Nonreciprocity has received much attention recently in the photonics community. However, nonreciprocal hyperbolicity has rarely been investigated in spite of its significance, and it has been limited to the perturbative regime in magneto-optical metamaterials. This work reports strong nonreciprocal hyperbolicity in a Weyl semimetal–dielectric multilayered metamaterial. The dispersion relations are analyzed in the nonperturbative regime, and their behaviors are investigated depending on structural and material parameters. Although the metamaterial consists of an intrinsically nonreciprocal Weyl semimetal, nonreciprocity can be obtained only when the Weyl semimetal layer is surrounded by dielectric layers with different refractive indices in the unit cell. The metamaterial slab exhibits hyperbolicity-induced negative refraction with significantly asymmetric transmittances and absorptances for forward and backward incidences, originating from nonreciprocal dissipation. In an idealized loss-free case, nevertheless, the structure does not show asymmetric transmission due to vanishing optical loss, leading to only an asymmetric phase of the transmission coefficient by nonreciprocal dispersion. Strong nonreciprocal hyperbolicity in Weyl semimetal–based multilayered metamaterials is of great significance from a fundamental point of view and has great value in practice as well due to the unnecessariness of applying an external field.

The optical measurements of Hanle and polarization recovery effects for localized charge carriers are the basic tools for determining parameters of the spin dynamics, such as, for example, the strength of the hyperfine interaction in quantum dots. We describe the dependence of the spin polarization of localized electrons on transverse and longitudinal magnetic fields taking into account the interplay between electron hopping and measurement back action. We show that these two have a qualitatively similar effect in the Faraday geometry, but compete in the Voigt geometry. This allows one to describe a broad range of the experimental results and study the fundamental effects of quantum measurements.

Chiral-induced spin selectivity (CISS) is a striking phenomenon in which spin-unpolarized electrons become spin polarized after traversing a chiral medium. Theoretical studies have shown that spin-orbit coupling, geometric chirality, and dephasing act cooperatively for this effect to emerge. Inspired by this, we demonstrate a solid-state realization of CISS in an engineered InAs/GaSb quantum well where geometric chirality and dephasing can be introduced controllably. Introducing a chiral structure produces a clear spin polarization whose sign reverses when the chirality is flipped and whose magnitude grows systematically with the number of dephasing electrodes, while achiral configurations exhibit no spin selectivity. The polarization remains robust even under strong Anderson disorder, showing that the engineered chiral structures provide an intrinsically stable route to spin-selective transport. These results establish a solid-state platform in the topological quantum well system for controllably generating the CISS effect.

High Poisson's ratio phenomenon in copper prior to shock melting has been observed and attributed to partial melting, due to its presumed simple solid structural phase diagram including only the face-centered cubic (fcc) phase. Recent shock-compression experiments indicate a possible transition to the body-centered cubic (bcc) structure under high pressure and temperature. Determination of the fcc-bcc phase boundary is essential for assessing copper's effectiveness as a pressure standard, and the fcc-bcc transition also provides an alternative mechanism for the high Poisson's ratio phenomenon. This study uses first-principles density functional theory to calculate the phase boundary by comparing the Gibbs free energies of the two phases. The derived phase boundary extends from approximately 80 GPa and 3400 K to over 1.2 TPa and 9000 K, consistent with prior experimental findings. Elastic properties of copper across the fcc-bcc phase boundary obtained from ab initio molecular dynamics simulations confirm that the decrease in the shear modulus and the increase in Poisson's ratio are due to the fcc-bcc transition rather than partial melting.

Transition metal pyrophosphates $A_2{M}_2{\mathrm{O}}_7$ ($A=\mathrm{Zn}$, Cu, Mg, Fe, Co, Ni, Cr) have recently gained significant attention owing to their giant negative thermal expansion (NTE) properties and the relevant applications. Of them, $\mathrm{Z}{\mathrm{n}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ serves as a model one with ${\mathrm{A}}^{2+}$ ions being Jahn-Teller inactive, exhibits a very low thermal expansion in the α phase at low temperature and giant NTE during $\alpha \to \beta$ phase transition. Yet, the underlying mechanism remains unclear. With temperature-dependent x-ray diffractions (XRD) and Rietveld analysis, a new concept of cooperative pseudo Jahn-Teller effect (PJTE) was proposed to account for such unique thermal expansion properties. Detailed analysis shows the strong interactions between neighboring $\mathrm{Z}{\mathrm{n}}^{2+}$ ions, which result in the abrupt elongation of Zn1-O10 in Zn3-O4 bond lengths in neighboring $\mathrm{Zn}1{\mathrm{O}}_6$ and $\mathrm{Zn}3{\mathrm{O}}_6$ octahedra, and hence the splitting of the hexagonal rings along shared O4-O10 edges and a distinct volume increase upon lowering the temperature during a $\beta \to \alpha$ phase transition. Further density functional theory calculations confirm that the $d$-electron energy levels of Zn split and tend toward lower energy states under the phase transition, which facilitates deformation and leads to the NTE. Moreover, owing to the strong cooperative PJTE, $\mathrm{Z}{\mathrm{n}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ is confined in the adiabatic potential energy surface (APES) well, giving rise to the very low thermal expansion behavior in the low temperature α phase.

