Papers

The ground state phase diagram of the Shastry-Sutherland model remains controversial. In particular, the nature of the transition between the plaquette valence bond solid (PVBS) phase and the Néel antiferromagnetic (AFM) phase is still under debate. While some studies suggest a direct transition between the two phases, others propose the existence of a narrow intermediate quantum spin liquid regime. To address this issue, we perform large-scale Density Matrix Renormalization Group calculations to determine the Néel AFM phase boundary in the Shastry-Sutherland model. By applying staggered boundary pinning fields and directly measuring the bulk staggered magnetization, and through systematic extrapolations with respect to truncation error as well as careful finite-size scaling, we find that the staggered magnetization remains finite across the controversial region $0.78 \lesssim J_{1}/J_{2} \leq 0.81$, which was suggested to host a quantum spin liquid phase in some studies. Together with the previously established consensus placing the PVBS phase boundary at $J_{1}/J_{2} \approx 0.78$, these results provide evidence against the existence of an intermediate quantum spin liquid phase and support a direct PVBS–Néel AFM transition in the Shastry-Sutherland model.

Since the discovery of charge density wave (CDW) and superconductivity, kagome metal AV3Sb5 (A = K, Rb, Cs) provides a new platform for exploring novel many-body quantum phenomena. In CsV3Sb5, a stripe-like CDW with commensurate wave vector q = 3/8 was observed under moderate pressures, which leads to a peculiar superconducting double-dome behavior in pressure-dependent phase diagram. Previous density functional theory (DFT) calculations indicate that the pressure-induced stripe-like CDW is beyond conventional phonon softening scenario, suggesting a nontrivial role of electronic correlations. However, an in-depth understanding for the pressure-induced unconventional CDW remains elusive. Here, we performed pressure-dependent 51V nuclear magnetic resonance (NMR) measurements on KV3Sb5 and RbV3Sb5. Although the superconducting double-dome behavior is absent in pressurized KV3Sb5 and RbV3Sb5, a pressure-induced CDW phase, ascribed to a possible incommensurate triple-Q CDW, is identified by NMR spectra in both materials, indicating that the pressure-induced unconventional CDW beyond DFT calculations is a common feature for kagome metal AV3Sb5. In contrast to the stripe-like CDW, the pressure-induced incommensurate triple-Q CDW does not strongly suppress the superconducting temperature (Tc) but coincide with an almost plateau behavior at intermediate pressure regime in the pressure-dependent superconducting phase diagram. Furthermore, by systematically analyzing the Korringa relation between Knight shift and nuclear spin-lattice relaxation rate in AV3Sb5, van Hove singularities (vHSs) driven electronic fluctuations are revealed as an effective knob for the pressure-induced unconventional CDW. Finally, our present findings underscore the pressure-induced unconventional CDW as a novel correlated quantum state in kagome metal AV3Sb5.

Building on the recently developed tensor-backflow method, which accurately describes energies and stripe states in the Fermi-Hubbard model, we investigate $d$-wave pairing in the two-dimensional $t$-$t'$-$U$ Hubbard model. For the $8\times8$ lattice, we improve the wave function using symmetry projections followed by one Lanczos step, whereas for the $12\times 12$ and $16\times 16$ lattices, we apply one Lanczos step without symmetry projection. We focus primarily on the parameter regime with filling $n=0.875$, on-site repulsion $U=8$ and next-nearest-neighbor hopping $t'=-0.2t$, a regime in which enhanced $d$-wave pairing has been reported. The resulting energies are competitive with those obtained using state-of-the-art neural quantum states. For example, on a $16\times 16$ lattice with periodic boundary conditions, the tensor-backflow wave function after one Lanczos step without explicit symmetry enforcement achieves a relative energy difference of $4.4\times 10^{-3}$ from the symmetry-preserving neural quantum state result. From the real space pair correlations, for $t'=-0.2t$, we observe stronger $d$-wave pair correlations together with the characteristic relative sign between horizontal and vertical bond-pair components. Compared with $t'=0$, finite negative $t'$ increases the spectral weight of the corresponding pair-density matrix, which indicates the enhanced overall $d$-wave pair fluctuations. The leading eigenvalue is enhanced on the $8\times8$ lattice for both with and without symmetry projections. For larger lattices such as $12\times 12$ and $16\times 16$, the leading pair-density matrix spectral weight is distributed among several nearly degenerate eigenmodes rather than being concentrated in a single dominant mode. This indicates enhanced and more broadly distributed $d$-wave pair fluctuations, but no single eigenvalue exhibits the extensive scaling required for ODLRO.

