Fundamental quantum transition timescales are accessible through the spin polarization of photoelectrons coming from initially spin-degenerate states for solid-state materials. In this work we investigate the modification of this timescale in the vicinity of a resonance in photoemission from a solid. We employ spin- and angle-resolved photoemission spectroscopy (SARPES) to study the valence band of $1T\text{−}{\mathrm{TiSe}}_2$ and $1T\text{−}{\mathrm{TiTe}}_2$, with an excitation photon energy coinciding with the Ti $3p\text{−}3d$ autoionization state. The energy derivative of the measured spin polarization, which is in the off-resonance case proportional to the transition time, reveals a sign reversal and significant magnitude decrease compared to off-resonance measurements. We show that this effect goes beyond the conventional semianalytical models used to translate spin polarization to the transition time delay. At the photoemission resonance, the underlying interference assumption of the model breaks down, and additional information about resonance strength is needed to extract the transition time delays.

We present a unified bond dipole theory for metal-semiconductor interfaces to explain the microscopic origin of interface dipoles and Fermi level pinning (FLP) in terms of Harrison's bond-orbital model. By combining first-principles calculations with tight-binding analysis, we show that localized bonding between semiconductor surface dangling bonds and metal orbitals is sufficient to generate a large interface dipole and induce strong FLP, even when only a single metal monolayer is present. Within this framework, metal-induced gap states (MIGS), dangling-bond-induced surface states (DBSS), and bonding states embedded in the valence band are all understood as different outcomes of the same underlying interface bonding mechanism, rather than as independent causes of FLP. We further establish that the key parameter governing FLP strength is the density of surface dangling bonds that can form new chemical bonds with the metal, which directly controls the magnitude of the bond-induced interface dipole. This picture naturally explains the weaker pinning observed in more ionic semiconductors than in covalent ones and provides practical guidance for engineering metal-semiconductor interfaces and tuning Schottky barrier heights.

The two-dimensional ferroelectric (FE) material ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ (CIPS) has garnered considerable interest due to its out-of-plane ferroelectricity at room temperature. However, a notable discrepancy exists between experiments and density functional theory (DFT) calculations regarding the ground state of CIPS thin films: experiments suggest a state with net polarization, while DFT predicts an antiferroelectric (AFE) state as the lowest-energy state. Here, we investigate the stability of polarization states in CIPS thin films by combining first-principles calculations with the deep potential (DP) method. Our results reveal that for films thicker than the bilayer, an AFE state that has intralayer AFE ordering in the inner layers and intralayer FE ordering in the two surface layers, has the lowest electronic energy. This state is significantly lower than the uniform FE state. In addition, we find that a ferrielectric (FiE) state with pure intralayer FE ordering is very close to the AFE state in energy. By using the DP model, we calculated the phonon free energy of CIPS thin films. For the monolayer, the intralayer FE ordering possesses a lower phonon free energy than the intralayer AFE ordering. This energetic preference for the intralayer FE ordering maintains as the thickness grows. Consequently, when the phonon-free energy is incorporated, the FiE state becomes energetically favorable over the AFE state for multilayers CIPS. Our findings demonstrate that the inclusion of vibrational entropy stabilizes the FiE state as the ground state in multilayers CIPS at finite temperatures, reconciling the previous discrepancy between experimental observations and DFT predictions. This insight is vital for understanding the FE properties of CIPS and its potential applications in devices.

Random permutation circuits were recently introduced as minimal models for local many-body dynamics that can be interpreted both as classical and quantum. Standard dynamical complexity indicators such as damage spreading and out-of-time-order correlators (OTOCs), show that these systems exhibit sensitivity to initial conditions in the classical setting and operator scrambling in the quantum setting. Here, we address their quantum chaoticity—a stricter property—by studying the time evolution of local operator entanglement (LOE). We show that the behavior of LOE in random permutation circuits depends on the dimension of the local configuration space $q$. When $q=2$, i.e., the circuits act on qubits, random permutations are Clifford and the LOE of any local operator is bounded by a constant, indicating that they are not truly chaotic. On the other hand, when the dimension of the local configuration space exceeds two, the LOE grows linearly in time. We prove this in the limit of large $q$ and present numerical evidence that a three-dimensional local configuration space is sufficient for a linear growth of LOE. Our findings highlight that quantum chaos can be produced by essentially classical dynamics. Moreover, we show that LOE can be defined also in the classical realm and put it forward as a universal indicator chaos, both quantum and classical.