Spin qubits in quantum dots are a promising technology for quantum computing due to their fast response time and long coherence times. An electromagnetic pulse is applied to the system for a specific duration to perform a desired rotation. To avoid decoherence, the amplitude and gate time must be highly accurate. In this work, we aim to study the impact of leakage during the gate time evolution of a spin qubit encoded in a double quantum dot device. We prove that, in the weak interaction regime, leakage introduces a shift in the phase of the time evolution operator, causing over- or under-rotations. Indeed, controlling the leakage terms is useful for adjusting the time needed to perform a quantum computation and increasing the coherence time of the readout process. This is crucial for running fault-tolerant algorithms and is beneficial for quantum error mitigation techniques.

The physical properties of $\mathrm{BaCoT}{\mathrm{e}}_2{\mathrm{O}}_7$ single crystals were investigated using magnetization, magnetostriction, electron spin resonance, and electric polarization under static and pulsed high magnetic fields. Experimental results reveal that single-crystal sample is an antiferromagnet at low temperatures, with an effective pseudospin $S_{\mathrm{eff}}$ of 1/2 and a relatively large anisotropic effective $g$ factor, which originates from the lowest Kramers doublet of $\mathrm{C}{\mathrm{o}}^{2+}$ with dominant $|S_z|=3/2$ character under strong spin-orbit coupling. When a magnetic field is applied along the easy magnetization $c$ axis, two successive magnetic phase transitions ($H_{\mathrm{c}1}$ and $H_{\mathrm{c}2}$) were observed, between the two critical fields, the Co ions with a ↑↑↑↓ spin configuration correspond to a 1/2 magnetization plateau. At critical field $H_{\mathrm{c}1}$, spins rotate from parallel (antiparallel) to nearly perpendicular to the magnetic field, at $H_{\mathrm{c}2}$, a change occurs from a ferrimagnetic state to a high-field coplanar spin configuration. Magnetostriction measurements indicate significant anisotropic spin-lattice coupling in $\mathrm{BaCoT}{\mathrm{e}}_2{\mathrm{O}}_7$. First-principles calculations based on the four-state method reveal comparable antiferromagnetic nearest-neighbor and next-nearest-neighbor exchange interactions ($J_{\mathrm{NN}}=-10.76$ meV and $J_{\mathrm{NNN}}=-9.33$ meV), which imply strong competing interactions and exchange frustration in the zigzag Co network of $\mathrm{BaCoT}{\mathrm{e}}_2{\mathrm{O}}_7$. The exchange interactions between the $\mathrm{Co}\cdots \mathrm{Co}$ bonds in the noncollinear spin configuration (with a canted ↑↑↓↓ spin arrangement) induced by the magnetic field give rise to inequivalent exchange coupling, resulting in the emergence of net electric dipole moments. Through analysis of the multistep transitions induced by pulsed magnetic fields in the block-ordered antiferromagnetic state, combined with magnetostriction and polarization measurements, and supported by the large exchange energy scale relative to the Néel temperature, the multiferroic behavior of $\mathrm{BaCoT}{\mathrm{e}}_2{\mathrm{O}}_7$ can be understood in terms of an exchange striction mechanism associated with its noncollinear spin order.

