Journal of Physics: Condensed Matter最新文献

The breaking of inversion symmetry combined with spin-orbit coupling, can give rise to intriguing quantum phases and collective excitations. Here, we report systematic temperature dependent Raman scattering and theoretical calculations of phonon modes across the inversion symmetry-breaking structural transitions in a quasi-one-dimensional compound (TaSe₄)₃I. Our investigation revealed the emergence of three additional Raman-active modes in Raman spectra of the low-temperature non-centrosymmetric (NC) structure of the material. From polarization dependent Raman spectra and phonon mode symmetry analysis, we have identified the origin of these three newly appeared additional Raman-active modes. Notably, two of these modes become Raman active due to the loss of inversion symmetry, while the third mode is identified as a soft phonon mode, arising from the distinctive vibrational motion of tantalum (Ta) atoms along the -Ta-Ta- chains. Furthermore, the temperature evolution of self-energy parameters indicates significant changes in the characteristics of the Raman modes across the transition. Latent heat measurements near the phase transition using Differential Scanning Calorimetry confirm the first-order nature of the transition. Theoretical analysis, including group theory and modeling, reaffirms the displacive first-order nature of the structural transition. Our findings establish (TaSe₄)₃I as a model quasi-one-dimensional system with broken inversion symmetry facilitated through a displacive first-order structural transition.

Controlling vibrational modes and energy gap by creating van der Waals (vdW) heterostructures through strain engineering is a novel approach to tailor the vibrational and electronic properties of two-dimensional materials. Numerous theoretical and experimental studies have significantly contributed to analyzing the properties of transition metal dichalcogenides, known for their multifunctional applications. In this study, we investigate the strain and stacking dependent vibrational properties of WSe₂/MoSe₂and MoSe₂/WSe₂/MoSe₂vdW heterostructures usingfirst-principlesbased density functional theory calculations. The dynamical stability of all vdW heterostructures makes them feasible in fabrication. Our phonon calculations and zone center phonon modes analysis signify that the interlayer interaction influences interlayer breathing and shear phonon modes, which play an important role in thermal properties. The effect of strain engineering on the vibrational modes and energy gap of vdW heterostructures are further discussed. The tensile and compressive biaxial strain on the vdW heterostructures results in phonon softening and hardening, respectively.

The interactions between the carbon skeleton and the metal atoms of a binary transition metal carbide (BTMC) are particular interest for industrial applications with openning physics and chemitry questions, especially in magnetoelectric (ME) functional materials and cemented carbides. Chromium and carbon BTMCs are a series of intermetallic compounds with typical chemical formulas and sharepolycrystalline powder c somehromium special characteristics.and carbon as precursors, In this paper,and synthesized s we usedingle-phase bluk Cr7C3 (orthorhombic, with space group: Pnma) with high density and good crystallinity by means of high-temperature and high-pressure quenching method (HTHPQM). We studied the material properties and electronic structures of Cr7C3studied with both experimental measurements and Density Functional Theory (DFT) ab intio simulations, and found that Cr7C3 is acompaction conductor(97.2 %), with anexcellent electrical conductivitythermostability (oxidation (2.32 10×at 1175 -3K)Ω·m), relative highand a magnetic phase transition from paramagnetism to soft ferromagnetism around 50 K, and the electromagnetic propertities are chiefly due to the abundancy of the 3d electrons of Cr, and the orbital hybridization between C and Cr with their 2p and 3d electrons is the reason for the crystal sturcture and high thermostability. Therefore, the prepared Cr7C3 is multifunctional material with better application prospects, and the HPHTQM is a simple and effective mothed to prepare samples as BTMCs. .

Previous studies of the transition metal chalcogenide Ta₂NiSe₅has identified two phase transitions occurring between 0-10 GPa, involving the excitonic insulator-to-semiconductor transition at 1 GPa and the semiconductor-to-semimetal transition at 3 GPa. However, there is still a lack of in-depth research on the changes in its physical properties changes above 10 GPa. In this study, Ta₂NiSe₅were investigated under high-pressure conditions using high-pressure x-ray diffraction and high-pressure x-ray absorption experiments. During the experimental process, a novel phase transition from the semimetal to the metal phase was observed between 10-60 GPa, specifically between 10-14 GPa, and the structure of the new phase was determined to be P2₁/m through first-principles calculations. This transition mechanism is attributed to the sliding of the weakly coupled layers of Ta₂NiSe₅within thea-cplane, leading to changes in the crystal lattice constants and symmetry. This research fills a gap in the understanding of Ta₂NiSe₅'s crystal structure under high pressure and contributes to the broader field of transition metal chalcogenides.

The measurement of topological numbers is crucial in the research of topological systems. In this article, we propose a protocol for obtaining the topological number (specifically, winding numbers in this case) of an unknown one-dimensional (1D) two-band topological system by comparing it with a known topological system. We consider two 1D two-band topological systems and their Bloch wavefunction overlap and verify a theorem. This theorem states that when the momentum varies by 2π, the number of cycles during which the magnitude of the wavefunction overlap varies from 0 to 1 and then back to 0 is equal to the absolute value of the difference between the topological numbers of these two systems. Furthermore, we propose two experimental schemes, one in a cold atom system and another one in a qubit system, which offer convenient and robust measurement methods for determining topological numbers of unknown states through quenching.