We investigated antiferromagnetic metal TbCuAs$_2$, which exhibits an anomalous resistivity upturn at low temperatures. This resistivity upturn has been proposed to originate from the material's magnetic ground state; however, the precise nature of the antiferromagnetic ordering in this compound has not been previously established. Here, we present a combined single crystal neutron diffraction, X-ray resonant magnetic scattering, and single crystal X-ray diffraction study of TbCuAs$_2$. These measurements unambiguously determine the Tb magnetic moment direction, the antiferromagnetic arrangement along high symmetry directions, the interplay between structure and magnetism, and their temperature dependence. Our observations are compared with previous studies on sister compounds in the rare-earth copper arsenide family ($R$CuAs$_2$, $R$ = Sm and Gd), which also displays resistivity anomalies. We suggest a common underlying physics governing the structural and magentic properties of rare-earth copper arsenides that exhibit low-temperature resistivity anomalies.

Determining the microscopic Hamiltonian of a quantum magnet from inelastic neutron scattering measurements remains a central challenge in condensed matter physics. While the dynamical spin structure factor contains, in principle, sufficient information about the underlying interactions, extracting Hamiltonian parameters from experimental spectra constitutes a highly nontrivial inverse problem due to the large parameter space and the presence of experimental noise. Here we demonstrate that neural networks can efficiently solve this inverse problem for a broad class of quantum magnets. As a benchmark, we consider an eight-parameter family of honeycomb lattice Heisenberg spin models in the fully polarized phase, where the dynamical spin structure factor can be computed exactly within linear spin-wave theory. Using a large synthetic dataset of neutron scattering spectra, we train neural networks to infer the underlying Hamiltonian parameters directly from the dynamical response. We compare the performance of three different architectures—fully connected neural networks (FCNNs), one-dimensional convolutional neural networks (CNN1Ds), and two-dimensional convolutional neural networks (CNN2Ds)—and find that all achieve high predictive accuracy. Remarkably, the trained models remain robust in the presence of substantial experimental uncertainty, reliably recovering the Hamiltonian parameters even when the input spectra are contaminated by random noise with amplitudes reaching $10\%$ of the signal intensity. Our results establish machine learning as a powerful framework for quantitative Hamiltonian reconstruction from neutron scattering data and provide a practical route toward automated characterization of quantum magnetic materials.

Matrix elements of simple operators are central to thermalization in chaotic quantum many-body systems. Their moments are often described statistically through the Eigenstate Thermalization Hypothesis. In this paper, we study a more refined characterization of these matrix elements: the eigenspectrum of simple operators once projected to microcanonical energy windows. The spectrum encodes all moments of the matrix elements at once, and is particularly relevant when the spectrum of the Hamiltonian is degenerate. Assuming that the eigenbasis of the simple operator is Haar-randomly oriented with respect to that of the Hamiltonian, we prove that the spectrum of an operator projected to a small microcanonical window obeys Gaussian random matrix statistics. We do this directly by studying the probability distribution inherited from the random orientation, as well as using tools from Free Probability Theory. We discuss the implications for BPS chaos and more generally for eigenstate thermalization.

