We investigate the ground-state phase diagram of the $S$ = 1/2 XXZ model on the two-dimensional Shastry-Sutherland lattice using exact diagonalization (ED), density-matrix renormalization group (DMRG), and cluster mean-field theory (CMFT) with DMRG as a solver. In the isotropic case ($\mathrm{\Delta }=1$), CMFT results reveal an intermediate empty plaquette (EP) phase that has a lower energy than the full plaquette (FP) phase. However, due to mean-field artifacts, CMFT alone is not suitable for accurately determining phase boundaries. Therefore, we combined three methods to map out the reliable phase diagram. Our calculations show that the EP phase narrows as $\mathrm{\Delta }$ deviates from unity and eventually vanishes. More importantly, we identify a spiral phase at small $\mathrm{\Delta }$, which has not been reported in previous studies. This phase is clearly captured by DMRG simulations on long cylindrical geometries. The competition between the EP, spiral, and $xy$-AFM phases near their boundaries provides a plausible explanation for the emergent spin-liquid-like behavior in ${\mathrm{Pr}}_2{\mathrm{Ga}}_2{\mathrm{BeO}}_7$, while shedding new light on the role of XXZ anisotropy in the Shastry-Sutherland XXZ model.

Hopf terms are topological theta terms that are associated with a host of interesting physics, including anyons, statistical transmutation, chiral edge states, and the spin quantum Hall effect. Here, we show that Hopf terms can appear in two-dimensional metals without spin-orbit coupling in the vicinity of spin-ordered phases. In their vicinity, their spinlike order parameters have a finite amplitude, but fluctuating orientation. When both a magnetic and a spin loop-current order parameter fluctuate in the system, we show that the phase is governed by the Hopf term and realizes a Hopf symmetry protected topological phase. This phase is protected by the unbroken $\mathrm{SU}\left(2\right)$ spin rotation symmetry, is gapped in the bulk, has chiral gapless edge states, and its spin-Hall conductance is quantized. Lattice models that realize this phase are introduced. In addition, we provide an elementary proof that the $\theta$ angle of the Hopf term must be quantized to multiples of $\pi$ in nonrelativistic systems, thereby precluding anyonic skyrmions in condensed matter systems.

This work provides a comprehensive study of charge-2 Dirac points (C2 DPs) in spinless systems, systematically analyzing their emergence and properties based on the 230 space groups and corresponding material candidates. By deriving the necessary symmetry constraints, we establish that the stabilization of C2 DPs requires two independent screw rotations that anticommute with each other, along with time-reversal symmetry. This symmetry-based framework allows us to identify only nine space groups capable of hosting C2 DPs, offering a clear guideline for identifying material candidates. Through high-throughput calculation, and based on the latest Materials Project database, we identify 57 candidate materials, including 47 nonmagnetic (NM) and 10 ferromagnetic (FM) systems, that exhibit C2 DPs at high-symmetry points or paths. To further explore the intrinsic properties of C2 DPs and their topological phase transitions, we select two representative materials: the NM material ${\mathrm{IO}}_3$ and the FM material ${\mathrm{PH}}_5{\mathrm{N}}_2{\mathrm{O}}_4$. Our analysis reveals that C2 DPs at high-symmetry points are symmetry-essential band crossings, which transform into pairs of Weyl points (WPs) under symmetry-breaking conditions. C2 DPs on high-symmetry paths are accidental crossings, which can be gapped without requiring symmetry breaking. These findings not only advance the understanding of C2 DPs in spinless systems but also provide a robust platform for experimental exploration and theoretical studies of topological phase transitions, paving the way for future discoveries in the field of topological materials science.