The characterization of hot phonons in metal halide perovskites has remained qualitative. Here, we define a physical quantity called “phonon blockade” to describe the retardation capability of the collective all-interacting q-state LO phonon population on carriers. We construct an effective phonon-temperature model to quantify this phonon blockade, the key features of which are confirmed by pump-pump-probe spectroscopy. This effective phonon temperature offers a universal framework for directly comparing the immediate influence of hot phonons under different materials and excitation conditions. Both model and experiment reveal a pronounced peak in the phonon blockade at approximately 0.2 ps. By precisely setting the interpulse delay to 0.2 ps in the pump-pump-probe sequence, we observed an exceptionally prolonged hot-carrier relaxation. This experiment directly correlates LO phonon accumulation with delayed cooling, revealing the core operating principle of the hot-phonon bottleneck effect in metal halide perovskites. These findings substantially advance the understanding of hot-carrier dynamics and open avenues for developing advanced perovskite-based hot-carrier solar cells.

Moiré materials have emerged as a rich platform for exploring strong correlation effects in low dimensions, with twisted bilayer graphene (TBG) as a paradigmatic example. To distill the essential ingredients driving moiré-induced phases, a simplified one-dimensional analog—a two-leg ladder with spatially modulated interleg hopping and a uniform magnetic flux—was recently introduced. This model, which we refer to as the moiré ladder, features a nearly flat lowest-energy band in a suitable parameter regime, capturing the band-flattening mechanism of TBG. We investigate the ground-state phase diagram of the moiré ladder using a combination of bosonization and density matrix renormalization group techniques, and we systematically disentangle the respective roles of the flux and the hopping modulation. At half-filling, previous numerical work identified a metal-insulator transition at finite interaction strength and an unexpected ferromagnetic ground state. Revisiting this, we show that the metal-insulator transition can be understood perturbatively within bosonization, governed by the number of Fermi points. In contrast, the ferromagnetic correlations are nonperturbative and require both flux and spatial modulation—neither alone is sufficient. We extend our analysis to other fillings: one-quarter, three-quarters, slightly above half-filling (half-filling plus two electrons), and slightly below half-filling (half-filling minus two electrons). At moderate interactions, we observe ferromagnetism below half-filling and antiferromagnetism above; at stronger interactions, ferromagnetism dominates across all studied fillings. Reducing the interaction strength relative to the bandwidth induces a transition back to antiferromagnetic behavior. These results reveal a robust and unconventional mechanism for one-dimensional ferromagnetism rooted in moiré band-structure effects and establish the moiré ladder as a minimal model for probing correlation-driven phases in moiré systems. Crucially, the analysis demonstrates that periodic interleg hopping alone does not engender new correlated phases; the magnetic flux is essential for the observed unconventional behavior.

In flat-band superconductors, the electron pairing is strongly enhanced so that the critical temperature scales linearly with the interaction strength. Identifying the governing pairing mechanism in flat-band superconducting systems is therefore a central task, which may be constrained by experimental probes via low-temperature scaling measurements. A key observable underlying the Meissner effect and the resulting divergent dc conductivity is the superfluid weight. While it is well established that the minimal quantum metric provides the dominant contribution to the superfluid weight in conventional superconductors with isolated flat bands, recent studies indicate that the unconventional pairing can generate additional nonlocal quantum geometric terms. This motivates us to derive the low-temperature scaling law of the superfluid weight in two-dimensional flat-band superconductors with sufficiently isolated bands. In particular, we consider the gap function with point or line nodes classified by the Weierstrass preparation theorem. Beyond the superfluid weight, we additionally deliver explicit low-temperature scaling laws of the order parameter, the tunneling conductance, the specific heat, the Sommerfeld coefficient, and the spin-lattice relaxation rate to provide complementary experimental discriminants of the underlying pairing symmetry. The implications of our results are also elucidated by applying them to a selection of superconducting states in $C_{6v}$-symmetric systems.

We demonstrate that the non-Hermitian quantum geometric tensor (QGT) governs nonlinear electrical responses in systems with a spectral line gap. The quantum metric, which is the symmetric component of the QGT and takes complex values in non-Hermitian systems, generates an intrinsic nonlinear conductivity independent of the scattering time. In contrast, the full complex-valued QGT induces a distinct conductivity that depends explicitly on the wave-packet width. Using one- and two-dimensional non-Hermitian models, we establish a direct link between nonlinear dynamics and the QGT, thereby connecting quantum state geometry to observable transport phenomena. Crucially, we reveal that the finite wave-packet width fundamentally alters non-Hermitian transport, a mechanism strictly absent in Hermitian systems. This framework elucidates non-Hermitian response theory by revealing how the complex geometry of quantum states, captured by the QGT, and the wave-packet width jointly encode transport in open and synthetic quantum matter.