We investigate uniaxial-stress effects on the magnetic phase diagram of the square-lattice itinerant magnet ${\mathrm{EuAl}}_4$, where strong coupling among spin, lattice, and charge produces a variety of helimagnetic phases, including rhombic and square skyrmion lattices. Combining resistivity and magnetization measurements with neutron scattering, we find that compressive stresses of only several tens of megapascal along [010] enhance antiferromagnetic character and shorten the magnetic modulation period in the lowest-temperature single-$\mathbf{Q}$ spiral state, thereby driving the critical temperatures and fields of multiple phases to higher values. First-principles calculations show that increasing orthorhombic lattice distortion deforms the Fermi surface relevant to the magnetism, providing compelling evidence that Fermi-surface nesting plays a crucial role in stabilizing the helical magnetic modulations in ${\mathrm{EuAl}}_4$.

Photoinduced amorphization in chalcogenide phase-change materials plays a key role in enabling ultrafast photonic functionality. Here, real-time time-dependent density-functional theory simulations are employed to elucidate the microscopic mechanism of ultrafast amorphization in ${\mathrm{Sb}}_2{\mathrm{Se}}_3$ under femtosecond laser excitation. The results reveal that the occupation of Sb–Se antibonding states weakens the covalent network and initiates local melting that develops into a percolated amorphous structure. At low temperature, coherent phonons drive ordered Peierls-like distortions, whereas thermal phonons at room temperature disrupt coherence and accelerate structural disorder. By incorporating a Boltzmann factor $\tau$ to restore detailed balance, the simulations capture hot-carrier cooling and electron-phonon energy transfer. This approach reveals the intrinsic correlation among photoexcitation, energy relaxation, and structural evolution, offering microscopic insight into ultrafast phase transitions.

Non-Hermitian acoustic systems featuring balanced gain and loss have gained significant popularity owing to their potential applications in multifunctional devices. In this paper, we introduce the concept of parity-time ($\mathcal{PT}$) symmetry to zero index metamaterials (ZIMs) to investigate the transport of sound waves through a $\mathcal{PT}$-ZIM junction in a waveguide system. The $\mathcal{PT}$-ZIM junction is initially established by doping two acoustic cylinders with identical geometry and conjugate refractive indices into the ZIM, with one being gain and the other loss. It is found that the balanced gain and loss induce a perfect resonance transmission (PRT) against a backdrop of perfect reflection, with the resonant linewidth being controllable and determined by the gain/loss factor. Furthermore, we demonstrate the pseudo-$\mathcal{PT}$-symmetry and present a more comprehensive PRT in scenarios where the cylinder geometries are nonidentical, and feature distinct gain and loss factors. The fundamental principle remains a delicate equilibrium between gain and loss, however, the sound localization effect in the cylinders is significantly enhanced due to the differentiation in radii. This work offers a pathway for exploring non-Hermitian acoustics in ZIM, holding promising applications in sensing and nonlinear acoustics.

