Understanding heat conduction in defective silicon is crucial for electronics and thermoelectrics. Conventional understanding relies on the phonon gas picture, treating defects as scattering centers that reduce phonon lifetimes without altering frequencies and group velocities. We go beyond the phonon gas picture by employing the Wigner transport equation to investigate heat conduction in vacancy-defective silicon. Our findings reveal that, while thermal conduction in pristine silicon stems mainly from particlelike propagation of vibrational modes, wavelike tunneling becomes increasingly important in the presence of vacancies. Contrary to the conventional belief that defects only perturb mode lifetimes, we demonstrate that vacancies also diminish velocity operators—a dominant factor in thermal conductivity reduction, surpassing even the effect of lifetime shortening. Furthermore, incorporating anharmonic frequencies and anharmonicity-renormalized interatomic force constants shows that, while anharmonicity suppresses thermal conductivity in pristine silicon, this effect weakens with vacancy concentration and reverses to enhance conductivity. These findings challenge conventional knowledge and provide insights into thermal conduction in defective materials.

Higher-spin quantum magnets with competing interactions offer a rich platform for exploring quantum phases that transcend the paradigms of spin-1/2 systems, owing to their enlarged local Hilbert spaces and the emergence of multipolar correlations. We investigate a one-dimensional spin-1 chain where quadrupolar order is promoted by two distinct mechanisms: conventional bilinear-biquadratic exchange and bond-directional antiferromagnetic Kitaev frustration. Using density matrix renormalization group calculations, we determine the complete ground-state phase diagram and uncover two emergent phases induced by the Kitaev interaction: a Kitaev nematic phase and a Kitaev-dimer phase. The Kitaev nematic phase emerges from a fragile biquadratic dimer state via a continuous quantum phase transition in the Ising universality class. The Kitaev dimer phase spontaneously breaks a screw symmetry to favor either $x$- or $y$-spin bonding, forming a gapped state that coexists with a crystalline order of alternating ${\mathbb{Z}}_2$ bond parities.

Despite considerable efforts over the last decade, the high-energy phase diagram of the random-field Heisenberg chain still eludes our understanding, in particular the nature of the non-ergodic many-body localized (MBL) regime expected at strong disorder. In this work, we revisit this paradigmatic model by studying the statistics of rare atypical events of strongly correlated spin pairs traversing the entire system. They occur for unexpectedly strong disorder, i.e., in a regime where standard estimates fail to detect any instability. We then identify these very peculiar high-energy eigenstates, which exhibit system-wide $\mathcal{O}\left(1\right)$ correlations, as nearly degenerate pairs of resonant cat states of the form ${|\mathrm{\Phi }\rangle }_{\pm }\sim |{\alpha }_1\rangle \pm |{\alpha }_2\rangle$, where $|{\alpha }_1\rangle$ and $|{\alpha }_2\rangle$ are spin basis states. We propose a simple and generic analytical description of this class of eigenstates that exhibit system-spanning entanglement. This analytical ansatz guides us in our search for rare hidden cat states in exponentially large many-body spectra. This also enables a systematic numerical inspection of the microscopic anatomy of these unconventional pairs, which appear in a wide range of disorder strengths. In the light of recent studies and ongoing debates on the MBL problem, our results offer perspectives and stimulating challenges to this very active field.

We report a study of de Haas-van Alphen oscillations in high-quality single crystals of cubic $\beta \text{−}{\mathrm{PtBi}}_2$. In combination with density functional theory calculations, we identify quantum oscillations associated with all Fermi surface sheets predicted by theory. Our results uncover three small electron pockets centered on a sixfold band-touching point located approximately 25 meV below the Fermi level at the $R$ point of the Brillouin zone. These findings firmly establish the presence of sixfold fermions in close proximity to the Fermi energy of $\beta \text{−}{\mathrm{PtBi}}_2$.

