We report the synthesis and physical properties of CdRuO3, a nominal Ru4+4d4ilmenite with edge-sharing RuO6honeycomb layers. Powder x-ray diffraction establishes a crystallographically non-dimerizedR-3 structure with equivalent Ru-Ru bonds and a strongly distorted RuO6environment. The compacted-pellet resistivity is nonmetallic but non-Arrhenius, while the heat capacity contains a finite residual linear term. Matched nonmagnetic calculations show that PBE+Uwithout spin-orbit coupling remains metallic or semimetallic up toUeff= 3 eV, whereas PBE+SOC+Uexhibits a strongUeffdependence and opens a direct gap of approximately 55 meV at Γ for Ueff= 2.5 eV. Spin-orbit coupling therefore markedly enhances the correlation sensitivity of the non-cubic Ru t2gmanifold. After subtraction of a dilute Curie-Weiss defect contribution, the susceptibility remains weakly nonmonotonic and is inconsistent with both an ordinary Pauli response and independent spin-only S = 1 moments. CdRuO3thus realizes the non-dimerized structural branch predicted for ruthenium ilmenites, but not a simple robust multiorbital metal.
We investigate quantum transport in a commensurate off-diagonal Aubry-André-Harper (AAH) chain with modulation parameter b =1/6, the smallest even-denominator supercell that supports band gap reconstruction at both zero and non-zero energies. Using a tight-binding framework combined with the Landauer-Büttiker formalism, we analyze coherent electron transport through finite lattices coupled to external electrodes. The phase-dependent energy spectrum exhibits a hierarchy of bulk-gap reconstructions associated with the six-site supercell modulation, giving rise to distinct transmission windows and resonant transport channels. Finite-size classes characterized by N=6m+r (0 ≤ r ≤ 5) modify the boundary-state configuration and shift the corresponding transmission win-
dows. In particular, lattices with odd number of sites exhibit robust zero-energy transmission channels arising from sublattice imbalance in the bipartite hopping network. To evaluate the stability of these features under realistic conditions, environmental decoherence is incorporated through Büttiker dephasing probes. While increasing dephasing progressively suppresses interference-assisted
transport, the underlying finite-size transport classification remains clearly identifiable over a broad parameter range. Our results establish clear transport signatures of commensurate off-diagonal modulation beyond the dimer limit and highlight the crucial role of supercell termination and decoherence in determining electron transport through finite AAH chains.
Intrinsically magnetic 2D materials provide an ideal platform for exploring magnetism in reduced dimensions and have attracted significant attention due to their potential applications in next-generation spintronic devices. The performance of such devices strongly depends on the structural quality and defect morphology of the underlying 2D materials. Point defects play a crucial role, acting either as beneficial tools for property engineering or as detrimental factors leading to device degradation. Recently, atomic iodine vacancies (V I ), atomic chromium vacancies (V Cr ), and vacancy complexes (V CrI3 ) have been experimentally identified. Motivated by experimental findings, we investigate the influence of vacancy defects on the structural, mechanical, electronic, and magnetic properties of single-layer CrI3 in the present work. Although several theoretical studies have reported the electronic and magnetic properties of CrI3 single layer with vacancy defects, a systematic investigation of influence of vacancies on mechanical properties remains largely unexplored. Our calculations show that the presence of vacancies significantly degrades the elastic properties. For a defect concentration of 1.39%, the Young's modulus decreases to 20.88 and 16.66 N/m for V I and V Cr , respectively. For vacancy complexes with concentrations of 5.56% (V CrI3 ) and 9.72% (V CrI6 ), the Young's modulus further reduces to 18.28 and 16.20 N/m, respectively, compared to 24.12 N/m for the pristine system. This reduction indicates a softening of the single-layer CrI 3 due to vacancies. Furthermore, we find that the mechanical properties of charged and neutral defects do not differ significantly and are primarily governed by structural distortions. On the other hand, vacancy defects alter the electronic character, either transforming the system from semiconducting to half-metallic or leading to a reduction in the band gap. Importantly, the magnetic properties remain robust in the presence of vacancy defects. Overall, the present study provides insights into influence of vacancy defects on the mechanical and electronic properties of single layer CrI3, thereby improving our understanding of defect engineering in 2D magnetic materials.
