Chiral spin liquids, which break time-reversal symmetry, are of great interest due to their topological properties and fractionalized excitations (anyons). In this work, we investigate chiral spin liquids (CSL) on the kagome lattice arising from the competition between the third-nearest-neighbor Heisenberg interaction across hexagons ($J_d$) and a staggered scalar spin chirality term ($J_{\chi }$). Using variational Monte Carlo methods, we map out the phase diagram and identify various gapped and gapless CSL phases, each characterized by a distinct flux pattern. Notably, the interplay between $J_d$ and $J_{\chi }$ induces a tricritical point, which we analyze using Landau-Ginzburg theory. Additionally, we identify potential signatures of these CSLs—including distinctive spin-spin correlations, anomalies in the static spin structure factor, longitudinal thermal conductivity, and magnetoelectric effects—which offer practical guidance for their future experimental detection.

CePtPb hosts a distorted kagome lattice of ${\mathrm{Ce}}^{3+}$ ions, providing a clean platform to investigate how reduced local symmetry and strong spin-orbit coupling reshape frustrated magnetism. Magnetization, specific heat, and magnetocaloric effect measurements, combined with a symmetry analysis of the single-ion anisotropy, demonstrate that the local $m2m$ site symmetry selects a nearly Ising-like Kramers doublet with easy axes lying within the $ab$ plane. This results in three distinct in-plane Ising directions and an overall easy-plane anisotropy. The low-energy magnetic response is well captured by a three-sublattice Ising model, which quantitatively reproduces the saturation magnetization for arbitrary in-plane field orientations, including [110] and $\left[1\overline{1}0\right]$, as well as the ratio of the field-induced critical fields. For $B\parallel \left[110\right]$, the phase diagram exhibits two quantum critical points at $B_{\mathrm{c}1}=0.25\mathrm{T}$ and $B_{\mathrm{c}2}=0.55\mathrm{T}$, arising from the sequential polarization of the three Ising sublattices. These results reveal that the system develops quasi-one-dimensional spin chains along the $c$ axis, emerging from the nominally three-dimensional crystal structure composed of stacked kagome layers, and illustrate how reduced local symmetry can drive effective dimensional reduction in rare-earth Ising magnets.

We explore the gapless topological phases of a $p$-wave superconductor, probing its rich topology and underlying quantum phenomena. The topology of the system is characterized by studying its entanglement properties. This study confirms the bulk-boundary correspondence in the entanglement spectrum, even without a full bulk gap. For contractible bipartitions, the entanglement entropy varies nonmonotonically with the chemical potential, displaying pronounced peaks at points where the bulk gap closes and reopens, signaling topological quantum phase transitions. This behavior remains robust in the thermodynamic limit. The entanglement entropy grows with system size for noncontractible bipartitions, obeying volume law even in the gapless phase. These findings reveal the subtle interplay between symmetry, entanglement, and topology in gapless systems, and emphasize the role of entanglement-based diagnostics in identifying unconventional topological phases beyond the gapped paradigm.

We develop a low-energy field theory for electrically charged crystals. Using the tools of fracton-elasticity duality, generalized to accommodate the magnetic one-form symmetry of electromagnetism, we show how the elastic and electromagnetic degrees of freedom couple to the different crystal defects and to one another. The resulting field theory is then used to calculate vacancy-vacancy interaction energy, and to study the consequences of vacancy proliferation. We find that the longitudinal mode, which in a perfect crystal has a finite gap due to plasma oscillations, becomes gapless in the presence of vacancies. Our framework lays a foundation for a study of defect interactions, their collective dynamics, and consequences of defect-mediated melting in charged crystals.

We investigate the generation of nonstabilizerness, or magic, in a multiparticle quantum walk by analyzing the time evolution of the stabilizer Rényi entropy $M_2$. Our study considers both single- and two-particle quantum walks in the framework of the XXZ Heisenberg model with varying interaction strengths. We demonstrate that the spread of magic follows the light-cone structure dictated by the system's dynamics, with distinct behaviors emerging in the easy-plane ($\mathrm{\Delta }<1$) and easy-axis ($\mathrm{\Delta }>1$) regimes. For $\mathrm{\Delta }<1$, magic generation is primarily governed by single-particle dynamics, while for $\mathrm{\Delta }>1$, doublon propagation dominates, resulting in a significantly slower growth of $M_2$. Furthermore, the magic exhibits logarithmic growth in time for both one- and two-particle dynamics. Additionally, by examining the Pauli spectrum, we show that the statistical distribution of level spacings exhibits Poissonian behavior, independent of interaction strength or particle number. Our results shed light on the role of interactions on magic generation in a many-body system.