In the present work, we revisit the problem of the inhomogeneous electron gas under the influence of a weak external potential, which allows us to calculate the gradient corrections to the density functional within linear response, an approach known as the gradient-expansion approximation. To obtain the exchange ($b_x$) and correlation ($b_c$) contributions to the coefficient $b_{\text{xc}}$, i.e., to the prefactor of the $q^2$ term of the proper-polarization function, we revisited all the previous calculations and expose misconceptions which led to incorrect conclusions. We used various ways to apply a necessary regularization to the singular Coulomb interaction potential. We found that the separate exchange ($b_x$) and correlation ($b_c$) contributions to the coefficient $b_{\text{xc}}$ have regularization-scheme-dependent values even though the regulator is set to zero at the end of the calculation. This implies that it is impossible to define such a separation meaningfully. On the contrary, we found that when the regulator is set to zero at the end of the calculation, the combination $b_{\text{xc}}$ is regularization-scheme independent and, thus, has a unique value. We conclude that it is incorrect to separate those two terms when constructing a generalized-gradient-approximation (GGA) contribution to the density functional. This appears to be a common approach in most popular GGA functionals, where various constraints are applied to each contribution separately.

The search for chiral Majorana fermions in quantum anomalous Hall insulator/$s$-wave superconductor heterostructures has attracted intense interest, yet remains controversial due to the lack of conclusive evidence. A key issue is that the heterostructure's metallization can produce half-integer conductance signatures resembling those of chiral Majorana fermions, thereby complicating their identification. Here, we investigate how the competition between metallization and chiral Majorana fermions depends on superconductor thickness, revealing its critical role through three distinct regimes: (i) For thin superconductors ($\sim 10\mathrm{nm}$), metallization shows periodic oscillations with thickness, matching the Fermi wavelength. (ii) Intermediate thicknesses ($\sim 100\mathrm{nm}$) exhibit periodic windows for observing chiral Majorana fermions. (iii) Thick superconductors ($\sim 1000\mathrm{nm}$) sustain stable chiral Majorana fermions that are insensitive to thickness variations. These results suggest that superconductor thickness is a key control parameter for advancing efforts to conclusively identify chiral Majorana fermions.

We study broadband terahertz (THz) conductivity and ultrafast photoconductivity spectra in lithographically fabricated multilayer epitaxial graphene nanoribbons grown on C-face of 6H-SiC substrate. THz near-field spectroscopy reveals local conductivity variations across nanoscale structural inhomogeneities such as wrinkles and grain boundaries within the multilayer graphene. Ultrabroadband THz far-field spectroscopy ($0.15\text{–}16\mathrm{THz}$) distinguishes doped graphene layers near the substrate from quasineutral layers (QNLs) further from the substrate. Temperature-dependent THz conductivity spectra are dominated by intraband transitions both in the doped and QNLs. Photoexcitation then alters mainly the response of the QNLs: these exhibit very high carrier mobility and large positive THz photoconductivity with picosecond lifetime. The response of QNLs strongly depends on the carrier temperature $T_{\mathrm{c}}$: the scattering time drops by an order of magnitude down to ∼10 fs upon an increase of $T_{\mathrm{c}}$ from 50 K to $T_{\mathrm{c}}>1000\mathrm{K}$, which is attributed to an enhanced electron-electron and electron-phonon scattering and to an interaction of electrons with mid-gap states.

The development of ${\text{Si}}_{1\text{−}x}{\text{Ge}}_x$ alloys has prompted interest in exploring the nature of point defects, particularly vacancies. This study employs Heyd-Scuseria-Ernzerhof hybrid functional to investigate the electronic properties of the vacancy in ${\text{Si}}_{1\text{−}x}{\text{Ge}}_x$ alloys, focusing specifically on Si, ${\text{Si}}_{504}{\text{Ge}}_8$, and ${\text{Si}}_{488}{\text{Ge}}_{24}$ compositions. It is found that for a fixed vacancy configuration, variations in alloy composition lead to nearly similar formation energies. The calculated $(1-/2-)$ levels for vacancies of the 0-0-0, 0-0-1, and 0-1-0 configuration in the two alloys are generally consistent with the experimental value of $E_C-0.29\mathrm{eV}$. For the $(0/1-)$ level, the results for the vacancy in Si and the vacancy of the 0-0-0 configuration in ${\text{Si}}_{504}{\text{Ge}}_8$ are very close. The acceptor levels of the vacancy in Si are found to be $E_C-0.29\mathrm{eV}$ for $(0/1-)$ level and $E_C-0.33\mathrm{eV}$ for $(1-/2-)$ level. These results are consistent with the corresponding acceptor levels obtained for the vacancy of the 0-0-0 configuration in ${\text{Si}}_{504}{\text{Ge}}_8$. These findings underscore the importance of alloying and local configuration in determining vacancy electronic properties and suggest that ${\text{Si}}_{1\text{−}x}{\text{Ge}}_x$ alloys offer a valuable platform for more accurate probing of vacancy acceptor levels in silicon.

