Journal of Physics: Condensed Matter最新文献

A deep learning-driven Ti-Al-Nb ternary interatomic potential is developed continuously through DP-GEN framework, combining first-principles accuracy with molecular dynamics scalability. The neural network potential demonstrates exceptional transferability in predicting critical properties of Nb-dopedγ-TiAl andα₂-Ti₃Al phases. Nb influence on shear deformation inα₂-Ti₃Al is investigated. Meanwhile, Nb-dopedα₂/γinterface tensile perpendicular to the interface and shear simulations along 1/2[11¯0] and 1/2[112¯] are performed in order to simulate the local configurations in Ti-Al PST single crystals. This model provides a computational framework for interfacial engineering in lamellar TiAl alloys.

The influence of a non-equilibrium classical environment on the parameters of a quantum heat converter in a closed circuit at a given (non-zero) output power is theoretically investigated. It is shown that the non-equilibrium of the electron distribution function in metal terminals contributes to the kinetic coefficients of the linear approximation. Analytical expressions of the Seebeck and Peltier coefficients are obtained, considering the non-equilibrium in the terminals when electric current and heat flow through the system. The influence of non-equilibrium on the theoretical power limit and efficiency of the heat engine at a fixed output power is also determined. Closed-form solutions were obtained for the quantum bound of the heat engine output power and the theoretical limit of the heat conversion efficiency at a given output power in quantum systems with a non-equilibrium environment for certain limited cases. A spectroscopic thermoelectric method for studying quantum systems is proposed.

The kagome lattices of theATi₃Bi₅family have recently garnered significant attention due to their superconducting and topological properties. Here, we conducted an in-depth analysis of the band structure of the prototypical titanium-based kagome lattice material, CsTi₃Bi₅, using Density Functional Theory. We revealed its topological properties and demonstrated that the Van Hove singularities can be effectively tuned to the Fermi level under 18 GPa. Our findings confirm the dynamic stability of the CsTi₃Bi₅system and further demonstrate that its elastic constants, which comply with Born's criteria, ensure mechanical stability. The Poisson's ratio and Pugh's ratio indicate good ductility, while the material exhibits relatively low hardness. Notably, the mechanical properties exhibit significant directional anisotropy under all pressure conditions. As a key material in kagome lattices, the research results on CsTi₃Bi₅provide theoretical insights for experimental studies and the preparation of similar materials.

The present investigation utilized first-principles methodologies to elucidate the electronic and magnetic characteristics of bulk CsMn₄As₃. Our results validate the Mott insulator behavior of this compound, which is in agreement with the existing literature. Through the application of the Heisenberg spin Hamiltonian approach and energy mapping methods, we determined the exchange interactions, highlighting potential spin frustration in the material. Verification of the mechanical and dynamical stability of CsMn₄As₃was conducted, followed by an assessment of its thermoelectric attributes. The observed low lattice thermal conductivity along thec-axis of the compound significantly contributes to a substantial figure of merit (ZT) of 0.8 at 500 K. Leveraging the inherent layered architecture of the material, we modeled a monolayer device and verified its structural integrity through phonon and molecular dynamics analyses. The monolayer exhibited metallic characteristics, prompting an investigation into its I-V response, which uncovered subtle negative differential conductance phenomena. These results underscore the imperative for continued experimental validation to unlock the potential for advanced electronic applications.

In this work, we investigate anα-T₃lattice in the form of a Corbino disk, characterized by inner and outer radiiR₁andR₂, threaded by a tunable magnetic flux. Through exact (analytic) solution of the stationary Dirac-Weyl equation, we compute the transmission probability of the carriers and hence obtain the conductance features for0<α⩽1(αdenotes the strength of the hopping between the central atom and one of the other two) which allows ascertaining the role of the flat band, alongwith scrutinizing the transport features from graphene to a dice lattice. Our results reveal periodic Aharonov-Bohm (AB) oscillations in the conductance, reminiscent of the utility of the Corbino disk as an electron pump. Further, these results are strongly influenced by parameters, such as, doping level, ratio of the inner and outer radii, magnetic flux, andα. Additionally, complex quantum interference effect resulting in the possible emergence of higher harmonic modes and split-peak structures in the conductance, become prominent for smallerαvalues and larger ratios of the radii. We also find that, away from the charge-neutrality point (zero doping), the conductance oscillations are more pronounced and sensitive to the various parameters, with the corresponding behavior largely governed via the evanescent wave transport. Further, the Fano factor reveals distinct transport regimes, transitioning from Poissonian to pseudo-diffusive forα < 1, and from ballistic to pseudo-diffusive at the dice limit (α = 1). Thus, this setup serves as a fertile ground for studying the generation of quantum Hall current and AB oscillations in a flat band system, alongwith demonstrating intricate appearance of higher harmonics in the electron transport. Finally, to put things in perspective, we have compared our results with those for graphene disks that highlight the difference between the two with regard to device applications.

