The observation of $\mathrm{high}\text{−}{T}_{\mathrm{c}}$ superconductivity in bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure provides a new venue for exploring novel unconventional superconductors and elucidating the mechanism of $\mathrm{high}\text{−}{T}_{\mathrm{c}}$ superconductivity. Subsequently, numerous chemical substitution studies have been reported, aiming to stabilize superconductivity at ambient pressure or significantly reduce the pressure threshold required for its occurrence. Here, we report the comprehensive study of sodium (Na) doping in the Ruddlesden-Popper nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7+\delta }$, where $\mathrm{N}{\mathrm{a}}^{+}$ substitutes for $\mathrm{L}{\mathrm{a}}^{3+}$ at the A-site with varying doping concentrations $\left(x\right)$. The structural, thermal, magnetic, and electronic transport properties of as-synthesized polycrystalline samples were systematically investigated. X-ray diffraction analysis reveals that the dominant structure has changed from the 327 Amam phase to the 4310 Bmab phase when $x\ge 0.075$, which is further corroborated by thermogravimetric analysis measurements. Substitution of $\mathrm{L}{\mathrm{a}}^{3+}$ with $\mathrm{N}{\mathrm{a}}^{+}$ within the 327 phase gives rise to a gradual expansion of the lattice. Meanwhile, resistivity measurements indicate that the resistivity anomaly associated with a density-wave-like (DW-like) transition is marginally suppressed and metallicity is significantly enhanced. Upon application of pressure, the DW-like transition can be further suppressed, whereas the low-T insulating behavior remains insensitive to pressure. These results offer critical insights into the roles of elemental substitution and charge carrier doping in steering the competing electronic phases in layered nickelates.

The nonlinear Hall effect has emerged as an essential field in condensed matter physics for its connection with the properties of quantum geometry and its potential application in electronic devices. However, when the nonlinear Hall current scales quadratically with a single driving electric field, it is difficult to regulate the direction of the Hall response by reversing the driving electric field. This limitation hinders the practical implementation of nonlinear Hall effect in logic memory applications. Here, we establish a symmetry-based framework for the nonvolatile control of the nonlinear Hall effect through ferroelectric switching in two-dimensional ferroelectric materials. We prove that ferroelectric switching reverses the effective spin-orbit field, thereby reversing the sign of the Berry curvature dipole and, consequently, the nonlinear Hall conductivity. Using symmetry analysis and tight-binding models, we identify 18 layer groups that allow a ferroelectric switchable nonlinear Hall effect driven by Berry curvature dipole. By first-principles calculations we demonstrate that the monolayer $\alpha \text{−}\mathrm{Bi}$ and ${\mathrm{NbOI}}_2$ are ideal platforms to verify our proposed switchable mechanism. Our results provide a generalized framework for the nonvolatile control of nonlinear Hall effect, paving the way for its potential application in logical storage through assisting in the detection of two-dimensional ferroelectric polarization states.

The existence of higher-order effects in magnetization in magneto-transport and magneto-optic phenomena is well known. These effects are of importance not only in research but also directly in applications. Anisotropic magneto-resistance, anisotropic magneto-thermopower, quadratic magneto-optic Kerr effect (QMOKE), Voigt effect, or x-ray linear magnetic dichroism (and birefringence)—all of these are effects of second order in magnetization. Recently, we have reported on systematic observations of the cubic-in-magnetization magneto-optic Kerr effect (CMOKE) in Ni(111) thin films. In this paper, we introduce the detailed theory of CMOKE by deriving the magneto-optic tensor of third order in magnetization, denoted as $\mathit{H}$, and comparing the strength of CMOKE for different crystal orientations theoretically and experimentally. In crystals with cubic symmetry, the tensor $\mathit{H}$ is described by two independent parameters $H_{123}$ and $H_{125}$. Together with the linear magneto-optic tensor $\mathit{K}$ and quadratic magneto-optic tensor $\mathit{G}$, the permittivity tensor is described up to third order in magnetization. We analytically describe equations of the magneto-optic Kerr effect (MOKE), including the contribution of QMOKE and CMOKE themselves for (001)- and (111)-oriented cubic crystal structures. Those are compared with experimental measurements of two samples with an (001)- and (111)-oriented fcc Ni layer, respectively. The experimental data are measured using the so-called eight-directional method, which was developed to separate linear and quadratic MOKE contributions and to observe their individual anisotropic dependence on the crystal lattice direction but is applicable to CMOKE contributions as well. Furthermore, we use Yeh's $4\times 4$ transfer matrix calculus to simulate and describe the experimental measurements phenomenologically from the permittivity tensor developed up to third order in magnetization. This allows us to obtain the values of the magneto-optic parameters of the Ni layer for both crystal orientations. We find that the MOKE anisotropy that stems from the magneto-optic tensor $\mathit{H}$ described as $\mathrm{\Delta }H=H_{123}-3H_{125}$, is much more pronounced for the (111)-oriented cubic crystal structure, for which it manifests as threefold in-plane angular dependencies of MOKE with longitudinal and also with transversal magnetization direction, respectively. For (001)-oriented cubic crystal structures, $\mathrm{\Delta }H$ should manifest as a fourfold angular dependence of the MOKE with longitudinal and transversal magnetization directions, but its amplitude is predicted to be smaller than in the case of the (111)-oriented cubic crystal structure, which may explain why the CMOKE has not yet been experimentally identified in (001)-oriented cubic crystal structures.

