The recently introduced BLOR corrective exchange-correlation functional [A. C. Burgess et al., Phys. Rev. B 107, L121115 (2023)] is, by construction, the unique simplified rotationally invariant $\mathrm{DFT}+U$ functional that enforces the flat plane condition separately on each effective orbital of a localized subspace. Detached from the Hubbard model, functionals of this type are both double-counting correction free and, when optimized in situ using appropriate error quantifiers, effectively parameter free. They are as computationally undemanding as conventional $\mathrm{DFT}+U$ functionals. In this work, the extension of the BLOR functional to address many-body errors (mBLOR) is derived. The mBLOR functional is built to enforce the flat plane condition on the entire subspace, rather than on each orbital individually. It depends solely on the total subspace occupancy and spin magnetization, bringing consistency with how Hubbard $U$ and Hund $J$ values are typically calculated, and very low complexity. In this way, interorbital errors are corrected on the same footing as the single-particle ones. Focusing on exact test cases with strong interorbital interactions, the BLOR and mBLOR functionals were benchmarked against contemporary $\mathrm{DFT}+U$ functionals using the total-energy extensivity condition on stretched homonuclear $p$-block dimers that represent various self-interaction and static-correlation error regimes, namely, singlet ${\mathrm{N}}_2$ and ${\mathrm{F}}_2$, non-spin polarized ${\mathrm{O}}_2$, and doublet ${\mathrm{Ne}}_2^{+}$. The BLOR functional outperformed all other $\mathrm{DFT}+U$ functionals tested, which often act to increase total-energy errors, yet it still yielded large errors in some systems. mBLOR instead yielded low-energy errors across all four strongly correlated dimers, while being constructed using only semilocal approximation ingredients. As mBLOR would not otherwise introduce a band-gap correction in the manner that is a desirable feature of $\mathrm{DFT}+U$, we developed a cost-free technique to reintroduce it automatically by moving the functional's unusual explicit derivative discontinuity into the potential. With this in place, mBLOR is the only known $\mathrm{DFT}+U$ functional that opens the band gap of stretched neutral homonuclear dimers without the aid of unphysical spin-symmetry breaking.

We investigate the passivity constraints on the relations between transmission, reflection, and absorption eigenvalues in linear time-invariant systems. Using techniques from matrix analysis, we derive necessary and sufficient conditions for the permissible combinations of these eigenvalues. Our analysis reveals that the set of allowable eigenvalue combinations forms a convex polyhedron in eigenvalue space, characterized by a trace equality and a set of linear inequalities. Surprisingly, we uncover a direct connection between this physical problem and Horn's inequalities, a fundamental result in matrix theory. We provide explicit examples for systems with varying numbers of input ports, demonstrating the increasing complexity of the constraints as system size grows. We apply our theory to analyze the implications of important phenomena, including open and closed channels, coherent perfect reflection and reflectionless scattering modes, and coherent perfect absorption and coherent zero absorption. Our findings not only offer a complete characterization of passivity constraints on wave transport eigenvalues but also establish an unexpected bridge between fundamental wave physics and advanced matrix theory, opening new avenues for research at their intersection. These results have significant implications for the design and optimization of passive wave devices across a wide range of applications in optics, acoustics, and mesoscopic physics.

Energy materials with disorder in site occupation are challenging for computational studies due to an exponential scaling of the configuration space. We herein present a grand-canonical optimization method that enables the use of quantum annealing (QA) for sampling the ionic ground state. The method relies on a Legendre transformation of the Coulomb energy cost function that strongly reduces the effective coupling strengths of the fully connected problem, which is essential for effectiveness of QA. The approach is expected to be applicable to a variety of materials optimization problems.

