Materials Science
- [1] arXiv:2405.09690 [pdf, ps, other]
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Title: The appeal of small molecules for practical nonlinear opticsComments: 11 pages, 5 figuresJournal-ref: Chem. Eur. J., 28, e202103168 (2022)Subjects: Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
Small organic molecules with a {\pi}-conjugated system that consists of only a few double or triple bonds can have significantly smaller optical excitation energies when equipped with donor- and acceptor groups, which raises the quantum limits to the molecular polarizabilities. As a consequence, third-order nonlinear optical polarizabilities become orders of magnitude larger than those of molecules of similar size without donor-acceptor substitution. This enables strong third-order nonlinear optical effects (as high as 1000 times those of silica glass) in dense, amorphous monolithic assemblies. These properties, accompanied by the possibility of deposition from the vapor phase and of electric-field poling at higher temperatures, make the resulting materials competitive towards adding an active nonlinear optical or electro-optic functionality to state-of-the-art integrated photonics platforms.
- [2] arXiv:2405.09759 [pdf, ps, other]
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Title: Ferroelectricity Driven by Orbital Resonance of Protons in CH$_3$NH$_3$Cl and CH$_3$NH$_3$BrComments: 5 pages, 5 figuresJournal-ref: J. Mater. Chem. C, 10, 1334-1338 (2022)Subjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
The $\beta$ and $\gamma$ phases of methylammonium chloride CH$_3$NH$_3$Cl and methylammonium bromide CH$_3$NH$_3$Br are identified to be ferroelectric $via$ pyroelectric current and dielectric constant measurements. The magnetic susceptibility also exhibits pronounced discontinuities at the Curie temperatures. We attribute the origin of spontaneous polarization to the emergence of two groups of proton orbital magnetic moments from the uncorrelated motion of the CH$_3$ and NH$_3$ groups in the $\beta$ and $\gamma$ phases. The two inequivalent frameworks of intermolecular orbital resonances interact with each other to distort the lattice in a non-centrosymmetric fashion. Our findings indicate that the structural instabilities in molecular frameworks are magnetic in origin as well as provide a new pathway toward uncovering new organic ferroelectrics.
- [3] arXiv:2405.09776 [pdf, ps, other]
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Title: Magnetic structure and magnetoelectric coupling in antiferromagnet Co5(TeO3)4Cl2B. Yu, L. Huang, J. S. Li, L. Lin, V. Ovidiu Garlea, Q. Zhang, T. Zou, J. C. Zhang, J. Peng, Y. S. Tang, G. Z. Zhou, J. H. Zhang, S. H. Zheng, M. F. Liu, Z. B. Yan, X. H. Zhou, S. Dong, J. G. Wan, J.-M. LiuComments: 31 pages, 9 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The van der Waals (vdW) layered multiferroics, which host simultaneous ferroelectric and magnetic orders, have attracted attention not only for their potentials to be utilized in nanoelectric devices and spintronics, but also offer alternative opportunities for emergent physical phenomena. To date, the vdW layered multiferroic materials are still very rare. In this work, we have investigated the magnetic structure and magnetoelectric effects in Co5(TeO3)4Cl2, a promising new multiferroic compound with antiferromagnetic (AFM) Neel point TN = 18 K. The neutron powder diffraction reveals the non-coplanar AFM state with preferred Neel vector along the c-axis, while a spin re-orientation occurring between 8 K and 15 K is identified, which results from the distinct temperature dependence of the non-equivalent Co sites moment in Co5(TeO3)4Cl2. What is more, it is found that Co5(TeO3)4Cl2 is one of the best vdW multiferroics studied so far in terms of the multiferroic performance. The measured linear ME coefficient exhibits the emergent oscillation dependence of the angle between magnetic field and electric field, and the maximal value is as big as 45 ps/m. It is suggested that Co5(TeO3)4Cl2 is an appreciated platform for exploring the emergent multiferroicity in vdW layered compounds.