The many-body bootstrap certifies ground-state properties by minimizing energy over correlators constrained only by positivity, without any variational wavefunction. Its cost, however, grows exponentially with the size of the operators involved, placing the long-range string correlators that diagnose topological phases out of reach. We overcome this by treating string operators as primary objects: bare and endpoint-dressed strings satisfy a closed operator algebra with one another and with local words, yielding a semidefinite program whose cost grows only polynomially with string length. A single computation then yields estimates of string correlators of all lengths. Rigorous two-sided bounds are obtained for each target string once the ground-state energy is pinned within a window. When benchmarked against density-matrix renormalization group computations on the cluster Ising and spin$-1$ Heisenberg chains, the method certifies the nonlocal string order of the cluster and Haldane phases directly from the Hamiltonian. Our rigorous certification of string order parameters reveal that the sharpness of the bounds is set by which operators enter the calculation, not by their length alone. By exploiting algebraic closure of strings and local words, our framework lifts spatially extended observables into polynomially tractable bootstrap variables, opening up a route to wavefunction-free certification of nonlocal order in quantum many-body systems.

We investigate the Raman response of sodium-doped cuprate oxychloride Na$\_x$Ca$\_{2-x}$CuO$\_2$Cl$\_2$ high-temperature superconductors across their entire phase diagram, from the antiferromagnetic to the superconducting region. In addition to the expected Raman-active phonon modes, we detect several additional modes that can be interpreted as being excited via a resonance process enabled by strong electron–phonon coupling. To verify the resonance effect, the Raman response at different incident photon energies was measured. At high energies, there is a well-defined $B\_{1g}$ mode in the antiferromagnetic phase, which can be interpreted as a bimagnon We follow its temperature and doping dependence, providing information on the multimagnon excitation in these cuprates, which can be theoretically linked to the exchange interaction.

Motivated by experimental studies on cuprate-manganite heterostructures, we study a correlated bilayer Hubbard model subject to a local interfacial exchange field using cluster dynamical mean-field theory in the underdoped cuprate regime. We find that superconductivity coexists with a manganite-induced Cu spin polarization. Remarkably, throughout this coexistence regime, the superconducting solution carries a larger magnetic moment than the corresponding constrained normal state. Analysis of the magnetic response shows that this reversal is driven by correlations, which enhance magnetism already in the normal state and even more strongly in the superconducting solution. At stronger exchange fields, superconductivity collapses abruptly, displaying hysteresis consistent with a first-order transition, and a strongly spin-polarized pseudogap emerges. These results show that, under strong electronic correlations, superconductivity can enhance rather than suppress interfacial magnetism.

We introduce the Unified Field Bosonization Technique (UFBT), a direct bosonization framework for strongly inhomogeneous one-dimensional Luttinger liquids (LLs) containing static impurities. UFBT incorporates impurity scattering through a symmetrized combination of bosonic phase fields and yields closed-form expressions for arbitrary N-point correlation functions for a broad class of static impurity potentials, including delta barriers, finite barriers and finite wells. The formalism requires neither renormalization-group analysis nor perturbative expansions, providing an analytical description of the inhomogeneous system at the bosonized level. The resulting correlation functions capture the leading singular contributions relevant to the present analysis. The technique is validated by recovering known limiting cases, showing agreement with the first-order perturbative expansion in the interaction strength, and demonstrating consistency with the Schwinger-Dyson equations. A key result is that the correlation function exponents remain independent of the impurity strength, while the impurity dependence is captured by the spatial structure and amplitudes of the correlation functions. The resulting correlation functions establish a foundation for analytical studies of transport, Friedel oscillations, and the local and dynamical density of states in strongly inhomogeneous Luttinger liquids.

Neutron diffraction is a versatile experimental technique capable of probing a material's magnetic properties. While diffraction is typically used to determine the magnetic structure of a material, magnetic diffuse scattering data from a diffraction experiment are also sensitive to the magnetic interactions in its Hamiltonian. However, accurately determining magnetic interaction parameters from neutron-scattering data involves an inverse scattering problem that is challenging to solve in general. Here, we investigate the effectiveness of a machine learning approach to predict the interaction parameters given magnetic diffuse-scattering data measured on powder samples, for a comprehensive survey of isotropic interactions on eight high-symmetry lattices. Across all lattices we considered, the machine-learning approach estimates the interaction parameters with high (~2%) accuracy, while avoiding the issue of false minima that is encountered with non-linear least squares refinement. Our results highlight that powder diffuse-scattering data can provide a compact "fingerprint" of the magnetic interactions for many materials.

