Traditional memory architectures are approaching their physical limitations in storage density and energy efficiency. As a result, the development of high-density, low-power memory devices has garnered significant research attention. The inherent bistability as well as topological protection of the topological vortex makes it a promising candidate for next-generation information storage with high storage density. However, controllable switching of multiple vortices within a single storage unit remains a critical challenge. This study focuses on a two-dimensional ferroelectric-dielectric composite consisting of a ${\mathrm{SrTiO}}_3$ matrix and four ${\mathrm{BaTiO}}_3$ nanoparticles, and proposes a novel control strategy to program the circulation of vortices in a single unit. Our phase-field simulation shows that four vortices can spontaneously evolve in the nanoparticles. Moreover, the composite can undergo both complete and partial multivortex switching under external electrical and mechanical loading, achieving $2^4$ distinct multivortex polarization states that can realize the function of a programmable 4-bit storage unit. The proposed design can theoretically achieve a storage density of up to $3.82\times {10}^{12}\text{bit}/{\text{in}}^2$, offering new physical insights derived from strategic guidance for the structural design and functional control of multistate ferroelectric memory devices.

We present a first-principles characterization of the excitation spectra of the representative transition metal dichalcogenide compound, $1T\text{−}{\mathrm{TiSe}}_2$, realized in the time-dependent density functional theory (TDDFT) framework. We discuss the origin and physical nature of different collective electronic excitations present in the spectra in the energy region below 30 eV in terms of interband transitions. We have found three kinds of electronic modes in agreement with experimental findings obtained in electron energy-loss spectroscopy and ellipsometry experiments. For the small in-plane momenta, these three modes interpreted as bulk $\sigma +\pi , \pi$, and interband plasmons are characterized by energies of 19.9, 6.7, and 2.3 eV, respectively. Along the out-of-plane axis, the energy of the bulk $\sigma +\pi$ plasmon is 20.6 eV. The $\pi$ plasmon is found at energies around 10 eV. We follow the dispersion of all these modes over an extended momentum range. Our calculations confirm the absence of the interband plasmon along the out-of-plane direction in the lower-energy part.

Intrinsic and extrinsic point defect control is essential to manipulate the electronic properties of two-dimensional semiconductors. However, complex defect chemistry and asymmetry in defect formation usually hinder accurate control of the carrier type and concentration, limiting their practical implementation in electronic and optoelectronic devices. This study presents a systematic first-principles investigation of defect thermodynamics and electronic behavior in monolayer $\mathrm{Zr}{\mathrm{S}}_2$ using density functional theory. Formation energies, charge-state transition levels, and point defect equilibrium concentrations as a function of temperature were evaluated using the hybrid HSE06 functional. Results indicate that sulfur vacancies dominate under Zr-rich conditions, leading to an intrinsic $n$-type conductivity, while sulfur interstitials become thermodynamically stable under S-rich conditions. Additionally, to alleviate the constraint posed by the lack of low-energy acceptor-like intrinsic defects, a group of extrinsic dopants, namely Y, Nb, P, and Cl, were systematically investigated in terms of their incorporation energetics and electronic behavior. Among them, substitutional Y on the Zr site is identified as a promising acceptor dopant owing to its low formation energy and high solubility under S-rich conditions. These results provide atomistic insights and a theoretical rationale for doping control in monolayer $\mathrm{Zr}{\mathrm{S}}_2$, thereby facilitating their implementation in next-generation electronic and optoelectronic devices.

We investigate quantum oscillation measurements in the Dirac nodal-line semimetal ${\mathrm{TaNiTe}}_5$ which exhibit a strongly enhanced amplitude in the magnetoresistance. We show that mechanical properties of the measurement setup in combination with de Haas–van Alphen oscillations in the magnetic torque can cause this enhancement in the measured resistance, without involvement of any topological properties in this material. To support the empirical data, a numerical model is provided, showing good agreement.

Phonons are quanta of lattice vibrations, and their modes (linear, circular, or stationary) are symmetry-determined. Circularly polarized phonons, possessing nonzero angular momentum (AM), have drawn widespread attention recently. Despite widespread use of pseudo-angular momentum (PAM) and circularly polarized light polarization flips to identify circularly polarized phonons in Raman scattering, their reliability is debated due to symmetry dependence, and experimental verification standards remain lacking. Here, we systematically study phonon chirality and associated phenomena across magnetic point groups. We establish that the AM-PAM correlation is governed by both crystalline symmetry and Wyckoff positions, dictating conditions where nonzero AM manifests in PAM signatures. Crucially, phonons belonging to distinct irreducible representations exhibit distinct experimental benchmarks, enabling direct determination of crystalline chirality and symmetry classification. Furthermore, we report the discovery of a signature for symmetry-induced phenomena, notably a half-wave plate-analogous effect induced by mirror-odd phonons. Meanwhile, we conducted five experiments to validate our theory.