We revisited the high-pressure phase diagram of superconductor β-ThRhGe by measuring electrical resistivity and ac magnetic susceptibility under hydrostatic pressures. In addition to the low-pressure superconducting phase (SC1), our results revealed the emergence of another high-$T_{\mathrm{c}}$ superconducting phase (SC2) at pressures above 1 GPa, which coexists with SC1 and enhances with pressure along with the collapse of orthogonal-monoclinic structural transition near $\sim 3$ GPa. The superconducting transition temperature $\left(T_{\mathrm{c}}\right)$ of SC1 increases linearly with a pressure coefficient $\mathrm{d}{T}_{\mathrm{c}}/\mathrm{d}P\approx 0.69$ K/GPa, but the SC2 exhibits a dome-shaped pressure dependence, reaching a maximum value of $\sim 9.3$ K around 6.3 GPa, which is the highest for the reported ternary equiatomic intermetallic compounds. Our results suggest that SC1 and SC2 have significantly different superconducting coupling strengths and effective electron masses, further demonstrating two distinct superconducting states. The analysis of normal-state properties suggests that the enhanced $T_{\mathrm{c}}$ may be related to phonon softening accompanying structural transitions, and/or quantum fluctuations caused by possible structural instability. The evolution of $T_{\mathrm{c}}$ as a function of pressure and the physical mechanism of superconducting states were discussed on comparison to the previous reports in $\beta \text{−}\mathrm{ThR}{\mathrm{h}}_{1-x}{\mathrm{Ir}}_x\mathrm{Ge}$.

We present two models with explicit long-range electrostatics in the form of Coulomb interactions. Both models include point charges depending on their local atomic environments, and the second model also conserves a total charge of an atomic system. We combine the proposed long-range models with the local moment tensor potential (MTP) and demonstrate that they reduce the training errors of the MTP models fitted on the same training sets including the ${\mathrm{CH}}_3{\mathrm{COO}}^{-}+4$ -methylphenol and ${\mathrm{CH}}_3{\mathrm{COO}}^{-}+4$ -methylimidazole organic dimers (nonperiodic systems) and the NaCl crystal (periodic system). For the organic dimers, the proposed models also give qualitatively correct predictions of the binding curves. Furthermore, in this study we introduce a method for calculating phonon spectra of isotropic materials only via these long-range models fitted to energies, forces, and stresses. The developed long-range model with point charges dependent on atomic environments and conserving total charge is capable of predicting the correct value of the LO-TO splitting in the $\mathrm{\Gamma }$-point in the isotropic NaCl. For this system, we also predict the dielectric constant from dipole moment fluctuations calculated with molecular-dynamics simulations conducted with the developed long-range model. The calculated dielectric constant is in good agreement with experiment. Finally, we demonstrate the broader applicability of the introduced approach by computing the phonon spectrum of uniaxial tetragonal ${\mathrm{PbTiO}}_3$. Although the method is formally derived for isotropic materials, we show that it is also a perspective for uniaxial materials (e.g., ${\mathrm{PbTiO}}_3$) as the spectrum obtained with our long-range interatomic potential corresponds to the one calculated with density functional theory.