Motivated by recent scanning tunneling microscopy experiments on chains of Co adatoms on Cu surfaces, we investigate the physics of a spin-3/2 Heisenberg chain with single-ion anisotropy $\left(D\right)$ on metallic and semimetallic surfaces. In the strong Kondo coupling $\left(J_k\right)$ limit, a perturbative analysis maps the system onto a Haldane spin-1 chain with single-ion anisotropy, ferromagnetically coupled to the metallic surface. This Haldane state, arising from the underscreening of the $S=3/2$ chain, is stable against small values of $D$ and is characterized by topological edge modes. The nature of the $D$-driven transitions out of this state depends on the metallic environment. Coupling to a metal (semimetal) constitutes a relevant (irrelevant) perturbation at the decoupled fixed point between the spin-1 chain and the two-dimensional electron gas. In the large positive $D$ limit, the system maps onto an anisotropic spin-$1/2$ Kondo system that has been studied. For large negative $D$, in the Ising phase, the spins are frozen. For small values of $J_k$, the nature of the metallic phase plays a dominant role. On a two-dimensional semimetal, the Kondo coupling is irrelevant at the decoupled fixed point, $J_k=0$, leading to a Kondo breakdown phase at weak coupling, irrespective of $D$. In contrast, on a two-dimensional metal, the resulting dissipative Ohmic bath acts as a marginally relevant perturbation at the decoupled fixed point, inducing antiferromagnetic ordering along the spin chain. In this case, $D$ drives a spin-flop transition between Ising- and XY-ordered phases. At $D=0$, we observe continuous transitions between the Kondo breakdown or dissipation-induced long-range ordered phases and the underscreened Haldane phase. This understanding of the phase diagrams is supported by scaling arguments as well as by unbiased, sign-free auxiliary-field quantum Monte Carlo simulations.

We investigate out-of-equilibrium entanglement dynamics in a generalization of the so-called $QSSEP$ model, which is a free-fermion chain with stochastic in space and time hopping amplitudes. In our setup, the noisy amplitudes are spatially modulated satisfying a $\nu$-site translation invariance but retaining their randomness in time. For each noise realization, the dynamics preserves Gaussianity, which allows to obtain noise-averaged entanglement-related quantities. The statistics of the steady-state correlators satisfy nontrivial relationships that are of topological nature. They reflect the Haar invariance under multiplication with structured momentum-dependent random $SU\left(\nu \right)$ matrices. We discuss in detail the case with $\nu =1$ and $\nu =2$. For $\nu =1$, i.e., spatially homogeneous noise, we show that the entanglement dynamics is describable by a stochastic generalization of the quasiparticle picture. Precisely, entanglement is propagated by pairs of quasiparticles. The entanglement content of the pairs is the same as for the deterministic chain. However, the trajectories of the quasiparticles are random walks, giving rise to diffusive entanglement growth.

Doping charges into noncoplanar spiral textures provide opportunities for the development of multifunctional memory devices. Here, we demonstrate that two-unit-cell-thick twisted bilayer ${\mathrm{SrTiO}}_3$ undergoes ferroelectric-to-magnetic ferroelectric and semiconducting-to-half-metallic transitions, thereby reviving and stabilizing the topological order inherent in twisted perovskite. The underlying mechanism for realizing the transitions is attributed to a quasi-two-dimensional electron gas localized around Ti atoms. Ti displacements occur along the out-of-plane polar direction, while the in-plane square-planar ${\mathrm{TiO}}_4$ cage retains fourfold rotation $\left(C_4\right)$ symmetry with the degenerate $d_{xz}$ and $d_{yz}$ orbitals. Doubly degenerate orbitals accommodate ultrahigh electron-doping concentrations, leading to the coexistence of half-metallicity and layer-antiferromagnetic order. The ground-state magnetic phase diagram is established, and the transition temperature is evaluated as a function of doping concentration. Furthermore, significant ionic displacements break inversion symmetry and permit a shear piezoelectric response. The twisted structure belongs to the point group 422, which restricts the piezoelectric tensor to pure face-shear components. These findings provide an intrinsic mechanism for achieving skyrmion patterns, half-metallicity, magnetism, and piezoelectric responses in ultrathin twisted bilayer perovskite.