Perovskite structured $\mathrm{LaNi}{\mathrm{O}}_3$ is a strongly correlated metal with intriguing thermal and magnetic properties. The volume dependence of calculated and measured physical properties can add additional critical information to develop a more in-depth understanding of this strongly correlated phenomenon. Taking advantage of recent single crystal $\mathrm{LaNi}{\mathrm{O}}_3$ growth using the floating-zone method, we have measured the thermal expansion, the magnetostriction, and the pressure dependence of the magnetic susceptibility, which then allows derivation of the Grüneisen parameters ${\gamma }_e=\frac{d\text{ln}N\left(E_F\right)}{d\text{ln}V}, {\gamma }_{\chi }=\frac{d\text{ln}\chi }{d\text{ln}V}$, as well as of electric and thermal transport properties. We simulate the volume dependence of structural and magnetic properties using Density Functional Theory calculations at the Generalized Gradient Approximation level. A large discrepancy between experimental values and calculated ones suggests that strong correlations are likely to be dynamic in nature. This study also provides a side-by-side comparison of measurements in single crystal and polycrystalline samples of $\mathrm{LaNi}{\mathrm{O}}_3$ to elucidate intrinsic materials properties. A broad hump at high temperatures in the temperature dependence of magnetization found in the single crystal sample of $\mathrm{LaNi}{\mathrm{O}}_3$ has been rationalized by a model that includes the influence of electron correlations on the Landau diamagnetism.

Altermagnets have garnered significant interest owing to their distinct crystallographic and spin symmetries, which exhibit vanishing net magnetization and momentum-dependent spin splitting. However, current research has primarily focused on inorganic altermagnetic materials. In this study, a two-dimensional (2D) Cairo pentagonal metal-organic framework (MOF) family, ${\text{TM}}_2$(TCNQ)${}_2$ [TM = transition metal, TCNQ = 7,7,8,8-tetracyanoquinodimethane], is presented as a versatile platform for $g$-wave altermagnets. The applied tensile strain along the [110] direction results in enhanced spin-splitting and induces a Lifshitz transition between $g$-wave and $d$-wave altermagnet, as evidenced in monolayer ${\mathrm{Ru}}_2$(TCNQ)${}_2$. Additionally, a tight-binding model composed of the $p\text{−}d$ orbital interactions for 2D Cairo pentagonal altermagnets accurately captures the $g$-wave-to-$d$-wave phase transition. Furthermore, the [110]-strained ${\mathrm{Ru}}_2$(TCNQ)${}_2$ exhibits fascinating anisotropic spin plasmon propagation, presenting exciting prospects for spintronic applications. This work opens a novel pathway for the design and investigation of altermagnetic candidates using 2D MOF platforms.

Magnetic topological materials hosting nonzero Berry curvature have emerged as a focus of intensive research because of their exceptional magnetoelectric coupling phenomena and potential applications in next-generation spintronic devices. In this work, we successfully synthesized high-quality GdAlSi single crystals, a prototypical member of $R\mathrm{Al}X$ ($R$ = rare earth elements; $X$ = Si/Ge) family that has been theoretically predicted to sustain a nontrivial Weyl semimetal state. Through systematic investigations of magnetic and transport properties, we identified two successive antiferromagnetic transitions at critical temperatures $T_{N1} \sim$ 31.9 K and $T_{N2} \sim$ 31.1 K, as evidenced by temperature-dependent resistivity, magnetic susceptibility, and specific heat measurements. Notably, applied magnetic fields exceeding 8 T induce a third magnetic transition ($T_{N3}$), generating a cascade of metamagnetic transitions that collectively form a dendritic phase diagram. This complex magnetic behavior is attributed to the interplay between localized $\mathrm{Gd}\text{−}4f$ moments and itinerant conduction electrons, possibly mediated by Dzyaloshinskii-Moriya interactions. Transport measurements revealed striking stepwise anomalies in magnetoresistance when crossing phase boundaries, accompanied by pronounced hysteresis loops arising from magnetic moment flopping processes. Our results not only establish GdAlSi as a rich platform for investigating correlated topological states, but also demonstrate its potential for engineering topological phase transitions through magnetic symmetry manipulation in Weyl semimetals.