Spectroscopic identification of distinct nonlinear photocurrents unveils quantum geometric properties of electron wave functions and the momentum-space topological structures. This is especially interesting, but still puzzling, for chiral topological semimetals with possibilities of hosting giant quantized circular photogalvanic effect. Here we report a comprehensive terahertz (THz) emission spectroscopic analysis of nonlinear photoconductivity of chiral multifold CoSi at 0.26 ∼ 1 eV. We find a large linear shift conductivity ($17\mu \mathrm{A}/{\mathrm{V}}^2$), and confirm a giant injection conductivity ($167\mu \mathrm{A}/{\mathrm{V}}^2$) as a consequence of strongly interfered nonquantized contributions from the vicinity of multifold nodes with opposite chiralities. The bulk injection current excited by the pump field with a complex wave vector is shown to carry both longitudinal and transverse components. Symmetry analyses further unveil weak nonlocal photon drag effect in addition to the photogalvanic effect. This work not only highlights chiral transition-metal monosilicides for midinfrared photovoltaic applications via various nonlinear optical channels, but also consolidates the THz spectroscopy for quantitative photovoltaic research.

We study the effect of bond disorder in extended Heisenberg-Kitaev models on the honeycomb lattice, relevant for materials such as $\alpha \text{−}{\mathrm{RuCl}}_3$, in the semiclassical limit using a combination of T-matrix and real-space spin-wave approaches. Focusing on the regime of large applied magnetic field, we discuss two distinct but related disorder-induced phenomena, namely spin textures in the vicinity of isolated impurities and magnetic excitations below the bulk gap. A finite impurity concentration smears the field-tuned phase transition and turns the isolated in-gap states into impurity bands. As a result, there is a large field regime above the bulk transition into the high-field phase where impurity-induced states fill the bulk spin gap. We illustrate the field dependence of these in-gap states for parameters relevant for $\alpha \text{−}{\mathrm{RuCl}}_3$, and we connect our results to heat-transport and NMR data which indicated their presence.

The superconducting and structural properties of elemental strontium metal were investigated under pressures up to 60 GPa while maintaining cryogenic conditions during pressure application. Applying pressure at low temperatures reveals differences in superconducting and structural phases compared to previous reports obtained at room temperatures. Notably, the superconducting critical temperature exhibits a twofold increase under compression after cryogenic cooling within the pressure range of 35–42 GPa, compared to cryogenic cooling after room-temperature compression. Subsequently, the transition width becomes significantly sharper above 42 GPa. Low-temperature x-ray diffraction measurements under pressure reveal that this change corresponds to the Sr-III to Sr-IV transition, with no evidence of any metastable structure. Furthermore, the monoclinic Sr-IV structure was observed to remain stable to much higher pressures—at least up to 60 GPa, without the appearance of the incommensurate Sr-V phase present at room temperature. This implies that thermal activation energy plays an important role in overcoming the presence of a kinetic barrier to the Sr-V phase at room temperature.

Magnetic metal-organic frameworks (MMOFs), where magnetic metal nodes are connected into a crystal structure by organic linkers, have a potential to host exotic magnetic states. We present a study of bulk magnetic properties of four metal-organic frameworks with the same boron imidazolate linkers, Cu-BIF, Co-BIF, Ni-BIF, and newly synthesized Zn-BIF, displaying a variety of lattice structures and nontrivial magnetic behaviors. While nonmagnetic Zn-BIF provides an offset of magnetic response, magnetic susceptibility measurements of the other three magnetic materials demonstrate the presence of weak magnetic interactions in these MOFs, which differ between materials by sign and size. Cu-BIF, where magnetic nodes are connected into octahedral cages, shows simple paramagnetic behavior. Triangular lattice Co-BIF shows antiferromagnetic interactions on the order of 1 K, and a spin-crossover-like effect in magnetic susceptibility due to thermal depopulation of excited crystal electric field levels. Magnetic properties of Ni-BIF suggest sizable ferromagnetic interactions. Using DC/AC susceptibility and variable-field DC magnetization, we detect cluster spin-glass behavior in Ni-BIF and discuss possible microscopic origins of this behavior. This work demonstrates the variety of magnetic properties possible with a single organic ligand and establishes the low energy scale of magnetic interactions through superexchange in boron imidazolate frameworks.

