Michael Deimetry, Timothy C. Petersen, Hamish G. Brown, Matthew Weyland, Scott D. Findlay
Differential Phase Contrast (DPC) imaging, in which deviations in the bright field beam are in proportion to the electric field, has been extensively studied in the context of pure elastic scattering. Here we discuss differential phase contrast formed from core-loss scattered electrons, i.e. those that have caused inner shell ionization of atoms in the specimen, using a transition potential approach for which we study the convergence properties. In the phase object approximation, we show formally that this is mainly a result of preservation of elastic contrast. Through simulation we demonstrate that whether the inelastic DPC images show element selective contrast depends on the spatial range of the ionization interaction, and specifically that when the energy loss is low the delocalisation can lead to contributions to the contrast from atoms other than that ionized. We further show that inelastic DPC images remain robustly interpretable to larger thicknesses than is the case for elastic DPC images, owing to the incoherence of the inelastic wavefields, though subtleties due to channelling remain.
{"title":"Differential phase contrast from electrons that cause inner shell ionization","authors":"Michael Deimetry, Timothy C. Petersen, Hamish G. Brown, Matthew Weyland, Scott D. Findlay","doi":"arxiv-2405.09043","DOIUrl":"https://doi.org/arxiv-2405.09043","url":null,"abstract":"Differential Phase Contrast (DPC) imaging, in which deviations in the bright\u0000field beam are in proportion to the electric field, has been extensively\u0000studied in the context of pure elastic scattering. Here we discuss differential\u0000phase contrast formed from core-loss scattered electrons, i.e. those that have\u0000caused inner shell ionization of atoms in the specimen, using a transition\u0000potential approach for which we study the convergence properties. In the phase\u0000object approximation, we show formally that this is mainly a result of\u0000preservation of elastic contrast. Through simulation we demonstrate that\u0000whether the inelastic DPC images show element selective contrast depends on the\u0000spatial range of the ionization interaction, and specifically that when the\u0000energy loss is low the delocalisation can lead to contributions to the contrast\u0000from atoms other than that ionized. We further show that inelastic DPC images\u0000remain robustly interpretable to larger thicknesses than is the case for\u0000elastic DPC images, owing to the incoherence of the inelastic wavefields,\u0000though subtleties due to channelling remain.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"50 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141059885","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}
Marc Joosten, Michal Repisky, Marius Kadek, Pekka Pyykkö, Kenneth Ruud
We present an all-electron, four-component relativistic implementation of electric field gradients (EFGs) at the nuclei using Gaussian-type orbitals and periodic boundary conditions. This allows us to include relativistic effects variationally, which is important for compounds containing heavy elements and for a property dependent the electronic structure close to the nuclei. The all-electron approach ensures an accurate treatment of both core and valence orbitals, as both are important in the evaluation of EFGs. Computational efficiency is achieved through the use of a recent implementation of density fitting in combination with quaternion algebra and restricted kinetic balance. We use the relativistic approach to calculate the EFGs in different arsenic, antimony and bismuth halides and oxyhalides, and explore the importance of relativistic effects on EFGs in solids and compare these with results obtained for molecular species. Our calculations contribute to establishing a reliable estimate for the nuclear quadrupole moment of 209Bi, for which our best estimate is -428(17) mb, in excellent agreement both with molecular data and a recent reevaluation of the nuclear quadrupole moment obtained from atomic data and ab initio calculations. Our results suggest that there is a need to revisit the experimental data for the EFGs of several bismuth oxyhalides.
