Two-dimensional transition metal dichalcogenides (TMDCs), such as ${\mathrm{MoS}}_2$ and ${\mathrm{WTe}}_2$, received extensive attention owing to their diverse crystal structures and intriguing physical properties. In contrast, there has been relatively limited research on transition-metal dioxides (TMDOs) despite sharing the same crystal structures with TMDCs. Here, we investigate the structural and electronic properties of monolayer $T$-phase ${\mathrm{MoO}}_2$ and ${\mathrm{WO}}_2$ using first-principles calculations. Our analysis reveals that their phonon dispersions have prominent imaginary modes, leading to the emergence of two charge density wave phases: $1{\mathit{\text{T}}}^{\prime }$ and $\sqrt{3}\times \sqrt{3}$. Interestingly, we find that $1{\mathit{\text{T}}}^{\prime }\text{−}{\mathrm{MoO}}_2$ and ${\mathrm{WO}}_2$ exhibit Dirac semimetal behavior, while their $\sqrt{3}\times \sqrt{3}$ phases are ferroelectric semiconductors, with out-of-plane spontaneous polarization of 3.99 and 3.94 pC/m, respectively. This work sheds light on structural and electronic properties of $T$-phase ${\mathrm{MoO}}_2$ and ${\mathrm{WO}}_2$, offering valuable insights for further experimental investigations into similar TMDOs materials.

We theoretically discover the possible emergence of reentrant Walker breakdowns for current-driven domain walls in layered antiferromagnets, in striking contrast to the unique Walker breakdown in ferromagnets. We reveal that the Lorentz contraction of domain wall width in antiferromagnets gives rise to nonlinear current dependence of the wall velocity and the predicted multiple Walker breakdowns. The dominant efficiency of the current-induced staggered spin-orbit torque over the spin-transfer torque to drive the domain wall motion is also demonstrated. These findings are expected to be observed in synthetic antiferromagnets experimentally and provide an important contribution to the growing research field of antiferromagnetic spintronics.

Chromium-based perovskites have drawn plenty of attention due to their intriguing magnetic properties and potential technique applications. While a complete understanding of the microscopic magnetic mechanisms underlying their macroscopic properties presents great challenges, especially when involving $t_{2g}\text{−}{e}_g$ ($t\text{−}e$) hybridization and rare earth (RE) $f$ orbitals. Here, with the recently discovered molecular analogue of perovskite $\left[{\mathrm{Ce}}_2^{\mathrm{III}}{\mathrm{Ce}}^{\mathrm{IV}}{\mathrm{Cr}}_8^{\mathrm{III}}{\mathrm{O}}_8{\left({\mathrm{O}}_2\mathrm{CPh}\right)}_{18}\left({\mathrm{HO}}_2\mathrm{CPh}\right)\right]$, abbreviated as ${\mathrm{Ce}}_3{\mathrm{Cr}}_8$, we combine first-principles calculations and a superexchange model to successfully identify an anomalous ferromagnetism (FM)-dominated superexchange interaction between Cr ions originated from the $t\text{−}e$ hybridization, which does not follow Goodenough-Kanamori rules. The great sensitivity of the $t\text{−}e$ hybridization with respect to the angle of Cr-O-Cr can lead to a significant change in the magnetic interaction of ${\mathrm{Ce}}_3{\mathrm{Cr}}_8$ with the angle of Cr-O-Cr varying within only a few degrees, e.g., a ground-state transition from FM to antiferromagnetism. Additionally, the Ce $f$ orbitals near the Fermi level can largely reduce this sensitivity by interacting with the Cr $d$ orbitals via the virtual charge transfer process. Our results are strongly supported by an extended superexchange model developed with the inclusion of $f$ orbitals within the $t\text{−}e$ hybridization framework. These findings complete the theory of superexchange magnetism in chromium-based perovskites including RE $f$ orbitals and in the meanwhile introduce a new avenue for fine-tuning the magnetic characteristics via modifying the transition metal $d$/RE $f$ interactions at the nanoscale.