We develop a comprehensive theoretical model for the interaction strength between a pair of exciton polaritons in microcavity devices. Ab initio numerical calculations for dipolar polaritons in one dimension are used as a starting point to build a Born-Oppenheimer theory that generally applies to generic—dipolar or nondipolar—polaritons in both one and two dimensions. This theory anticipates that the strong coupling to the cavity mode leads to a drastic enhancement of the polariton interactions as compared to bare excitons, and predicts unexpected scaling laws in the interaction strength as a function of system parameters. Comparisons with available experimental data are drawn and specific suggestions to validate it with new experiments are made. Finally, promising strategies towards the observation of a strong polariton blockade regime are sketched.

We derive a minimal low-energy model for Bernal bilayer graphene and related rhombohedral graphene multilayers at low electronic densities by constructing Wannier orbitals defined in real-space supercells of the original primitive cell. Starting from an ab initio electronic structure theory comprising the atomic carbon $p_z$ orbitals, momentum locality of the Fermi surface pockets around $K,K^{\prime }$ is circumvented by back folding the $\pi$ bands to the concomitant mini-Brillouin zone of the supercell, reminiscent of their (twisted) moiré counterparts. The supercell Wannier functions reproduce the spectral weight and Berry curvature of the microscopic model and offer an intuitive real-space picture of the emergent physics at low electronic densities being shaped by flavor-polarized wave packets with mesoscopic extent. By projecting an orbital-resolved, dual-gated Coulomb interaction to the effective Wannier basis, we find that the low-energy physics of Bernal bilayer graphene is governed by weak electron-electron interactions. Our study bridges between existing continuum theories and ab initio studies of small Fermi pocket systems such as rhombohedral graphene stacks by providing a symmetric lattice description of their low-energy physics.

Gateable semiconductor quantum dots (QDs) provide a versatile platform for analog quantum simulations of electronic many-body systems. In particular, QD arrays offer a natural representation of the interacting $\pi$-electron system of small hydrocarbons. Here we investigate the prospects for extending QD simulators to encompass also the nuclear degrees of freedom. We represent the molecular vibrational modes by single-mode microwave resonators coupled capacitively to the QDs and study the gate-tunable energy transfer from a voltage-biased triple quantum dot (TQD) system to a single damped resonator mode. We determine the QD population inversions, the corresponding charge and energy currents as well as the resonator photon number, using Lindblad master equations and lowest-order perturbation theory within Keldysh Green function formalism. Along the way, we discuss the merits and shortcomings of the two methods. A central result is the interrelation of a pronounced minimum in the charge current with a maximum in energy transfer, arising from a gate-tunable interference effect in the molecular orbitals of the TQD electron system.

Motivated by recent developments on altermagnetism, we investigate the Hubbard model on the Shastry-Sutherland lattice, where the on-site repulsion between electrons induces the onset of a staggered magnetic order in which opposite magnetic sublattices are related to each other only by rotations and glide reflections, and not by inversion nor translations. As a consequence, the magnetic phase displays an altermagnetic character, i.e., a finite (nonrelativistic) Zeeman splitting of the electronic excitations, despite the absence of a net magnetization. By means of a variational Monte Carlo approach based on Jastrow-Slater wave functions, which accounts for electronic correlations beyond the single-particle approximation, we study how $d$-wave altermagnetism shows up in the ground-state properties and in the spectral function of the system. We characterize the metal-insulator transition between altermagnetic phases at half-filling and the stability of altermagnetism as a function of doping. The calculation of the single-particle spectral function displays the spin-split nature of the electronic excitations, also within the Mott insulating regime. We discuss possible realizations of the model in the context of organic $\alpha$- or $\kappa$-(BEDT-${\mathrm{TTF})}_2\mathrm{X}$ charge transfer salts.

We highlight the exotic quantum criticality of quasi-two-dimensional single-component fermions at half filling that are minimally coupled to a dynamical Ising gauge theory. With the numerical matrix product state based infinite density matrix renormalization group method, we discover a robust quantum critical line in the infinite cylinder geometry, where gauge confinement and dimerized translation symmetry breaking emerge simultaneously. We investigate how the transition can be split by a ${\mathbb{Z}}_2$ topologically ordered dimerized phase that is stabilized by additional short-range repulsive interactions. We conjecture a $u\left(1\right)$ deconfined criticality scenario, propose a corresponding low-energy effective field theory of the exotic quantum critical point in the two-dimensional limit, and identify its shortcomings.