我们利用高斯型轨道和周期边界条件，提出了一种全电子、四分量的原子核电场梯度（EFGs）相对论实现方法。这使我们能够在不同程度上包含相对论效应，这对于含有重元素的化合物和依赖于靠近原子核的电子结构的特性来说非常重要。全电子方法确保了对核轨道和价轨道的精确处理，因为两者在 EFG 评估中都很重要。我们使用相对论方法计算了不同砷、锑和铋卤化物和氧卤化物中的 EFGs，探讨了相对论效应对固体中 EFGs 的重要性，并将这些结果与分子物种的计算结果进行了比较。我们的计算有助于为 209Bi 的核四极矩建立一个可靠的估计值，我们的最佳估计值为-428(17) mb，与分子数据以及最近通过原子数据和 ab initio 计算获得的核四极矩重新评估结果非常一致。我们的结果表明，有必要重新研究几种氧卤化铋的 EFG 的实验数据。
{"title":"Electric-field gradients at the nuclei from all-electron, four-component relativistic density-functional theory using Gaussian-type orbitals","authors":"Marc Joosten, Michal Repisky, Marius Kadek, Pekka Pyykkö, Kenneth Ruud","doi":"arxiv-2405.07832","DOIUrl":"https://doi.org/arxiv-2405.07832","url":null,"abstract":"We present an all-electron, four-component relativistic implementation of\u0000electric field gradients (EFGs) at the nuclei using Gaussian-type orbitals and\u0000periodic boundary conditions. This allows us to include relativistic effects\u0000variationally, which is important for compounds containing heavy elements and\u0000for a property dependent the electronic structure close to the nuclei. The\u0000all-electron approach ensures an accurate treatment of both core and valence\u0000orbitals, as both are important in the evaluation of EFGs. Computational\u0000efficiency is achieved through the use of a recent implementation of density\u0000fitting in combination with quaternion algebra and restricted kinetic balance.\u0000We use the relativistic approach to calculate the EFGs in different arsenic,\u0000antimony and bismuth halides and oxyhalides, and explore the importance of\u0000relativistic effects on EFGs in solids and compare these with results obtained\u0000for molecular species. Our calculations contribute to establishing a reliable\u0000estimate for the nuclear quadrupole moment of 209Bi, for which our best\u0000estimate is -428(17) mb, in excellent agreement both with molecular data and a\u0000recent reevaluation of the nuclear quadrupole moment obtained from atomic data\u0000and ab initio calculations. Our results suggest that there is a need to revisit\u0000the experimental data for the EFGs of several bismuth oxyhalides.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"42 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931448","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 present a model of electron-atoms (elastic) scattering of electrons in matter, applicable in a wide electron energy range from ~eV up to relativistic ones. The approach based on the dynamic-structure factor considers dynamical screening of atomic nuclei in a target by valence (collective) and core-shell electrons, dependent on the incident electron velocity. The model allows simulating electron transport in matter with a unified approach to the elastic scattering. The cross section recovers the limiting cases of the electron-phonon scattering in the low energy limit, and a screened-ion scattering with the decreasing screening reducing to the scattering on a bare nucleus in the high energy limit.
{"title":"Wide energy range cross section of elastic electron scattering in matter: dependence of dynamical screening of target atoms on electron velocity","authors":"N. Medvedev, D. I. Zainutdinov, A. E. Volkov","doi":"arxiv-2405.06950","DOIUrl":"https://doi.org/arxiv-2405.06950","url":null,"abstract":"We present a model of electron-atoms (elastic) scattering of electrons in\u0000matter, applicable in a wide electron energy range from ~eV up to relativistic\u0000ones. The approach based on the dynamic-structure factor considers dynamical\u0000screening of atomic nuclei in a target by valence (collective) and core-shell\u0000electrons, dependent on the incident electron velocity. The model allows\u0000simulating electron transport in matter with a unified approach to the elastic\u0000scattering. The cross section recovers the limiting cases of the\u0000electron-phonon scattering in the low energy limit, and a screened-ion\u0000scattering with the decreasing screening reducing to the scattering on a bare\u0000nucleus in the high energy limit.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"90 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931450","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}
Alexey S. Kotykhov, Konstantin Gubaev, Vadim Sotskov, Christian Tantardini, Max Hodapp, Alexander V. Shapeev, Ivan S. Novikov
We propose a novel method for fitting machine-learning interatomic potentials with magnetic degrees of freedom, namely, magnetic Moment Tensor Potentials (mMTP). The main feature of the methodology consists in fitting mMTP to magnetic forces (negative derivatives of energies with respect to magnetic moments) derived from spin-polarized density functional theory calculations. We test our method on the bcc Fe-Al system with different composition. Specifically, we calculate formation energies, equilibrium lattice parameter, and total cell magnetization. Our findings demonstrate a precise match between values calculated with mMTP and those obtained by DFT at zero temperature. Additionally, using molecular dynamics, we estimate the finite temperature lattice parameter and capture the cell expansion as was previously revealed in experiment. We demonstrate that mMTPs fitted to magnetic forces, increase the relaxation reliability, which is the percent of successfully relaxed structures (i.e. with almost zero forces, stresses, and magnetic moments after the optimization of geometry). Eventually, we show that the proposed methodology can provide an accurate and reliable mMTP with reduced number of computationally complex spin-polarized density functional theory calculations.