Developing effective approaches to modulate the nonlinear optical (NLO) responses of materials is of great importance to design novel optoelectric devices. Recent studies have reported two distinct pressure-induced second-harmonic generation (SHG) modulation behaviors in $\mathrm{NbO}{\mathrm{I}}_2$, with one enhanced and the other suppressed. These observations have sparked considerable interest in the underlying physical mechanism. Using first-principles calculations, we have declared the structure evolution path of $\mathrm{NbO}{\mathrm{I}}_2$ under pressure, where spontaneous polarization decreases, and the Peierls distortion ratio holds. The SHG susceptibility exhibits a global reduction across all frequencies due to suppressive quantum geometric quantities. On the other hand, a series of artificial structures with different Peierls distortion ratios was designed to explain the SHG boost in experiments, which is attributed to modified electronic dispersion relations. In addition, by applying uniaxial strain to the polarization axis, our results show that optical transition probability overtakes the shift vector as the primary contributor in polarization-dependent SHG. Hence, we demonstrate tunable SHG response governed by distinct microscopic mechanisms in the $\mathrm{NbO}{\mathrm{I}}_2$ system. Our findings not only contribute to clarifying different pressure-induced SHG behaviors in $\mathrm{NbO}{\mathrm{I}}_2$ but also deepen our understanding of SHG evolution under external fields.

Dynamical mean-field theory computations of the electron self-energy of the Hubbard-Holstein model as a function of electron-phonon and electron-electron interactions are analyzed to gain insight into the dependence of electron-phonon couplings on correlation strength in quantum materials. We find that the electron-phonon interaction is strongly suppressed by electronic correlations, while electron-electron correlation effects at Fermi liquid scales are only weakly modified by coupling to phonons, with phonon-induced modifications most evident at high frequencies on the order of the electronic bandwidth. Implications for beyond-density functional theories of the electron-phonon interaction are discussed.

For electronic structure calculations of periodic extended systems based on many-body wave functions, we investigate the utility of a similarity transformation of the Hamiltonian in the thermodynamic limit, followed by a treatment of the resulting transcorrelated Hamiltonian within a supercell approximation. Using a correlation factor fulfilling the long-range asymptotic condition of the uniform electron gas, the effective potential of the transcorrelated Hamiltonian decays much faster than the original Coulomb potential. This is found to significantly speed up the convergence of the supercell energies towards the thermodynamic limit.

Delocalization error prevents density functional theory (DFT) from reaching its full potential, causing problems like systematically underestimated band gaps and misaligned energy levels at interfaces. We introduce lrLOSC to correct delocalization error in materials over a wide range of band gaps. We predict 11 materials' fundamental gaps to within $0.22\mathrm{eV}$ while offering a nonzero total energy correction; molecular properties are improved with a parallel implementation of the same theory [J. Yu et al., J. Phys. Chem. Lett. 16, 2492 (2025)]. lrLOSC is an essential step toward modeling molecules, materials, and their interfaces within the same DFT framework.

We investigate the physical properties and lattice relaxation of important photoexcited states in a charge-transfer-type metal-organic framework ${\left({\mathrm{NPr}}_4\right)}_2{[\mathrm{Fe}}_2{\left({\mathrm{Cl}}_2\mathrm{An}\right)}_3]$. We construct the one-dimensional spinless fermion model for the material and numerically calculate the photoexcited states and the lattice-relaxed states from them. The ground state is a charge-ordered (CO) state with a uniform lattice. The dominant peak in the light absorption spectrum corresponds to an optically allowed bond order wave (BOW) state with charge disproportionation (CD). This Franck-Condon BOW state forms as a linear combination of two degenerate inversion-symmetry-broken BOW states, which have different phases of bond order alternation, combined with the CD, and the inversion symmetry is restored in the state. The Franck-Condon BOW state is strongly coupled to the lattice deformation of bond length alternation, and lattice relaxation can occur even in this rigid material. The lattice-relaxed state originating from the Franck-Condon state is a BOW state with CD, where inversion symmetry is broken due to bond length alternation, making it an electronic ferroelectric state. The largest peak in the induced light absorption spectrum from this lattice-relaxed BOW state results from excitation to another BOW state with CD, which has the opposite phase of bond order alternation. This state is also an electronic ferroelectric, with its polarization opposite to that of the lattice-relaxed BOW state from the Franck-Condon state. This shows that polarization can be reversed instantly through resonant photoexcitation from the lattice-relaxed state.