With the increasing miniaturization of electronic components and the need to optimize thermal management, it has become essential to understand heat transport at metal-semiconductor interfaces. While it has been recognized decades ago that an electron-phonon channel may take place at metal-semiconductor interfaces, its existence is still controversial. Here we investigate thermal transport at metal-silicon interfaces using the combination of first-principles calculations and nonequilibrium Green's function (NEGF). We explain how to correct NEGF formalism to account for the out-of-equilibrium nature of the energy carriers in the vicinity of the interface. The relative corrections to the equilibrium distribution are shown to arise from the spectral mean free paths of silicon and may reach $15\%$. Applying these corrections, we compare the predictions of NEGF to available experimental data for Au-Si, Pt-Si, and Al-Si interfaces. Based on this comparison, we infer the value of the electron-phonon interfacial thermal conductance by employing the two-temperature model. We find that interfacial thermal transport at Au-Si interfaces is mainly driven by phonon-phonon processes, and that electron-phonon processes play a negligible role in this case. By contrast, for Al-Si interfaces, we show that phonon-phonon scattering alone cannot explain the experimental values reported so far, and we estimate that the electron-phonon interfacial conductance accounts for one third of the total conductance. This work demonstrates the importance of the electron-phonon conductance at metal-silicon interfaces and calls for systematic experimental investigation of thermal transport at these interfaces at low temperatures. It paves the way for an accurate model to predict the conductance associated to the interfacial electron-phonon channel.

The breakdown of the quasiparticle approximation (QPA) for phonons in strongly anharmonic materials necessitates advanced first-principles frameworks for accurate lattice dynamics and thermal transport predictions. We develop a comprehensive beyond-quasiparticle approximation (BQPA) approach incorporating both three- (3ph) and four-phonon (4ph) interactions and apply it to investigate lattice thermal conductivity $\left({\kappa }_{\mathrm{L}}\right)$ in MgO, PbTe, and AgCl – materials that span a broad spectrum of anharmonicity, from weak to severe anharmonic regimes with overdamped phonons. We reveal that while BQPA consistently increases ${\kappa }_{\mathrm{L}}$ relative to QPA due to phonon softening when considering only 3ph interactions, the inclusion of additional 4ph interactions hardens the phonon spectrum and suppresses this enhancement, bringing BQPA and QPA predictions into close agreement via subtle spectral competition effects across all three compounds. These findings highlight that accurate modeling of ${\kappa }_{\mathrm{L}}$ in strongly anharmonic materials requires treating both full phonon spectral function and higher-order anharmonicity on equal footing. Our work establishes a systematic framework for modeling thermal transport in systems with overdamped phonons and provides critical insights for materials design beyond the limits of conventional phonon transport theory.

Two-dimensional honeycomb lattices, characterized by their low coordination numbers, provide a fertile platform for exploring various quantum phenomena due to the intricate interplay between competing magnetic interactions, spin-orbit coupling, and crystal electric fields. Beyond the widely studied $J_{\mathrm{eff}}=1/2$ honeycomb systems, $S=3/2$ honeycomb lattices offer a promising alternative route for exploring spin-$S$ Kitaev models and the effects of bond disorder. Herein, we present crystal structure, thermodynamic, neutron diffraction, and muon spin relaxation ($\mu \mathrm{SR}$) measurements, complemented by density functional theory (DFT) calculations on an unexplored $3d$ transition-metal-based compound ${\mathrm{Co}}_2{\mathrm{Te}}_3{\mathrm{O}}_8$, where ${\mathrm{Co}}^{2+}$ ($S=3/2$) ions form a distorted honeycomb lattice in the crystallographic $bc$ plane without any antisite disorder between constituent atoms. A clear $\lambda$-type anomaly around $T_{\mathrm{N}}\approx 55\mathrm{K}$ in both magnetic susceptibility and specific heat data indicates the onset of a long-range ordered state below 55 K. The dominant antiferromagnetic interaction between $S=3/2$ moments is evidenced by a relatively large negative Curie-Weiss temperature (${\theta }_{\mathrm{CW}}=-103\mathrm{K}$) derived from magnetic susceptibility data and supported by DFT calculations. The signature of long-range antiferomagnetic order state in the thermodynamic data is corroborated by neutron diffraction and $\mu \mathrm{SR}$ results. Furthermore, $\mu \mathrm{SR}$ experiments reveal the coexistence of static and dynamic local magnetic fields below $T_{\mathrm{N}}$, along with a complex magnetic structure that can be associated with $\mathit{XY}$-like antiferromagnet, as confirmed by neutron diffraction experiments.

In this work, we investigate the control of quantum vacuum friction (QVF) experienced by a rotating nanosphere near a graphene sheet. Our study reveals that the friction torque of QVF acting on nanospheres can be tuned by one to two orders of magnitude through an applied magnetic field. This modulation arises from the tunable coupling between the magnetoplasmon polaritons (MPPs) of graphene and the localized surface phonon polaritons (LSPhPs) of nanospheres. Moreover, a dissipationless friction known as the axial Casimir force (ACF), is also investigated. At a low temperature, the ACF of nanospheres exhibits a quantized staircase behavior as a function the chemical potentials and magnetic fields. At room temperature, the quantization disappears, while the ACF increases by approximately five orders of magnitude. Our study of magnetic control of QVF may find applications in particle manipulations.