{"title":"Fitting to magnetic forces improves the reliability of magnetic Moment Tensor Potentials","authors":"Alexey S. Kotykhov, Konstantin Gubaev, Vadim Sotskov, Christian Tantardini, Max Hodapp, Alexander V. Shapeev, Ivan S. Novikov","doi":"arxiv-2405.07069","DOIUrl":"https://doi.org/arxiv-2405.07069","url":null,"abstract":"We propose a novel method for fitting machine-learning interatomic potentials\u0000with magnetic degrees of freedom, namely, magnetic Moment Tensor Potentials\u0000(mMTP). The main feature of the methodology consists in fitting mMTP to\u0000magnetic forces (negative derivatives of energies with respect to magnetic\u0000moments) derived from spin-polarized density functional theory calculations. We\u0000test our method on the bcc Fe-Al system with different composition.\u0000Specifically, we calculate formation energies, equilibrium lattice parameter,\u0000and total cell magnetization. Our findings demonstrate a precise match between\u0000values calculated with mMTP and those obtained by DFT at zero temperature.\u0000Additionally, using molecular dynamics, we estimate the finite temperature\u0000lattice parameter and capture the cell expansion as was previously revealed in\u0000experiment. We demonstrate that mMTPs fitted to magnetic forces, increase the\u0000relaxation reliability, which is the percent of successfully relaxed structures\u0000(i.e. with almost zero forces, stresses, and magnetic moments after the\u0000optimization of geometry). Eventually, we show that the proposed methodology\u0000can provide an accurate and reliable mMTP with reduced number of\u0000computationally complex spin-polarized density functional theory calculations.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140935762","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}
Alexander Yue, Rubem Mondaini, Qiujiang Guo, Richard T. Scalettar
Quantum state transfer (QST) describes the coherent passage of quantum information from one node in a network to another. Experiments on QST span a diverse set of platforms and currently report transport across up to tens of nodes in times of several hundred nanoseconds with fidelities that can approach 90% or more. Theoretical studies examine both the lossless time evolution associated with a given (Hermitian) lattice Hamiltonian and methods based on the master equation that allows for losses. In this paper, we describe Monte Carlo techniques which enable the discovery of a Hamiltonian that gives high-fidelity QST. We benchmark our approach in geometries appropriate to coupled optical cavity-emitter arrays and discuss connections to condensed matter Hamiltonians of localized orbitals coupled to conduction bands. The resulting Jaynes-Cummings-Hubbard and periodic Anderson models can, in principle, be engineered in appropriate hardware to give efficient QST.