The Gilbert damping parameter α plays a central role in magnetization dynamics and is crucial for the performance of spintronic devices. Here, we investigate the composition-dependent damping anisotropy in epitaxial ${\mathrm{Fe}}_{100-x}{\mathrm{Co}}_x$ thin films grown on MgO(001). Angular-dependent broadband ferromagnetic resonance measurements reveal weak damping anisotropy in pure Fe, clear fourfold anisotropy in ${\mathrm{Fe}}_{70}{\mathrm{Co}}_{30}$ and ${\mathrm{Fe}}_{150}{\mathrm{Co}}_{50}$, and the largest angular variation in ${\mathrm{Fe}}_{30}{\mathrm{Co}}_{70}$, where the maximum damping ratio reaches 259%. Anisotropic magnetoresistance measurements show a composition-dependent trend that is broadly consistent with the evolution of damping anisotropy. First-principles calculations further suggest that local tetragonal distortions associated with chemical disorder can modify the spin-orbit-coupled electronic structure and thereby contribute to the anisotropic Gilbert damping. These results show that compositional tuning in epitaxial FeCo alloys provides an effective route to modulate anisotropic magnetic relaxation and offers guidance for the design of spintronic materials with tailored dynamical properties.

The tensor-network renormalization group (TNRG) is an accurate numerical real-space renormalization group method for studying phase transitions in both quantum and classical systems. Continuous phase transitions, as an important class of phase transitions, are usually accompanied by spontaneous breaking of various symmetries. However, the understanding of symmetries in the TNRG is well established mainly for global on-site symmetries like $U\left(1\right)$ and $SU\left(2\right)$. In this paper, we demonstrate how to incorporate lattice symmetries (including reflection and rotation) and $\mathcal{PT}$ symmetry in the TNRG in two dimensions (2D) through a case study of the hard-square lattice gas with nearest-neighbor exclusion. This model is chosen because it is well understood and has two continuous phase transitions whose spontaneously broken symmetries are lattice and $\mathcal{PT}$ symmetries. Specifically, we write proper definitions of these symmetries in a coarse-grained tensor network and propose a TNRG scheme that incorporates these symmetries. We demonstrate the validity of the proposed method by estimating the critical parameters and the scaling dimensions of the two phase transitions of the model. The technical development in this paper has made the 2D TNRG a more well-rounded numerical method.

The realization of Landau levels with a high density of states has recently attracted considerable attention in wave systems. Since classical waves are inert to real magnetic fields, researchers have adopted a purely geometric approach to design pseudomagnetic fields (PMFs) by shifting twofold Dirac cones in momentum space. Here, we extend the twofold Dirac cone case and demonstrate acoustic Landau levels based on a gradient acoustic crystal with a fourfold Dirac cone. By linearly tuning a dimensionless factor, we generate two PMFs with identical amplitudes but opposite directions, thereby obtaining twofold degenerate acoustic Landau levels. Through measurements of the total energy spectra of the gradient acoustic crystal, we experimentally demonstrate the existence of these acoustic Landau levels. Furthermore, we demonstrate one-way sound propagation of the associated pseudospin-dependent edge states using two types of chiral sound sources and verify their robustness by introducing two types of defects. The observed twofold degenerate acoustic Landau levels and their corresponding pseudospin-dependent edge states may have potential applications in sonic lasers, enhancing sound emission, and nonlinear wave mixing.

We investigate thermodynamic operation of a quasiperiodic lattice with an exact mobility edge, described by the Biddle–Das Sarma model. We use this model as the working medium of a quantum Otto cycle and map its operating mode as a function of the hopping-range parameter $p$, the initial and final potential strengths $V_i$ and $V_f$, and two idealized protocols for the isolated strokes. In a nonadiabatic protocol, where the density matrix is approximately unchanged during the isolated strokes, the cycle supports only two modes: a heater and an accelerator. In an adiabatic protocol, where level populations are preserved while the spectrum is deformed, two additional modes appear: a heat engine and a refrigerator. In addition, the efficiency of the heat engine and the coefficient of performance of the refrigerator are analyzed. Our results show that mobility-edge systems can realize multiple thermodynamic functions within a single platform and provide guidance for switching between modes by tuning $p$, $V_i$, and $V_f$.