In this work, we investigate many-body phase transitions in a one-dimensional anisotropic XY model subject to a complex-valued transverse field. Within the biorthogonal framework, we calculate the ground-state correlation functions and entanglement entropy, confirming that their scaling behavior remains identical to that in the Hermitian XY model. The preservation of Hermitian phase transition features in the non-Hermitian setting is rooted in the persistence and emergence of symmetries and their breaking. Specifically, the ferromagnetic (FM) phase arises from the breaking of a $Z_2$ symmetry, while the Luttinger liquid (LL) phase is enabled by the emergence of a $\text{U}\left(1\right)$ symmetry together with the degeneracy of the real part of the energy spectrum. The nontrivial topology of the LL phase is characterized by the winding number around the exceptional point (EP). Given that non-Hermitian systems are inherently open, our findings suggest a new avenue for exploring universal critical phenomena associated with conventional quantum phase transitions, which are typically vulnerable to decoherence and environmental disruption in conventional open quantum systems.

Using artificial dissipation to tame entanglement growth, we chart the emergence of diffusion in a generic interacting lattice model for varying U(1) charge densities. We follow the crossover from ballistic to diffusive transport above a scale set by the scattering length, finding the intuitive result that the diffusion constant scales as $D\propto 1/\rho$ at low densities $\rho$. Our numerical approach generalizes the Dissipation-Assisted Operator Evolution algorithm: in the spirit of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, we effectively approximate nonlocal operators by their ensemble averages, rather than discarding them entirely. This greatly reduces the operator entanglement entropy, while still giving accurate predictions for diffusion constants across all density scales. We further construct a minimal model for the transport crossover, yielding charge correlation functions which agree well with our numerical data. Our results clarify the dominant contributions to hydrodynamic correlation functions of conserved densities, and serve as a guide for generalizations to low-temperature transport.

High-order harmonic generation (HHG) in solids provides a compact route to attosecond light sources, but its efficiency and tunability remain key challenges. Here, we investigate HHG from $\mathrm{Cu}\left(111\right)\text{/}n\text{−}\mathrm{ML}$ NaCl heterostructures and identify a previously unreported interfacial mechanism that simultaneously enhances the harmonic yield and extends the cutoff. Under fixed laser conditions, the cutoff increases nearly linearly with NaCl thickness, and this scaling remains robust against variations in driving-field parameters. The underlying physics arises from the confinement of Cu surface electrons within the screening length, their enhanced acceleration due to a reduced effective mass, and efficient transfer into NaCl bands during field-driven Bloch oscillations. Furthermore, we demonstrate that applying a bias voltage significantly amplifies the harmonic yield, enabling the synthesis of stronger attosecond pulses. The interplay between the Cu skin effect and the emergent periodicity of NaCl thus provides a controllable platform for engineering strong-field responses, offering opportunities for robust attosecond pulse generation and ultrafast photonic applications.

We present a first-principles study of the nonlinear optical properties of sliding ferroelectric bilayers based on ${\mathrm{MoSe}}_2$ and Janus MoSSe. Two Janus configurations are considered: (i) one bilayer where the two intralayer polarizations caused by Janus chemical asymmetry cancel each other out, yielding photocurrent spectra comparable to pristine ${\mathrm{MoSe}}_2$ bilayers; (ii) another bilayer where the intralayer polarizations add up, for which the photoresponses are strongly enhanced. Our results show that photocurrent generation in the polar Janus structures is predominantly governed by vertical chemical asymmetry, with limited dependence on the sliding direction. These findings highlight complementary design strategies: interlayer sliding enables sensitivity to external tuning, while the Janus intralayer polarization enhances photoresponses in the visible range. The interplay between composition and stacking therefore provides a versatile platform for tailoring light-matter interactions in two-dimensional ferroelectric materials.

The rapidly growing class of atomically thin and tunable van der Waals materials is intensely investigated both in the context of fundamental science and for new technologies. There is in this connection a widespread need for new ways to probe the electronic properties of these layered materials, since their two-dimensional (2D) character makes conventional probes less efficient. Here, we show how excitons trapped in a moiré lattice can be used as a spatially resolved optical probe for electron spin density correlations in such materials. The electrons in the material of interest virtually tunnel to the moiré lattice, where they scatter on the excitons, after which they tunnel back. This gives rise to an effective spin-dependent and spatially localized potential felt by the electrons, which in turn leads to energy shifts that can be measured spectroscopically in the exciton spectrum. Using second-order perturbation theory combined with a solution to the exciton-electron scattering problem, we show that the electrons mediate an interaction between two excitons resulting in an energy shift proportional to their two-point spin density-density correlation function evaluated at the exciton positions. We then discuss two specific applications of our setup. First, we show that quantum phase transitions between different in-plane antiferromagnetic orders in a 2D lattice give rise to large and measurable shifts in the exciton spectrum in the critical regions. Second, we analyze how different pairing symmetries of superconducting phases can be probed. This demonstrates that our scheme opens up new ways to probe electron spin density correlations, which is a key property of many quantum phases predicted to exist in the new 2D materials.