The orbital character of the so-called $A$-pocket in infinite-layer nickelates remains under debate. We investigate bulk NdNiO$_2$ using density-functional theory combined with dynamical mean-field theory and identify the $A$-pocket as a strongly hybridized state with substantial interstitial-$s$, Nd-$d_{xy}$ and Ni-d_${xz/yz}$ contributions. Our angle-resolved photoemission spectroscopy simulations reproduce the main polarization-dependent features measured experimentally. Removing the interstitial-$s$ matrix element leads to a clear disagreement with the measured Fermi surface maps, even though the interstitial-$s$ contribution is not dominant. Suppressing instead the Nd-d$_{xy}$ or Ni-$_{dxz/yz}$ matrix elements leaves the maps almost unchanged, because these are small at the zone corner. More generally, our results demonstrate that assigning the microscopic origin of spectral features in infinite-layer nickelates requires treating orbital hybridizations and photoemission matrix elements together.

Pfaffian quantum Monte Carlo extends auxiliary field methods to anomalous fermionic Hamiltonians, opening access to pairing systems and Hubbard–Stratonovich decompositions that are unavailable in determinant formulations. We show that this flexibility can be combined with the global updates of Hybrid Monte Carlo (HMC), leading to an algorithm scaling as $\mathcal{O}(N_\tau L^3)$, similar to its determinant quantum Monte Carlo (DQMC) counterpart without pseudofermions. The central observation is that the molecular dynamics force depends only on the magnitude of the Pfaffian weight, which admits a determinant representation and leads to a simplified force expression. This construction also yields unequal-time Majorana correlators at essentially no additional cost. We demonstrate the method for the interacting Kitaev chain using the imaginary and symmetric Majorana hopping channel. The resulting noncommuting auxiliary-field bond operators are treated through an even-odd decomposition. Their block structure permits an analytic reduction to a sparse effective interaction matrix of bandwidth two and allows explicit force expressions. Results agree with exact diagonalization and resolve low-energy modes localized at opposite boundaries, together with their increasing overlap near the topological transition of the non-interacting system. These findings establish HMC as an efficient sampling framework for Pfaffian auxiliary-field simulations.

In ultrafast spin dynamics additional modes in the THz range appear which cannot be captured by conventional Landau-Lifshitz equations. Extending these equations by further time derivatives (inertial Landau-Lifshitz-Gilbert equation) solves the issue only partly. Here we suggest to explain these modes by retarded Lindbladian relaxation. In spite of the simplicity of this phenomenological approach the agreement with the experimental data is promising: physically plausible parameters describe the position and the large width of these resonances. The salient feature of several almost equidistant resonance peaks is in-line with experimental evidence as well.

We investigate Floquet–spin-orbit compensation in the three-band $\alpha$-$T_3$ system, which interpolates between graphene at $\alpha=0$ and the dice lattice at $\alpha=1$. By tuning the interplay between an off-resonant circularly polarized optical field and intrinsic spin–orbit coupling, we identify three distinct pairwise band-degeneracy conditions in the quasienergy spectrum: (i) valley–spin degeneracy, (ii) spin–band degeneracy, and (iii) flat–dispersive band degeneracy. The flat band is not an artifact of a two-band reduction but rather an exact property of the continuum Hamiltonian at this compensation point, where the complete three-band Hamiltonian supports a momentum-independent dark state. A winding-two low-energy Hamiltonian and a finite-momentum Berry-curvature maximum, whose radius scales as the square root of the detuning, emerge from detuning this contact. We further show that the intrinsic transverse thermoelectric response encodes these spectrum patterns. The flat- and quadratic-band degeneracy can be predicted for $0<\alpha<1/2$ because the two response scales linked to the linear contacts have a monotonic ratio independent of the common spin–orbit energy scale. This allows an inverse determination of $\alpha$ and of the common spectral scale. The analytical results are confirmed by full three-band Kubo calculations, which also define the regime in which this inverse characterization is still observable. These results connect an experimentally accessible, Berry-curvature-sensitive thermoelectric response to tunable Floquet–spin–orbit band geometry.