To clarify the origin of the pseudogap and strange metal states as well as their mutual relationship in cuprate superconductors, a comprehensive study on the spectral function, Fermi surface, resistivity, and dynamical spin susceptivity of the Hubbard model on the square lattice has been conducted by means of the ladder dual-fermion approximation with an electron self-energy correction similar in spirit to Moriyaesque $\lambda$ correction. It is found that the appearance of these two states requires that the characteristic hole concentration below which the Mott-Heisenberg and Slater mechanisms of electron localization occurs $p_{\mathrm{MS}}$ nearly coincides with the hole concentration where the Van Hove singularity (VHS) point, i.e., the renormalized quasiparticle energy ${\tilde{\varepsilon }}_{\mathit{X}}^{*}$ at the X point $\mathit{k}=(\pi ,0)$, is in the vicinity of the Fermi level. When this condition is met, ${\tilde{\varepsilon }}_{\mathit{X}}^{*}$ is pinned at which the nesting condition of the antiferromagnetic (AFM) fluctuations is fulfilled almost everywhere on the Fermi surface in a wide range of the hole concentration in a metallic state, i.e., the strange metal state. The spin fluctuations of the strange metal state are nearly quantum critical and the dynamical spin susceptivity is well described by overdamped spin wave having the $\omega /T$ scaling with the relaxation rate at the Planckian limit, $\hslash \mathrm{\Gamma }\approx 2k_{\mathrm{B}}T$. Because of these distinctive features of the strange metal state, the $\mathit{k}$ dependence of scattering rate of electrons is small and electrons behave as the marginal Fermi liquid, where the imaginary part of their self-energy has Im ${\mathrm{\Sigma }}_{\mathit{k}}\left(\omega \right)=Tf(\omega /T)$ scaling, resulting in $T$-linear resistivity. In contrast, the pseudogap state is magnetically in the renormalized classical regime and the pseudogap is formed near the X point where the nesting condition of the short-range AFM order is fulfilled. Although the main origin of these two states is the AFM fluctuation, the end point of the pseudogap phase $p^{*}$ is placed near $p_{\mathrm{MS}}$ and the strange metal state is present not just around the quantum critical point of the AFM fluctuation $p_{\mathrm{QCP}}$ at low temperatures as expected in the Hertz-Millis-Moriya theory but extends toward $p^{*}$ due to the pinning of the VHS point. These results are consistent with the resistivity in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (LSCO), where the linear coefficient is maximum at $p^{*}$, the first-order-like sudden drop in the intensity of the angle resolved photoemission spectra at the Brillouin zone boundary at $p^{*}$ found in ${(\mathrm{Bi},\mathrm{Pb})}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+d}$ and the extended quantum critical behavior of spin fluctuations at low temperatures in the inelastic neutron scattering experiments of LSCO in the strange metal state.

The optical properties of calcium fluoride (fluorspar, ${\mathrm{CaF}}_2$) are mainly determined by a strongly temperature-dependent giant infrared (IR) peak and a series of nearly temperature-independent ultraviolet (UV) peaks. We find that the temperature dependence of the IR peak can be modeled, to good accuracy, by a radiation-reaction improved coupled-oscillator model (RRCO model), with temperature-dependent parameters. For the UV peaks, we find a convenient functional form which covers both the real as well as the imaginary parts of the dielectric function and provides a comparison to first-principles calculations based on time-dependent density-functional theory. The result is a compact functional form for the dielectric function of undoped ${\mathrm{CaF}}_2$ applicable to wide frequency and temperature ranges $(0<\hslash \omega <60\mathrm{eV},$ $22{}^{\circ }\mathrm{C}<T<500{}^{\circ }\mathrm{C})$. With the help of the temperature-dependent dielectric function, we obtain temperature-dependent values of the short-range and long-range asymptotics of atom-surface interactions with ${\mathrm{CaF}}_2$, for hydrogen, as well as ground-state and metastable helium. The giant IR absorption peak of ${\mathrm{CaF}}_2$ is shown to lead to a delayed onset of the fully retarded Casimir-Polder limit in the long-range interaction regime. We present arguments supporting a more general applicability of the RRCO model to materials of general interest.