Octahedral tilting is a fundamental structural distortion in perovskites, governing key phenomena such as lattice stabilizing, soft phonon dynamics, group-theoretical analysis, phase transitions, ferroelectricity, and even for tunable electronic band gap. However, its influence on lattice thermal conductivity $\left({\kappa }_L\right)$ remains poorly understood. In the archetypal perovskite ${\mathrm{SrTiO}}_3$, tilting in the low-temperature tetragonal phase is known to enhance ${\kappa }_L$ by suppressing specific phonon scattering channels around $200{\mathrm{cm}}^{-1}$. Here, we investigate the thermal transport in strontium stannate $\left({\mathrm{SrSnO}}_3\right)$, another perovskite oxide that undergoes temperature-driven phase transitions, and reveal a completely opposite effect. Through a systematic study across its orthorhombic, tetragonal, and cubic phases, we demonstrate that octahedral tilting in the tetragonal phase of ${\mathrm{SrSnO}}_3$ anomalously triggers acoustic phonon softening. This softening manifests as reduced frequencies and group velocities in low-frequency (<3 THz) acoustic modes, creating a large decrease for heat transport, particularly along the $c$ axis. Consequently, ${\kappa }_L$ is significantly suppressed, decreasing from $7.48\mathrm{W}{\mathrm{m}}^{-1}{\text{K}}^{-1}$ to $6.06\mathrm{W}{\mathrm{m}}^{-1}{\text{K}}^{-1}$ as the tilting angle increases by a mere $1^{\circ }$. These findings identify tilting-induced acoustic softening as a pivotal mechanism for limiting and controlling anisotropic thermal transport in ${\mathrm{SrSnO}}_3$, presenting a stark contrast to the established behavior in ${\mathrm{SrTiO}}_3$.

Most studies on Goos-Hänchen and photonic spin Hall beam shifts are focused on reciprocal, or direction-independent, beam shifts. In this work, we present a strategy to induce nonreciprocal beam shifts in the reflected field from a planar heterostructure by exploiting direction- and polarization-dependent coupling between the incident field and the structure. We show that the heterostructure's resonant modes lead to polarization-dependent, nonreciprocal reflection at specific incident angles. This behavior enables controlled tuning of the direction-dependent transformation of optical momentum. Consequently, we observe nonreciprocal Goos-Hänchen and photonic spin Hall shifts in the reflection plane, manifesting as lateral and transverse displacements, respectively. These shifts arise from the conversion of linear momentum and orbital angular momentum into spin angular momentum. The results are verified using three independent approaches—comsol multiphysics simulations, the stationary phase method, and Gaussian beam scattering calculations—with excellent agreement among them.

Graphene monolayer is a material with zero band gap, because of which its applications in optoelectronics are limited. The question arises, can we modify the optoelectronic properties of graphene by doping it with other atoms? Synthesis of 2D monolayer of graphene doped with hetero-atoms such as boron and nitrogen, and a few computational studies of their structural and electronic properties were previously reported. In this work, we aim to answer this question for graphene quantum dots (GQDs), i.e., how can we tune their optoelectronic performance by replacing their carbon rings with ${\left(\mathrm{BN}\right)}_3$ (borazine) hexagonal rings? In this work, we have studied in detail the geometry, electronic structure, and optical absorption spectra of fourteen different borazine-ring doped diamond-shaped GQDs, using a computational methodology based on the first-principles density functional theory (DFT). We refer to the doped structures as BN-GQDs, which differ from each other in the location, orientation, and the number of borazine rings. We computed their optical absorption spectra using the time-dependent density-functional theory (TDDFT), and carefully examined: (a) for the single-ring doped BN-GQDs the influence of the location of the ring on their optical properties, and (b) for the double ring doped systems, the influence of the location, mutual distance and orientation of the rings on their absorption spectra. Frontier molecular orbitals of all the structures considered here are studied in detail in order to understand the nature of low-lying optical excitations. We also analyzed the point-group symmetries of considered BN-GQDs, and performed a group-theoretic analysis of the influence of their reduced symmetries, on their optical properties. Our results indicate that BN-ring doping can achieve a significant control over the optical properties of GQDs. The comparison of the optical absorption spectra of the BN-GQDs with the parent GQD shows remarkable spectral broadening with optical gap spanning over infrared to visible region of the spectrum. Thus, systematic BN-ring doping provides easy tunability of the electronic and optical properties of BN-GQDs to a considerable extent which is very promising for their optoelectronic applications.

