We theoretically investigate collective excitations in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states of Pauli-limited superconducting films. When the long-range Coulomb interaction is absent, excitation spectra consist of two gapless and three gapped modes. The gapless modes are the Nambu-Goldstone modes associated with the spontaneous breaking of the $\mathrm{U}\left(1\right)$ symmetry and the translational symmetry. The gapped modes include the Higgs mode and the twofold degenerate modes that cause the oscillation of the domain width and grayness of FFLO nodal planes. We find that the long-range Coulomb interaction only gaps out the gapless phase mode through the Anderson-Higgs mechanism, while the other modes remain unaffected. Furthermore, the field evolution of the dispersion of the gapless elastic mode, the Nambu-Goldstone mode associated with the translational symmetry breaking, is associated with that of the bandwidth of the mid-gap Andreev bound states. We demonstrate that the signature of the elastic mode can be detected by measuring the density-density response function.

The abundant chemical compositions in ternary hydrides bring much more possibility to explore high-temperature superconductors under lower pressure. Here we constructed 115 ternary hydrides on the basis of the element substitution using 16 metal elements within five reported prototype structures. We conducted a three-step approach to screen and study these candidate structures in the aspects of dynamical stability, formation energy, and relative enthalpy, respectively. Based on this approach, we found three metastable compounds with hydrogen clathrate cages in the space group of $P\overline{3}m1$, including ${\mathrm{Y}}_2{\mathrm{CdH}}_{18}$, ${\mathrm{Y}}_2{\mathrm{InH}}_{18}$, and ${\mathrm{Ca}}_2{\mathrm{SnH}}_{18}$. All of the structures are superconductive under high pressure with $T_{\mathrm{c}}$ above 110 K, which is larger than the superconductive temperature of liquid nitrogen. By comparing the bonding factors with other 12 reported ternary hydride systems, we proposed that the bond strength alone is limited to evaluate the stable pressure and the H-H bond strength could provide prospects on the $T_{\mathrm{c}}$ values. Our study enriches the database of novel ternary hydrides under high pressure, and provides insight to consider relatively active elements than I B, II B, and III A elements or $f$ electron elements for ternary hydrides designing, shedding light on future theoretical and experimental research.

The interplay between superconductivity and topological properties has garnered significant research interest due to its potential implications for novel quantum materials. Here, we systematically investigate the structural, topological, and electronic transport properties of π-SnS nanocrystals under high pressure. A pressure-induced superconducting transition is observed at 30.4 GPa, characterized by a dome-shaped behavior with a maximum superconducting transition temperature $\left(T_{\mathrm{c}}\right)$ of 3.7 K, which persists up to 91 GPa. Synchrotron x-ray diffraction reveals two structural phase transitions: from $P{2}_{1}3\text{−}\mathrm{I}$ to $P{2}_{1}3\text{−}\mathrm{II}$ at 9.3 GPa, and subsequently to $Pm\overline{3}m$ at 44.8 GPa. Furthermore, theoretical calculations indicate that both novel high-pressure phases of SnS exhibit topological properties coexisting with superconductivity. The theoretical results reveal an evolution from trivial semiconductors to weak topological and ultimately to strong topological materials. Our findings suggest that π-SnS provides an excellent platform for exploring the interplay between superconductivity and the topological characteristics of electronic systems.

This study employs first-principles density-functional theory (DFT) calculations to explore the elastic and mechanical properties of ferroelectric hafnia $\left({\mathrm{HfO}}_2\right)$ in its polar orthorhombic $Pca{2}_1$ phase under varying hydrostatic pressure conditions up to 30 GPa. Utilizing a plane-wave basis set and Perdew-Burke-Ernzerhof generalized-gradient approximation for solids in our DFT calculations, we investigate both pure and yttrium-substituted ${\mathrm{HfO}}_2$. Our findings reveal an anomalous reduction in the $C_{33}$ component of the elastic tensor with increasing pressure, which becomes significant above 15 GPa and signals a potential pressure-driven structural phase transition at higher pressure. The analysis of atomic displacements under pressure sheds light on the unusual mechanical behavior and phase stability of this material. Additionally, we observe a transition from an indirect band gap to a direct band gap with increasing pressure, which could have significant implications for optical applications. The effects of yttrium substitution on the mechanical and electronic properties are further examined, revealing that yttrium substitution softens the elastic response of this material and reduces the electronic band gap. These results enhance our understanding of elastic and mechanical responses of ferroelectric hafnia and its potential for applications in microelectronics, piezoelectric devices, and nonvolatile ferroelectric random-access memories. Further experimental validation is recommended to confirm our predictions and explore the practical implications of the observed phase transitions and electronic behavior of the ferroelectric hafnia under high-pressure conditions.