Recent work has constructed Abelian Chern-Simons theories as categorical TQFTs, allowing us to naturally incorporate categorical defects and construct defect extensions of Abelian Chern-Simons TQFTs. We first identify the Turaev-Viro realizations of Abelian Chern-Simons theory in the center and doubled pointed modular cases, clarifying the distinction between single bulk realizations and canonical doubled ones. Then we obtain Turaev-Viro partition functions in terms of Reidemeister-torsion densities. Alternatively, the Alterfold construction supplies the associated topological boundaries, domain walls, and condensation sectors, establishing an explicit Alterfold/Chern-Simons dictionary. We show that the finite quadratic module is the invariant controlling the bulk theory, its topological symmetries, orientation-reversal invariance, and defects. We further show that multicomponent Abelian BF theory arises as the extended TQFT of an off-diagonal Abelian Chern-Simons theory, placing it naturally within the same extended framework. Finally, we demonstrate that recently proposed Abelian Chern-Simons dualities do not define a genuine TQFT duality. These results provide a concrete model for defects in Abelian topological orders and suggest a route toward the non-Abelian case.

Matrix product operator (MPO) serves as a fundamental component in tensor network simulations of quantum many-body dynamics. We employ an MPO construction that introduces additional propagation channels to embed both periodic boundary conditions and finite-range couplings directly into an open boundary MPO. We apply this construction within the time-dependent variational principle (TDVP) framework to simulate quench dynamics in a spin-1/2 chain with finite-range interactions, and benchmark the results numerically against the fourth-order Runge-Kutta method, finding excellent agreement for both single-body and two-body observables. The approach offers a practical route for tensor network simulations of many-body dynamics in periodic finite-range systems.

Engineering emergent ferromagnetism at correlated-oxide interfaces offers a powerful route to creating collective states that do not exist in the parent materials. Here, we show that interfacial valence reconstruction in NdNiO$_3$/CaMnO$_3$ superlattices generates dual-sublattice ferromagnetism involving both Mn and Ni. Depth-resolved standing-wave X-ray photoelectron spectroscopy reveals enhanced Mn$^{3+}$ character on the CaMnO$_3$ side of the interface and enhanced Ni$^{2+}$ character on the NdNiO$_3$ side, establishing the configurations required for Mn$^{4+}$-O-Mn$^{3+}$ double exchange and Ni$^{2+}$-O-Mn$^{4+}$ superexchange, respectively. At low temperature, element-specific XMCD reveals ferromagnetic responses from both sublattices, with the Ni response concentrated predominantly in the Ni$^{2+}$-derived spectral component that SW-XPS independently shows to be enhanced at the interface. Together, these results show that cooperative double exchange within CaMnO$_3$ and superexchange across the interface couple the Mn and Ni sublattices, providing a general strategy for engineering interfacial ferromagnetism in correlated oxides.

For “ideal anyons,” the Berry phase associated with a closed loop of an anyon around another is robust, i.e., independent of the size and shape of the loop, and directly yields the braid statistics. This is not the case for fractional quantum Hall (FQH) quasiparticles (QPs), which are charged and have finite size. The Berry phase $\Theta$ associated with a loop of a fractionally charged QP around another contains two contributions: $\Theta=\Theta_{\rm AB}+\Theta_{\rm braid}$, where $\Theta_{\rm AB}$, the Aharonov-Bohm phase, is proportional to the enclosed area, and $\Theta_{\rm braid}$ is the order-one contribution from braid statistics. The latter is obtained by determining $\Theta$ for a closed loop twice, once with and once without the other QP inside, and taking the difference. It is known that even small uncertainties in the enclosed areas can produce corrections to $\Theta_{\rm AB}$ larger than $\Theta_{\rm braid}$. We consider how the Berry phase depends on the shape of the QP, which, unlike its charge, is not topological and varies along the path in response to the local potential. Our calculations show that practically imperceptible differences in the shape of the outer QP in the two experiments can produce a non-universal value for the braid statistics, revealing an additional challenge for a precise determination of the braid statistics. We discuss these results in the context of interference experiments. We also note that the fractional phase jumps in these experiments can be understood without assuming QPs with sharply quantized fractional charges at the edges of the FQH system; instead, they directly measure the fractionally quantized vorticity of bulk QPs.