Topological materials, known for their edge states robust against local perturbations, hold promise for next-generation quantum technologies, but remain scarce in nature and challenging to realize in static systems. The Su-Schrieffer-Heeger chain is a one-dimensional system with a well-known topological phase protected by chiral symmetry, although its static control is limited. To overcome these limitations, we propose to use high-frequency monochromatic driving and modulated amplitude pulses to induce and switch the Floquet topological phases even when the chiral symmetry is dynamically broken. Using a Kramers-Henneberger-like transformation, we encode all Floquet sidebands into a single effective Hamiltonian. We demonstrate that both monochromatic and experimental pulse protocols (Gaussian and fast-beating envelopes) can induce topological edge states, enabling dynamic phase switching. Notably, fast-beating modulations require significantly lower-field amplitudes than monochromatic ones, especially with a larger intracell dimer separation. Our findings offer an experimentally feasible route for Floquet engineering, paving the way for ultrafast and energy efficient control of topological phases in quantum platforms, opening up different possibilities in the field of dynamic quantum materials.

Within the quantum field-theoretical approach describing the evolution of a quadratic Liouvillian in the basis of Keldysh contour coherent states, we investigate the spectral and transport properties of a dissipative superconducting system coupled to normal Fermi reservoirs. We derive a generalization of the Meir-Wingreen formula and Onsager matrix for a superconducting system subject to an arbitrary number of fermionic baths. Following Kirchhoff's rule, we obtain an expression describing the dissipation-induced loss current and formulate modified quantum kinetic equations. For wide-band contacts locally coupled to individual sites, we find that each contact reduces the degeneracy multiplicity of the nonequilibrium steady state by one. These results are numerically verified through several cases of the extended Kitaev model at symmetric points with a single contact. Furthermore, in the linear response regime at low temperatures, we demonstrate that (non)degenerate nonequilibrium steady states correspond to (non)quantized conductance peaks. Revisiting a paradigmatic problem of resonant transport in the Majorana mode of the Kitaev model, we demonstrate that dissipation accounts for the zero-bias peak suppression and its asymmetry.

We study the origin of the large topological Hall effect in the single-crystalline ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$, which orders antiferromagnetically at the Néel temperature $T_{\mathrm{N}}=7.4\mathrm{K}$. Measurements of magnetoresistance and Hall resistivity disclose anomalies that evolve with temperature and magnetic field, closely tracking the magnetization process. Analysis of these data identifies three possible mechanisms responsible for the enhanced Berry curvature driving the observed topological Hall effect. Below and above $T_{\mathrm{N}}$, Weyl states are the main sources of large momentum-space Berry curvature, though their formation mechanisms differ in these two temperature ranges. Below $T_{\mathrm{N}}$, breaking of $C_3$ symmetry generates Dirac points that split into Weyl nodes in an applied magnetic field, whereas above $T_{\mathrm{N}}$, strong spin fluctuations can induce Weyl states. The third contribution, which occurs below $T_{\mathrm{N}}$, arises from scalar spin chirality developing within antiferromagnetic domain walls, which generates a real-space Berry curvature.

Weak ergodicity breaking in interacting quantum systems may occur because of the existence of a subspace dynamically decoupled from the rest of the Hilbert space. In two-orbital spinful lattice systems, we construct such subspaces that are, in addition, distinguished by strongest interorbital and spin-singlet or spin-triplet, long-range superconducting pairing correlations. All unconventional pairing types we consider are local in space and unitary. Alternatively to orbitals, the additional degree of freedom could originate from the presence of two layers or through any other mechanism. Required Hamiltonians are rather non-exotic and include chemical potential, Hubbard, and spin-orbit interactions typically used for two-orbital superconducting materials. Each subspace is spanned by a family of group-invariant quantum many-body scars combining both $2e$ and $4e$ pairing/clustering contributions. One of the basis states has the form of a BCS wavefunction and can always be made the ground state by adding a mean-field pairing potential. Analytical results in this work are lattice-, dimension-, and (mostly) system size-independent. We confirm them by exact numerical diagonalization in small systems.