Raman spectroscopy is a widely used experimental technique to study the vibrational properties of solids. Atomic scale simulations can be used to predict such spectra, but reliable studies at finite temperatures are challenging, mainly due to the requirement of accurate and computationally efficient models for the dielectric susceptibility. Here, we have used molecular dynamics simulations together with a density functional theory-based model for the dielectric susceptibility to determine the Raman spectrum of barium zirconate, ${\mathrm{BaZrO}}_3$ (BZO), a well-studied oxide perovskite. At ambient conditions, where the system is cubic, we find excellent agreement with experimentally measured Raman spectra. Our study establishes that the relatively sharp spectra seen experimentally are due to second-order scattering. At higher pressures, where BZO is tetragonal, all first-order Raman active modes are identified. Additionally, slightly below the phase transition, in the cubic phase, a broad central Raman peak appears. The origin of this type of peak is controversial and extensively debated in connection with the dynamics of the halide perovskites. Here, we show that it is also present in a hard oxide perovskite, and it originates from the highly overdamped R-tilt mode in the cubic structure.

The current primary challenge in valley electronics research is to achieve large-scale spontaneous valley polarization. In this paper, using first-principles calculations, we predict a promising class of two-dimensional ferromagnetic semiconductors, namely Janus $\mathrm{Tb}X\mathrm{H}$ $(X=\text{Br},\mathrm{Cl},\mathrm{I})$ monolayers. Our first-principles calculations reveal that these materials can achieve a valley polarization of up to 112 meV due to ferromagnetic exchange and spin-orbit coupling effects. Additionally, we explored how biaxial strain affects their magnetic anisotropy energy and valley polarization. These results highlight the crucial role of strain in modulating spin and valley properties while also opening different avenues for utilizing ferromagnetic semiconductor materials in spintronics and valleytronics applications.

The non-Hermitian systems exhibit extreme sensitivity to the boundary conditions. The change in the eigenspectrum with tuning boundary parameter is intimately connected to the non-Hermitian skin effect. The single-particle systems are affected by the boundary perturbations; however, the interplay of a random disorder potential and nonreciprocal hopping under boundary perturbations of an interacting many-body system is not yet clear. In this work, we examine the boundary sensitivity of a non-Hermitian interacting fermionic system in the presence of a random disorder potential. A nonzero boundary parameter results in real-complex spectral transitions with nonreciprocal (or unidirectional) hopping at weak disorder, while the many-body localization at strong disorder washes away real-complex transitions leading to dynamical stability and real eigenvalue spectrum. We show that the boundary-driven real-complex spectral transitions of the non-Hermitian chain are accompanied by the corresponding changes in the level statistics and nearest level-spacing distributions. The intriguing features of nonreciprocity and boundary sensitivity are further revealed using the averaged inverse participation ratios. Finally, we find distinct behavior in the quench dynamics of local particle density, population imbalance, and entanglement entropy of charge-density-wave ordered state that corroborate the real-complex and localization transitions. Our results provide a route to understanding disordered many-body systems under a generalized boundary.

Time-reversal symmetry breaking without magnetization gives rise to spin-split bands in altermagnets, where a rotational transformation instead of a translation or inversion connects the opposite-spin sublattices. However, this spin splitting is momentum dependent, and the direct spectroscopic probe remains untapped. Here we report that momentum-resolved second harmonic generation (SHG) can do this job. In ${\mathrm{RuO}}_2$, the first peak in SHG arises from the electronic transition touching the bands near the Fermi level and can identify its band gap. The other peaks are referred to the deeper transitions far away from the Fermi level. All of them are rooted in the third-order Pancharatnam-Berry tensor that manifests as triple multiplied Berry connections and represents an intrinsic band geometric property. More importantly, the energy shifts of the peaks in SHGs from the spin-up channel relative to the spin-down one indicate the spin splittings at different energy levels. Our findings are also true for ${\mathrm{CuF}}_2$ and MnTe. This study uncovers the second-order nonlinearity of momentum-resolved SHG as a local probe for the spin-split bands in altermagnets.