- [4] arXiv:2405.09793 [pdf, ps, html, other]
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Title: Assessing carrier mobility, dopability, and defect tolerance in the chalcogenide perovskite BaZrS$_3$Zhenkun Yuan, Diana Dahliah, Romain Claes, Andrew Pike, David P. Fenning, Gian-Marco Rignanese, Geoffroy HautierSubjects: Materials Science (cond-mat.mtrl-sci)
The chalcogenide perovskite BaZrS$_3$ has attracted much attention as a promising solar absorber for thin-film photovoltaics. Here, we use first-principles calculations to evaluate its carrier transport and defect properties. We find that BaZrS$_3$ has a phonon-limited electron mobility of 37 cm$^2$/Vs comparable to that in halide perovskites but lower hole mobility of 11 cm$^2$/Vs. The defect computations indicate that BaZrS$_3$ is intrinsically n-type due to shallow sulfur vacancies, but that strong compensation by sulfur vacancies will prevent attempts to make it p-type. We also establish that BaZrS$_3$ is a defect-tolerant absorber with few low formation energy, deep intrinsic defects. Among the deep defects, sulfur interstitials are the strongest nonradiative recombination centers which in sulfur-rich conditions would limit the carrier lifetime to 10 ns. Our work highlights the material's intrinsic limitations in carrier mobility and suggests suppressing the formation of sulfur interstitials to reach long carrier lifetime.
- [5] arXiv:2405.09830 [pdf, ps, other]
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Title: Unveiling the Direct Piezoelectric Effect on Piezo-phototronic Coupling in Ferroelectrics: First Principle Study Assisted Experimental ApproachKoyal Suman Samantaray, Sourabh Kumar, P Maneesha, Dilip Sasmal, Suresh Chandra Baral, B.R. Vaishnavi Krupa, Arup Dasgupta, K Harrabi, A Mekki, Somaditya SenSubjects: Materials Science (cond-mat.mtrl-sci)
A new study explores the distinct roles of spontaneous polarization and piezoelectric polarization in piezo-phototronic coupling. This investigation focuses on differences in photocatalytic and piezo-photocatalytic performance using sodium bismuth titanate (NBT), a key ferroelectric material. The research aims to identify which type of polarization has a greater influence on piezo-phototronic effects. A theoretical assessment complements the experimental findings, providing additional insights. This study explores the enhanced piezo-phototronic performance of electrospun nanofibers compared to sol-gel particles under different illumination conditions (11W UV, 250W UV, and natural sunlight). Electrospun nanofibers exhibited a rate constant (k) improvement of 2.5 to 3.75 times, whereas sol-gel particles showed only 1.3 to 1.4 times higher performance when ultrasonication was added to photocatalysis. Analysis using first-principle methods revealed that nanofibers had an elastic modulus (C33) about 2.15 times lower than sol-gel particles, indicating greater flexibility. The elongation of lattice along z-axis in the case of nanofibers reduced the covalency in the Bi-O and Ti-O bonds. These structural differences led to reduced spontaneous polarization and piezoelectric stress coefficients (e31 & e33). Despite having lower piezoelectric stress coefficients, higher flexibility in nanofibers led to a higher piezoelectric strain coefficient, 2.66 and 1.97 times greater than sol-gel particles, respectively. This improved the piezo-phototronic coupling for nanofibers.
- [6] arXiv:2405.09842 [pdf, ps, other]
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Title: Why Superconducting Ta Qubits Have Fewer Tunneling Two-Level Systems at the Air-Oxide Interface Than Nb QubitsSubjects: Materials Science (cond-mat.mtrl-sci)
Superconducting qubits are a key contender for quantum computing elements, but they often face challenges like noise and decoherence from two-level systems (TLS). Tantalum (Ta) qubits are notable for their long T$_1$ coherence times nearing milliseconds, mainly due to fewer TLS, though the cause was unclear. Our research explored this by analyzing the air-oxide interface with density functional theory, particularly comparing Nb oxide (Nb$_2$O$_5$) and Ta oxide (Ta$_2$O$_5$). We discovered that Ta$_2$O$_5$ forms a smoother surface with fewer dangling O atoms and TLS than Nb$_2$O$_5$. The greater atomic mass of Ta also lowers the TLS tunnel splittings below the qubit's operating frequency. Furthermore, using external electric fields or SO$_2$ passivation can significantly reduce TLS on Nb surfaces, potentially improving their coherence times.