To investigate the emergent properties that may arise from the interplay of different instabilities in orbitally degenerate systems, we consider the representative case of mixed compounds of ${\mathrm{CaFeO}}_3$ and ${\mathrm{LaMnO}}_3$, having isoelectronic B cations. First-principles study of the mixed systems reveals an intricate interplay of charge transfer, Jahn-Teller distortion, and charge disproportionation, influencing the electronic and magnetic properties of the mixed compounds. Although the ground states of both parent compounds are insulating, one being nearly ferromagnetic (FM; ${\mathrm{CaFeO}}_3$) and another antiferromagnetic (AFM; ${\mathrm{LaFeO}}_3$), several of the mixed compounds among the studied compositions, e.g., ${\mathrm{Ca}}_{0.75}{\mathrm{La}}_{0.25}{\mathrm{Fe}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_3, {\mathrm{Ca}}_{0.625}{\mathrm{La}}_{0.375}{\mathrm{Fe}}_{0.625}{\mathrm{Mn}}_{0.375}{\mathrm{O}}_3, {\mathrm{Ca}}_{0.375}{\mathrm{La}}_{0.625}{\mathrm{Fe}}_{0.375}{\mathrm{Mn}}_{0.625}{\mathrm{O}}_3$, and ${\mathrm{Ca}}_{0.25}{\mathrm{La}}_{0.75}{\mathrm{Fe}}_{0.25}{\mathrm{Mn}}_{0.75}{\mathrm{O}}_3$, turned out to be FM half-metals. The computed $T_c$ values for ${\mathrm{Ca}}_{0.75}{\mathrm{La}}_{0.25}{\mathrm{Fe}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_3$ and ${\mathrm{Ca}}_{0.25}{\mathrm{La}}_{0.75}{\mathrm{Fe}}_{0.25}{\mathrm{Mn}}_{0.75}{\mathrm{O}}_3$ are found to be reasonably high, having potential applications for spintronics. The ${\mathrm{Ca}}_{0.5}{\mathrm{La}}_{0.5}{\mathrm{Fe}}_{0.5}{\mathrm{Mn}}_{0.5}{\mathrm{O}}_3$ and ${\mathrm{Ca}}_{0.125}{\mathrm{La}}_{0.875}{\mathrm{Fe}}_{0.125}{\mathrm{Mn}}_{0.875}{\mathrm{O}}_3$ compounds, on the other hand, exhibit insulating, AFM behavior, ${\mathrm{Ca}}_{0.875}{\mathrm{La}}_{0.125}{\mathrm{Fe}}_{0.875}{\mathrm{Mn}}_{0.125}{\mathrm{O}}_3$ being FM and insulating. This results in several electronic and magnetic phase transitions as a function of $x$ in ${\mathrm{Ca}}_x{\mathrm{La}}_{1-x}{\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}{\mathrm{O}}_3$ mixed compounds. Furthermore, an interesting atomic-scale microstructure appears from the competing nature of metal-oxygen covalency.

We present electrical-resistivity measurements on the prototypical heavy-fermion ferromagnet ${\mathrm{UGe}}_2$ under pulsed magnetic field up to 60 T. An anisotropic field-induced suppression of the electronic correlations is revealed. The electrical resistivity strongly decreases when a magnetic field $\mathbf{H}$ is applied along the easy magnetic axis $\mathbf{a}$, while it remains almost unchanged when $\mathbf{H}$ is applied along the hard magnetic axes $\mathbf{b}$ and $\mathbf{c}$. The field-induced destabilization of the ferromagnetic state is also anisotropic: the anomaly at the Curie temperature $T_C$ disappears in fields higher than $\gtrsim 1\mathrm{T}$ for $\mathbf{H}\parallel \mathbf{a}$ and in fields higher than $\gtrsim 20\mathrm{T}$ for $\mathbf{H}\parallel \mathbf{b},\mathbf{c}$. At temperatures below 2 K, we observe quantum oscillations in fields larger than 50 T applied along $\mathbf{b}$, which support the presence of a two-dimensional Fermi surface similar to that previously observed at low fields.

The interplay between epitaxial strain, magnetic compensation, Curie temperature, and anisotropy in ferrimagnetic insulators remains a central question with both fundamental and technological significance. Here, we present a comparative theoretical study of strain effects on ${\mathrm{Gd}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (GIG) thin films grown along [001] and [111] orientations. Using density functional theory and an ab initio-based effective Hamiltonian, we study the evolution of the magnetic compensation temperature ($T_M$), Curie temperature ($T_C$), and perpendicular magnetic anisotropy (PMA) under epitaxial strain. Our results show a linear enhancement of both $T_M$ and $T_C$ under compressive strain, with (001)-oriented films exhibiting a notably higher strain sensitivity than (111)-oriented counterparts. PMA was also found to have a nearly linear strain dependence with a strong orientation dependence, and to reverse when Gd $4f$ electrons were treated as core states—hinting at a possible strong temperature dependence of PMA. Our results offer clarity to experimental variability in $T_M$ and provide a microscopic basis for tailoring magnetic compensation, Curie temperature and anisotropy in rare-earth-based spintronics.

Metal borides such as ${\mathrm{MgB}}_2$ distinguish themselves from cuprate, iron-based, and hydride superconductors by integrating structural stability, high hardness, and simple stoichiometry, making them exceptionally suited for practical applications. Here, we predict two hard superconducting phases of ${\mathrm{ZrB}}_6$ ($P6$/mmm and $\mathit{Cm}$) that are dynamically stable at ambient pressure. Sharing a characteristic three-boron-layer sandwich structure, these phases nevertheless exhibit strikingly distinct superconducting behaviors. The $P6$/mmm phase achieves a high $T_c$ of 34 K, the highest among transition metal borides, which is enabled by strong electron-phonon coupling from synergistic flat bands and high-frequency boron phonons. In contrast, the $\mathit{Cm}$ phase exhibits a much lower $T_c$ of 5.8 K due to the absence of such electronic features. Notably, both phases also possess high Vickers hardness values of 33.6 and 39.8 GPa, respectively. Our results not only identify ${\mathrm{ZrB}}_6$ as a promising platform for hard superconductors but also provide a design strategy toward multifunctional materials for high-field magnet and fusion energy technologies.