Silicon, diamond, and their compound silicon carbide play pivotal roles in electronic science and technology. Trivalent impurities such as B and Al are the typical choices for $p$-type doping in these semiconductors. Intriguingly, B dominates in Si and diamond, while Al is preferred in SiC for industrial applications, despite their chemical similarity. Using first-principles calculations, we perform a comparative analysis of B- and Al-related defects across the three hosts. We show that in the elemental hosts, B is favored due to its lower $2p$ orbital energy than Al $3p$ orbital energy. In SiC, the ionicity leads to strong localization of the valence-band maximum on the C sublattice, rendering large perturbation and high acceptor level if substituting on the anion C site. At the cation Si site, Al exhibits a small size mismatch, a shallower transition level, and a lower formation energy, making it the more efficient dopant. Interstitial defects are either energetically unfavorable (in Si and diamond) or contribute similar compensation effects for B and Al (in SiC), and thus do not alter the observed trends. These results not only provide a unified atomistic explanation for acceptor doping in Si, diamond, and SiC, but also offer a physically transparent picture that links dopant efficiency to band-edge character, site preference, and lattice relaxation.

We generalize a previously established ab initio approach—originally developed for hexagonal close-packed (hcp) metals—to accommodate solids with both internal and external degrees of freedom. This extension enables the thermodynamic and thermoelastic characterization of insulators, including those with nonvanishing piezoelectric and pyroelectric tensors. Utilizing Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) within the quasiharmonic approximation, we derive the pressure and temperature dependence of these properties. Specifically, we investigate internal degrees of freedom using two distinct frameworks: the Zero Static Internal Stress Approximation (ZSISA) and Full Free Energy Minimization (FFEM). We then compare these approximations by computing internal and external thermal expansions, as well as temperature-dependent piezoelectric and pyroelectric tensors. Finally, we demonstrate the generalized formalism by calculating the thermodynamic properties of wurtzite ZnO across a broad range of pressures and temperatures.

The high-pressure behavior of two Mn-based honeycomb-structured magnetoelectric materials, ${\mathrm{Mn}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$ (MNO) and ${\mathrm{Mn}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$ (MTO), has been investigated using Raman spectroscopy, synchrotron x-ray diffraction, and density functional theory (DFT) calculations. In MTO, application of a small pressure of only ∼0.5 GPa induces an isostructural transition driven by local symmetry breaking. With further increase in pressure, three additional isostructural transitions are observed, around 3.2, 6, and 10 GPa, followed by the onset of a long-range structural transition near 14 GPa, where the ambient $P\text{−}3c1$ phase begins to transform to a $P2/c$ phase. These two phases coexist up to 27 GPa. The Nb analog, MNO, also exhibits similar isostructural transitions at approximately 2, 6.6, and 10 GPa; however, the onset of the mixed $P2/c$ and $P\text{−}3c1$ phases occurs at a slightly lower pressure ($\sim 12.5\mathrm{GPa}$), with coexistence extending up to 26.5 GPa. These long-range transitions are supported by pressure-dependent enthalpy variations derived from DFT computations. Rietveld refinement reveals pronounced anisotropic lattice compression ($\sim 42–49\%$) between the $c$ and $a$ axes, leading to a notable reduction in the $c/a$ ratio. This anisotropy may enhance interlayer coupling under pressure and could potentially influence magnetic interactions, as suggested by the emergence of Raman modes resembling those reported at low temperatures, along with anomalous variations in Raman mode linewidth and intensity, warranting further direct investigations of the magnetic response under compression. The pronounced changes in Raman self-energy parameters, anomalies in the reduced pressure–Eulerian strain profile, and the onset of local symmetry breaking at much lower pressures in MTO than in MNO highlight the crucial role of differing spin-orbit coupling strength and orbital hybridization effects associated with ${\mathrm{Nb}}^{5+}$ and ${\mathrm{Ta}}^{5+}$ cations.