The excitation of solid materials with femtosecond optical pulses induces non-equilibrium states that are interesting for both fundamental and application-related reasons, as their properties can be quite different from those generated by e.g. thermal excitation or chemical doping. However, once several degrees of freedom such as electronic and lattice excitations, or multiple components in a heterostructure, couple strongly, analyzing the resulting ultrafast dynamics on femto- to picoseconds requires element-sensitive spectroscopy on these timescales. This Topical Review discusses how new insights into ultrafast charge and energy transfer dynamics in solids and at interfaces can be gained from time-resolved soft x-ray absorption spectroscopy (XAS). The state-of-the-art of the pump-probe XAS method at large scale facilities, namely synchrotron Femtoslicing sources and x-ray free electron lasers, is reviewed, with an emphasis on the opportunities and challenges of the respective facilities that motivate new methodological developments. For three selected material systems, it is then shown how x-ray absorption spectroscopy with femtosecond time resolution, in conjunction with theoretical calculations, is able to reveal and characterize non-equilibrium states by analyzing the transient electronic structure as well as lattice excitation via characteristic, time-dependent spectral features. Finally, future opportunities through the further development of laboratory-based soft x-ray sources and the combination of time-resolution with non-linear XAS are presented.
For a simple model fluid, the Yukawa fluid, the condition for dynamic crossover, known as the Frenkel line, is defined. The condition is related to the fact that the roton minimum in the dispersion relation of longitudinal acoustic-like excitations exists only when the collective vibrational dynamics of particles dominates in the liquid. Based on the self-consistent relaxation theory for the Yukawa fluid, thermodynamic states are determined in which the roton minimum disappears. The obtained values of the state parameters for the Frenkel line are consistent with the results of studies in which the position of this line on the phase diagram of the Yukawa fluid was determined using molecular dynamics simulations. It is shown that the Frenkel line in this system can be determined directly from the structural characteristic - the static structure factor. A physical interpretation of the roton minimum frequency for simple liquids near the Frenkel line is proposed.
Inorganic halide perovskite RbSrI3 has recently attracted attention as a lead-free material for radiation detection and optoelectronic applications. However, most theoretical studies have assumed an ideal cubic structure as the ground-state phase, despite the strong tendency of halide perovskites toward polymorphism and experimental evidence for an orthorhombic structure. Here, we resolve this discrepancy through a comprehensive first-principles density functional theory (DFT) investigation using the GGA-PBE functional and the projector augmented-wave method as implemented in VASP. The HSE06 hybrid functional was additionally employed to validate the calculated electronic band gaps. Energetic, dynamical, and finite-temperature thermodynamic analyses consistently identify the distorted orthorhombic Cmcm phase as the true ground state, while the cubic phase is dynamically unstable. Importantly, we show that energetic ordering alone is insufficient to establish the proper ground state, since lattice-dynamical stability is essential for distinguishing a true minimum from an unstable or saddle-point structure. The instability of the high-symmetry phase is traced to an A-site-driven lattice mismatch, in which the undersized Rb+ cation gives rise to soft Rb-I vibrational modes that drive cooperative octahedral rotations. Crystal orbital Hamilton population analysis further shows that octahedral tilting strengthens Rb-I interactions while reducing antibonding Sr-I contributions, thereby stabilizing the distorted structure. Octahedral tilting also modifies the optoelectronic response, increasing the GGA-PBE band gap from 3.32 eV in cubic Pm-3m to 3.76 eV in orthorhombic Cmcm phase. Higher-level HSE06 calculations confirm this trend, giving corresponding band gaps of 4.34 and 4.77 eV, respectively. The structural distortion also modifies the optical spectra significantly. These results establish the correct structural reference for RbSrI3 and provide a microscopic framework linking geometric mismatch, lattice dynamics, chemical bonding, and optoelectronic behavior in lead-free halide perovskites.
In solids, high-harmonic generation (HHG) has emerged as a crucial technique for studying ultrafast electron dynamics and band structure properties. Topological quantum materials, including topological insulators, semimetals and topological superconductors are an emerging class of materials distinguished by their unique edge or surface states along with nontrivial Berry curvature and topological invariants. These fundamental properties impart distinctive signatures onto their high-harmonic spectra, offering a novel nonlinear-optical window into topological order. Several theoretical and experimental investigations have shown that HHG in topological materials exhibits distinct signatures, including significant circular dichroism, enhanced harmonic yields, and distinctive ellipticity dependence, highlighting its sensitivity to underlying topological properties. This article aims to describe the basic dynamics that drive HHG in these materials, point out important theoretical and experimental results, and evaluate which spectral features may be genuinely topology-specific, which are topology-sensitive but not unique, and which remain debated. We organized the review into three main sections covering topological insulators, semimetals, and superconductors. For each class, after providing a basic overview, we explore the distinctive HHG mechanisms and spectral characteristics.