We identify a mechanism in which soft nonunitary fluctuations of the pair condensate can suppress phase coherence in a two-dimensional Rashba superconductor proximate to easy-plane ferromagnetic order. This spin polarization couples linearly to the supercurrent through a Lifshitz invariant, acting as an emergent gauge field for the superconducting $\mathrm{U}(1)$ phase. Integrating out soft magnetic fluctuations renormalizes the effective superfluid stiffness and drives the system into a "smectic" superconducting state, characterized by a finite-momentum helical phase texture and a long-wavelength stiffness that vanishes in one direction. Consequently, vortices no longer have a logarithmically divergent energy cost, and the quasi-long-range superconducting order is destroyed at any finite temperature. Weak lattice anisotropy pins the ferromagnetic order, cutting off the smectic-like behaviour at long wavelengths and thereby restoring a finite effective stiffness. Nonetheless, near the onset of magnetic order, the enhanced magnetic susceptibility leads to a vortex-deconfined regime for arbitrarily weak magnetoelectric coupling. The results provide insight into how intertwined superconducting and easy-plane ferromagnetic orders can reshape phase coherence, with relevance to rhombohedral graphene proximitized by a transition-metal dichalcogenide substrate.

Inspired by recent ARPES studies on multilayer ($n\geq3$ layers) cuprate superconductors, we use the unrestricted Hartree-Fock approximation to explore the ground-state phase diagram of two coupled, inequivalently doped square-lattice Hubbard layers. In the decoupled-layer limit, the lightly hole-doped ground state is typically an incommensurate spin-stripe state. However, with sufficiently strong interlayer coupling, stripe order is destabilized relative to a commensurate Néel-ordered metal. The resulting state exhibits a reconstructed Fermi surface with hole pockets centered at $(\pm\pi/2,\pm\pi/2)$ that are similar in character to those seen in experiments. Our results illustrate the qualitatively new physics that can arise from interlayer coupling in multilayer cuprates.

We present a bootstrap framework that yields rigorous two-sided bounds on ground-state observables of quantum systems with quenched disorder. The key idea is to extend the operator algebra to include classical disorder variables and to encode the disorder distribution through a set of moments. The method directly bounds disorder-averaged expectation values for finite or infinite lattice systems and for arbitrary disorder distributions. In contrast to conventional approaches, we do not need to sample disorder realizations, which enables us to make thorough use of symmetries that hold only on average rather than for each disorder realization. Additionally, we show that multi-replica operators can be used to access disorder fluctuations such as the variance of an observable. We apply the method to the one-dimensional random transverse-field Ising model (RTFIM) with discrete, uniform, and Gaussian disorder, obtaining tight bounds on the disorder-averaged ground-state energy density and short-range spin-spin correlators, as well as bounds on the disorder variance of the energy density. Additionally, we show that the difference between the upper and lower bounds on the disorder-averaged ground-state energy density, which we term the bootstrap gap, can be used to map out the phase diagram of the RTFIM. The bootstrap gap is small and flat within the paramagnetic and ferromagnetic phases at weak disorder, grows upon entering the Griffiths regions, and peaks along the critical line.

Anomalies of generalized symmetries are closely related to the statistics of topological excitations. Truncating a symmetry transformation to a finite region produces an operator that creates symmetry defects on its boundary; we call this a symmetry patch operator. Such operators resemble hopping operators that create topological excitations at the boundary of their support, but this geometric similarity does not justify identifying the two. For finite Abelian groups in one spatial dimension, we prove that if the same family of local operators defines both valid hopping operators and compatible symmetry patches, the type-III component of the anomaly is $-2$ times that of the statistics. We establish a one-to-one correspondence between statistics and anomaly by treating hopping operators as symmetric operators that commute with the global symmetry, following the description of symmetry through the algebra of local symmetric operators. We explain this correspondence through gauging by coupling boundary matter to a Dijkgraaf-Witten gauge field in one higher spatial dimension. Hopping operators act on the gauge-invariant degrees of freedom. After fixing the background gauge field, the residual gauge transformations become the global symmetry, and the gauge invariance of hopping operators becomes the requirement that they commute with this symmetry.