The magnetic phase diagram, magnetoelastic coupling, and uniaxial pressure effects of centrosymmetric magnetic skyrmion-hosting ${\mathrm{GdRu}}_2{\mathrm{Si}}_2$ are investigated by means of high-resolution capacitance dilatometry in fields up to 15 T supported by specific-heat and magnetization studies. In addition to the previously reported phases in the $H\text{−}T$ phase diagram, we observe a third antiferromagnetic phase in zero magnetic field. We present the magnetic phase diagram and find two unreported phases, one of which features a comparably giant uniaxial pressure dependence. Our dilatometric measurements show magnetoelastic effects associated with the various magnetic ordering phenomena. We determine the uniaxial pressure dependencies of the various phases, in particular of the skyrmion lattice phase which is enhanced at higher fields and temperatures and also widens at a rate of 0.07 T/GPa when uniaxial pressure is applied along the $c$ axis. The relevance of fluctuations is further highlighted by the presence of a tricritical point indicated by our thermodynamic data at the phase boundary separating two double-$Q$ magnetic configurations between which the skyrmion pocket phase evolves upon further cooling.

The Lindblad quantum master equation is one of the central approaches to the physics of open quantum systems. In particular, boundary driving enables the study of transport, where a steady state emerges in the long-time limit, which features a constant current and a characteristic density profile. While the Lindblad equation complements other approaches to transport in closed quantum systems, it has become clear that a connection between closed and open systems exists in certain cases. Here, we build on this connection for magnetization transport in the spin-1/2 XXZ chain with and without integrability-breaking perturbations. Specifically, we study the question of whether the time evolution of the open quantum system can be described on the basis of classical correlation functions, as generated by the Hamiltonian equations of motion for real vectors. By comparing the results to exact numerical simulations of the Lindblad equation, we find a good accuracy of such a description for a range of model parameters which is consistent with previous studies on closed systems. While this agreement is an interesting physical observation, it also suggests that classical mechanics can be used to solve the Lindblad equation for comparatively large system sizes which lie outside the possibilities of a quantum mechanical treatment. We also point out counterexamples and limitations for the quantitative extraction of transport coefficients. Remarkably, our classical approach to large open systems allows us to detect superdiffusion at the isotropic point.

Single-pulse all-optical switching of magnetization (AOS) in Co/Gd–based synthetic ferrimagnets carries promises for hybrid spintronic-photonic integration. A crucial next step progressing toward this vision is to gain insight into AOS and multidomain state (MDS) behavior using longer pulses, which is compatible with state-of-the-art integrated photonics. In this work, we present our studies on the AOS and MDS of [Co/Gd] ${}_n (n=1,2)$ using ps optical pulses across a large composition range. We theoretically and experimentally show that a large Gd layer thickness can enhance the AOS energy efficiency and maximum pulse duration. We have identified two augmenting roles of Gd in extending the maximum pulse duration. On the interatomic level, we found that more Gd offers a prolonged angular momentum supply to Co. On the micromagnetic level, a higher Gd content brings the system to be closer to magnetic compensation in the equilibrized hot state, thereby reducing the driving force for thermally assisted nucleation of domain walls, combating the formation of a MDS. Our study presents a composition overview of AOS in $[\mathrm{Co}/{\mathrm{Gd]}}_n$ and offers useful physical insights regarding AOS fundamentals as well as the projected photonic integration.