{"title":"Quantum State Transfer in Interacting, Multiple-Excitation Systems","authors":"Alexander Yue, Rubem Mondaini, Qiujiang Guo, Richard T. Scalettar","doi":"arxiv-2405.06853","DOIUrl":"https://doi.org/arxiv-2405.06853","url":null,"abstract":"Quantum state transfer (QST) describes the coherent passage of quantum\u0000information from one node in a network to another. Experiments on QST span a\u0000diverse set of platforms and currently report transport across up to tens of\u0000nodes in times of several hundred nanoseconds with fidelities that can approach\u000090% or more. Theoretical studies examine both the lossless time evolution\u0000associated with a given (Hermitian) lattice Hamiltonian and methods based on\u0000the master equation that allows for losses. In this paper, we describe Monte\u0000Carlo techniques which enable the discovery of a Hamiltonian that gives\u0000high-fidelity QST. We benchmark our approach in geometries appropriate to\u0000coupled optical cavity-emitter arrays and discuss connections to condensed\u0000matter Hamiltonians of localized orbitals coupled to conduction bands. The\u0000resulting Jaynes-Cummings-Hubbard and periodic Anderson models can, in\u0000principle, be engineered in appropriate hardware to give efficient QST.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"181 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140935722","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}
Seung Gyo Jeong, In Hyeok Choi, Sreejith Nair, Luca Buiarelli, Bita Pourbahari, Jin Young Oh, Nabil Bassim, Ambrose Seo, Woo Seok Choi, Rafael M. Fernandes, Turan Birol, Liuyan Zhao, Jong Seok Lee, Bharat Jalan
Altermagnetism refers to a wide class of compensated magnetic orders featuring magnetic sublattices with opposite spins related by rotational symmetry rather than inversion or translational operations, resulting in non-trivial spin splitting and high-order multipolar orders. Here, by combining theoretical analysis, electrical transport, X-ray and optical spectroscopies, and nonlinear optical measurements, we establish a phase diagram in hybrid molecular beam epitaxy-grown RuO2/TiO2 (110) films, mapping the broken symmetries along the altermagnetic/electronic/structural phase transitions as functions of film thickness and temperature. This phase diagram features a novel altermagnetic metallic polar phase in strained 2 nm samples, extending the concept of multiferroics to altermagnetic systems. These results provide a comprehensive understanding of altermagnetism upon epitaxial heterostructure design for emergent novel phases with multifunctionalities.
{"title":"Altermagnetic Polar Metallic phase in Ultra-Thin Epitaxially-Strained RuO2 Films","authors":"Seung Gyo Jeong, In Hyeok Choi, Sreejith Nair, Luca Buiarelli, Bita Pourbahari, Jin Young Oh, Nabil Bassim, Ambrose Seo, Woo Seok Choi, Rafael M. Fernandes, Turan Birol, Liuyan Zhao, Jong Seok Lee, Bharat Jalan","doi":"arxiv-2405.05838","DOIUrl":"https://doi.org/arxiv-2405.05838","url":null,"abstract":"Altermagnetism refers to a wide class of compensated magnetic orders\u0000featuring magnetic sublattices with opposite spins related by rotational\u0000symmetry rather than inversion or translational operations, resulting in\u0000non-trivial spin splitting and high-order multipolar orders. Here, by combining\u0000theoretical analysis, electrical transport, X-ray and optical spectroscopies,\u0000and nonlinear optical measurements, we establish a phase diagram in hybrid\u0000molecular beam epitaxy-grown RuO2/TiO2 (110) films, mapping the broken\u0000symmetries along the altermagnetic/electronic/structural phase transitions as\u0000functions of film thickness and temperature. This phase diagram features a\u0000novel altermagnetic metallic polar phase in strained 2 nm samples, extending\u0000the concept of multiferroics to altermagnetic systems. These results provide a\u0000comprehensive understanding of altermagnetism upon epitaxial heterostructure\u0000design for emergent novel phases with multifunctionalities.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931446","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}
M. Matzelle, Wei-Chi Chiu, Caiyun Hong, Barun Ghosh, Pengxu Ran, R. S. Markiewicz, B. Barbiellini, Changxi Zheng, Sheng Li, Rui-Hua He, Arun Bansil
A key insight of Einstein's theory of the photoelectric effect is that a minimum energy is required for photoexcited electrons to escape from a material. For the past century it has been assumed that photoexcited electrons of lower energies make no contribution to the photoemission spectrum. Here we demonstrate the conceptual possibility that the energy of these 'failed' photoelectrons-primary or secondary-can be partially recycled to generate new 'tertiary' electrons of energy sufficient to escape. Such a 'recycling' step goes beyond the traditional three steps of the photoemission process (excitation, transport, and escape), and, as we illustrate, it can be realized through a novel Auger mechanism that involves three distinct minority electronic states in the material. We develop a phenomenological three-band model to treat this mechanism within a revised four-step framework for photoemission, which contains robust features of linewidth narrowing and population inversion under strong excitation, reminiscent of the lasing phenomena. We show that the conditions for this recycling mechanism are likely satisfied in many quantum materials with multiple flat bands properly located away from the Fermi level, and elaborate on the representative case of SrTiO3 among other promising candidates. We further discuss how this mechanism can explain the recent observation of anomalous intense coherent photoemission from a SrTiO3 surface, and predict its manifestations in related experiments, including the 'forbidden' case of photoemission with photon energies lower than the work function. Our study calls for paradigm shifts across a range of fundamental and applied research fields, especially in the areas of photoemission, photocathodes, and flat-band materials.