- [7] arXiv:2405.09890 [pdf, ps, other]
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Title: Fe-FeH Eutectic Melting Curve and the Estimates of Earth's Core Temperature and CompositionSubjects: Materials Science (cond-mat.mtrl-sci); Geophysics (physics.geo-ph)
Fe and FeH form a binary eutectic system above ~40 GPa. Here we performed melting experiments in a laser-heated diamond-anvil cell (DAC) and obtained the Fe-FeH eutectic melting curve between 52 and 175 GPa. Its extrapolation shows the eutectic temperature to be 4700 K at the inner core boundary (ICB), which is lower than that in Fe-FeSi but is higher than those in the Fe-S, Fe-O, and Fe-C systems. In addition, its dT/dP slope is comparable to those of the melting curves of Fe and FeH endmembers, suggesting that the eutectic liquid composition changes little with increasing pressure and is about FeH0.6 at the ICB pressure. We also estimated the effect of each light element on depressing the liquidus temperature at 330 GPa based on a combination of binary eutectic temperature and composition and found that the effect is large for C and S, moderate for H and O, and small for Si when considering the amount of each element that reduces a certain percentage of a liquid iron density. Furthermore, we searched for a set of possible outer core liquid composition and ICB temperature (the liquidus temperature of the former at 330 GPa should match the latter), which explains the outer core density deficit that depends on core temperature. The results demonstrate that relatively low core temperatures, lower than the solidus temperature of a pyrolitic lowermost mantle at the core-mantle boundary (CMB), are possible when the core is poor in Si.
- [8] arXiv:2405.09897 [pdf, ps, html, other]
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Title: Towards Informatics-Driven Design of Nuclear Waste FormsVinay I. Hegde, Miroslava Peterson, Sarah I. Allec, Xiaonan Lu, Thiruvillamalai Mahadevan, Thanh Nguyen, Jayani Kalahe, Jared Oshiro, Robert J. Seffens, Ethan K. Nickerson, Jincheng Du, Brian J. Riley, John D. Vienna, James E. SaalComments: 35 pages, 9 figures, 2 tablesSubjects: Materials Science (cond-mat.mtrl-sci)
Informatics-driven approaches, such as machine learning and sequential experimental design, have shown the potential to drastically impact next-generation materials discovery and design. In this perspective, we present a few guiding principles for applying informatics-based methods towards the design of novel nuclear waste forms. We advocate for adopting a system design approach, and describe the effective usage of data-driven methods in every stage of such a design process. We demonstrate how this approach can optimally leverage physics-based simulations, machine learning surrogates, and experimental synthesis and characterization, within a feedback-driven closed-loop sequential learning framework. We discuss the importance of incorporating domain knowledge into the representation of materials, the construction and curation of datasets, the development of predictive property models, and the design and execution of experiments. We illustrate the application of this approach by successfully designing and validating Na- and Nd-containing phosphate-based ceramic waste forms. Finally, we discuss open challenges in such informatics-driven workflows and present an outlook for their widespread application for the cleanup of nuclear wastes.
- [9] arXiv:2405.09898 [pdf, ps, other]
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Title: NH3 gas sensing over 2D Phosphorene sheet: A First-Principles StudyComments: 21 pages, Figures 8Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
First-principles based calculations were executed to investigate the sensing properties of ammonia gas molecules on two-dimensional pristine black phosphorene towards its application as a gas sensor and related applications. We discuss in detail, the interaction of ammonia gas molecules on the phosphorene single sheet through the structural change analysis, electronic band gap, Bader charge transfer, and density-of-states calculations. Our calculations indicate that the phosphorene could be used as a detector of ammonia, where good sensitivity and very short recovery time at room temperature have confirmed the potential use of phosphorene in the detection of ammonia.
- [10] arXiv:2405.09956 [pdf, ps, html, other]
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Title: Data-Assimilated Crystal Growth Simulation for Multiple Crystalline PhasesSubjects: Materials Science (cond-mat.mtrl-sci)
To determine crystal structures from an X-ray diffraction (XRD) pattern containing multiple unknown phases, a data-assimilated crystal growth (DACG) simulation method has been developed. The XRD penalty function selectively stabilizes the structures in the experimental data, promoting their grain growth during simulated annealing. Since the XRD pattern is calculated as the Fourier transform of the pair distribution function, the DACG simulation can be performed without prior determination of the lattice parameters. We applied it to C (graphite and diamond) and SiO$_2$ (low-quartz and low-cristobalite) systems, demonstrating that the DACG simulation successfully reproduced multiple crystal structures.