The quantum simulation of entangled spin systems can play a central role in quantum magnetic materials discovery. Additionally, the simulation of spectroscopic signatures, such as the dynamical structure factor accessed in inelastic neutron scattering (INS), necessitates a long timescale for circuit evolution. This is because the energy resolution is directly related to the time over which the circuit could be meaningfully evolved. However, canonical Trotterization requires deep circuits precluding such long-time evolution—even for a small number of qubits. Here we demonstrate “direct” resource efficient fast-forwarding (REFF) measurements with short-depth circuits that can be used to capture longer time dynamics of spin Hamiltonians. We showcase the results of the dynamics of a quantum spin dimer, the basic quantum unit of emergent many-body spin systems, whose density of states we simulate accurately. The long temporal evolution and measurement of the two-spin correlation functions enable the calculation of the dynamical structure factor $S(\mathbf{Q}=0,\omega )$ measured in the neutron scattering cross-section. We exhibit the clarity of the triplet gap and the triplet splitting of the quantum dimer with class-leading fidelity that enables comparison to experimental neutron data. Our results on current circuit hardware outline an important workflow to predict and benchmark against the outputs of INS experiments of quantum magnets.

Motivated by the recently discovered high-$T_c$ bilayer nickelate superconductor ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, we comprehensively research a bilayer $2\times 2\times 2$ cluster for different electronic densities $n$ by using the Lanczos method. We also employ the random-phase approximation to quantify the first magnetic instability with increasing Hubbard coupling strength, also varying $n$. Based on the spin structure factor $S\left(q\right)$, we have obtained a rich magnetic phase diagram in the plane defined by $n$ and $U/W$, at fixed Hund coupling, where $U$ is the Hubbard strength and $W$ the bandwidth. We have observed numerous states, such as A-AFM, Stripes, G-AFM, and C-AFM. At half-filling, $n=2$ (two electrons per Ni site, corresponding to $N=16$ electrons), the canonical superexchange interaction leads to a robust G-AFM state $(\pi ,\pi ,\pi )$ with antiferromagnetic couplings both in-plane and between layers. By increasing or decreasing electronic densities, ferromagnetic tendencies emerge from the “half-empty” and “half-full” mechanisms, leading to many other interesting magnetic tendencies. In addition, the spin-spin correlations become weaker both in the hole or electron doping regions compared with half-filling. At $n=1.5$ (or $N=12$), density corresponding to ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, we obtained the “Stripe 2” ground state (antiferromagnetic coupling in one in-plane direction, ferromagnetic coupling in the other, and antiferromagnetic coupling along the $z$ axis) in the $2\times 2\times 2$ cluster. In addition, we obtained a much stronger AFM coupling along the $z$ axis than the magnetic coupling in the $xy$ plane. The random-phase approximation calculations with varying $n$ give very similar results as Lanczos, even though both techniques are based on quite different procedures. Additionally, a state with $q/\pi =(0.6,0.6,1)$ close to the E-phase wavevector is found in our RPA calculations by slightly reducing the filling to $n=1.25$, possibly responsible for the E-phase SDW recently observed in experiments. Our predictions can be tested by chemically doping ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

Elastic wave manipulation using large arrays of resonators is driving the need for advanced simulation and optimization methods. To address this we introduce and explore a robust framework for wave control: quasinormal modes (QNMs). Specifically, we consider the problem for thin elastic plates, where the Green's function formalism is well known and readily exploited to solve multiple scattering problems. By studying the associated nonlinear eigenvalue problem we derive a dispersive QNM expansion, providing a reduced-order model for efficient forced response computations which reveals physical insight into the resonant mode excitation. Furthermore, we derive eigenvalue sensitivities with respect to resonator parameters and apply a gradient-based optimization to design quasi-bound states in the continuum and position eigenfrequencies precisely in the complex plane. Scattering simulations validate our approach in structures such as graded line arrays and quasicrystals. Drawing on QNM concepts from electromagnetism we demonstrate significant advances in elastic metamaterials, highlighting their potential for tailored wave manipulation.