Subwavelength arrays of plasmonic nanoparticles allow us to control the behavior of light at the nanoscale. Here, we develop an eigenmode analysis, employing a coupled electromagnetic dipole formalism, which permits us to isolate the contribution to the far-field radiation of each array mode. Specifically, we calculate the far-field radiation patterns by bulk, edge, and corner out-of-plane eigenmodes in a finite 2D Su-Schrieffer-Heeger (SSH) array of plasmonic nanoparticles with out-of-plane dipolar resonances. The breaking of symmetries in multipartite unit cells is exploited to tailor the optical properties and far-field radiation of the resonant modes. We prove that the antisymmetric modes are darker and have higher Q factors than their symmetric counterparts. Also, the out-of-plane nature of the dipolar resonances imposes that all bulk $\mathrm{\Gamma }$ modes are dark, while corner and edge states need extra in-plane symmetries to cancel the far-field radiation; radiation patterns in turn become more complex and concentrated along the array plane with increasing array size.

We study diffusive magnetotransport in highly $p$-doped large-area twisted bilayer graphene in $1^{\circ }$, $7^{\circ }$, $9^{\circ }$, and ${20}^{\circ }$ samples. All samples exhibit weak localization, from which we extract the phase coherence length and intervalley scattering lengths, and from that determine that dephasing is caused by electron-electron scattering and intervalley scattering is caused by point defects. We observe signatures of universal conductance fluctuations in the $9^{\circ }$ sample, which has high mobility and is near the van Hove singularity. Further improvements in sample quality and applications to large-area moiré materials will open new avenues to observe quantum interference effects.

The precise on/off switching of the current channel via gate voltage in transistors constitutes the foundational principle of modern electronics. This paradigm of electric field control over charge carriers has not only revolutionized information processing technologies but has also inspired research frontiers in manipulating the intrinsic properties of materials through external fields. Here, we propose a physical mechanism based on electric field control of optical absorption and emission (OAE) switching, realizing gate-controlled OAE switching, and provide specific implementation schemes. We first demonstrate the theoretical maximum of the transition dipole moment (TDM) in a one-dimensional system and propose that one-dimensional topological insulators precisely satisfy this condition. More importantly, we find that under electric field modulation, the TDM of the system can be reduced from its theoretical maximum to near zero, thereby enabling gate-controlled switching of OAE. This mechanism is validated through first-principles calculations on polyacetylene quantum dots. Our findings establish a mechanism for the electric-field modulation of optical properties, thereby enabling OAE switching and opening avenues toward advanced electro-optic devices.

The behavior of the uranium mononitride (UN) crystal structure at nonambient conditions is disputed, with studies proposing various mutually exclusive distortions and transformations of the conventional face-centered-cubic structure at extreme temperatures and pressures. In this study, we investigated the UN lattice with diamond anvil cell x-ray diffraction experiments at pressures up to 92 GPa and with density functional theory calculations at temperatures up to 1000 K and pressures up to 90 GPa. We determined that while the UN structure is nearly cubic at ambient conditions, its lattice angle ($\alpha$) varies as a function of pressure and temperature, meaning its structure can be more precisely described as face-centered-rhombohedral with $\alpha \approx {90}^{\circ }$. Over the range of conditions we investigated, UN exhibits a single, isostructural phase transition at $\approx 35\mathrm{GPa}$, where $\alpha$ collapses to $\approx {86}^{\circ }$. Measurements and calculations agree that the compressibility of UN increases significantly beyond this transition, with the bulk modulus falling from $\approx 200\mathrm{GPa}$ in the low-pressure phase to $121\pm 3\mathrm{GPa}$ (according to calculations) or $58\pm 4\mathrm{GPa}$ (according to measurements) in the high-pressure phase. Our measurements also allowed us to constrain the bulk modulus of $\alpha \text{−}{\mathrm{U}}_2{\mathrm{N}}_3$ to $240\pm 10\mathrm{GPa}$.