The anisotropic antisymmetric Dzyaloshinskii-Moriya (DM) interactions between local magnetic moments ${\mathit{\mu }}_i$ and ${\mathit{\mu }}_j$, which can be induced by an external electric field (EF) are investigated in the framework of density functional theory by considering all $3d, 4d$, and $5d$ freestanding transition metal dimers. The possibilities of triggering and reversibly tuning chiral magnetic couplings by electric means are demonstrated. The dependence of the DM-coupling vector ${\mathit{D}}_{ij}$ on the EF strength $E$ is shown to be approximately linear for $\left|E\right|\le 0.6$ V/Å, with only minor third-order corrections. The first- and third-order zero-field electric susceptibility of the DM couplings are determined and analyzed as a function of $d$-band filling. The correlations between them and the chirality of the spin-orbit energy are displayed. From a microscopic perspective, the EF-induced DM couplings are shown to stem from the permanent electric dipole moments ${\mathit{p}}^0$ that are already present in the field-free dimers whenever their local magnetic moments are not collinear. The symmetry rules governing ${\mathit{p}}^0$ and its chirality are discussed. Finally, the dependence of the EF-induced DM couplings on the degree of noncollinearity of the magnetic order is quantified by varying systematically the angle $\theta$ between the local moments. While the electronic calculations show that the changes in the effective ${\mathit{D}}_{ij}$ can be quite important for arbitrary $\theta$, one also observes that ${\mathit{D}}_{ij}$ depends weakly on $\theta$ and is thus transferable within a limited range of noncollinear magnetic arrangements, provided that they are not too far from the lowest-energy configuration.

Noncentrosymmetric superconductors offer fascinating phenomena of quantum transport and optics such as nonreciprocal and nonlinear responses. Time-reversal symmetry breaking often plays an essential role in the emergence and enhancement of nonreciprocal transport. In this paper, we show the nonreciprocal optical responses in noncentrosymmetric superconductors arising from time-reversal symmetry breaking by demonstrating them in $s$-wave superconductors with a Rashba spin-orbit coupling and a magnetic field. Numerical results reveal the superconductivity-induced bulk photocurrent and second harmonic generation, which are forbidden at the zero magnetic field. We discuss the properties and mechanisms of the superconducting nonlinear responses emerging under the magnetic field. In particular, we investigate the magnetic field dependence of the photocurrent conductivity and clarify the essential ingredients, which give a contribution unique to superconductors under the magnetic field. This contribution is dominant in the low-carrier-density regime although the corresponding joint density of state is tiny. We attribute the enhancement to the quantum geometry. Moreover, the nonlinear conductivity shows peculiar sign reversal at the transition to the topological superconducting state. We propose a bulk probe of topological transition and quantum geometry in superconductors.

We investigate the planar Hall effect (PHE) in two-dimensional (2D) superconductors with spin-orbit interactions, where transport anisotropy is induced by an in-plane magnetic field. While PHE typically arises from the breaking of basal mirror symmetry, when the field exclusively couples to spin degrees of freedom, it remains negligible in noninteracting systems. In this study, we explore anisotropic paraconductivity as an alternative mechanism for PHE observed in 2D superconductors in the normal state. Due to the momentum dependence of spin-orbit interactions, the field-induced pair breaking exhibits anisotropy. To elucidate this phenomenon, we compute the PHE for the Rashba spin-orbit interaction. Our analysis reveals that Cooper pairs propagating along the field experience stronger pair breaking compared to those moving perpendicular to the field. This physical insight is corroborated by explicit calculations of paraconductivity.