We have investigated the pressure-dependent electronic structure, phonon stability, and anomalous Hall response of the recently discovered altermagnet ${\mathrm{FeSb}}_2$ from density functional theory (DFT) and Wannier function analysis. From density functional perturbation theory (DFPT) calculations, we have found that ${\mathrm{FeSb}}_2$ remains dynamically stable up to 10 GPa, evidenced by positive phonon frequencies. Our spin-polarized band structure reveals that the crossing nodes between the spin-up and spin-down bands near the Fermi energy occur precisely at the $\mathrm{\Gamma }$ and Z high-symmetry points. The Fermi crossing is mostly exhibited by band-24, band-25, and band-26. The nonrelativistic spin-splitting (NRSS) along ${\mathrm{M}}^{\prime }$- $\mathrm{\Gamma }$ -M and A-Z-${\mathrm{A}}^{\prime }$ high symmetry paths is attributed to the symmetry operation [$C_2\left|\right|C_{2y}t$] and broken time-reversal symmetry ($\mathcal{T}$). Significant changes in the band structure are observed under applied pressure, as evidenced by the shift of the crossing node between bands 24 and 26 toward higher energies. The NRSS exhibited by band-24 along ${\mathrm{M}}^{\prime }-\mathrm{\Gamma }$ -M symmetry is notably small. Although the strength of NRSS associated with band-26 along the A-Z-${\mathrm{A}}^{\prime }$ path is substantial, it decreases under applied pressure. We have calculated and presented the anomalous Hall conductivity (AHC) over the energy range from $-1.5$ to 1.5 eV. The pronounced positive AHC peak at ambient pressure becomes spectrally broadened, and changes sign at 10 GPa as a result of pressure-induced modifications to the band structure and the associated redistribution of Berry curvature near the Fermi level. Furthermore, we quantify the orbital magnetization within the modern theory framework, which reaches a magnitude of 0.29 ${\mu }_B$ at zero pressure. Our results identify ${\mathrm{FeSb}}_2$ as a tunable altermagnetic candidate, where applied pressure can modulate both topological transport and dynamical stability, opening new avenues for strain-engineered Hall responses in compensated magnetic systems.

First-order phase transitions, characterized by a discontinuous change in the order parameter, are intriguing phenomena in condensed matter physics. However, the underlying, material-specific, microscopic mechanisms often remain unclear. Here, we unveil a high-temperature incommensurate charge-order precursor with the wave vector ${\mathbf{q}}^{*}=(0,\frac{1}{4}+\delta ,\frac{1}{2})$ in the 1T' phase of ${\mathrm{TaTe}}_2$, which competes with fluctuating high-temperature Ta trimer bonding states at ${\mathbf{q}}_{\mathrm{CO}}=(0,\frac{1}{3},0)$. The precursor state follows the temperature dependence of the hidden incommensurability of the quasi-1D nested Fermi surface. In contrast, the low-temperature commensurate charge order at ${\mathbf{q}}_{\mathrm{CO}}$, characterized by a charge disproportionation of the inequivalent Ta sites, appears to be driven by local chemical bonding. Dynamical lattice calculations identify an imaginary optical mode at ${\mathbf{q}}^{*}$, involving an in-plane vibration of the Ta atoms forming a chainlike structure that renormalizes below $T_{\mathrm{CO}}$. Our experimental and theoretical observations suggest that the controversial first-order phase transition, as captured by phenomenological Ginzburg-Landau theory, results from the competition between two order parameters: one involving Fermi surface nesting and the other involving local chemical bonding.

Materials with ultralow lattice thermal conductivity (LTC) are of fundamental and technological importance for thermal management and thermoelectric energy conversion, yet identifying crystalline solids that intrinsically suppress heat transport remains challenging. Here, we present a comprehensive first-principles investigation of lattice thermal transport in the tetragonal chalcogenides ${\text{Tl}}_2{\text{CdSnTe}}_4$, ${\text{Tl}}_2{\text{CdGeTe}}_4$, and ${\text{Tl}}_2{\text{HgSnSe}}_4$. By integrating temperature-dependent effective potential theory, anharmonic phonon renormalization, four-phonon scattering, and the multichannel transport formalism, we predict exceptionally low in-plane LTC values of 0.32, 0.30, and $0.29\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 300 K, placing these materials among the lowest reported for bulk inorganic crystals. The ultralow thermal transport originates from pronounced rattling dynamics of Tl atoms, which induce localization of low-frequency vibrational modes and strongly suppress heat-carrying acoustic phonons. Beyond conventional particlelike transport, coherent contributions become increasingly important at elevated temperatures, leading to a weak temperature dependence of LTC. We further show that tensile strain enhances anharmonicity and reduces LTC, while mass perturbation via isovalent substitution yields additional suppression through enhanced phonon scattering, reaching $0.16\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ under 1% strain. These results establish Tl-based chalcogenides as a promising class of intrinsically ultralow-LTC materials and highlight the effectiveness of combining heavy-atom rattling, strain, and compositional tuning for phonon engineering in these materials.