The cubic ${\mathrm{Cu}}_3\mathrm{Au}$-type $X{\mathrm{Pt}}_3$ family ($X=\mathrm{V}$, Cr, and Mn) is a topological semimetal characterized by anticrossing gapped nodal lines near the Fermi level, which give rise to significant Berry curvatures and thus the to the anomalous Hall effect (AHE). Among the three members, ${\mathrm{CrPt}}_3$ has been experimentally verified to exhibit a large anomalous Hall conductivity (AHC), while its counterparts ${\mathrm{MnPt}}_3$ and ${\mathrm{VPt}}_3$ remain largely unexplored. Here, a series of ${\mathrm{MnPt}}_3$ thin films with varying thicknesses (20–70 nm) was epitaxially grown on the MgO substrates using magnetron sputtering and was systematically investigated by magnetization, electrical resistivity, and Hall resistivity measurements. ${\mathrm{MnPt}}_3$ films undergo a ferromagnetic transition at a Curie temperature $T_{\mathrm{C}}$, which increases as the film thickness increases, reaching $\sim 344$ K for the 70-nm-thick film. All the anomalous Hall transport properties of ${\mathrm{MnPt}}_3$ films, including the resistivity, conductivity, and angle, exhibit a strong correlation with their magnetic properties. The scaling analysis suggests that the intrinsic Berry-curvature mechanism dominates the observed AHE, while the extrinsic contributions are much smaller. The intrinsic AHC increases as the film thickness increases, while the extrinsic AHC is thickness independent. Such an enhanced intrinsic AHC in the ${\mathrm{MnPt}}_3$ films is most likely attributed to the strain effect, implying that it serves as an effective method to tune the electronic band topology in the $X{\mathrm{Pt}}_3$ topological semimetal.

Josephson parametric devices are widely used in superconducting quantum computing research but suffer from an inherent gain-bandwidth trade-off. This limitation is partly overcome by coupling the device to its input/output transmission line via a bandpass filter, leading to wider bandwidth at undiminished gain. Here we perform a nonperturbative circuit analysis in terms of dressed transmission-line modes for representative resonant coupling circuits, going beyond the weak-coupling treatment. The strong frequency dependence of the resulting coupling coefficients implies that the Markov approximation commonly employed in cQED analysis is inadequate. By retaining the full frequency dependence of the coupling, we arrive at a non-Markovian form of the quantum Langevin equation with the frequency-dependent complex-valued self-energy of the coupling in place of a single damping parameter. We also consistently generalize the input-output relations and unitarity conditions. Using the exact self-energies of elementary filter networks–-a series and parallel $\mathrm{LC}$ circuit and a simple representative bandpass filter consisting of their combination—we calculate the generalized parametric gain factors. Compared with their Markovian counterpart, these gain profiles are strongly modified. We find bandwidth broadening not only in the established parameter regime, where the self-energy of the coupling is in resonance with the device and its real part has unity slope, but also within off-resonant parameter regimes where the real part of the self-energy is large. Our results offer insight for the bandwidth engineering of Josephson parametric devices using simple coupling networks.

A high superconducting critical temperature ($T_c$) under normal laboratory conditions in a material that is chemically simple and stable, like an elemental metal, is a hitherto unattained goal of modern science and technology. Certain elemental metals are known to display reasonably high $T_c$ only under extraordinarily high pressures, where their spectroscopic characterization and application are tightly restricted. Here we show that a $T_c$ exceeding 20 K can be realized on pure elemental Ce under uniaxial pressure created simply by pressing a sharp metallic needle on the metal. This is a breakthrough because pure Ce does not superconduct under ambient conditions and the application of 54 GPa of hydrostatic pressure yields only a low $T_c$ of 1.8 K in the metal. In addition, by driving the area under the needle in a mechanically controlled way to the ballistic transport regime, we spectroscopically characterized the superconducting energy gap in a high-pressure superconducting phase and found that superconducting Ce respects the conventional Bardeen-Cooper-Shrieffer theory.