The pyrochlore lattice materials can exhibit geometrical frustration, while the related many-body electronic states remain elusive. In this work, we performed scanning tunneling microscopy measurements on the pyrochlore superconductor $\mathrm{Cs}{\mathrm{Bi}}_2$ and spin liquid $\mathrm{P}{\mathrm{r}}_2\mathrm{I}{\mathrm{r}}_2{\mathrm{O}}_7$ at 0.3 K. For the first time, we obtained atomically resolved images of their (111) surfaces, revealing a hexagonal lattice or a kagome lattice. Tunneling spectroscopy in $\mathrm{Cs}{\mathrm{Bi}}_2$ reveals a nearly fully opened superconductivity gap. The ratio of $2\mathrm{\Delta }/k_B{T}_{\mathrm{C}}=4.7$ suggests relatively strong coupling superconductivity, as compared with that in kagome superconductors $A{\mathrm{V}}_3\mathrm{S}{\mathrm{b}}_5$ $(A=\mathrm{K},\mathrm{Rb},\mathrm{Cs})$. In contrast to the previous study categorizing $\mathrm{Cs}{\mathrm{Bi}}_2$ as a type-I superconductor, the applied magnetic field induces a hexagonal vortex lattice in which each vortex core exhibits an intriguing threefold symmetry state. In $\mathrm{P}{\mathrm{r}}_2\mathrm{I}{\mathrm{r}}_2{\mathrm{O}}_7$, we observed a spatially homogeneous Kondo-lattice resonance, which is compared with that in the kagome Kondo-lattice material $\mathrm{Cs}{\mathrm{Cr}}_6\mathrm{S}{\mathrm{b}}_6$. We further discover that the Kondo resonance exhibits a spatial modulation with threefold symmetry, and the applied magnetic field induces a Zeeman splitting of the Kondo resonance with intriguing atomic site dependence. We discuss the relations of these many-body electronic phenomena with the pyrochlore lattice geometry and its charge or spin frustration. Our systematic observations offer atomic-scale insights into the many-body electronic structures of the geometrically frustrated pyrochlore superconductors and spin liquids.

We develop a perturbative renormalization group (RG) theory for the topological heavy fermion (THF) model, describing magic-angle twisted bilayer graphene (MATBG) as an emergent Anderson lattice. Our theory focuses on an energy window where the interactions can be treated perturbatively within the THF model, providing insights into the low-energy physics. In particular, the realistic parameters place MATBG near an intermediate regime where the Hubbard interaction $U$ and the hybridization energy $\gamma$ are comparable, motivating the need for RG analysis. Our approach analytically tracks the flow of single-particle parameters and Coulomb interactions within an energy window below $0.1\mathrm{eV}$, providing implications for distinguishing between Kondo-like ($U\gg \gamma$) and projected-limit/Mott-semimetal ($U\ll \gamma$) scenarios at low energies. We show that the RG flows generically lower the ratio $U/\gamma$ and drive MATBG toward the chiral limit, consistent with the previous numerical study based on the Bistritzer-MacDonald model. The framework presented here also applies to other moiré systems and stoichiometric materials that admit a THF description, including magic-angle twisted trilayer graphene, twisted checkerboard model, and Lieb lattice, among others, providing a foundation for developing low-energy effective theories relevant to a broad class of topological flat-band materials.

We investigate the zero-temperature properties of a mobile impurity immersed in a bath of bosonic particles confined to a square lattice. We analyze the regimes of attractive and repulsive coupling between the impurity and the bath particles for different strengths of boson-boson interactions in the bath, using exact large-scale quantum Monte Carlo simulations in the grand canonical ensemble. For weak coupling, the polaron mass ratio is found to decrease around the Mott insulator (MI) to superfluid (SF) transition of the bath, as predicted by recent theory, confirming the possible use of the impurity as a probe for the transition. For strong coupling in the MI regime, instead, the impurity is found to modify the bath density by binding to an extra bath particle or a hole, depending on the sign of the polaron-bath interactions. While the binding prevents the aforementioned use of the polaron mass ratio as an MI-SF transition probe, we show that it can be used instead as a probe of the binding itself. Our exact numerical results provide a benchmark for comparing lattice Bose polaron theories and are relevant for experiments with cold atoms trapped in optical lattices, where the presence of a confining harmonic potential can be modeled by a slowly varying local chemical potential.