Transition metal nitrides are well-known 3D superconductor materials. However, there is a lack of knowledge related to their two-dimensional (2D) counterparts, which have several potential technological applications. In this work, we predict, using an evolutionary algorithm coupled with a first-principles approach, a set of novel 2D superconductive structures based on tungsten nitride. Through a systematic process including energetic and dynamical analysis, three thermodynamically stable compositions along with metastable compounds were studied in the following stoichiometries: W₄N₂, W₂N₂, and W₂N₃. Their superconductive temperature (Tc) values, estimated by means of the Eliashberg superconductive theory and the McMillan equation, range from 2.3 to 21.6 K, where the highestTcvalue corresponds to a W₂N₃metastable hexagonal system. A systematic analysis of the structural, electronic, vibrational and electron-phonon (e-ph) properties, allowed us to recognize the variables that modulate theTcin theses systems. The superconductive behavior is strongly affected by changes in the nitrogen density of states at Fermi level, the e-ph coupling constant and the lattice symmetry. The present results aim to encourage further theoretical and experimental efforts over non fully explored superconductors in two dimensions.

Metallic interfaces are locations where hydrogen (H) is expected to segregate and lead to the formation and stabilization of defects. This work focuses on the tungsten/copper (W/Cu) interface built according to theWbcc(001)/Cuhcp(112¯0)orientation. H behavior is subsequently determined at the interface and in its vicinity with electronic structure calculations based on the density functional theory. The electronic and vibrational properties determined in this way followed a thermodynamic treatment to deliver the solubility of H as a function of the temperature and chemical potential. The 96 interstitial positions we investigated reveal that H predominantly occupies the octahedral (Oh) sites in the copper network. Reversely, H exclusively occupies the tetrahedral (Td) sites in the tungsten network. The solubility of H is higher in the interface plane where both octahedral and tetrahedral sites are occupied. Despite this work is a first step toward kinetic modeling of hydrogen transport across the W/Cu interface, we conclude that theWbcc(001)/Cuhcp(112¯0)would behave like a sink where hydrogen isotopes could accumulate.

Miniaturization of ferroelectrics for technological applications has proven challenging due to the suppression of electric polarization caused by increasing depolarization fields as material thickness decreases. The emergence of ferroelectricity in two-dimensional (2D) van der Waals (vdW) materials offers a potential solution to this challenge, prompting significant research efforts over the past decade. While intrinsic 2D vdW ferroelectrics are scarce, polar stacking provides a more general approach to introducing ferroelectricity in these materials. This review revisits the fundamental concept of stacking ferroelectricity, complemented by symmetry analysis for constructing polar stackings, and both classical and quantum perspectives on the origin of stacking ferroelectrics. We present key advances in polarization dynamics and briefly summarize various physical phenomena directly coupled to stacking ferroelectricity, including multiferroic, magnetoelectric, and valleytronic effects, along with their related applications. Finally, we discuss future challenges and potential developments in the field of 2D stacking ferroelectricity.

Two-dimensional (2D) materials hold great promise for the next-generation optoelectronics applications, many of which, including solar cell, rely on the efficient dissociation of exciton into free charge carriers. However, photoexcitation in atomically thin 2D semiconductors typically produces exciton with a binding energy of ∼500 meV, an order of magnitude larger than thermal energy at room temperature. This inefficient exciton dissociation can limit the efficiency of photovoltaics. In this study, employing the first principles approach-DFT, GW + BSE, and analytical model, we demonstrate the role of asymmetric halogenation, dielectric environment, and magnetic field in 2D Ti₂O MOene as an efficient strategy for regulating exciton binding energy (EBE) towards spontaneous exciton dissociation. Our study goes beyond the exciton ground state and quantifies the degree of spatial delocalization of exciton in excited states as well. We determine the quantitative impact of varying dielectric screening and magnetic field strength on EBE for different excited states (1 s, 2 s, 3 s, 4 s, and so on). Importantly, we reveal the significant role of orbital orientation (whether in-plane or out-of-plane) and symmetry (related to the angular momentum quantum number) in understanding the spatial localization of excitons and their binding energy. Additionally, a high dielectric constant in 2D MOene enables easier exciton dissociation, similar to that observed in 3D bulk semiconductors, while also harnessing the advantages of 2D materials. This makes it an effective material that combines the best of both 3D bulk and 2D structures. The study offers a promising strategy for designing next-generation optoelectronic devices.

The study of emerging contaminants (ECs) in water resources has garnered significant attention due to their potential risks to human health and the environment. This review examines the contribution from computational approaches, focusing on the application of machine learning (ML) and molecular dynamics (MD) simulations to understand and optimize experimental applications of ECs adsorption on carbon-based nanomaterials. Condensed matter physics plays a crucial role in this research by investigating the fundamental properties of materials at the atomic and molecular levels, enabling the design and engineering of materials optimized for contaminant removal. We provide a comprehensive discussion of various force fields (FFs) such as AMBER, CHARMM, OPLS, GROMOS, and COMPASS, highlighting their unique features, advantages, and specific applications in modeling molecular interactions. The review also delves into the development and application of reactive potentials like ReaxFF, which facilitate large-scale atomistic simulations of chemical reactions. Additionally, we explore how ML models, including sGDML and SchNet, significantly enhance the potential and refinement of classical models by providing high-level quantum descriptions at reduced computational costs. The integration of ML with MD simulations allows for the accurate parameterization of FFs, offering detailed insights into adsorption mechanisms. Through a qualitative analysis of various ML models applied to the study of ECs on carbon materials, we identify key physical and chemical descriptors influencing adsorption capacities. Despite these advancements, challenges such as the limited diversity of ECs studied and the need for extensive experimental validation persist. This review underscores the importance of interdisciplinary collaboration, particularly the contributions of condensed matter physics, in developing innovative materials and strategies to address the environmental challenges posed by ECs.