Quantum many-body dynamics is difficult to simulate because the global wavefunction develops extensive complexity, whereas local observables may retain only an intrinsic, system-size-independent complexity. This distinction is especially relevant in thermalizing systems, where local subsystems lose microscopic information and relax towards equilibrium. We introduce a variational time-evolution principle that exploits this separation by replacing global-state fidelity with a cost function defined on local reduced density matrices. The resulting locally optimized matrix-product-state (LOMPS) algorithm retains coherent short-time dynamics while using the simplification generated by thermalization at later times, and admits closed-form equations of motion analogous to the time-dependent variational principle. The same principle yields a quantum-classical algorithm in which a quantum processor evaluates the local cost and a noise-robust classical procedure performs the optimization. Proof-of-principle implementations on Quantinuum H2 and IBM Heron processors recover the characteristic local dynamics.

Distinguishing altermagnetism from conventional ferromagnetism and antiferromagnetism typically relies on momentum-space probes. Here, we show that the real-space spreading of a localized spin excitation provides a distinctive dynamical fingerprint of altermagnetic order. Using linear spin-wave theory on a two-dimensional checkerboard lattice with nearest-neighbor and next-nearest-neighbor couplings J_1 and J_2, we demonstrate that finite J_2 produces direction-dependent magnon group velocities and splits the two magnon branches. The resulting propagation remains closer to that of an antiferromagnet than a ferromagnet, retaining an approximately circular outer wavefront, while the direction-dependent magnon velocities produce a pronounced cross-like spatial structure inside this front. We further show that changing the sign of J_2 to enter the unfrustrated regime (J_2<0) increases the characteristic propagation velocities and interchanges the diagonal directions of enhanced propagation, corresponding to a pi/2 rotation of the anisotropic spatial pattern. These results establish spacetime dynamics as a complementary probe of altermagnetic magnons, providing a route to identifying unconventional magnetic order through real-space propagation patterns in solid-state and synthetic quantum systems.

Quantum critical theories with continuously varying critical exponents remain challenging to access experimentally. Here, we propose quantum-dot architectures for realizing the quantum Ashkin-Teller and XYZ/eight-vertex models using resonator-mediated and direct Coulomb interactions, respectively. We focus on the Ashkin-Teller and eight-vertex critical lines, which are connected by a non-local duality relating local order parameters to topological string operators. The resulting platforms provide microscopic control over the parameters explicitly controlling critical exponents, with the Coulomb-based implementation enabling stronger interaction regimes. We demonstrate that continuously varying critical behavior can already be resolved in short chains. For experimentally realistic parameters, the accessible interaction range is expected to produce changes in the critical exponents of order $10\%$ for the Ashkin-Teller model and substantially larger changes for the eight-vertex model. In both cases, the predicted variations lie well above the estimated measurement uncertainties.

A verified Kubo-Martin-Schwinger (KMS) relation, after a drive has ceased, is not sufficient evidence to prove equilibrium. We demonstrate this in a large-$N$ large-$q$ Sachdev-Ye-Kitaev (SYK) quench protocol. Although all post-quench fermion correlators are exactly thermal, a second quench back to the initial Hamiltonian reveals hidden memory of the initial state. It is encoded in correlators connecting to times before the first quench. This memory is an extensive nonequilibrium (NEQ) witness with its decay rate being the Lyapunov exponent $\lambda_L$. Thus $\lambda_L$ sets the rate at which the state becomes effectively indistinguishable from a Gibbs state. Despite being a unitary interacting many-body system, the complete NEQ real-time evolution is obtained exactly in the large-$N$, large-$q$ limit, making the setup ideal for analytically studying thermalization.