The topological characteristics of thep-wave Kitaev chains on a square lattice with nearest-neighbor and next-nearest-neighbor inter-chains hopping and pairing are investigated. Besides gapless exact zero-energy modes, this model exhibits topological gapless phase hosting edge modes, which do not reside strictly at zero energy. However, these modes can be distinguished from the bulk states. These states are known as pseudo- or quasi-Majorana Modes (qMMs). The exploration of this system's bulk spectrum and Berry curvature reveals singularities and flux-carrying vortices within its Brillouin zone. These vortices indicate the presence of four-fold Dirac points arising from two-fold degenerate bands. Examining the Hamiltonian under a cylindrical geometry uncovers the edge properties, demonstrating the existence of topological edge modes. These modes are a direct topological consequence of the Dirac semimetal characteristics of the system. The system is analyzed under open boundary conditions to distinguish the multiple Majorana zero modes and qMMs. This analysis includes a study of the normalized site-dependent local density of states, which pinpoints the presence of localized edge states. Additionally, numerical evidence confirms the topological protection of the edge states due to the finite-size effect and their robustness against disorder perturbations. The emergence of topological edge states and Dirac points with net zero topological charge indicates that this model is a weak topological superconductor.

Specific heat and thermal expansion properties are investigated in two non-magnetic rare-earth cage compounds, LaB₆and LaPt₄Ge₁₂, which represent extremes in guest-to-cage mass ratio. Using simplified phonons dispersions for the two lowest branches, a theoretical framework is proposed for the low temperature thermodynamic analysis of cage compounds. Within the quasi-harmonic approximation, the Grüneisen rule is found to break down even at low temperatures. However, under the influence of the flattened branches, it should be approximatively restored at intermediates temperatures. The model accurately describes LaB₆specific heat below 50 K. In the LaPt₄Ge₁₂case, the description is rapidly inadequate with increasing the temperature, which points to the interference of additional low frequency phonon branches. Subsequently, thermal expansion measurements are used to investigate the Grüneisen rule in these two compounds. As predicted, there appears to be distincts Grüneisen regimes at low temperature. This study will help distinguish between phonon and magnetic contributions to the thermal expansion in the RB₆and RPt₄Ge₁₂series.

Unraveling the nonlinear regime of light-matter interaction in quantum materials at ultrafast timescales has remained elusive over the past few decades. The primary obstacle entailed finding a resonant pump as well as a suitable, resonant probe that could effectively excite and capture the interaction pathways of the collective modes within their inherent timescales. Intriguingly, the characteristic energyscales of the said interactions and the timescales of ensuing dynamics lie in the THz range, making THz radiation not only an apt probe but also an ideal resonant tool for driving the collective modes out of equilibrium. In the said direction, 2D-THz spectroscopy serves as a state-of-the-art technique for unveiling the correlation dynamics of quantum materials through table-top experiments. On a microscopic level, this offers valuable insights into the competing interactions among the charge, spin, lattice, and orbital degrees of freedom. Though the field of 2D-THz spectroscopy is relatively new and yet to be explored in its full potential, this review highlights the progress made in investigating various coupling channels of collective modes, namely magnons, phonons, polaritons, etc in different insulating and semiconducting systems. We also provide pedagogical introduction to the 2D-THz spectroscopy and foresee its emergence alongside cutting-edge experimental tools, reshaping our understanding of quantum materials with new perspectives.

We show that twisted bilayers of silicene or germanene can be utilized for a novel transistor concept that relies on the quantum valley Hall effect. The application of an electric field normal to the twisted bilayer allows to tailor the size of the bandgap in AB- and BA-stacked domains of the twisted bilayer. In contrast to twisted bilayer graphene, the AB and BA bandgaps in twisted bilayer silicene and germanene are not inverted for small electric fields. However, above a critical electric field, the bandgaps invert, giving rise to a two-dimensional triangular network of topologically protected channels. The possibility to controllably switch these topologically protected states on and off using an electric field, combined with its inherent robustness against defects and impurities, establishes a foundation for a new type of transistor with an exceptional resilience.

Magnetic materials phase reconstruction using Lorentz transmission electron microscopy (LTEM) measurements have traditionally been achieved using longstanding methods such as off-axis holography (OAH) fast-Fourier transform technique and the transport-of-intensity equation (TIE). The increase in access to processing power alongside the development of advanced algorithms have allowed for phase retrieval of nanoscale magnetic materials with greater efficacy and resolution. Specifically, reverse-mode automatic differentiation (RMAD) and the extended electron ptychography iterative engine (ePIE) are two recent developments of phase retrieval that can be applied to analyzing micro-to-nano- scale magnetic materials. This work evaluates phase retrieval using TIE, RMAD, and ePIE in simulations of Permalloy (Ni₈₀Fe₂₀) nanoscale islands, or nanomagnets. Extending beyond simulations, we demonstrate total phase retrieval and image reconstructions of a NiFe nanowire using OAH and RMAD in LTEM and ePIE in Lorentz-mode-4D scanning transmission electron microscopy experiments and determine the saturation magnetization through corroborations with micromagnetic modeling. Finally, we demonstrate the efficacy of these methods in retrieving the total phase and highlight its use in characterizing and analyzing the proximity effect of the magnetic nanostructures.