Nonequilibrium molecular dynamics simulations were carried out to explore the coupling behaviors of spallation and microjetting in single-crystal (SC) and nanocrystalline (NC) Al at the atomic scale. Both SC and NC models exhibited void collapse, serving as an indispensable element complementary to the classical ductile fracture mechanisms dominated by nucleation, growth, and coalescence. Two representative mechanisms—compressive collapse and spontaneous collapse—were uncovered, with a unique behavior in which a coalesced void also collapsed. It was also discovered that the spallation might either cause the microjet to disappear or accelerate fragmentation, with the disappearance effectuating a peculiar transformation from coexisting spallation and microjetting to pure spallation. The difference between SC and NC microjetting models residing in that grain boundary not only caused a larger peak velocity of the spike tip due to the inhomogeneous deformation but also restrained the Richtmyer-Meshkov instability growth to some extent owing to energy dissipation. The jet sheet fragmentation was attributed to three mechanisms: void nucleation, growth, and coalescence for the jet body; longitudinal necking induced by the tensile stress for the residual one-dimensional jet body; and transverse necking induced by the shear and tensile stresses for the jet head.

Strontium titanate ($\mathrm{SrTi}{\mathrm{O}}_3$) is the most known material from the family of quantum paraelectrics. Thanks to its extremely “soft” lattice, its functionality can be easily tuned by applying both external stimuli (pressure, strain, electric field) and through doping or isotope exchange. In this paper, we present the results of a detailed study of two $\mathrm{M}{\mathrm{n}}^{2+}$ centers in Mn-doped $\mathrm{SrTi}{\mathrm{O}}_3$ single crystals using both continuous wave and pulsed electron paramagnetic resonance (EPR) spectroscopy at frequencies from 9.5 to 427 GHz and temperatures from 5 to 296 K. The first center is created by a $\mathrm{M}{\mathrm{n}}^{2+}$ ion at the $\mathrm{S}{\mathrm{r}}^{2+}$ lattice site in an off-center position. Its spectroscopic characteristics were determined for both fast and slow motion regimes of the impurity ion. In particular, all spin transitions allowed by the $\mathrm{M}{\mathrm{n}}^{2+}$ spin were well resolved in the slow motion regime. The second center is created by a $\mathrm{M}{\mathrm{n}}^{2+}$ ion at the $\mathrm{T}{\mathrm{i}}^{4+}$ position in the center of the oxygen octahedron. It has been established that the surrounding of this ion undergoes strong distortion when cooled below the phase transition temperature $T_c=105$ K, stimulated by the rotation of the oxygen octahedron. The present data also perfectly explain the previously obtained EPR data from measurements of $\mathrm{SrTi}{\mathrm{O}}_3$:Mn ceramics at low microwave frequencies (9–10 GHz).

We propose to implement a Kitaev chain based on an array of alternating normal and superconductor hybrid quantum dots embedded in semiconductors. In particular, the orbitals in the dot and the Andreev bound states in the hybrid are now on an equal footing, and both emerge as low-energy degrees of freedom in the Kitaev chain, with the couplings being induced by direct tunneling. Due to the electron and hole components in the Andreev bound state, this coupling is simultaneously of the normal and Andreev types, with their ratio being tunable by varying one or several of the experimentally accessible physical parameters, e.g., strength and direction of the Zeeman field, as well as changing the proximity effect on the normal quantum dots. As such, it becomes feasible to realize a two-site Kitaev chain in a simple setup with only one normal quantum dot and one hybrid segment. Interestingly, when scaling up the system to a three-site Kitaev chain, next-nearest-neighbor couplings emerge as a result of high-order tunneling, lifting the Majorana zero energy at the sweet spot. This energy splitting is mitigated in a longer chain, approaching topological protection. Our proposal has two immediate advantages: obtaining a larger energy gap from direct tunneling, and creating a Kitaev chain using a reduced number of quantum dots and hybrid segments.