We investigate many-body topological and transport properties of a one-dimensional Su–Schrieffer–Heeger (SSH) topological chain coupled to the quantum field of a cavity mode. The quantum conductance is determined via Green's function formalism in terms of the light-matter eigenstates calculated via exact diagonalization for a finite number of electrons. We show that the topology of the cavity-embedded many-electron system is described by a generalized electron-photon Zak marker. We reveal how the quantization of transport is modified by the cavity vacuum fields for a finite-size chain and how it is impacted by electronic disorder. Moreover, we show that electron-photon entanglement produces dramatic differences with respect to the predictions of mean-field theory, which strongly underestimates cavity-modified transport.

Recent studies have revealed a general procedure for incorporating disorder into the semiclassical model of carrier transport, whereby the predictions of quantum linear response theory can be recovered within a quantum kinetic approach based on a disorder-averaged density-matrix formalism. Here, we present a comprehensive generalization of this framework to the nonlinear response regime. In the presence of an electrostatic potential and random impurities, we solve the quantum Liouville equation to second order in an applied electric field and derive the carrier densities and equations of motion. In addition to the anomalous velocity arising from the Berry curvature and the Levi-Civita connection of the quantum metric tensor, a host of extrinsic velocities emerge in the equations of motion, reflecting the various possibilities for random interband walks of the carriers in this transport regime. Furthermore, several scattering and conduction channels arise, which can be classified in terms of distinct physical processes, revealing numerous unexplored mechanisms for generating nonlinear responses in disordered condensed matter systems.

Recent experiments showing an integer quantum anomalous Hall effect in pentalayer rhombohedral graphene have been interpreted in terms of a valley-polarized interaction-induced Chern band. The resulting many-body state can be viewed as an anomalous Hall crystal (AHC), with a further coupling to a weak moiré potential. We explain the origin of the Chern band and the corresponding AHC in the pentalayer system. To describe the competition between AHC and Wigner crystal (WC) phases, we propose a simplified low-energy description that predicts the Hartree-Fock phase diagram to good accuracy. This theory can be fruitfully viewed as “superconducting ring” in momentum space, where the emergence of Chern number is analogous to the flux quantization in a Little-Parks experiment. We discuss the possible role of the moiré potential, and emphasize that even if in the moiréless limit, the AHC is not favored (beyond Hartree-Fock) over a correlated Fermi liquid, the moiré potential will push the system into a “moiré-enabled AHC”. We also suggest that there is a range of alignment angles between R5G and hBN where a $C=2$ insulator may be found at integer filling.

Moiré transition metal dichalcogenide (TMD) materials provide an ideal playground for studying the combined interplay of strong interactions and band-topology over a range of electronic fillings. Here we investigate the panoply of interaction-induced electronic phases that arise at a total commensurate filling of ${\nu }_T=2$ in moiré TMD heterobilayers, focusing specifically on their renormalized band-topology. We carry out a comprehensive self-consistent parton mean-field analysis on an interacting mixed-valence Hamiltonian describing AB-stacked ${\mathrm{MoTe}}_2$/${\mathrm{WSe}}_2$ to highlight different ingredients that arise due to “Mottness,” band-flattening, an enhanced excitonic tendency, and band inversion, leading to correlated topological semi-metals and insulators. We also propose a possible route towards realizing fractionalized insulators with emergent neutral fermionic excitations in this and other closely related platforms.

Recent experiments in twisted bilayer ${\mathrm{WTe}}_2$ revealed the existence of anisotropic Luttinger liquid behavior. To generically characterize such anisotropic twisted bilayer systems, we study a model of a twisted bilayer of two-dimensional (2D) arrays of coupled wires, which effectively form an array of coupled moiré wires. We solve the model by the transfer matrix method, and identify quasi-1D electron bands in the system at small twist angles. With electron interactions added, we show that the moiré wires have an effective Luttinger parameter $g_{\text{eff}}$ lower than that of the microscopic wires. This leads to a sliding Luttinger liquid (SLL) temperature regime, in which power-law current voltage relations arise. For parameters partly estimated from ${\mathrm{WTe}}_2$, a microscopic interaction $U\sim 3\mathrm{eV}$ yields a temperature regime of SLL similar to that in the ${\mathrm{WTe}}_2$ experiments.