- [11] arXiv:2405.10222 [pdf, ps, html, other]
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Title: Kramers nodal line in the charge density wave state of YTe$_3$ and the influence of twin domainsShuvam Sarkar, Joydipto Bhattacharya, Pramod Bhakuni, Pampa Sadhukhan, Rajib Batabyal, Christos D. Malliakas, Marco Bianchi, Davide Curcio, Shubhankar Roy, Arnab Pariari, Vasant G. Sathe, Prabhat Mandal, Mercouri G. Kanatzidis, Philip Hofmann, Aparna Chakrabarti, Sudipta Roy BarmanSubjects: Materials Science (cond-mat.mtrl-sci)
Recent studies have focused on the relationship between charge density wave (CDW) collective electronic ground states and nontrivial topological states. Using angle-resolved photoemission and density functional theory, we establish that YTe$_3$ is a CDW-induced Kramers nodal line (KNL) metal, a newly proposed topological state of matter. YTe$_3$ is a non-magnetic quasi-2D chalcogenide with a CDW wave vector ($q_{\rm cdw}$) of 0.2907c$^*$. Scanning tunneling microscopy and low energy electron diffraction revealed two orthogonal CDW domains, each with a unidirectional CDW and similar YTe$_3$. The effective band structure (EBS) computations, using DFT-calculated folded bands, show excellent agreement with ARPES because a realistic x-ray crystal structure and twin domains are considered in the calculations. The Fermi surface and ARPES intensity plots show weak shadow bands displaced by $q_{\rm cdw}$ from the main bands. These are linked to CDW modulation, as the EBS calculation confirms. Bilayer split main and shadow bands suggest the existence of crossings, according to theory and experiment. DFT bands, including spin-orbit coupling, indicate a nodal line along the $\Sigma$ line from multiple band crossings perpendicular to the KNL. Additionally, doubly degenerate bands are only found along the KNL at all energies, with some bands dispersing through the Fermi level.
- [12] arXiv:2405.10318 [pdf, ps, html, other]
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Title: Gauge theory of giant phonon magnetic moment in doped Dirac semimetalsComments: 7 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a quantum theory for phonon magnetic moment in doped Dirac semimetals. Our theory is based on an emergent gauge field approach to the electron-phonon coupling, applicable for both gapless and gapped systems. We find that the magnetic moment is directly proportional to the electrical Hall conductivity through the phonon Hall viscosity. Our theory is combined with the first-principles calculations, allowing us to quantitatively implement it to realistic materials. Magnetic moments are found to be on the order of Bohr magneton for certain phonon modes in graphene and $\text{Cd}_3 \text{As}_2$. Our results provide practical guidance for the dynamic generation of large magnetization in the topological quantum materials.
New submissions for Friday, 17 May 2024 (showing 12 of 12 entries )
- [13] arXiv:2405.09616 (cross-list from cond-mat.str-el) [pdf, ps, html, other]
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Title: Theory of possible sliding regimes in twisted bilayer WTe$_2$Comments: Main text: 9 pages with 3 figures and 1 table. Supplementary material: 26 pages with 6 figures and 1 tableSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
Inspired by the observation of increasingly one-dimensional (1D) behavior with decreasing temperature in small-angle twisted bilayers of WTe$_2$ (tWTe$_2$), we theoretically explore the exotic sliding regimes that could be realized in tWTe$_2$. At zero displacement field, while hole-doped tWTe$_2$ can be thought of as an array of weakly coupled conventional two-flavor 1D electron gases (1DEGs), the electron-doped regime is equivalent to coupled four-flavor 1DEGs , due to the presence of an additional "valley'' degree of freedom. In the decoupled limit, the electron-doped system can thus realize phases with a range of interesting ordering tendencies, including $4k_F$ charge-density-wave and charge-$4e$ superconductivity. Dimensional crossovers and cross-wire transport due to inter-wire couplings of various kinds are also discussed. We find that a sliding Luther-Emery liquid with small inter-wire couplings is probably most consistent with current experiments on hole-doped tWTe$_2$.
- [14] arXiv:2405.09731 (cross-list from physics.chem-ph) [pdf, ps, other]
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Title: Impacts of Hot Electron Diffusion, Electron-Phonon Coupling, and Surface Atoms on Metal Surface Dynamics Revealed by Reflection Ultrafast Electron DiffractionComments: 25 pages, 5 figuresSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci)
Metals exhibit nonequilibrium electron and lattice subsystems at transient times following femtosecond laser excitation. In the past four decades, various optical spectroscopy and time-resolved diffraction methods have been used to study electron-phonon coupling and the effects of underlying dynamical processes. Here, we take advantage of the surface specificity of reflection ultrafast electron diffraction (UED) to examine the structural dynamics of photoexcited metal surfaces, which are apparently slower in recovery than predicted by thermal diffusion from the profile of absorbed energy. Fast diffusion of hot electrons is found to critically reduce surface excitation and affect the temporal dependence of the increased atomic motions on not only the ultrashort but sub-nanosecond times. Whereas the two-temperature model with the accepted physical constants of platinum can reproduce the observed surface lattice dynamics, gold is found to exhibit appreciably larger-than-expected dynamic vibrational amplitudes of surface atoms while keeping the commonly used electron-phonon coupling constant. Such surface behavioral difference at transient times can be understood in the context of the different strengths of binding to surface atoms for the two metals. In addition, with the quantitative agreements between diffraction and theoretical results, we provide convincing evidence that surface structural dynamics can be reliably obtained by reflection UED even in the presence of laser-induced transient electric fields.