{"title":"Recycling failed photoelectrons via tertiary photoemission","authors":"M. Matzelle, Wei-Chi Chiu, Caiyun Hong, Barun Ghosh, Pengxu Ran, R. S. Markiewicz, B. Barbiellini, Changxi Zheng, Sheng Li, Rui-Hua He, Arun Bansil","doi":"arxiv-2405.06141","DOIUrl":"https://doi.org/arxiv-2405.06141","url":null,"abstract":"A key insight of Einstein's theory of the photoelectric effect is that a\u0000minimum energy is required for photoexcited electrons to escape from a\u0000material. For the past century it has been assumed that photoexcited electrons\u0000of lower energies make no contribution to the photoemission spectrum. Here we\u0000demonstrate the conceptual possibility that the energy of these 'failed'\u0000photoelectrons-primary or secondary-can be partially recycled to generate new\u0000'tertiary' electrons of energy sufficient to escape. Such a 'recycling' step\u0000goes beyond the traditional three steps of the photoemission process\u0000(excitation, transport, and escape), and, as we illustrate, it can be realized\u0000through a novel Auger mechanism that involves three distinct minority\u0000electronic states in the material. We develop a phenomenological three-band\u0000model to treat this mechanism within a revised four-step framework for\u0000photoemission, which contains robust features of linewidth narrowing and\u0000population inversion under strong excitation, reminiscent of the lasing\u0000phenomena. We show that the conditions for this recycling mechanism are likely\u0000satisfied in many quantum materials with multiple flat bands properly located\u0000away from the Fermi level, and elaborate on the representative case of SrTiO3\u0000among other promising candidates. We further discuss how this mechanism can\u0000explain the recent observation of anomalous intense coherent photoemission from\u0000a SrTiO3 surface, and predict its manifestations in related experiments,\u0000including the 'forbidden' case of photoemission with photon energies lower than\u0000the work function. Our study calls for paradigm shifts across a range of\u0000fundamental and applied research fields, especially in the areas of\u0000photoemission, photocathodes, and flat-band materials.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"127 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931444","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 different types of magnetism arise mainly from how electrons move and interact with each other. In this work, we show how protons (H$^+$) also exhibit magnetic behavior. We measured the magnetic susceptibility of the ammonium halides and identified pronounced increases at 232 K, 233 K and 243 K for NH$_4$I, NH$_4$Br and NH$_4$Cl, respectively, which all coincide to the geometric ordering of its ammonium cations. With extensive literature establishing the fact that the ammonium cations exhibit rotational motion even towards the lowest temperatures, we take into account that the orbital motion of the protons carries a magnetic moment and find it to be larger than that of the paired electrons. Consequently, the structural phase transitions are magnetically-driven as the system attempts to lift 8-fold energy degeneracies of the proton orbitals via Jahn-Teller distortions. Our findings identify that NH$_4$$^+$ cations are capable of comprising magnetism which appears to be ubiquitous in ammonia-based molecular solids.