Disordered two-dimensional (2D) lattices, including hexatic and various glassy states, are observed in a wide range of 2D systems including colloidal nanoparticle assemblies and fluxon lattices. Their disordered nature determines the stability and mobility of these systems, as well as their response to the external stimuli. Here we report on the controlled creation and characterization of a disordered 2D lattice of nontopological magnetic bubbles in the noncentrosymmetric ferrimagnetic alloy ${\mathrm{Mn}}_{1.4}\mathrm{PtSn}$. By analyzing the type and frequency of fundamental lattice defects, such as dislocations, the orientational correlation, as well as the induced motion of the lattice in an external field, a nonergodic glassy state, stabilized by directional application of an external field, is revealed.

We compute the (0-11) surface spectral function, the surface density of states (DOS), and the quasiparticle interference (QPI) patterns, both in the normal state and superconducting state of ${\mathrm{UTe}}_2$. We consider all possible nonchiral and chiral order parameters (OPs) that could, in principle, describe the superconductivity in this compound. We describe the formation of surface states whose maximum intensity energy depends on the nature of the pairing. We also study the QPI patterns resulting from the scattering of these surface states. Along the lines of [Nat. Phys. 21, 1555 (2025)], we show that the main feature distinguishing between various OPs is a QPI peak that is only observed experimentally in the superconducting state. The energy dispersion and the stability of this peak is consistent among the nonchiral OPs only with a $B_{3u}$ pairing. Moreover, $B_{3u}$ is the only nonchiral pairing that shows a peak at zero energy in the DOS, consistent with the experimental observations.

In the era of noisy, intermediate-scale quantum devices, the efficient preparation of many-body resource states is a task of paramount importance. In this paper we focus on the deterministic preparation of matrix product states (MPS) in constant depth by utilizing measurements and classical communication to fuse smaller states into larger ones. We place strong constraints on the MPS that can be prepared using this method, which we refer to as MPS fusion. Namely, we establish that it is necessary for the MPS to have a flat entanglement spectrum. Using the recently introduced split-index MPS (SIMPS) representation, we then introduce a family of states that belong to interesting phases of matter protected by non-onsite symmetries, including anomalous and noninvertible symmetries, and also serve as resources for long-range quantum teleportation, but which lie beyond the scope of ordinary MPS fusion. It is shown constructively that these states can be prepared in constant depth using a broader class of measurement-assisted protocols, which we dub SIMPS fusion. Even in cases when MPS fusion is possible, using SIMPS fusion can give rise to significantly reduced resource overhead. We also discuss constraints on SIMPS fusion and propose a general framework for fusion that encompasses the MPS and SIMPS protocols. Our results therefore simultaneously establish the boundaries of conventional MPS fusion and push the envelope of which states can be prepared using measurement-assisted protocols.

Depending on the coupling to the environment, symmetries of open quantum systems manifest in two distinct forms, the strong and the weak. We study spontaneous symmetry breaking among phases with strong symmetry, weak symmetry, and no symmetry. Concrete Liouvillian models with strong and weak symmetry are constructed, and different scenarios of symmetry-breaking transitions are investigated from complementary approaches. It is demonstrated that strong symmetry always spontaneously breaks, either completely or into the corresponding weak symmetry. For strong $U\left(1\right)$ symmetry, we show that strong-to-weak symmetry breaking leads to gapless Goldstone modes dictating diffusion of the symmetry charge in translationally invariant systems. We conjecture that this relation among strong-to-weak symmetry breaking, gapless modes, and symmetry-charge diffusion is general for continuous symmetries. It can be interpreted as an ingapability condition for Lindbladian with strong $U\left(1\right)$ symmetry and weak translation symmetry, according to which the gapless spectrum does not require noninteger filling. We also investigate the scenario where the strong symmetry breaks completely. In the symmetry-broken phase, we identify an effective Keldysh action with two Goldstone modes, describing fluctuations of the order parameter and diffusive hydrodynamics of the symmetry charge, respectively. We show that weak $U\left(1\right)$ SSB naturally leads to time crystalline order. Additionally, it is found that in the presence of strong symmetry, the spontaneous breaking of weak symmetry can depend on the symmetry sector. For the particular model studied here, we uncover a transition from a symmetric phase with a Bose surface to a symmetry-broken phase with long-range order induced by tuning the filling. It is also shown that in both weak and strong symmetry cases, the long-range order of $U\left(1\right)$ symmetry breaking is possible in spatial dimension $d\ge 3$. Our work outlines the typical scenarios of spontaneous symmetry breaking in open quantum systems, puts forward a theoretical framework to characterize them, and highlights their physical consequences.