- [15] arXiv:2405.09840 (cross-list from cond-mat.supr-con) [pdf, ps, html, other]
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Title: Impurity bands, line-nodes, and anomalous thermal Hall effect in Weyl superconductorsComments: 13 pages, 7 figuresSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We investigate the anomalous thermal Hall effect (ATHE) in Weyl superconductors realized by the $E_{1u}$ ($p$-wave and $f$-wave) chiral superconducting order for the point group $D_{6h}$. Using the quasiclassical Eilenberger theory, we analyze the influence of the impurity scattering and the line nodal excitations on the ATHE, and compare it with the intrinsic (topological) contribution. Because the transverse response is sensitive to the slope of the density of states at the Fermi surface, the extrinsic ATHE vanishes in both the weak (Born) and strong (unitarity) scattering limits. The thermal Hall conductivity (THC) is maximal at intermediate impurity strengths when there is a large slope of the density states in the impurity bands close to the Fermi energy. Under these conditions, the extrinsic ATHE dominates the intrinsic ATHE even at low temperatures. The extrinsic ATHE is sensitive to line nodal excitations, whereas the intrinsic ATHE is not. When the line nodes in the gap involve the sign change of the order parameter, the extrinsic contribution to the THC is suppressed even though the phase space for low energy excitation is large. In contrast, if the nodes are not accompanied by such a sign change, the extrinsic ATHE is significantly enhanced. Our results form a basis for the comprehensive analysis of anomalous thermal transport in Weyl superconductors.
- [16] arXiv:2405.10103 (cross-list from physics.app-ph) [pdf, ps, other]
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Title: One-step Pulsed Laser Deposition of Metal oxynitride/Carbon Composites for Supercapacitor ApplicationComments: 18 pages, 7 Figures, 1 table, 4 supplementary figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Advanced material composite of nanocarbons and metal-based materials provides a synergistic effect to obtain excellent electrochemical charge-storage performance and other properties. Herein, 3D porous carbon-metal oxynitride nanocomposites with tunable carbon/metal and oxygen/nitrogen ratio are synthesized uniquely by simultaneous ablation from two different targets by single-step pulsed laser deposition at room temperature. Co ablation of titanium and vanadium nitride targets together with graphite allowed us to synthesize carbon-metal oxynitride porous nanocomposite and exploit them as a binder-free thin film supercapacitor electrode in aqueous electrolyte. We show that the elemental composition ratio and hence the structural properties can be tuned by selecting target configuration and by manipulating the ablation position. We investigate how this tuning capability impacts their charge-storage performances. We anticipate the utilization of as-synthesized various composites in a single PLD production run as next-generation active materials for flexible energy storage and optoelectronic applications.
- [17] arXiv:2405.10135 (cross-list from cs.CE) [pdf, ps, html, other]
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Title: Self-supervised feature distillation and design of experiments for efficient training of micromechanical deep learning surrogatesSubjects: Computational Engineering, Finance, and Science (cs.CE); Materials Science (cond-mat.mtrl-sci)
Machine learning surrogate emulators are needed in engineering design and optimization tasks to rapidly emulate computationally expensive physics-based models. In micromechanics problems the local full-field response variables are desired at microstructural length scales. While there has been a great deal of work on establishing architectures for these tasks there has been relatively little work on establishing microstructural experimental design strategies. This work demonstrates that intelligent selection of microstructural volume elements for subsequent physics simulations enables the establishment of more accurate surrogate models. There exist two key challenges towards establishing a suitable framework: (1) microstructural feature quantification and (2) establishment of a criteria which encourages construction of a diverse training data set. Three feature extraction strategies are used as well as three design criteria. A novel contrastive feature extraction approach is established for automated self-supervised extraction of microstructural summary statistics. Results indicate that for the problem considered up to a 8\% improvement in surrogate performance may be achieved using the proposed design and training strategy. Trends indicate this approach may be even more beneficial when scaled towards larger problems. These results demonstrate that the selection of an efficient experimental design is an important consideration when establishing machine learning based surrogate models.