We present a multiconfigurational, relativistic embedded-cluster study of the local electronic structure of ruthenium dioxide ($\mathrm{RuO_2}$), a candidate altermagnetic material. Starting from free $\mathrm{Ru}$ ions, we progressively build up the local environment through a $\mathrm{Ru+Q_6}$ electrostatic model, a bare $\mathrm{[RuO_6]^{8-}}$ ligand model, and finally a high-accuracy $\mathrm{RuO_6}$@CTEP embedded cluster that reproduces the crystalline surroundings. All systems are treated at the SA-CASSCF and NEVPT2+SOC levels of theory to capture strong electron correlation and spin-orbit coupling on an equal footing. While the formal local site symmetry of the $\mathrm{Ru}$ sites in $\mathrm{RuO_2}$ is orthorhombic ($D_{2h}$), we find that the calculated $4d$-orbital energy spectrum and its splitting pattern behave much closer to the higher tetragonal ($D_{4h}$) symmetry, preserving a strong quasi-degeneracy among the relevant $4d$ orbitals. Since the local $xy$ quadrupolar order responsible for altermagnetic spin splitting in independent-particle models relies on this symmetry reduction, its suppression by orbital quasi-degeneracy offers a natural explanation for why altermagnetism is not observed in bulk $\mathrm{RuO_2}$ experiments, in contrast to the robust altermagnetic signatures reported in strained thin films.

Gauge theoretic descriptions of 2D quantum magnets are defined on a restricted physical Hilbert space by imposing Gauss's law. In this work, we study an unconstrained compact lattice QED$_{2+1}$ coupled to bond phonons, in which local Gauss operators are conserved, but their eigenvalues are not a priori fixed. Using exact auxiliary-field quantum Monte Carlo simulations at $N_f = 2$, we investigate how the physical Gauss sector becomes energetically favourable, and how this process is connected to confinement and symmetry breaking. We identify an orthogonal semimetallic (OSM) phase, in which fermions striped off their gauge charge and form a Dirac liquid. This phase mixes various Gauss sectors, and becomes unstable when Gauss's law is explicitly enforced. Upon the imposition of Gauss's law, compactness allows for monopole excitations carrying antiferromagnetic (AFM) and valence-bond-solid (VBS) quantum numbers. Gauge field fluctuations and spinon-phonon coupling tune between the competition of such monopoles and generate a phase diagram with OSM, AFM and VBS orders. The transitions out of the OSM phase coincide with the dynamical generation of Gauss's law, while the competition between AFM and VBS charged monopoles produces a transition consistent with deconfined quantum criticality. Thus our results establish that upon the projection to the physical Hilbert space, deconfinement in compact lattice QED$_{2+1}$ is always unstable towards either AFM or VBS order.

Charge order is conventionally characterized by a static modulation of the electronic density, while its collective excitations remain less developed from a quasiparticle perspective than those of spin-ordered systems. Here, we formulate the collective excititations of charge order within an effective charge-pseudospin model, in which the charge-ordered ground state is represented by staggered pseudospin order. Quantizing fluctuations around this ordered state via a Holstein–Primakoff transformation, we reveal two branches of bosonic quasiparticles with degenerate, gapped dispersions that carry opposite quantized electric charges $\pm 2e$. We therefore term these charge-$2e$ bosons “bichargons,” closely paralleling the two magnon branches of a bipartite antiferromagnet that carry opposite spin angular momenta. We show that a temperature gradient drives the diffusion of thermally excited bichargons, generating a charge Seebeck response when the degeneracy between the oppositely charged branches is lifted by tuning the chemical potential away from the charge-neutrality point. In contrast, despite carrying finite electric charges, a thermal bichargon gas remains electrically insulating under a static electric field because bichargon quasiparticle number is not conserved. An ac electric field, however, can parametrically generate coherent pairs of oppositely charged bichargons that support a finite dc drift current in the presence of a bias electric field, offering a bosonic analogue of photoconductivity mediated by photoexcited electron–hole pairs in semiconductors. Our results establish bichargons as a new class of collective bosonic charge carriers in charge-ordered systems and extend the quasiparticle paradigm of magnons in spin-ordered systems to the charge sector, with electric charge replacing spin angular momentum as the transported quantity.