A central question in superconductivity is how a semimetal such as antimony, normally nonsuperconducting, can host a robust superconducting state upon Au incorporation. We investigate this problem in metastable ${\mathrm{Sb}}_{0.83}{\mathrm{Au}}_{0.17}$, which crystallizes in the simple cubic $\alpha \text{−}\mathrm{Po}$-type structure stabilized through high-pressure and high-temperature synthesis. Bulk measurements of magnetic susceptibility, resistivity, and heat capacity establish type-II superconductivity with $T_c\approx 8\mathrm{K}$. The superconducting state exhibits strong electron-phonon coupling (${\lambda }_{\mathrm{ep}}=0.91$) and the single-gap $s$-wave model yields a superconducting gap of $\mathrm{\Delta }=$ 2.02 $k_B{T}_c$, exceeding the BCS weak-coupling limit. Heat-capacity data reveal low-energy Einstein modes and a pronounced Boson peak in the $\frac{C_{\mathrm{phonon}}}{T^3}$ vs $T$ plot, highlighting phonon softening as a key factor in the enhanced coupling. We argue that the emergence of superconductivity is driven by the cooperative effect of soft phonons and strong electron-phonon interactions. Density-functional theory calculations indicate a finite density of states at the Fermi level, consistent with a metallic behavior in contrast to the semimetallic nature of pristine Sb.

We investigate the pressure-dependent magnetism of the quasi-one-dimensional solid solution ${\mathrm{Ca}}_{1\text{−}x}{\mathrm{Na}}_x{\mathrm{Cr}}_2{\mathrm{O}}_4$ using neutron diffraction, Cr K-edge x-ray absorption spectroscopy, and muon spin rotation/relaxation. Na substitution is known to increase oxygen-ligand hole density (partial ${\mathrm{Cr}}^{3+}$ to ${\mathrm{Cr}}^{4+}$ character) and to drive the evolution from incommensurate order in ${\mathrm{CaCr}}_2{\mathrm{O}}_4$ to commensurate antiferromagnetism in ${\mathrm{NaCr}}_2{\mathrm{O}}_4$, suggesting a complex interplay between charge doping and structural changes. Here we apply hydrostatic pressure to tune the lattice without altering the nominal hole count, thereby separating compression effects from ligand-hole physics. For $x=0$ and $x=0.5$ the magnetic transition temperature is essentially pressure independent within our explored range, whereas in ${\mathrm{NaCr}}_2{\mathrm{O}}_4$ long-range order is progressively suppressed with pressure, as seen by a decrease of $T_N$ and of the magnetic Bragg intensity. Over the same pressure range, Cr K-edge x-ray absorption spectroscopy shows no resolvable change in the average Cr valence or coordination, and the refined corner-sharing Cr–O–Cr geometry remains nearly invariant within uncertainty. Extrapolating the pressure dependence of the magnetic order parameter suggests a critical pressure $P_c=107\left(8\right)$ kbar for complete suppression of long-range order. These results support ligand-hole density as the primary control parameter across ${\mathrm{Ca}}_{1\text{−}x}{\mathrm{Na}}_x{\mathrm{Cr}}_2{\mathrm{O}}_4$, with pressure acting as a secondary electronic tuning knob that weakens ordering in the Na-rich end member without inducing a new magnetic phase.

