We investigate the quench dynamics in the dipolar Bose-Hubbard model (DBHM) in one dimension. The boson hopping is constrained by dipole conservation and shows fractonic dynamics. The ground states at large Hubbard interaction $U$ are Mott insulators at integer filling and a period-2 charge density wave (CDW) at half-integer filling. We focus on Mott-to-Mott and CDW-to-CDW quenches and find that dipole correlation spreading shows the light-cone behavior with the Lieb-Robinson (LR) velocity proportional to the dipole kinetic energy $J$ and the square of the density in the case of Mott quench at integer filling. An effective model for postquench dynamics is constructed under the dilute-dipole approximation and fits the numerical results well. For the CDW quench, we observe a much reduced LR velocity of order $J^2/U$ and additional periodic features in the time direction. The emergence of a CDW ground state and the reduced LR velocity at half-integer filling can both be understood by careful application of the second-order perturbation theory. The oscillatory behavior arises from quantum scars in the quadrupole sector of the spectrum and is captured by a PXP-like model that we derive by projecting the DBHM to the quadrupolar sector of the Hilbert space.

We present a thorough experimental investigation on single crystals of the rare-earth based frustrated quantum antiferromagnet ${\mathrm{Pr}}_3{\mathrm{BWO}}_9$, a purported spin-liquid candidate on the breathing kagome lattice. This material possesses a disordered ground state with an unusual excitation spectrum involving a coexistence of sharp spin waves and broad continuum excitations. Nevertheless, we show through a combination of thermodynamic, magnetometric, and spectroscopic probes with detailed theoretical modeling that it should be understood in a completely different framework. The crystal field splits the lowest quasidoublet states into two singlets moderately coupled through frustrated superexchange, resulting in a simple effective Hamiltonian of an Ising model in a transverse magnetic field. While our neutron spectroscopy data do point to significant correlations within the kagome planes, the dominant interactions are out-of-plane, forming frustrated triangular spin-tubes through two competing ferro-antiferromagnetic bonds. The resulting ground state is a simple quantum paramagnet, where the presence of strongly hyperfine-coupled nuclear moments and weak structural disorder causes significant modifications to both thermodynamic and dynamic properties.

We bring forward a unified framework for the study of the superfluid stiffness and the quantum capacitance of superconducting platforms exhibiting conventional spin-singlet pairing. We focus on systems which in their normal phase contain topological band touching points or crossings, while in their superconducting regime feature a fully gapped energy spectrum. Our unified description relies on viewing these two types of physical quantities as the charge current and density response coefficients obtained for slow spatiotemporal variations of the superconducting phase. Within our adiabatic formalism, the two coefficients are given in terms of Berry curvatures defined in synthetic spaces. Our paper lays the foundation for the systematic description of topological diagonal superfluid responses induced by singularities dictating the synthetic Berry curvatures. We exemplify our approach for concrete one- and two-dimensional models of superconducting topological (semi)metals. We discuss topological phenomena which arise in the superfluid stiffness of bulk systems and the quantum capacitance of Josephson junctions. We show that both coefficients become proportional to a topological invariant which counts the number of topological touchings or crossings of the normal phase band structure. These topological effects can be equivalently viewed as manifestations of chiral anomaly. Our predictions appear experimentally testable in topological semimetals with proximity-induced pairing, such as in graphene-superconductor hybrids at charge neutrality.

We investigate the Lindblad equation in the context of boundary-driven magnetization transport in spin-$1/2$ chains. Our central question is whether the nonequilibrium steady state of the open system, including its buildup in time, can be described on the basis of the dynamics in the closed system. To this end, we rely on a previous study [Heitmann et al., Phys. Rev. B 108, L201119 (2023)], in which a description in terms of spatio-temporal correlation functions was suggested in the case of weak driving and small system-bath coupling. Because this work focused on integrable systems and periodic boundary conditions, we here extend the analysis in three directions: (1) We consider nonintegrable systems, (2) we take into account open boundary conditions and other bath-coupling geometries, and (3) we provide a comparison to time-evolving block decimation. While we find that nonintegrability plays a minor role, the choice of the specific boundary conditions can be crucial due to potentially nondecaying edge modes. Our large-scale numerical simulations suggest that a description based on closed-system correlation functions is a useful alternative to already existing state-of-the-art approaches.