Abstract We report high-resolution synchrotron x-ray diffraction and x-ray resonant magnetic scattering (XRMS) studies of the low-temperature crystal and magnetic structures of DyCuAs 2 , a member of the RE CuAs 2 family exhibiting a resistivity minimum above the antiferromagnetic (AFM) transition temperature. Synchrotron diffraction measurements reveal that DyCuAs 2 preserves tetragonal symmetry down to low temperature within the experimental resolution, although pronounced anomalies in both lattice parameters a and c are observed near the AFM transition temperature, T N ≈ 7 K, indicating strong magnetoelastic coupling. XRMS measurements at the Dy L 3 edge establish commensurate AFM ordering below T N with AFM Bragg peaks at q = (0, 0, 0.5). Representation analysis and calculations of the AFM Bragg peak intensities identify the magnetic structure as the Γ 10 representation, consisting of in-plane Dy moments stacked along the c axis in a + + − − sequence. The magnetic structure is therefore identical to that previously reported for SmCuAs 2 . Comparison among DyCuAs 2 , SmCuAs 2 , and GdCuAs 2 suggests that in-plane AFM order and the associated magnetic frustration on the tetragonal lattice are closely connected to the emergence of the resistivity minimum in the RE CuAs 2 family. At the same time, the enhanced lattice response and stronger magnetic-field sensitivity observed in DyCuAs 2 imply that magnetoelastic and spin–orbit interactions additionally play important roles in determining the robustness of this anomalous transport behavior.
Abstract The reaction mechanism of the N atom interaction with a single-layer MoS 2 , two-dimensional transition metal dichalcogenide, is considered in detail. These mechanisms were studied by DFT (density functional theory) modeling using both static and dynamic approaches. The most important processes for pristine and modified MoS 2 surfaces are revealed. For incident N atoms both the scattering and recombination with adsorbed atoms are prevailed. Various formation mechanisms for vacancies and other defects by thermal and hot N atoms are proposed and discussed. The results of dynamic DFT simulations are used to illustrate the reaction pathways.
The paper reviews the theoretical and experimental progress achieved in the last 25 years in understanding the novel physics of artificial atoms and molecules as arising from the formation of Wigner molecules (WMs) of localized (to a stronger or lesser extent) fermionic or bosonic particles, which are finite quantum analogs of the more familiar bulk Wigner crystal (WC). The term artificial atoms, as used here, encompasses a broad range of recently fabricated quantum nanodevices and experimental apparatuses consisting of a finite number of mutually repelling confined particles, including two-dimensional semiconductor and moiré transition metal dichalcogenide quantum dots, as well as trapped ultracold neutral atoms or ions. These nano-sized or micro-sized artificial devices and apparatuses (in single well or multi-well of variable-shape arrangements) hold a great promise for technological applications in the field of quantum information and quantum computers, as well as for advances in fundamental many-body physics. Prominent quantum effects of Wigner molecularization (WM) are the strong quenching of the spectral energy gaps, the appearance of rovibational spectra (in analogy with natural molecules), entanglement, and pinning due to an external perturbation. In high magnetic fields or at rapid rotation, Wigner molecules (WMs) provide an alternative theory to the fractional quantum Hall effect. The physics of WMs is shown to derive from the solutions of the many-body Schrödinger equation (MBSE) in the regime of strong interparticle correlations arising from the dominance of the potential over the kinetic energy, or from a high magnetic field, as well as from a rapid rotation. With the help of a hierarchical scheme of computational approaches involving group-theoretical projection techniques beyond the mean field and exact configuration interaction, in parallel to experimental investigations, WMs are shown to provide an ideal platform for investigating the interplay between symmetry-preserving (stationary, referred to as rotating or sliding WMs) and broken-symmetry (superposition-necessitating, referred to as pinned or static WMs) solutions of the MBSE. In the process, a germane view of the phenomenon of symmetry breaking, based exclusively on finite systems and referred to as emergent symmetry breaking, is developed as a replacement to the formalistic spontaneous symmetry breaking that requires invocation of a singular thermodynamic limit. Attention is drawn to the counterintuitive fact that the very MBSE, which was inspired by de Broglie's undulatory matter waves and successfully explained the shell structure of delocalized electrons in atomic physics, is nevertheless capable of yielding contrasting solutions, which relate to corpuscular geometries of localized particles. This unforeseen behavior classifies the recent developments concerning WM and WC as an example of weak emergence, and thus of an arrow of reductionist explanation according to Weinberg's reasoning. Finally, this review, demonstrating the unexpected mathematical effectiveness beyond original expectations of the Schrödinger equation, is dedicated as a tribute to its 100 year anniversary.