We conduct a comprehensive density functional theory study to explore the intricate magnetic properties of frustrated Mn monolayer on the Ag(111) surface. Spin-polarized scanning tunneling microscopy demonstrates that a Néel magnetic state characterizes such an interface, which contradicts systematic ab initio predictions made in the last two decades indicating that the ground state is collinear row-wise antiferromagnetic (RW-AFM) state. Here, we employ the all-electron full-potential Korringa-Kohn-Rostoker Green's function method and find that the ground state is a chiral magnetic Néel state, with magnetic moments rotating in the surface plane following a unique sense of rotation, as dictated by the underlying in-plane magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Changing the stacking of the Mn monolayer from fcc to hcp switches the chiral nature of the Néel state. Once allowing disordered magnetic states, as described within the disordered local moment approach, we reveal the possibility of stabilization of a RW-AFM state. We conjecture that at low temperatures, the chiral Néel state prevails, while at higher temperatures, the magnetic exchange interactions are modified by magnetic disorder, which can then induce a transition towards a RW-AFM state. Our work addresses a long-term experimental-theoretical controversy and provides significant insights into the magnetic interactions and stability of Mn films on noble metal substrates, contributing to the broader understanding of the different magnetic facets of frustrated magnetism in thin films.

Quantum geometry appears as a key factor in understanding the optical properties of quantum materials, with the anticipation on diverging or quantized responses near the Dirac and Weyl points. Here, we investigate linear and nonlinear optical responses—optical conductivity and injection current—in a magnetic Rashba semiconductor in the mid-infrared region, with varying the Fermi energy across the Dirac point. We reveal that the linear optical conductivity reflects quantum metric, which remains finite irrespective of the diminishing joint density-of-states at lower photon energy. It is also confirmed that the magnetic injection current enhances depending on the energy of the Fermi level relative to the Dirac point. These optical spectra are nicely reproduced by our theoretical calculations with geometrical effects taken into account.

The site-decorated Ising model is introduced to advance the understanding and experimental realization of the recently discovered one-dimensional (1D) finite-temperature ultranarrow phase crossover in an external magnetic field, while mitigating the geometric complexities of traditional bond-decorated models. The unconventional frustration and physics are clarified by exactly mapping the 1D site-decorated Ising model in a magnetic field onto a zero-field bond-decorated $J_1\text{−}{J}_2$ Ising model with conventional geometrical frustration. Furthermore, although higher-dimensional Ising models in an external field remain unsolved exactly, an exact solution for a spin-reversal transition—driven by an exotic, hidden half-ice, half-fire state induced by site decoration—is derived. This transition, triggered by a slight variation in temperature or magnetic field—without changing its direction—even in the weak-field limit, offers a promising route toward energy-efficient applications such as data storage and processing. The results suggest that site decoration offers an avenue for materials and device design, particularly in systems such as mixed $d\text{−}f$ compounds, optical lattices, and neural networks, calling for further studies with site-decorated Heisenberg models. In addition, the site-decorated model offers a rigorous test ground for artificial intelligence (AI) in science, as the analytic derivation of the present results was not only validated but also improved by a general-purpose large language model, inspiring the use of AI as scientific discoverer.

Here, we report a scanning tunneling microscopy study on an $s$-wave superconductor NaAlSi, revealing the coexistence of stripe order and superconductivity. This stripe order manifests as a unidirectional spatial charge modulation with a commensurate period of four times the lattice constant. This modulation undergoes a phase shift in the differential conductance maps under opposite bias voltages, while its period remains approximately constant over an energy range of $\pm 50\mathrm{meV}$. These features suggest that this stripe is likely a static charge order. Furthermore, we find that the stripe order imposes a periodic modulation on the intensity of the superconducting coherence peaks. This work provides interesting perspectives on the intricate interplay between stripe order and $s$-wave superconductivity.

The recent advent of a new class of magnetic material named as altermagnet (AM), characterized by a combination of momentum-dependent spin splitting with zero net magnetization, has opened up promising prospects for spintronic applications. We theoretically explore how the altermagnetic spin splitting affects the thermoelectric quasiparticle current in AM-based superconducting heterostructures. Our setup comprises of a bilayer system where a $d$-wave AM is proximity coupled to an ordinary $s$-wave superconductor (SC). We calculate the thermoelectric current carried by the quasiparticles applying a finite thermal bias across the junction. The behavior of the thermoelectric current with the system's base temperature and chemical potential is very similar to that in traditional SC heterostructures. Remarkably, the dissipative thermoelectric current found in the AM junction is spin split and thus generates finite spin polarization in the AM-based junction, which can approach $100\%$ spin polarization in the strong altermagnetic phase. We further investigate the thermoelectric current in AM-based Josephson junction (JJ) and illustrate how to achieve almost perfect diode effect in this AM-based JJ characterized by its efficiency $\sim 100\%$ with its sign decided by the strength of the AM, enhancing the potential for spin-caloritronics applications.