Transport measurements on thin films of the prototypical altermagnet MnTe have yielded conflicting reports including the anomalous Hall effect (AHE) with opposite signs and resistivity independent of thickness. In this work, we resolve these discrepancies by disentangling the bulk and surface contributions to the AHE for various crystal terminations. Using first-principles calculations and symmetry-based effective models, we demonstrate that, while the bulk hosts a characteristic $g$-wave Fermi surface, metallic surface states within the bulk gap acquire ferromagnetlike spin polarization and dominate the AHE at experimentally relevant Fermi levels. Although the surface magnetization direction is determined by the terminating spin sublattice, the sign of the surface AHE follows the bulk Néel order for any fixed termination. Both bulk and surface contributions share a common symmetry origin with a small but finite out-of-plane orbital magnetization, which reverses together with the AHE upon Néel-order reversal. Furthermore, realistic interfacial chemistry sets the magnitude and overall sign of the surface AHE—a Te capping layer reverses it relative to an InP substrate interface—while the locking to the bulk Néel order persists for each interface. Our results establish how interface design can be used to control magnetotransport in altermagnetic thin films.

Hydrogen (H) is a ubiquitous and electrically active impurity in semiconductors, playing a decisive role in shaping their optical and electrical properties, particularly in wide band-gap materials such as gallium nitride (GaN). Although postgrowth activation dissociates Mg-N-H complexes, a substantial concentration of residual H remains in $p$-GaN, and its dominant atomic configurations and dynamic behavior under device-relevant operating conditions remain poorly understood. Here, we directly identify the nitrogen-vacancy-hydrogen $\left(V_{\mathrm{N}}\text{-H}\right)$ complex in $p$-GaN by combining polarization- and angle-resolved Fourier-transform infrared spectroscopy with first-principles phonon calculations. We observe a localized vibrational mode at $1727\mathrm{c}{\mathrm{m}}^{-1}$ that emerges under forward electrical bias and elevated temperature. The mode exhibits a nearly isotropic in-plane polarization response along with a pronounced out-of-plane component. The key experimental vibrational characteristics, including peak position, polarization dependence, and angle variation, are in good agreement with the first-principles calculations, providing a consistent vibrational fingerprint that supports the assignment of the mode to a $V_{\mathrm{N}}\text{-H}$ configuration. Building on this identification, we further propose a physically grounded kinetic picture in which electron injection under forward bias enables H released from the GaN lattice to participate in $V_{\mathrm{N}}\text{-H}$ formation. These findings resolve a long-standing question regarding residual H in $p$-GaN and offer critical insight into both H-related defect physics and device degradation mechanisms, with broad implications for the reliability of GaN-based electronic and optoelectronic devices.

We analyze the effects of electron-electron and electron-phonon interactions in the dynamics of a system of two or three electrons that can be trapped to a localized state and detrapped to extended band states of a quantum dot using a simple model in which the valence and conduction bands of the quantum dot are modeled by two single-particle energy levels and the trap is described by one single-particle level within the band gap. In spite of its simplicity the time dependent problem has no analytical solution but a numerically exact one can be found at a relatively low computational cost. Within this model, we study the time evolution of the electron occupancies of conduction and valence bands and the trap state, as well as the statistical factors influencing light emission of different energies. In most of the analyzed cases, the system dynamics has a very short transient determined by the hopping parameters, that can be of tens of femtoseconds, followed by a quasistationary regime in which the electron occupancies either oscillate periodically around their time-averaged values or remain nearly constant. We find signatures of strong electronic correlations in the electronic motion for negative values of the effective electron-electron Coulomb interaction that are not translated to the statistical factors for light emission. These factors always show fast oscillations associated to electrons hopping back and forth from the conduction band to the trap, irrespective of the motion of the valence band electrons. Our calculations show that light emission of different energies is always possible except in the special cases in which the valence band is initially filled with two electrons. In these cases the valence band can lose and recover electrons periodically but exciton emission is negligible at any time. We use this fact to attempt to give a possible explanation for the increase in the intensity of exciton emission with the concomitant decrease in the intensity of the green emission lines upon continuous illumination with ultraviolet radiation, experimentally observed for ZnO nanoparticles suspended in an alcohol.