Numerical simulations find that there are multiple plateaus in the magnetization curve of the spin-$\frac{1}{2}$ Kagome antiferromagnetic Heisenberg model (KAFH) at fractional magnetization $m=1/9,1/3,5/9,7/9$. While it is well known that the $m=1/3,5/9,7/9$ plateaus feature a $\sqrt{3}\times \sqrt{3}$ valence bond crystal (VBC) ordering pattern with a David-star-shaped motif, the origin of the narrow plateau at $m=1/9$ remains elusive. Some researchers claim that a subtle translational symmetry-breaking pattern with the same $\sqrt{3}\times \sqrt{3}$ periodicity occurs at the $m=1/9$ plateau. However, it has also been argued that the $m=1/9$ plateau may harbor a novel $Z_3$ chiral spin-liquid phase. The main challenge to resolve this controversy is to reduce the bias of the method used to describe the magnetization process of such a strongly frustrated quantum magnet, for which intricate competition between different symmetry-breaking patterns is generally expected. For this purpose, we have proposed the most general variational ansatz based on the resonating valence bond (RVB) picture that is consistent with the spin symmetry of the system. To optimize such a general RVB ansatz, which can describe all kinds of spatial symmetry-breaking pattern on equal footing but at the same time contains a huge number of variational parameters, we have developed a new optimization algorithm, the finite-depth Broyden-Fletcher-Goldfarb-Shanno algorithm. The new algorithm can achieve good balance between numerical efficiency, numerical stability, and storage demand and can deal with optimization problem containing millions of parameters at ease. We applied such an advanced optimization algorithm to the general RVB ansatz and mapped out the magnetization curve of the spin-$\frac{1}{2}$ KAFH. We find that a peculiar VBC state with a $3\times 3$ periodicity and a windmill-shaped motif has significantly lower energy than the claimed $Z_3$ chiral spin liquid state and other proposed VBC states around the $m=1/9$ plateau. We find that there are strong spatial modulations in the local magnetization at the $1/9$ plateau, so strong that even its polarization can be reversed. Our general RVB ansatz also well reproduces all other more conventional magnetization plateaus of the spin-$\frac{1}{2}$ KAFH. We find that the local magnetization is always strongly inhomogeneous below the saturating field for such a strongly frustrated quantum magnet.

The variational discrete action theory (VDAT) at $\mathcal{N}=3$ is a potent tool for accurately capturing Mott and Hund physics at zero temperature in $d=\infty$ at a cost comparable to the Gutzwiller approximation, which is recovered by VDAT at $\mathcal{N}=2$. Here we develop a qubit parametrization of the gauge constrained algorithm of VDAT at $\mathcal{N}=3$ for the multiorbital Hubbard model with general density-density interactions. The qubit parametrization yields an explicit variational trial energy, and the variational parameters consist of the momentum density distribution, the shape of a reference fermi surface, and the pure state of a qubit system with dimension of the local Hilbert space. To illustrate the power of the qubit parametrization, we solve for the ground-state properties of the multiorbital Hubbard model with Hund coupling for local orbital number $N_{\text{orb}}=2–7$. A Taylor series expansion of the partially optimized trial energy is used to explain how the Hund's coupling changes the order of the Mott transition. For the case of the $SU\left(2N_{\text{orb}}\right)$ Hubbard model, an explicit approach for computing the critical $U_c$ for the Mott transition is provided, yielding an analytical expression for $U_c$ in the large $N_{\text{orb}}$ limit. Additionally, we provide an analytical solution for the ground-state properties of the single-band Hubbard model with a special density of states. Finally, we demonstrate that the qubit parametrization can also be applied to $\mathcal{N}=2$, for both G-type and B-type variants, where the G-type yields an identical expression to the slave spin mean-field theory. The qubit parametrization not only improves the efficiency and transparency of VDAT at $\mathcal{N}=3$, but also provides the key advances for the construction of a one-body reduced density matrix functional capable of capturing Mott and Hund physics.

Quantum phase transitions are characterized by the universal scaling laws in the critical region surrounding the transitions. This universality is also manifested in the critical real-time dynamics through the quantum Kibble-Zurek mechanism. In recent experiments on a Rydberg atom quantum simulator, the Kibble-Zurek mechanism was used to probe the nature of quantum phase transitions. In this paper, we analyze the caveats associated with this method and develop strategies to improve its accuracy. Focusing on two minimal models—transverse-field Ising and quantum three-state Potts, both in one dimension—we study the effect of boundary conditions, the location of the endpoints, and some subtleties in the definition of the kink operators. In particular, we show that the critical scaling of the most intuitive types of kinks is extremely sensitive to the correct choice of endpoint, while more advanced types of kinks exhibit remarkably robust universal scaling. Furthermore, we show that when kinks are tracked over the entire chain, fixed boundary conditions improve the accuracy of the scaling. Surprisingly, the Kibble-Zurek critical scaling appears to be equally accurate whether the fixed boundary conditions are chosen to be symmetric or antisymmetric. We also show that the density of kinks extracted in the central part of long chains obeys the predicted universal scaling for all types of boundary conditions. Finally, we test our kink definition for the Ising transition on the period-2 phase of the Rydberg model and show that it is more robust against the endpoint than the standard definition.