不同类型的磁性主要源于电子如何移动和相互影响。在这项研究中，我们展示了质子（H$^+$）也如何表现出磁性。我们测量了卤化铵的磁感应强度，发现 NH$_4$I、NH$_4$Br 和 NH$_4$Cl 分别在 232 K、233 K 和 243 K 时磁感应强度明显增加，这都与铵阳离子的几何排序相吻合。大量文献证实，铵阳离子在最低温度下会出现旋转运动，我们考虑到质子的轨道运动带有磁矩，并发现其磁矩大于成对电子的磁矩。因此，结构相变是由磁力驱动的，因为系统试图通过扬-泰勒畸变来解除质子轨道的 8 倍能量退变性。我们的研究结果表明，NH$_4$$^+$ 阳离子能够产生磁性，而这种磁性在氨基分子固体中似乎无处不在。
{"title":"Magnetic Ordering of Ammonium Cations in NH$_4$I, NH$_4$Br and NH$_4$Cl","authors":"Fei Yen, Lei Meng, Tian Gao, Sixia Hu","doi":"arxiv-2405.03163","DOIUrl":"https://doi.org/arxiv-2405.03163","url":null,"abstract":"The different types of magnetism arise mainly from how electrons move and\u0000interact with each other. In this work, we show how protons (H$^+$) also\u0000exhibit magnetic behavior. We measured the magnetic susceptibility of the\u0000ammonium halides and identified pronounced increases at 232 K, 233 K and 243 K\u0000for NH$_4$I, NH$_4$Br and NH$_4$Cl, respectively, which all coincide to the\u0000geometric ordering of its ammonium cations. With extensive literature\u0000establishing the fact that the ammonium cations exhibit rotational motion even\u0000towards the lowest temperatures, we take into account that the orbital motion\u0000of the protons carries a magnetic moment and find it to be larger than that of\u0000the paired electrons. Consequently, the structural phase transitions are\u0000magnetically-driven as the system attempts to lift 8-fold energy degeneracies\u0000of the proton orbitals via Jahn-Teller distortions. Our findings identify that\u0000NH$_4$$^+$ cations are capable of comprising magnetism which appears to be\u0000ubiquitous in ammonia-based molecular solids.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883184","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}
Jaspal Singh Bola, Ryan M. Stolley, Prashanna Poudel, Joel S. Miller, Christoph Boheme, Z. Valy Vardeny
This study revisits the electroabsorption (EA) spectrum of polyacetylene, as functions of the electric field strength, isomerization degree, and light polarization states. The EA spectrum of $cis$-$(CH)_x$ reveals an oscillatory feature that follows the Stark shift-related first derivative of the materials absorption spectrum that contains v(0-1) and v(0-2) sidebands of the excited $C=C$ stretching vibration that agrees well with the Raman spectrum. EA spectrum of $trans $-$(CH)_x$ does not match the first derivative of the materials absorption spectrum, and the phonon sideband frequency does not agree with the RS spectrum. EA spectrum of $trans $-$(CH)_x$ reveals a band below the first allowed $1B_u$ exciton. We interpret this feature as due to the electric field activated even-parity dark (forbidden) exciton, namely $mA_g$ ($m >1$), showing that the nonluminescent $trans $-$(CH)_x$ is due to the reverse order of the excited states, where a dark $mA_g$ exciton lies below the allowed $1B_u$ exciton. This agrees with the unusual phonon sideband in $trans $-$(CH)_x$ absorption, since the excited state attenuation caused by the fast internal conversion from $1B_u$ to $mA_g$ influences the apparent frequency that determines the phonon sideband. Consequently, from the EA and RS spectra we estimate the $1B_u$ lifetime in $trans $-$(CH)_x$ to be $sim 30$ fs. Integrated EA spectrum of $trans $-$(CH)_x$ shows a traditional Huang-Rhys type series with a relaxation parameter, $S sim 0.5$. This indicates that the EA spectrum of the $trans $ isomer is also determined by a Stark shift related to the first derivative of the absorption spectrum, but preferentially for the longest chains in the films chain lengths distribution. This is due to the $N^3$ response of the non-linear susceptibility, $chi^{(3)}$ ($sim$EA), dependence on the chain length having $N$ monomers.