There are two seemingly unrelated puzzles about the cuprate superconductors. The first puzzle concerns the strong non-BCS behavior around $x_c$, the end point of the superconducting dome on the overdoped side, where the cuprate is believed to be well described by the Fermi-liquid theory. This is the most evident in the observed ${\rho }_s\left(0\right)-T_c$ scaling and the large amount of uncondensed optical spectral weight at low energy. The second puzzle concerns the remarkable robustness of the $d$-wave pairing against the inevitable disorder effect in such a doped system, which is also totally unexpected from the conventional BCS picture. Here we show that these two puzzles are deeply connected to the origin of a third puzzle about the cuprate superconductors, namely, the mysterious quantum critical behavior observed around $x^{*}$, the so called pseudogap end point. Through a systematic variational Monte Carlo (VMC) study of the disordered 2D $t-J$ model from the resonating valence bond (RVB) perspective, we find that the $d$-wave pairing in this model is remarkably more robust against the disorder effect than that in a conventional $d$-wave BCS superconductor. We find that such remarkable robustness can be attributed to the spin-charge separation mechanism in the RVB picture, through which the $d$-wave RVB pairing of the charge-neutral spinons becomes essentially immune to the disorder potential except for the secondary effect related to the modulation of the local doping level by the disorder. We propose that there exists a Mott transition at $x^{*}$, where the RVB pairing in the underdoped regime is transmuted into the increasingly more BCS-like pairing for $x>x^{*}$, whose increasing fragility against the disorder effect leads to the non-BCS behavior and the ultimate suppression of superconductivity around $x_c$.

Halide perovskite (HP) materials have recently emerged as a class of semiconductors with immense promise for various optoelectronic applications, ranging from solar cells to light-emitting diodes. One of the unique attributes of HPs is their tunable band gaps with different factors governing their value. The first factor is related to relativistic corrections [“mass-Darwin,” connected to the $n{s}^2$ lone pairs, and spin-orbit coupling (SOC)] that induce an orbital shift or degeneracy splitting, resulting in a band-gap reduction. The second factor involves the structural configuration: in HPs the local symmetry of each Wyckoff position tends to be broken, inducing an opening of the band gap. Based on high-throughput density functional theory calculations, this paper systematically studies a possible self-cancelation on the band-gap correction for HPs when the polymorphous configuration—structural effects—and the SOC—electronic effects—are included. Our results indicate that the nature of interplay between SOC and symmetry breaking (SB) is that they are independent decoupling effects to describe the band-gap magnitude in halide perovskites. As a result of that, we observe a transitivity of the band-gap description; i.e., if we know the band gap of halide perovskites without SB and SOC, we can independently add the effects of band-gap reduction due to SOC and band-gap opening due to SB, regardless of the order in which these effects are considered.

We theoretically consider a junction composed of a ferromagnetic insulator (FI) and a two-dimensional electron gas (2DEG) with Rashba- and Dresselhaus-type spin-orbit interactions. Using the Boltzmann equation, we calculate an electric current in 2DEG induced by the inverse Rashba-Edelstein effect when imposing the temperature difference between the FI and 2DEG. We clarify how the induced current depends on the magnetization direction of the FI, spin texture on the Fermi surface of 2DEG, and temperature. Our result provides an important foundation for an accurate analysis of the inverse Rashba-Edelstein effect induced by thermal spin injection.

We present a study of complex energy braiding in a one-dimensional non-Hermitian system with $n\mathrm{th}$-order long-range asymmetrical coupling. Our work highlights the emergence of novel topological phenomena in such systems beyond the conventional nearest-neighbor interaction. The modified SSH model displays $n$ distinct knot and link combinations in the complex energy-momentum space under periodic boundary conditions, which can be controlled by varying the coupling strengths. A topological invariant, namely the braiding index, is introduced to characterize the different complex energy braiding profiles, which depends on the zeros and poles of the characteristic polynomials. Furthermore, we demonstrate that the non-Hermitian skin effect can be localized at one or both ends, signifying conventional or bipolar localization, depending on the sign of the braiding index. Phase transitions between different braiding phases with the same (opposite) sign of the topological invariant occur at Type-1 (Type-2) exceptional points, with Type-1 (Type-2) phase transitions accompanied by single (multiple) exceptional points. We propose an experimental setup to realize the various braiding schemes based on the RLC circuit framework, which provides an accessible avenue for implementation without recourse to high-dimensional momentum space required in most other platforms.