The discovery of superconductivity under high pressure with $T_c$ exceeding 80 K in a bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ has led to a strong desire to realize similar high $T_c$ phenomena at ambient pressure. As one possible path toward realizing superconductivity at ambient pressure, we here propose to consider ${\mathrm{Sr}}_3{\mathrm{Ni}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$ as a possible candidate. In this study, we theoretically investigate the electronic structure of ${\mathrm{Sr}}_3{\mathrm{Ni}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$ and its structural stability. Our phonon calculation shows that this compound with the $I4/mmm$ tetragonal structure is dynamically stable even at ambient pressure. The characteristic crystal field in this compound lowers the $\mathrm{Ni}\text{−}{d}_{3z^2-r^2}$ orbital energy, by which the $\mathrm{Ni}\text{−}{d}_{3z^2-r^2}$ orbital becomes rather closer to the half filling in ${\mathrm{Sr}}_3{\mathrm{Ni}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$ than ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. As a result, we find that superconductivity is enhanced even though a relatively strong orbital hybridization between the $t_{2g}$ and $e_g$ orbitals is somewhat detrimental for superconductivity. We also check the formation enthalpy, which shows that the high-pressure synthesis can be a good way to actually produce ${\mathrm{Sr}}_3{\mathrm{Ni}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$. We find that ${\mathrm{Sr}}_3{\mathrm{Ni}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$ is a promising new candidate of bilayer-nickelate superconductors, which can possess even higher $T_c$ than pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, at ambient pressure.

Nonadiabatic effects in the electron-phonon coupling are important whenever the ratio between the phononic and the electronic energy scales—the adiabatic ratio—is non-negligible. For superconducting systems, this gives rise to additional diagrams in the superconducting self-energy, the vertex, and cross-corrections. In this work, we explore these corrections in a two-dimensional single-band system through the crossover between the weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein regimes. By focusing on the pseudogap phase, we identify the parameter range in which the pairing amplitude is amplified by nonadiabatic effects and, due to controlled approximations, we map them throughout the BCS-BEC crossover. These effects become stronger as the system is driven deeply in the crossover regime, for phonon frequencies of the order of the hopping energy and for large enough electron-phonon coupling. Finally, we provide the phase space regions in which the effects of nonadiabaticity are more relevant for unconventional superconductors.

We investigate the emergence of spacetime supersymmetry (SUSY) in an interacting Kitaev chain model with explicit microscopic $\mathcal{N}=1$ quantum mechanical SUSY. As the interaction strength is varied, the model transitions from a weak-coupling gapless phase with spontaneously broken SUSY to a strong-coupling phase with restored SUSY. In this paper, we numerically determine the transition point and investigate the phase structure around it. The weak-coupling phase is governed by the Ising conformal field theory (CFT) with central charge $c=1/2$, which agrees with the prediction made in our previous paper. At the SUSY restoration transition, which borders the strong-coupling gapped phase, the transition belongs to the $c=7/10$ tricritical Ising universality with emergent superconformal invariance. Crucially, the phase structure around the transition closely aligns with the scenario proposed by Zamolodchikov and others based on the integrable deformation of CFTs. These findings provide a concrete example of a lattice model where explicit microscopic supersymmetry at criticality enriches the understanding of phase transitions governed by supersymmetric conformal field theories.

We consider the dynamical electronic response function in theoretical frameworks that include nonlocal exchange interactions, such as the Bethe-Salpeter equation with the frequency independent approximation of the screened interaction, Hartree-Fock, and range-separated Hybrid DFT approaches. Within these pictures, we demonstrate that any time-dependent electronic linear response function allows for a formulation which is variational in the electronic density matrix. To achieve our goal, we consider the usual form of a response function, written in terms of a screened and a bare electronic vertices (“bare-screen”), and perform an exact rewriting in terms of purely screened electronic vertices (“screen-screen”). Within the “screen-screen” formulation, the response function can be written as a stationary point of a functional of the exact density matrix. Further, we show that the imaginary part of any electronic response can be written in the form of a generalized Fermi golden rule, by introducing an exact complementary rewriting in terms of vertices related by complex conjugation (“screen*-screen”). The screen-screen formulation can be further extended partitioning the electronic interaction in separate contributions, expressing the response in terms of partially screened electronic vertices (“partial screen-partial screen”), preserving the stationary properties. We numerically validate the effectiveness of our formalism by calculating the optical conductivity of graphene, which exhibits strong excitonic effects. To do so, we solve the Bethe-Salpeter Equation on a tight-binding model, including exchange effects in the response of graphene. Our findings show the advantages of the variationality of the screen-screen formulation over the others both in convergence properties and robustness with density-matrix approximations.

