYS - Mesoscale and Nanoscale Physics","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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