The recent introduction of superlattice potentials has opened new avenues for engineering tunable electronic band structures featuring topologically nontrivial moiré-like bands. Here we consider the optoelectronic properties of Bernal-stacked graphene subjected to a superlattice potential, which is introduced either electrostatically or through lattice twisting, to show that it exhibits a giant shift-current response that is orders of magnitude larger than existing predictions in twisted multilayer systems. Effects of a gate voltage and the strength and phase of the superlattice potential on the shift current are delineated systematically across various topological regimes. Our study gives insight into the nature of nonlinear responses of materials and how these responses could be optimized by tuning the superlattice potential.

A fundamental characteristic of non-Hermitian quantum systems is the nonunitary time evolution under a Euclidean inner product. Until now, a consensus on the mathematical formulation for the dynamics of non-Hermitian quantum systems has been lacking. Here, we focus on the quantum metric framework, in which the state normalization is preserved through a fundamental redefinition of the inner product of the Hilbert space. We generalize this framework to the $\mathcal{PT}$-broken region and provide a method to construct the metric operator of a general two-band non-Hermitian model. Then we redefine the Loschmidt echo and investigate the nonadiabatic dynamics in non-Hermitian quantum systems. Taking the $\mathcal{PT}$-symmetric staggered tight-binding chain model as an example, we demonstrate that the long-time average of the rate function can be used to characterize the $\mathcal{PT}$ phase transitions. In the non-Hermitian SSH model, we investigate the dynamical quantum phase transitions (DQPTs) and show that this framework can remove the accidental DQPTs and thus build a bridge between DQPTs and equilibrium topological phase transitions.

Ground-state auxiliary-field quantum Monte Carlo (AFQMC) methods have become key numerical tools for studying quantum phases and phase transitions in interacting many-fermion systems. Despite the broad applicability, the efficiency of these algorithms is often limited by the bottleneck associated with the local update of the field configuration. In this work, we propose two update schemes, the delayed update and block force-bias update, both of which can generally and efficiently accelerate ground-state AFQMC simulations. The delayed update, with a predetermined delay rank, is an elegantly improved version of the local update, accelerating the process by replacing multiple vector-vector outer products in the latter with a single matrix-matrix multiplication. The block force-bias update is a block variant of the conventional force-bias update, which is a highly efficient scheme for dilute systems but suffers from the low acceptance ratio in lattice models. Our modified scheme maintains the high efficiency while offering flexible tuning of the acceptance ratio, controlled by the block size, for any desired fermion filling. We apply these two update schemes to both the standard and spin-orbit coupled two-dimensional Hubbard models, demonstrating their speedup over the local update with respect to the delay rank and block size. We also explore their efficiencies across varying system sizes and model parameters. Our results identify a speedup of $\sim 8$ for systems with 1600 lattice sites. Furthermore, we have investigated the broader applications as well as an application diagram of these update schemes to general correlated fermion systems.

We present a real-frequency third-order strong-coupling impurity solver which employs quantics tensor cross interpolation (QTCI) for an efficient evaluation of the diagram weights. Applying the method to dynamical mean-field theory (DMFT) calculations of the single-band Hubbard model on the Bethe lattice, we clarify the interaction and temperature range in which the third-order approach yields accurate results. Since the calculations are implemented on the real-time/frequency axis, the detailed structure of spectral functions can be obtained without analytical continuation, as we demonstrate with examples for paramagnetic, antiferromagnetic, and photodoped states. Our work establishes a viable path toward high-order, real-frequency impurity solvers for both equilibrium and nonequilibrium DMFT studies.

We calculate the spin correlations that result from the motion of a single dopant in the hard-core Fermi-Hubbard model, as the geometry evolves from a square to a triangular lattice. In particular, we consider the square lattice with an additional hopping along one diagonal, whose strength is continuously varied. We use a high-temperature expansion which expresses the partition function as a sum over closed paths taken by the dopant. We sample thousands of diagrams in the space of closed paths using the quantum Monte Carlo approach of Raghavan and Elser [Phys. Rev. Lett. 75, 4083 (1995)], which is free of finite-size effects and allows us to simulate temperatures as low as $T\sim 0.3\left|t\right|$, even in cases where there is a sign problem. For the case of a hole dopant, we find a crossover from kinetic ferromagnetism to kinetic antiferromagnetism as the geometry is tuned from square to triangular, which can be observed in current quantum gas microscopes.