Transition metal dichalcogenides (TMDs) are a fascinating class of layered materials, distinguished by weak interlayer van der Waals forces. Their atomically thin structure and ability to form various layered assemblies provide exceptional electronic and optical properties, positioning TMDs at the forefront of condensed matter research and next-generation technologies. The presence of strong quantum confinement and reduced dielectric screening gives rise to tightly bound excitonic quasiparticles with large binding energies, enabling their existence even at room temperature. The collective interaction of these quasiparticles with other carriers or excitations yields a rich landscape of many-body effects and emergent phenomena. In this perspective, we present a unified overview of excitonic physics and many-body interactions in layered TMDs, highlighting recent developments and open challenges. We discuss how the strong quantum confinement, spin-orbit coupling, and many-body interactions shape the electronic and optical properties of various TMDs. Finally, we discuss future opportunities for TMDs-based technologies, including superabsorption, exciton crystals, single-photon emission, coupling to ferroic and correlated degrees of freedom. This perspective connects recent advances in excitonic and many-body physics in layered TMDs, highlighting emerging opportunities for quantum, photonic, and optoelectronic technologies.
Several studies on Au-induced nanowires on Ge(001) have provided results that have led to contradictory interpretations concerning the dimensionality of the electronic structure and the existence of a Tomonaga-Luttinger liquid. In this work, we present local density-of-states maps that reveal a distinctly striped electronic structure. These stripes run in a slight zigzag course that is oriented almost orthogonally to the nanowires, which are visible in scanning tunneling microscopy images. Power law exponents extracted from a large number of different measurements agree with predictions for a Tomonaga-Luttinger liquid. Furthermore, exponents obtained from channel ends are significantly enhanced, an additional hallmark of a Tomonaga-Luttinger liquid. The findings strengthen the assumption that a quasi-one-dimensional channel is located in a deeper layer, which offers a reconciling explanation to previously conflicting interpretations.
Twisted carbon nanotubes support phonons involving not only torsion, naturally associated with microrotation, but also radial breathing, which requires a scalar stretch degree of freedom. We derive an effective microstretch theory for these modes starting from nonlinear elasticity on a cylindrical surface. By linearizing the equation of motion around a uniformly twisted equilibrium configuration, we obtain the dynamical matrix for the twisting, longitudinal, and radial-breathing modes. This matrix coincides with that of a one-dimensional microstretch theory, and the corresponding elastic constants are expressed in terms of the Lamé constants, the nanotube radius, and the twist rate. The twist generates chiral couplings in the effective theory, which hybridize the three modes and open an anticrossing in the phonon dispersion. We also discuss the relation between this twist-induced mechanism and intrinsic chirality in chiral nanotubes, where symmetry allows analogous effective chiral couplings even without an externally applied twist. These results provide a microscopic basis for the microstretch description of phonons in twisted carbon nanotubes and clarify how structural chirality enters the effective couplings.
An overview is presented of how the measurement of the complex elastic moduli as a function of temperature and frequency, often called mechanical or anelastic spectroscopy (AS), provides information and insight in many fields of solid state physics and materials science. Rather than focusing on topics where the use of AS is consolidated, like polymers, glasses and metallurgy, topics of timely interest are considered, aligning with application-driven research on functional properties or their degradation. Notable examples are phase transitions, not only ferroelastic, but also ferroelectric, magnetic and electronic, and point defects. The research on ultralow damping, already critical in electronics, communication and metrology, is gaining renewed relevance for the improvement of gravitational wave detectors and it will be even more so for qubit technology, where decoherence is due to the interaction with low energy excitations and hence damping. In order to fill the communication gap with more familiar spectroscopies, AS is also briefly introduced using the formalism of spectral density. In addition, a few examples are mentioned where the combined use of AS with other spectroscopies is particularly informative.
Low-dimensional materials exhibit extraordinary properties that make them promising candidates for advanced technologies. Although they have been investigated extensively, most of the research has focused on layered two-dimensional materials. Here, inspired by recent advances in atomically thin metallenes, we further reduce dimensionality and use density-functional theory simulations to study the geometry, energetics, elasticity, and electronic structure ofnon-magnetic one-dimensional (1D) atomic chains of elemental metals. We find that nearly all chains have a buckled ground state, nine chains are distorted, and three chains-Cd, Hg, and Sr-are semiconducting with an electronic gap. We also find that transition metals retain a substantial fraction of their three-dimensional bulk cohesive energy even in 1D chains. We assessed chains' dynamical stabilities by molecular dynamics simulations and found thatof them are thermodynamically stable atK. Finally, we performed chain pulling simulations to investigate the straightening dynamics of selected stable chains. Given that experimental techniques have recently reached the 1D-chain limit, our systematic study provides a foundation and timely guide to accelerating synthesis and characterization of these materials.