{"title":"The influence of dark excitons on the electroabsorption spectrum of polyacetylene","authors":"Jaspal Singh Bola, Ryan M. Stolley, Prashanna Poudel, Joel S. Miller, Christoph Boheme, Z. Valy Vardeny","doi":"arxiv-2405.03012","DOIUrl":"https://doi.org/arxiv-2405.03012","url":null,"abstract":"This study revisits the electroabsorption (EA) spectrum of polyacetylene, as\u0000functions of the electric field strength, isomerization degree, and light\u0000polarization states. The EA spectrum of $cis$-$(CH)_x$ reveals an oscillatory\u0000feature that follows the Stark shift-related first derivative of the materials\u0000absorption spectrum that contains v(0-1) and v(0-2) sidebands of the excited\u0000$C=C$ stretching vibration that agrees well with the Raman spectrum. EA\u0000spectrum of $trans $-$(CH)_x$ does not match the first derivative of the\u0000materials absorption spectrum, and the phonon sideband frequency does not agree\u0000with the RS spectrum. EA spectrum of $trans $-$(CH)_x$ reveals a band below the\u0000first allowed $1B_u$ exciton. We interpret this feature as due to the electric\u0000field activated even-parity dark (forbidden) exciton, namely $mA_g$ ($m >1$),\u0000showing that the nonluminescent $trans $-$(CH)_x$ is due to the reverse order\u0000of the excited states, where a dark $mA_g$ exciton lies below the allowed\u0000$1B_u$ exciton. This agrees with the unusual phonon sideband in $trans\u0000$-$(CH)_x$ absorption, since the excited state attenuation caused by the fast\u0000internal conversion from $1B_u$ to $mA_g$ influences the apparent frequency\u0000that determines the phonon sideband. Consequently, from the EA and RS spectra\u0000we estimate the $1B_u$ lifetime in $trans $-$(CH)_x$ to be $sim 30$ fs.\u0000Integrated EA spectrum of $trans $-$(CH)_x$ shows a traditional Huang-Rhys type\u0000series with a relaxation parameter, $S sim 0.5$. This indicates that the EA\u0000spectrum of the $trans $ isomer is also determined by a Stark shift related to\u0000the first derivative of the absorption spectrum, but preferentially for the\u0000longest chains in the films chain lengths distribution. This is due to the\u0000$N^3$ response of the non-linear susceptibility, $chi^{(3)}$ ($sim$EA),\u0000dependence on the chain length having $N$ monomers.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"49 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140882955","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}
A python code (mvp.py) is presented for computing the mean-value point (MVP) in the Brillouin zone first introduced by Baldereschi [1]. The code allows calculations of the MVP for any input crystal structure. Having MVP allows approximating the Brillouin zone integrals of relatively smooth, periodic functions defined in the reciprocal space by the value of the same function at only one, mean-value, k-point. This approximation decreases computational cost at a relatively small decrease in accuracy. The MVP coordinates for the 14 Bravais lattices are evaluated and the underlying theory is discussed.
{"title":"A Python code for calculating the mean-value (Baldereschi's) point for any crystal structure","authors":"Vladan Stevanovic","doi":"arxiv-2405.00925","DOIUrl":"https://doi.org/arxiv-2405.00925","url":null,"abstract":"A python code (mvp.py) is presented for computing the mean-value point (MVP)\u0000in the Brillouin zone first introduced by Baldereschi [1]. The code allows\u0000calculations of the MVP for any input crystal structure. Having MVP allows\u0000approximating the Brillouin zone integrals of relatively smooth, periodic\u0000functions defined in the reciprocal space by the value of the same function at\u0000only one, mean-value, k-point. This approximation decreases computational cost\u0000at a relatively small decrease in accuracy. The MVP coordinates for the 14\u0000Bravais lattices are evaluated and the underlying theory is discussed.","PeriodicalId":501211,"journal":{"name":"arXiv - PHYS - Other Condensed Matter","volume":"133 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140826966","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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