We investigate the structural and thermodynamic properties of high-pressure ice by incorporating quantum anharmonicity at a nonperturbative level. Quantum fluctuations reduce the critical pressure of the phase transition between phase VIII (with asymmetric H bonds) and phase X (with symmetric H bonds) by 65 GPa from its classical value of 116 GPa at 0 K. Moreover, quantum effects make it temperature independent over a wide temperature range (0–300 K), in agreement with experimental estimates obtained through vibrational spectroscopy and in striking contrast to the strong temperature dependence found in the classical approximation. The equation of state shows fingerprints of the transition in accordance with experimental evidence. Additionally, we demonstrate that, within our approach, proton disorder in phase VII has a negligible impact on the occurrence of phase X. Finally, we reproduce with high accuracy the 10-GPa isotope shift caused by the hydrogen-to-deuterium substitution.

We show that high-harmonic spectroscopy offers an advanced avenue for probing electronic properties of quasicrystals beyond the linear response regime. Focusing on Aubry-André-Harper (AAH) chains, we extract the multifractal spectrum from the harmonic emission intensity—an essential indicator of the spatial distribution of electronic states in quasicrystals. Additionally, we address the detection of mobility edges, vital energy thresholds that demarcate localized and extended eigenstates within generalized AAH models. The precise identification of these mobility edges sheds light on the metal-insulator transition and the behavior of electronic states near these boundaries. Merging high-harmonic spectroscopy with the AAH model provides a powerful framework for understanding the interplay between localization and extended states in quasicrystals for an extremely wide energy range not captured within linear response studies, thereby offering valuable insights for guiding future experimental investigations.

We study many-body phase transitions in a one-dimensional ferromagnetic transversed field Ising model with an imaginary field, and show that the system exhibits three phase transitions: one second-order phase transition and two $\mathcal{PT}$ phase transitions. The second-order phase transition occurring in the ground state is investigated via biorthogonal and self-normal entanglement entropy, for which we develop an approach to perform finite-size scaling theory to extract the central charge for small systems. Compared with the second-order phase transition, the first $\mathcal{PT}$ transition is characterized by the appearance of an exceptional point in the full energy spectrum, while the second $\mathcal{PT}$ transition only occurs in specific excited states. Furthermore, we interestingly show that both exceptional points are second-order in terms of scalings of imaginary parts of the energy. This work provides an exact solution for many-body phase transitions in non-Hermitian systems.

Recently, the discovery of collinear symmetric-compensated antiferromagnets (AFMs) with intrinsic spin splitting has attracted enormous interest of many researchers. In this paper, we predict the spin-layer coupling in altermagnetic bilayers with tunable spin and valley splitting properties via first-principles calculations. Based on the analysis of magnetic symmetry, we find manipulating magnetic order and stacking configuration as a strategy. Compared with conventional AFM bilayers, the joint symmetry in altermagnetic bilayer can be significantly modulated by different magnetic orders and stackings of the two sublayers. Furthermore, we demonstrate that the layer-dependent spin degeneracy/splitting widely exists in altermagnets with different crystal structures. The spin splitting in an altermagnetic bilayer with various interlayer couplings is highly tunable by external electric field. In contrast with spin splitting introduced by conventional spin-orbit coupling, the concepts of emerging layertronics and altermagnets are combined to manipulate spin properties by spin-layer coupling, ensuring both long spin relaxation time and complete spin splitting for practical applications of spintronic devices.

We investigate the Josephson diode effect (JDE) in topological Josephson junctions. By both analytic and numerical calculations, we find that while a Josephson junction in the topological phase may exhibit higher diode efficiency compared to that in the trivial phase, this behavior is not universal. The presence of Majorana bound states is not a sufficient condition for a large diode effect. Furthermore, the diode efficiency undergoes substantial changes only in specific regions along the topological phase transition boundary, and a significant diode effect does coincide with the topological phases. Thereby our paper suggests the utilization of topological superconductivity for enhanced JDE, and also the Josephson diode effect may serve as an indicator for topological superconductor phase. These results suggest a nuanced relationship between the topological aspects of Josephson junctions and Josephson diode effect.