In this paper, we demonstrate the phase transition of 1T-WTearmchair and zigzag edge nanoribbons under the application of an out-of-plane electric field normal to the monolayer plane. Density functional theory, Heyd-Scuseria-Ernzerhof and maximally localized Wannier functions are utilized to determine the properties of the material, and the transport calculations are performed using non-equilibrium green's function method and tight-binding model. By using these calculations, we have observed that 1T-WTechanges its phase from topological insulator to trivial insulator after the application of a critical electric field,= 0.216. Moreover, the edge transport phenomena, which are observed in both nanoribbons of 1T-WTe, can contribute to the development of low-energy, dissipationless devices, particularly for designing a topological field-effect transistor.
Twisted bilayer hexagonal boron nitride (h-BN) has become an important moiré system because its polar lattice and stacking-dependent interactions connect electronic, magnetic, ferroelectric, and optical phenomena. Unlike twisted bilayer graphene, its narrow band-edge states are not tied to a single magic angle. Instead, they emerge over a broader angular range as the interlayer potential, hybridization, and lattice reconstruction confine electrons and holes in distinct regions of the moiré pattern. These states have motivated proposals for spin-density-wave order, unconventional superconductivity, and itinerant magnetism, although the intrinsic minibands have not yet been observed directly, and controlled filling remains challenging. At small angles, reconstruction produces domains with opposite out-of-plane polarization and in-plane components near their boundaries. These polarization patterns make twistedh-BN a clear example of stacking-induced ferroelectricity and a platform for meron-like polar textures. The same reconstructed landscape also reshapes the excitonic response. Recent experiments on three-dimensionalh-BN moiré quantum wells have demonstrated efficient deep-ultraviolet confinement and emission, while in atomically thin twisted bilayers the relative roles of moiré trapping, self-trapping, defects, and strain remain to be established. Beyond its intrinsic properties, the polar interface can impose a tunable periodic potential on nearby materials and act as an active moiré substrate. This topical review examines fabrication, structural classification, lattice reconstruction, electronic structure, correlated and magnetic phases, ferroelectricity, polar textures, and excitonic response, with emphasis on the current balance between theory and experiment.
The reaction mechanism of the N atom interaction with a single-layer MoS2, two-dimensional transition metal dichalcogenide, is considered in detail. These mechanisms were studied by DFT (density functional theory) modeling using both static and dynamic approaches. The most important processes for pristine and modified MoS2surfaces are revealed. For incident N atoms both the scattering and recombination with adsorbed atoms are prevailed. Various formation mechanisms for vacancies and other defects by thermal and hot N atoms are proposed and discussed. The results of dynamic DFT simulations are used to illustrate the reaction pathways.
Deformation modifies the structure of metallic glasses, driving their configurational state far from equilibrium. In this work, we investigate how deformation kinetics governs this process through the interplay between the input of external mechanical work and intrinsic structural relaxation. Using a Pd20Pt20Cu20Ni20P20high-entropy metallic glass as a model system, we combine high temperature tensile deformation with calorimetric measurements to characterize the structural state reached after homogeneous plastic flow. Increasing strain rate enhances the flow stress and the amount of mechanical work input, whereas slow deformation allows more extensive structural relaxation. The results quantify how strain rate governs the competition between deformation-induced configurational excitation and concurrent relaxation. This determines the threshold strain rate where rejuvenation becomes dominant, enabling precise control over the energy state of amorphous materials near the glass transition.
We revisit the enhancement of electron-phonon coupling predicted near an electronic quantum phase transition in a two-state, one-phonon model. In an earlier analysis, one of us predicted that the diagonal Born-Oppenheimer correction generated a sharp barrier in the potential-energy surface, localised low-lying phonon states on either side of the transition point, and produced a pronounced hardening of the phonon modes. Here we ask whether this enhanced coupling survives in the exact coupled electron-phonon problem. We solve the full model by direct diagonalisation, obtaining the exact coupled electron-phonon excitation spectrum, and analyse its ground state using the parametric representation of the electron-nuclear wavefunction. We find that the exact solution recovers the adiabatic picture obtained by including the diagonal Born-Oppenheimer correction when the electronic levels are well separated, but that this picture is progressively smoothed and weakened as the electronic and phononic energy scales become comparable. In the near-degenerate regime, the exact solution crosses over to a diabatic description. Thus, the associated localisation and phonon-hardening signatures are not artefacts of the Born-Oppenheimer approximation, but survive in renormalised form in the exact theory when the electronic levels remain sufficiently well separated.