- [18] arXiv:2405.10151 (cross-list from physics.atom-ph) [pdf, ps, html, other]
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Title: Relativistic EELS scattering cross-sections for microanalysis based on Dirac solutionsZezhong Zhang, Ivan Lobato, Hamish Brown, Dirk Lamoen, Daen Jannis, Johan Verbeeck, Sandra Van Aert, Peter D. NellistComments: 52 pages, 8 figuresSubjects: Atomic Physics (physics.atom-ph); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Quantum Physics (quant-ph)
The rich information of electron energy-loss spectroscopy (EELS) comes from the complex inelastic scattering process whereby fast electrons transfer energy and momentum to atoms, exciting bound electrons from their ground states to higher unoccupied states. To quantify EELS, the common practice is to compare the cross-sections integrated within an energy window or fit the observed spectrum with theoretical differential cross-sections calculated from a generalized oscillator strength (GOS) database with experimental parameters. The previous Hartree-Fock-based and DFT-based GOS are calculated from Schrödinger's solution of atomic orbitals, which does not include the full relativistic effects. Here, we attempt to go beyond the limitations of the Schrödinger solution in the GOS tabulation by including the full relativistic effects using the Dirac equation within the local density approximation, which is particularly important for core-shell electrons of heavy elements with strong spin-orbit coupling. This has been done for all elements in the periodic table (up to Z = 118) for all possible excitation edges using modern computing capabilities and parallelization algorithms. The relativistic effects of fast incoming electrons were included to calculate cross-sections that are specific to the acceleration voltage. We make these tabulated GOS available under an open-source license to the benefit of both academic users as well as allowing integration into commercial solutions.
Cross submissions for Friday, 17 May 2024 (showing 6 of 6 entries )
- [19] arXiv:2112.12850 (replaced) [pdf, ps, html, other]
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Title: Skyrmion lattice in centrosymmetric magnets with local Dzyaloshinsky-Moriya interactionComments: 19 pages and 8 figuresJournal-ref: Materials Today Quantum 2, 100006 (2024)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
It is common for the local inversion symmetry to break in crystals, even though the whole crystal has global inversion symmetry. This local inversion symmetry breaking allows for a local Dzyaloshinsky-Moriya interaction (DMI) in magnetic crystals. Here we show that the local DMI can stabilize a skyrmion as a metastable excitation or as a skyrmion crystal in equilibrium. We consider the crystal structure with layered structure as an example, where local inversion is violated in each layer but a global inversion center exists in the middle of the two layers. These skyrmions come in pairs that are related by inversion symmetry. The two skyrmions with opposite helicity in a pair form a bound state. We study the properties of a skyrmion pair in the ferromagnetic background and determine the equilibrium phase diagram, where a robust lattice of skyrmion pairs is stabilized. Our results point to a new direction to search for the skyrmion lattice in centrosymmetric magnets.
- [20] arXiv:2307.10369 (replaced) [pdf, ps, other]
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Title: Enumeration and representation theory of spin space groupsXiaobing Chen, Jun Ren, Yanzhou Zhu, Yutong Yu, Ao Zhang, Pengfei Liu, Jiayu Li, Yuntian Liu, Caiheng Li, Qihang LiuComments: To appear in Phys. Rev. X. 158 pages, including the main text (41 pages including 3 tables and 7 figures) and appendix. There is another Supplementary table with the full list of spin space groups at this https URLSubjects: Materials Science (cond-mat.mtrl-sci)
Those fundamental physical properties, such as phase transitions, Weyl fermions, and spin excitation, in all magnetic ordered materials, were ultimately believed to rely on the symmetry theory of magnetic space groups. Recently, it has come to light that a more comprehensive group, known as the spin space group (SSG), which combines separate spin and spatial operations, is necessary to fully characterize the geometry and underlying properties of magnetic ordered materials. However, the basic theory of SSG has seldom been developed. In this work, we present a systematic study of the enumeration and the representation theory of SSG. Starting from the 230 crystallographic space groups and finite translation groups with a maximum order of 8, we establish an extensive collection of over 100000 SSGs under a four-index nomenclature as well as the International notation. We then identify inequivalent SSGs specifically applicable to collinear, coplanar, and noncoplanar magnetic configurations. To facilitate the identification of SSG, we develop an online program (this http URL) that can determine the SSG symmetries of any magnetic ordered crystals. Moreover, we derive the irreducible co-representations of the little group in momentum space within the SSG framework. Finally, we illustrate the SSG symmetries and physical effects beyond the framework of magnetic space groups through several representative material examples, including a well-known altermagnet RuO2, spiral spin polarization in the coplanar antiferromagnet CeAuAl3, and geometric Hall effect in the noncoplanar antiferromagnet CoNb3S6. Our work advances the field of group theory in describing magnetic ordered materials, opening up avenues for deeper comprehension and further exploration of emergent phenomena in magnetic materials.