Topological electrides have attracted extensive attention, not only serving as good platforms for studying Dirac fermion, Weyl fermion, and diverse quasiparticles beyond the Dirac and Weyl fermions, but also hosting rich physical and chemical properties such as low work function, high conductivity, and high electron mobility. Motivated by the synthesized YCl and ${\mathrm{Y}}_2{\mathrm{Cl}}_3$ electrides with nontrivial topology, we have explored the Y-Cl binary system under pressure. Based on the first-principles calculations and crystal-structure prediction techniques, we find a $t$-YCl phase with the space group of $P4$/nmm that is both thermodynamically and lattice dynamically stable, and also recoverable to the ambient condition. Based on the $\mathit{k}·\mathit{p}$ method and irreducible representation analyses, we propose that $t$-YCl has a topological nodal chain surrounding the $Z$ point in the Brillouin zone without spin-orbit coupling (SOC), and evolves into a Dirac semimetal phase with two Dirac points protected by $R_{4\mathrm{z}}$ symmetry when taking SOC into consideration. In addition, based on the band representation (BR) analyses, we find the highest occupied bands belong to $A$1@2a BR. Since both the Y and Cl atoms occupy the 2c Wyckoff positions, i.e., no atom in $t$-YCl system locates at the 2a Wyckoff positions, it thus suggests the unconventional nature of an uncompensated state at the 2a Wyckoff position. Remembering the ionic compound nature, the unconventional $t$-YCl phase hosts great potential to be an electride material, which has been further verified by our electron localization function calculations, with the uncompensated state at 2a Wyckoff position contributed by the interstitial quasiatoms. Our work provides a good theoretical and experimental platform for the study of pressure-induced topological electride states.

While the Hamiltonians used in standard quantum mechanics are Hermitian, it is also possible to extend the theory to non-Hermitian Hamiltonians. Particularly interesting are non-Hermitian Hamiltonians satisfying parity–time $\left(\mathcal{P}\mathcal{T}\right)$ symmetry, or more generally pseudo-Hermiticity, since such non-Hermitian Hamiltonians can still exhibit real eigenvalues. In this article, we present a quantum simulation of the time-dependent non-Hermitian non-$\mathcal{P}\mathcal{T}$-symmetric Hamiltonian used in a pseudo-Hermitian extension of the Landau–Zener–Stückelberg–Majorana (LZSM) model. The simulation is implemented on a superconducting processor by using Naimark dilation to transform a non-Hermitian Hamiltonian for one qubit into a Hermitian Hamiltonian for a qubit and an ancilla; postselection on the ancilla state ensures that the qubit undergoes nonunitary time evolution corresponding to the original non-Hermitian Hamiltonian. We observe properties such as the dependence of transition probabilities on time and the replacement of conservation of total probability by other dynamical invariants in agreement with predictions based on a theoretical treatment of the pseudo-Hermitian LZSM system.

We present a direct comparison between the stroboscopic and nonstroboscopic effective approaches for ultracold atoms in shaken honeycomb lattices, focusing specifically on the optimal driving introduced by A. Verdeny and F. Mintert [Phys. Rev. A 92, 063615 (2015)]. In the fast-driving regime, we compare the effective nonstroboscopic Hamiltonian derived through a perturbative expansion with a nonperturbative calculation of the stroboscopic Floquet Hamiltonian, obtained through a direct numerical approach. We find that the leading off-diagonal tunneling coefficients, which define the undriven model, retain their isotropic nature under the effect of the driving, and their values are independent of the computational approach used. This consistency ensures the robustness of certain topological properties, such as the position of Dirac points, as expected. Conversely, the next-to-leading diagonal tunneling coefficients, generated dynamically, can vary across different approaches without affecting the system topology. This suggests that the topological phase diagram is most conveniently represented in terms of the physical parameters characterizing the driving and directly accessible in experiments, rather than in terms of the tunneling parameters.