We investigate the charging dynamics of Sachdev-Ye-Kitaev (SYK) models as quantum batteries, highlighting their capacity to achieve quantum charging advantages. By analytically deriving the scaling of the charging power in SYK batteries, we identify the two key mechanisms underlying this advantage: the use of operators scaling extensively with system size $N$ and the facilitation of operator delocalization by specific graph structures. A graph-theoretic framework is introduced in which the charging process is recast as a random walk on a graph, enabling a quantitative analysis of operator spreading. Our results establish rigorous conditions for the quantum advantage in SYK batteries and extend these insights to graph-based SYK models, revealing broader implications for energy storage and quantum dynamics. This work opens avenues for leveraging quantum chaos and complex network structures in optimizing energy transfer processes.

The quasiparticle wave function of a many-electron system is traditionally defined as the eigenfunction of the quasiparticle eigenvalue equation involving the self-energy. In this article a different concept of a quasiparticle wave function is derived from the general definition of the Green's function without reference to self-energy. The proposed quasiparticle wave function can decay in time, and in contrast to the traditional one it contains not only the main quasiparticle mode but also other modes due to coupling to collective excitations in the system. In the recently developed dynamical exchange-correlation potential formalism, this definition of a quasiparticle wave function leads to an equation of motion with an effective field, which appears to have a simple form expected to be amenable to realistic approximations. A simple model for the effective potential is proposed which is suitable for materials whose valence electrons are dominated by itinerant $s\text{−}p$ electrons such as simple metals.

This study explores the synthesis and electronic structure of ${\mathrm{FeSb}}_2$, an altermagnet (AM) candidate, through torque magnetometry and ab initio density functional theory calculations. The temperature-dependent magnetic susceptibility data reveal an antiferromagnetic ground state below room temperature. To probe its electronic properties, we conducted high-field torque magnetometry up to 41 T and observed clear de Haas–van Alphen (dHvA) oscillation with a major peak at 65 T. Angular and temperature-dependent dHvA measurements were further conducted to map the Fermi surface parameters of ${\mathrm{FeSb}}_2$. Interestingly, the spin-polarized electronic bands display asymmetric behavior between spin-up and spin-down states. The presence of a nonrelativistic spin splitting band in the collinear antiferromagnet depicted a strong evidence of altermagnetism in ${\mathrm{FeSb}}_2$. Three bands intersect the Fermi level, forming the Fermi surface of ${\mathrm{FeSb}}_2$. The band-resolved Fermi pockets exhibit $d$-wave symmetry and display asymmetry between the spin-up and spin-down states. These findings provide valuable insights into the electronic and magnetic structure of ${\mathrm{FeSb}}_2$ and strongly support its classification as an AM.

We study the normal and lateral components of the Casimir-Lifshitz (CL) force between a nanoparticle and a 1D graphene grating deposited on a fused silica slab. For this purpose, the scattering matrix approach together with the Fourier modal method augmented with local basis functions are used. We find that, by covering a fused silica slab by a graphene grating, the spectrum of the normal CL force at small frequencies is increased by about 100% for a grating filling fraction of 0.5, and even more when the slab is completely covered. The typically employed additive approximation (the weighted average of the force with and without the graphene coating) cannot provide any information on the lateral CL force and, as we show, cannot provide an accurate estimation for the normal CL force. When the nanoparticle is laterally shifted ($x_A$), the normal CL force is modulated and remains attractive. On the contrary, the lateral CL force changes signs twice in each period, showing a series of alternating stable and unstable lateral equilibrium positions occurring in the graphene strips and the grating slits regions, respectively. Finally, we show that the lateral shift effect is sensitive to the geometric factor $d/D$ ($d$ is the separation distance, and $D$ is the grating period). We identify two clear regions: a region ($d/D<1.0$) where the lateral shift significantly affects the CL energy and a region ($d/D\ge 1.0$) where this effect is negligible, with a crossover at $d\approx D$. Our predictions can have relevant implications to experiments and applications of the CL normal and lateral forces acting on nanoparticles interacting with structured objects at the nanoscale and microscale, and are also directly valid for atoms close to these nanostructures.