- [21] arXiv:2312.17594 (replaced) [pdf, ps, html, other]
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Title: Utilizing the Janus MoSSe surface polarization in designing complementary metal-oxide-semiconductor field-effect transistorsJournal-ref: Physical Review Applied 21 (4), 044046, 2024Subjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Janus transition metal dichalcogenides (JTMDs) have attracted much attention because of their outstanding electronic and optical properties. The additional out-of-plane dipole in JTMDs can form n- and p-like Ohmic contacts, and this may be used in device applications such as pin diodes and photovoltaic cells. In this study, we exploit this property to design n- and p-type metal-oxide-semiconductor field effect transistors (MOSFETs). First, we use density-functional theory calculations to study the inherent dipole field strength in the trilayer JTMD MoSSe. The intrinsic dipole of MoSSe causes band bending at both the metal/MoSSe and MoSSe/metal interfaces, resulting in electron and hole accumulation to form n- and p-type Ohmic contact regions. We incorporate this property into a 2D finite-element-based Poisson-drift-diffusion solver to perform simulations, on the basis of which we design complementary MOSFETs. Our results demonstrate that JTMDs can be used to make n- and p-MOSFETs in the same layer without the need for any extra doping.
- [22] arXiv:2401.07581 (replaced) [pdf, ps, html, other]
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Title: Spin-currents via the gauge-principle for meta-generalized-gradient exchange-correlation functionalsJacques K. Desmarais, Jefferson Maul, Bartolomeo Civalleri, Alessandro Erba, Giovanni Vignale, Stefano PittalisComments: Accepted for publication in Physical Review LettersSubjects: Materials Science (cond-mat.mtrl-sci)
The prominence of density functional theory (DFT) in the field of electronic structure computation stems from its ability to usefully balance accuracy and computational effort. At the base of this ability is a functional of the electron density: the exchange-correlation energy. This functional satisfies known exact conditions that guide the derivation of approximations. The strongly-constrained-appropriately-normed (SCAN) approximation stands out as a successful, modern, example. In this work, we demonstrate how the SU(2) gauge-invariance of the exchange-correlation functional in spin current density functional theory allows us to add an explicit dependence on spin currents in the SCAN functional (here called JSCAN) -- and similar meta-generalized-gradient functional approximations -- solely invoking first principles. In passing, a spin-current dependent generalization of the electron localization function (here called JELF) is also derived. The extended forms are implemented in a developer's version of the \textsc{Crystal23} program. Applications on molecules and materials confirm the practical relevance of the extensions.
- [23] arXiv:2405.09371 (replaced) [pdf, ps, other]
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Title: Formation of Beta-Indium Selenide Layers Grown via Selenium Passivation of InP(111)B SubstrateKaushini S. Wickramasinghe, Candice Forrester, Martha R. McCartney, David J. Smith, Maria C. TamargoComments: 19 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Indium selenide, In2Se3, has recently attracted growing interest due to its novel properties, including room temperature ferroelectricity, outstanding photoresponsivity, and exotic in-plane ferroelectricity, which open up new regimes for next generation electronics. In2Se3 also provides the important advantage of tuning the electrical properties of ultra-thin layers with an external electrical and magnetic field, making it a potential platform to study novel two-dimensional physics. Yet, In2Se3 has many different polymorphs, and it has been challenging to synthesize single-phase material, especially using scalable growth methods, as needed for technological applications. In this paper, we use aberration-corrected scanning transmission electron microscopy to characterize the microstructure of twin-free single-phase ultra-thin layers of beta-In2Se3, prepared by a unique molecular beam epitaxy approach. We emphasize features of the In2Se3 layer and In2Se3/InP interface which provide evidence for understanding the growth mechanism of the single-phase In2Se3. This novel approach for forming high-quality twin-free single phase two-dimensional crystals on InP substrates is likely to be applicable to other technologically important substrates.