We report the existence of a large set of ferromagnetic scarred states in the one-dimensional transverse-field Ising model with long-range interactions, in a regime with no ferromagnetic phase at finite temperature. These scarred states are distributed over different spectral regions, surrounded by a paramagnetic sea. We show that simple initial conditions, consisting of a few small magnetic domains, selectively populate these scarred states. This leads to the appearance of a special dynamical phase, which we call the scarred ferromagnetic phase. As a consequence, initial states with a small number of small magnetic domains evolve towards ferromagnetic equilibrium states, whereas initial states with larger domains or no magnetic structure relax to the expected thermal paramagnetic equilibrium state.

The one-dimensional (1D) $J_1-J_2$ quantum spin model can be viewed as a strong-coupling analog of the Schrieffer-Su-Heeger model with two inequivalent alternating Ising couplings along the wire, associated to the physics of resonating valence bonds. Similar to the quantum Ising model, which differently presents a long-range Néel ordered phase, this model also maps onto a $p$-wave superconducting wire which shows a topological phase transition with the emergence of low-energy Majorana fermions. We show how signatures of the topological phase transition for the $p$-wave superconducting wire, i.e., a half Skyrmion, are revealed through local (short-range) spin observables and their derivatives related to the capacitance of the pairing fermion model. Then, we present an “edge” correspondence through the edge spin susceptibility in the $J_1-J_2$ model revealing that the topological phase transition is a metal of Majorana fermions. We justify that the spin magnetization at an edge at very small transverse magnetic field is a good marker of the topological invariant and of Majorana zero modes. We identify a correspondence between the quantum information of resonating valence bonds and the charge fluctuations in a $p$-wave superconductor through our method “the bipartite fluctuations”. Physical properties of this 1D model are in fact robust when including additional interactions, which is optimistic for practical applications, e.g., in quantum circuits.

Phase change materials (PCMs) enable the controlled modulation of physical properties through phase transitions induced by external stimuli, including temperature, pressure, irradiation, or electric and magnetic fields. Of particular interest is trititanium pentoxide (${\mathrm{Ti}}_3{\mathrm{O}}_5$), a promising PCM for heat storage, which exhibits a low pressure threshold for the $\lambda$ to $\beta$ phase transition. Although the phase transitions of bulk ${\mathrm{Ti}}_3{\mathrm{O}}_5$ have been extensively studied and well understood, research on its surface properties and associated phase transformations remains limited due to the computational challenge of modeling pressure effects on the surface at the atomic scale. Here we introduce a computational framework that combines a machine-learned interatomic potential trained on high-fidelity density functional theory data with explicit pressure simulation via repulsive slab potentials. We identify a hitherto unknown stable surface reconstruction and a kinetically favorable layer-by-layer transition mechanism. On-the-fly probability enhanced sampling simulations reveal that pressure significantly reduces the free energy barrier, predicting a phase transition at only 700 bar, in good agreement with the experimental value. This work presents a feasible and generally applicable protocol for modeling pressure effects in PCMs, paving the way for improved understanding and application of materials under operational conditions.

Ferroelectric (FE) instability in the puckered lattice of arsenic (α-As) is investigated using density functional theory (DFT) calculations. A bilayer (BL) structure with the most stable AA-stacked configuration is found to exhibit spontaneous ferroelectric polarization arising from an intralayer distortion analogous to that observed in α-Bi monolayers. Unlike conventional two-dimensional (2D) ferroelectricity, which is typically driven by sliding-induced charge transfer, the observed polarization in α-As primarily originates from a lattice contraction along the armchair direction caused by inverted band occupation facilitated through interlayer electron hopping. The calculated polarization reaches $0.63\times {10}^{-10}\mathrm{C}/\mathrm{m}$ with the associated transition barrier 5.4 meV/u.c., and our molecular dynamics simulations using machine-learned interatomic potential show the FE ordering persisting up to ∼100 or 300 K under a uniaxial compression of 0% or −4%, respectively. These results provide new insight into distinct mechanism of 2D ferroelectricity governed by interlayer electronic coupling.