The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Ni}}_3$. It is an isoelectronic analog of the prototypical Kondo insulator ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pt}}_3$ and of the recently discovered Weyl-Kondo semimetal ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pd}}_3$. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Ni}}_3$ relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65–70 meV, about eight times larger than that in ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pt}}_3$ and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pd}}_3$. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence ${\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Ni}}_3\text{−}{\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pd}}_3\text{−}{\mathrm{Ce}}_3{\mathrm{Bi}}_4{\mathrm{Pt}}_3$, but instead with increasing partial electronic density of states of the $d$ orbitals at the Fermi energy. This work opens the possibility to investigate the conditions under which topological states develop in this series of strongly correlated 3-4-3 materials.

We use a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) to investigate the potential emergence of a charge-disproportionated insulating phase in ${\mathrm{SrCrO}}_3$, whereby the Cr cations disproportionate according to $3{\text{Cr}}^{4+}\to 2{\text{Cr}}^{3+}+{\text{Cr}}^{6+}$ and arrange in ordered planes perpendicular to the cubic [111] direction. We show that the charge disproportionation couples to a structural distortion where the oxygen octahedra around the nominal ${\mathrm{Cr}}^{6+}$ sites contract, while the octahedra surrounding the ${\mathrm{Cr}}^{3+}$ sites expand and distort. Our results indicate that the charge-disproportionated phase can be stabilized for realistic values of the Hubbard $U$ and Hund's $J$ parameters, but this requires a scaling of the DFT+DMFT double-counting correction by at least 35%. The disproportionated state can also be stabilized in $\mathrm{DFT}+\mathcal{U}$ calculations for a specific magnetic configuration with antiparallel magnetic moments on adjacent ${\mathrm{Cr}}^{3+}$ sites and no magnetic moment on the ${\mathrm{Cr}}^{6+}$ sites. While this phase is higher in energy than other magnetic states that can arise in ${\mathrm{SrCrO}}_3$, the presence of an energy minimum suggests that the charge-disproportionated state represents a metastable state of ${\mathrm{SrCrO}}_3$.

We investigate the interplay of spin-orbit coupling, electronic correlations, and lattice distortions in the $5d^1$ double perovskite ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$. Combining density-functional theory (DFT) and dynamical mean-field theory (DMFT), we establish the Mott insulating character of ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$ in both its cubic and tetragonal paramagnetic phases. Despite substantial spin-orbit coupling, its impact on the formation of the insulating state is minimal, consistent with theoretical expectations for $d^1$ systems. We further characterize the electronic properties of the cubic and tetragonal phases by analyzing spectral functions and local occupations in terms of multipole moments centered on the Re sites. Our results confirm the presence of ferroically ordered $z^2$ quadrupoles in addition to the antiferroic $x^2-y^2$-type order. We compare two equivalent but complementary descriptions in terms of either effective Re-$t_{2g}$ frontier orbitals or more localized atomiclike Re-$d$ and O-$p$ orbitals. The former maps directly on a physically intuitive picture in terms of nominal $d^1$ Re cations, while the latter explicitly demonstrates the role of hybridization with the ligands in the spin-orbit splitting and the formation of the charge quadrupoles around the Re sites. Finally, we compare our $\mathrm{DFT}+\mathrm{DMFT}$ results with a previous $\mathrm{DFT}+U$ study of the tetragonal paramagnetic state. We find good qualitative agreement for the dominant charge quadrupoles, but also notable differences in the corresponding spectral functions, underscoring the need for more comparative studies between these two methods.

The Kondo lattice is one of the classic examples of strongly correlated electronic systems. We conduct a controlled study of the Kondo lattice in one dimension, highlighting the role of excitations created by the composite fermion operator. Using time-dependent matrix product state methods, we compute various correlation functions and contrast them with both large-N mean-field theory and the strong-coupling expansion. We show that the composite fermion operator creates long-lived, charge-e and spin-1/2 excitations, which cover the low-lying single-particle excitation spectrum of the system. Furthermore, spin excitations can be thought to be composed of such fractionalized quasiparticles with a residual interaction which tend to disappear at weak Kondo coupling.