- [24] arXiv:2204.00921 (replaced) [pdf, ps, html, other]
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Title: Effects of self-avoidance on the packing of stiff rods on ellipsoidsSubjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO)
Using a statistical-mechanics approach, we study the effects of geometry and self-avoidance on the ordering of slender filaments inside non-isotropic containers, considering cortical microtubules in plant cells, and packing of genetic material inside viral capsids as concrete examples. Within a mean-field approximation, we show analytically how the shape of the container, together with self-avoidance, affects the ordering of the stiff rods. We find that the strength of the self-avoiding interaction plays a significant role in the preferred packing orientation, leading to a first-order transition for oblate cells, where the preferred orientation changes from azimuthal, along the equator, to a polar one, when self-avoidance is strong enough. While for prolate spheroids the ground state is always a polar-like order, strong self-avoidance results with a deep meta-stable state along the equator. We compute the critical surface describing the transition between azimuthal and polar ordering in the three dimensional parameter space (persistence length, eccentricity, and self-avoidance) and show that the critical behavior of this system is in fact related to the butterfly catastrophe model. We calculate the pressure and shear stress applied by the filament on the surface, and the injection force needed to be applied on the filament in order to insert it into the volume. We compare these results to the pure mechanical study where self-avoidance is ignored, and discuss similarities and differences.
- [25] arXiv:2303.08395 (replaced) [pdf, ps, html, other]
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Title: Stationary Two-State System in Optics using Layered MaterialsComments: 6 pages, 2 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
In scenarios where electrons are confined to a flat surface, such as graphene, quantizing electrodynamics reveals intriguing insights. We find that one of Maxwell's equations manifests as part of the Hamiltonian, leading to novel constraints on physical states due to residual gauge invariance. We identify two quantum states with zero energy expectation values: one replicates the scattering and absorption of light, a phenomenon familiar in classical optics, while the other is more fundamentally associated with photon creation. These states form an inseparable two-state system, giving a new formula for reflection and transmission coefficients with photon emission effects. Notably, there exists a special thickness of the surface where these states decouple, offering intriguing possibilities for exploring physics through symmetry-based perturbations involving concepts of parity, axial gauge fields, and surface deformation.
- [26] arXiv:2403.07565 (replaced) [pdf, ps, html, other]
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Title: Logarithmic critical slowing down in complex systems: from statics to dynamicsComments: 22 pages, 2 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
We consider second-order phase transitions in which the order parameter is a replicated overlap matrix. We focus on a tricritical point that occurs in a variety of mean-field models and that, more generically, describes higher order liquid-liquid or liquid-glass transitions. We show that the static replicated theory implies slowing down with a logarithmic decay in time. The dynamical equations turn out to be those predicted by schematic Mode Coupling Theory for supercooled viscous liquids at a $A_3$ singularity, where the parameter exponent is $\lambda=1$. We obtain a quantitative expression for the parameter $\mu$ of the logarithmic decay in terms of cumulants of the overlap, which are physically observable in experiments or numerical simulations.
- [27] arXiv:2403.19597 (replaced) [pdf, ps, html, other]
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Title: Reference Energies for Double Excitations: Improvement and ExtensionComments: 25 pages, 3 figures (Supporting Information available)Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Theory (nucl-th)
In the realm of photochemistry, the significance of double excitations (also known as doubly-excited states), where two electrons are concurrently elevated to higher energy levels, lies in their involvement in key electronic transitions essential in light-induced chemical reactions as well as their challenging nature from the computational theoretical chemistry point of view. Based on state-of-the-art electronic structure methods (such as high-order coupled-cluster, selected configuration interaction, and multiconfigurational methods), we improve and expand our prior set of accurate reference excitation energies for electronic states exhibiting a substantial amount of double excitations [this http URL Loos et al. J. Chem. Theory Comput. 2019, 15, 1939]. This extended collection encompasses 47 electronic transitions across 26 molecular systems that we separate into two distinct subsets: (i) 28 "genuine" doubly-excited states where the transitions almost exclusively involve doubly-excited configurations and (ii) 19 "partial" doubly-excited states which exhibit a more balanced character between singly- and doubly-excited configurations. For each subset, we assess the performance of high-order coupled-cluster (CC3, CCSDT, CC4, and CCSDTQ) and multiconfigurational methods (CASPT2, CASPT3, PC-NEVPT2, and SC-NEVPT2). Using as a probe the percentage of single excitations involved in a given transition ($\%T_1$) computed at the CC3 level, we also propose a simple correction that reduces the errors of CC3 by a factor of 3, for both sets of excitations. We hope that this more complete and diverse compilation of double excitations will help future developments of electronic excited-state methodologies.