We present the density-functional theory (DFT) calculations which provide us with microscopic atomic reaction processes of the Mg acceptor migration in GaN through the vacancy-mediated diffusion processes. For the exchange-correlation energy, we adopt a hybrid approximation in which the exchange energy is treated partly by the exact Hartree-Fock expression and hereby reproduces the experimentally observed band gap. We identify all the possible elementary processes of the Mg migration through the vacancy mechanism and obtain the corresponding energy profiles, thus determining the migration energies along various crystallographic directions in wurtzite GaN. We find clear anisotropic migration behavior corroborated by a substantial difference in the migration energies. We find that the rate-limiting process of the long-range Mg diffusion via the vacancy mechanism is not the Mg hopping process but the Ga hopping process to the nearby vacant site. This finding infers the similarity between the Mg diffusion and self-diffusion. Further calculations of the formation energies of the relevant point defects and their migration barriers computed in this paper, as well as the relevant energetics for the interstitial mechanism explored previously in our calculations, infer that the interstitial mechanism is important in the Mg diffusion under, at least, equilibrium conditions. However, the vacancy mechanism is also found to be important under the experimental condition in which relevant defects, Ga vacancies, are injected.

The optical response of two-dimensional systems is strongly influenced by tightly bound excitons. Despite its relevance in helping predict device performance, the current derivation of the two-dimensional Elliott equation is rarely used to estimate exciton binding energy and band gap in these systems, primarily due to its lack of an analytical form and the complexity introduced by substrate interactions. In this work, we present a new approach based on optical absorption measurements via an extended Elliott band fluctuations model, which notably provides analytical expressions for isotropic systems. Our method accurately captures the optical absorption near the band edge, fully incorporating spin–orbit band splitting and substrate effects via the Keldysh effective potential. It also includes the influence of surface and interface contributions to the dielectric environment, which give rise to localized defect-related absorption features. We apply this approach to key transition metal dichalcogenides $({\mathrm{MoS}}_2,$ ${\mathrm{MoSe}}_2,$ ${\mathrm{WS}}_2, \text{and} {\mathrm{WSe}}_2)$ exhibiting small and large spin-orbit band splitting, on various substrates and over a broad temperature range. The results show good agreement with magnetoabsorption and photoluminescence measurements, allowing for an accurate description of excitonic properties using only optical measurements and is readily extendable to other 2D isotropic materials.

Electron-mediated voltage control of exchange coupling (EM-VCEC) has been proposed as a mechanism for magnetization switching via modulation of spin-dependent electron reflection. However, its experimental verification has been challenging due to the coexistence of slower, voltage-induced ionic effects. Here, we fabricate magnetic tunnel junction (MTJ) devices that enable nanosecond timescale voltage application. Our results reveal rapid exchange coupling modulation on the nanosecond timescale, consistent with an electronic origin. The observed enhancement and saturation at low temperatures further rule out ionic migration, conclusively confirming the electronic nature of the mechanism. These results establish EM-VCEC as a viable mechanism for fast and energy-efficient voltage-driven magnetic switching.

Terahertz emissions from magnetic heterostructures comprising Fermi-level engineered 3D topological insulators, ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, are compared to assess how tuning the chemical potential absent any compositional change affects the resultant emission properties. Despite an enhancement in spin-orbit torque efficiency exhibited by bulk-insulating ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ heterostructures, an ∼5-fold reduction in the terahertz emission amplitude is observed as compared to its bulk-conducting counterpart. Such discrepancy between reciprocal measurements of spin-charge conversion is understood to result from a loss of interface transparency to spin currents due to the low carrier density and high sheet resistance of bulk-insulating ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, resulting in a pronounced conductivity mismatch between the metallic ferromagnet and topological insulating thin films that constitute our spintronic terahertz emitters.

Motivated by the recent observation of giant room-temperature magnon spin conductivity in an ultrathin ferromagnetic insulator [X.-Y. Wei, et al., Nat. Mater. 21, 1352 (2022)], we investigate thickness-dependent magnon spin transport in thin antiferromagnetic insulators (AFIs). We study the prototypical AFI hematite, known for its exceptionally low magnetic damping and two distinct magnetic phases: a low-temperature uniaxial easy-axis phase and a high-temperature biaxial easy-plane phase. Using stochastic micromagnetic simulations, we investigate thickness-dependent magnon spin transport across both magnetic phases. Our results uncover a crossover from quasi-three-dimensional to quasi-two-dimensional magnon spin transport at a critical thickness determined by the frequency or energy of the excited magnons. Below this critical thickness, we observe a pronounced enhancement in the magnon diffusion length in both magnetic phases. This rise is attributed to a change in the effective magnon density of states, reflecting the reduced phase space available for scattering in the thinner, quasi-two-dimensional regime. Understanding and controlling long-distance magnon spin transport in AFIs is crucial for developing next-generation spintronic nanodevices, especially as materials approach the two-dimensional limit.