Recent experiments [Persky et al., Nature (London) 607, 692 (2022)] demonstrate a magnetic memory effect in $4Hb\text{−}{\mathrm{TaS}}_2$ above its superconducting transition temperature, where Abriokosov vortices are spontaneously generated by lowering the temperature at zero magnetic field after field training the normal state. Motivated by the experiment, we propose the chiral quantum spin liquid (QSL) stabilized in the constituent layers of $4Hb\text{−}{\mathrm{TaS}}_2$ as a mechanism. We model $4Hb\text{−}{\mathrm{TaS}}_2$ as coupled layers of the chiral QSL and the superconductor. Through the Kondo coupling between the localized moments and conduction electrons, there is mutual transmutation between spinons and vortices during the thermal-cycling process, which yields the magnetic memory effect observed in experiments. We also propose a mechanism to stabilize chiral and nematic superconductivity in $4Hb\text{−}{\mathrm{TaS}}_2$ through the Kondo coupling of conduction electrons to the chiral QSL. Our picture suggests $4Hb\text{−}{\mathrm{TaS}}_2$ as an exciting platform to explore the interplay between QSL and superconductivity through the Kondo effect.

The layered perovskite ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ serves as a model material of the two-dimensional (2D) Fermi liquid but also exhibits various emergent phenomena including the non-Fermi-liquid (NFL) behavior under external perturbations such as uniaxial pressure and chemical substitutions. Here we present the thermoelectric transport of electron-doped system ${\mathrm{Sr}}_{2-y}{\mathrm{La}}_y{\mathrm{RuO}}_4$, in which a filling-induced Lifshitz transition occurs at the Van Hove singularity (VHS) point of $y\approx 0.2$. We find that the sign of the low-temperature thermopower becomes negative only near the VHS point, where the NFL behavior has been observed in the earlier study. This observation is incompatible with either a numerical calculation within a constant relaxation-time approximation or a toy-model calculation for the 2D Lifshitz transition adopting an elastic carrier scattering. As a promising origin of the observed negatively enhanced thermopower, we propose a skewed NFL state, in which an inelastic scattering with a considerable odd-frequency term plays a crucial role to negatively enhance the thermopower.

The quest to identify and observe Majorana fermions in physics and condensed-matter systems remains an important challenge. Here, we introduce a qubit (spin-$1/2$) from the occurrence of two delocalized zero-energy Majorana fermions in a model of two spins-$1/2$ on the Bloch sphere within the fractional one-half topological state. We address specific protocols in time with circularly polarized light and the protection of this delocalized spin-$1/2$ state related to quantum information protocols. We also show how disorder can play a positive and important role allowing singlet-triplet transitions and resulting in an additional elongated region for the fractional phase, demonstrating the potential of this platform related to applications in topologically protected quantum information. We generalize our approach with an array and Majorana fermions at the edges in a ring geometry.

In this theoretical study, we explore the dispersion and basic properties of optical microcavities filled with liquid crystal (LC) media that contain embedded quantum wells. As a result of the strong coupling between cavity photons and excitons, exciton polariton quasiparticles arise in these structures. LC-filled microcavities have an advantage of the ability to manipulate the spin (polarization) of the photonic component of the polariton states by controlling the orientation of LC molecules using an external electric field. This enables the engineering of controllable synthetic Hamiltonians for the polariton eigenmodes in microcavity structures. The introduction of synthetic spin-orbit interaction via placing of the quantum wells at particular positions in the LC-filled cavity enables control over the propagation of exciton polaritons, leading to various spatial effects. Through numerical calculations, we successfully reproduce the birefringence and zitterbewegung phenomena exhibited by exciton polaritons propagating within the microcavity plane. We also examine the conditions required for strong coupling when utilizing perovskite layers as hosts for excitons. While the strong coupling regime can be also achieved in this material system, the manifestations of the synthetic spin-orbit interaction are suppressed owing to stronger disorder and nonradiative processes.