We propose an altermagnet/altermagnet topological superconductor/altermagnet (AM/AMTSC/AM) heterojunction exhibiting a filtering effect, where the vast majority of incident electrons are locally reflected, and only a small portion passes through the center region of the AMTSC. Within an appropriate parameter range, the AMTSC hosts chiral Majorana edge states (CMES), causing the transmission coefficient and the crossed Andreev reflection coefficient of the heterojunction to remain equal and exhibit quantized plateaus. By tuning system parameters, the number of CMES can be changed, thereby controlling the plateau values to be 1/2, 1/4, or 0. When the system has anisotropy, the plateaus corresponding to the AMTSC with $s$-wave pairing and $s+s_{\pm }$-wave pairing exhibit different variation trends. In the absence of anisotropy, quantized plateaus can also appear for the $s+d$-wave pairing. Moreover, the chemical potential and the spin polarization orientation angle of the AM can also adjust the plateau values and enrich these variations. All these phenomena originate from the CMES in the AMTSC and the tunneling between them, which exhibit strong robustness against disorder and can work stably over a wide range of system parameters.

We investigate the spectral properties of all-to-all interacting spin Hamiltonians acting on exactly $k$ spins, whose coupling coefficients are drawn from a normal distribution with mean $\mu$ and variance ${\sigma }^2$. For $\mu =0$, we demonstrate that their associated random matrix ensemble—Gaussian orthogonal ensemble, Gaussian unitary ensemble, or Gaussian symplectic ensemble—is determined by the parity of system size $L$ and locality $k$, following standard time-reversal symmetry classification. For couplings with a nonzero mean, we map the Hamiltonians to deformed random matrix ensembles and analyze conditions for an energy gap between the ground state and the first excited state. For $\mu <0$, we find two distinct regimes: For $k\gg \sqrt{L}$, the gap closes at critical disorder ${\sigma }_c\approx \left|\mu \right|$. Near this transition, the energy gap $\mathrm{\Delta }$ exhibits universal quadratic scaling $\mathrm{\Delta }/L\sim {(\sigma -{\sigma }_c)}^2$. When $k\ll \sqrt{L}$, ${\sigma }_c$ scales with $\left|\mu \right|$, but lacks a sharp transition. Our work introduces a semisolvable model that captures universal features of random-matrix statistics and spectral gap formation, providing a foundation for systematic extensions to more general many-body systems.

Thermal transport in highly anharmonic, amorphous, or alloyed materials often deviates from the predictions of conventional phonon-based models. First-principles approaches have introduced a coherent contribution to account for these deviations and to explain ultralow lattice thermal conductivity, but direct experimental evidence for this mechanism remains elusive. Here, we propose that the frequency-dependent lattice thermal conductivity, $\kappa \left(\nu \right)$, provides a direct signature of coherent transport. Specifically, we show that peaks in $\kappa \left(\nu \right)$ arise from the frequency nesting of modes with identical wave vectors. Applying this approach to CuCl, we identify clear signatures of coherent transport in its dynamical lattice thermal conductivity. We revisit the interpretation of thermoreflectance experiments and argue that the conventional understanding breaks down in strongly anharmonic crystals, alloys, and amorphous materials. Finally, we discuss experimental pathways to measure $\kappa \left(\nu \right)$, offering a new route to verify coherent contributions in thermal transport.

Inspired by the experimental realization of direct kagome spin ice [Yue et al., Nat. Nanotechnol. 19, 1101 (2024)], the theoretical six-vertex model on the kagome lattice is systematically simulated using the directed loop Monte Carlo method. Four distinct vortex lattice phases are identified: (i) antiferromagnetic leg states and vortex lattice order on both triangular and honeycomb faces, with a winding number $k=1$; (ii) ferromagnetic leg states and vortex lattice order on both types of faces, with $k=-2$ on the honeycomb faces and $k=1$ on the triangular faces; (iii) paramagnetic leg states and vortex lattice order on the triangular faces with $k=1$; and (iv) paramagnetic leg states and vortex lattice order on the honeycomb faces with $k=1$. As for ferromagnetic to different types of paramagnetic phase, besides the Ising universality class with $y_t=1$, varying critical exponents have also been found with different values of vertex weights. The transition between the third type and fourth type of vortex lattice phases occurs with the new exponent $y_t=1.340\left(3\right)$. The third and fourth types of the vortex lattice phase to the vortex disorder phase are found to be of the Berezinskii-Kosterlitz-Thouless type. These findings contribute to the search for and understanding of ice on complex lattices.