We address the problem of boundary $s$-wave superconductivity on rectangular honeycomb lattices: nanoflakes, armchair, and zigzag nanotubes. We discuss how the presence of edges and corners in these systems can significantly alter the superconducting correlations at a macroscopic length scale, leading to either nontrivial enhancement or suppression of the superconducting gap value near the boundaries. This in turn results in different critical temperatures of the gap closure at boundaries compared to the bulk gap. The effects are macroscopic but strongly depend on the atomic-level structure of the boundaries.

Complex energy eigenvalues and the non-Hermitian skin effect are two notable properties of non-Hermitian systems. These properties result in the localization of all eigenstates at the system boundaries, which can undermine the dynamic stability and experimental detection of topological edge states. In this paper, we investigate the one-dimensional non-Hermitian Su-Schrieffer-Heeger model with next-nearest-neighbor nonreciprocal hopping. By examining the energy spectrum and state distributions of the system, we demonstrate that the zero energy topological edge state and nonzero energy gap state can be distinguished from the non-Hermitian skin states. Additionally, we analyze the localization properties of these two states using the directional inverse participation ratio and investigate the non-Hermitian skin effect through the energy spectrum on the complex plane and the spectral winding number. Furthermore, we present phase diagrams of separation factor that illustrate the separation phenomenon between the edge or gap state and skin states. This work reveals the intriguing relationship between topological properties and non-Hermitian skin effects in one-dimensional nonreciprocal systems.

Bulk dislocation lattice defects are instrumental in identifying translationally active topological insulators (TATIs), featuring band inversion at a finite momentum ${\mathbf{K}}_{\mathrm{inv}}$. As such, TATIs host robust gapless modes around the dislocation core, when the associated Burgers vector $\mathbf{b}$ satisfies ${\mathbf{K}}_{\mathrm{inv}}·\mathbf{b}=\pi$ (modulo $2\pi$). From the time evolution of appropriate density matrices, we show that when a TATI via a real time ramp enters into a trivial or translationally inert topological insulating phase, devoid of gapless dislocation modes, the signatures of the preramp defect modes survive for a long time. More intriguingly, as the system ramps into a TATI phase from any translationally inert insulator, the signature of the dislocation mode dynamically builds up near its core, which is prominent for slow ramps. We exemplify these generic outcomes for two-dimensional time-reversal symmetry breaking insulators. Proposed dynamic responses at the dislocation core can be experimentally observed in quantum crystals, optical lattices, and metamaterials with a time tunable band gap.

We show that thin layers of EuO, a ferromagnetic insulator, can be achieved by topotactic reduction under titanium of a ${\mathrm{Eu}}_2{\mathrm{O}}_3$ film deposited on top of a graphene template. The reduction process leads to the formation of a 7-nm-thick EuO smooth layer, without noticeable structural changes in the underlying chemical vapor deposited graphene. The obtained EuO films exhibit ferromagnetism, with a Curie temperature that decreases with the initially deposited ${\mathrm{Eu}}_2{\mathrm{O}}_3$ layer thickness. By adjusting the thickness of the ${\mathrm{Eu}}_2{\mathrm{O}}_3$ layer below 7 nm, we promote the formation of EuO at the very graphene interface: the EuO/graphene heterostructure demonstrates the anomalous Hall effect (AHE), which is a fingerprint of proximity-induced spin polarization in graphene. The AHE signal moreover persists above $T_c$ up to 350 K due to a robust super-paramagnetic phase in EuO. This original high-temperature magnetic phase is attributed to magnetic polarons in EuO: we propose that the high strain in our EuO films grown on graphene stabilizes the magnetic polarons up to room temperature. This effect is different from the case of bulk EuO in which polarons vanish in the vicinity of the Curie temperature $T_c=69$ K.

Incommensurate magnetic order in the spin-3/2 antiferromagnet ${\mathrm{Na}}_3{\mathrm{RuO}}_4$ is uncovered by neutron diffraction combined with ab initio calculations. The crystal structure of ${\mathrm{Na}}_3{\mathrm{RuO}}_4$ contains two triangular motifs on different length scales. The magnetic ${\mathrm{Ru}}^{5+}$ ions form a lozenge (diamond) configuration, with tetramers composed of two isosceles triangles. These tetramers are further arranged in layers, such that an effective triangular lattice is formed. The tetramers are nearly antiferromagnetic but frustration between them leads to an incommensurately modulated magnetic structure described by the propagation vector $\vec{k}=(0.242\left(1\right),0,0.313\left(1\right))$. We show that the long-range Ru-O-O-Ru couplings between the tetramers play a major role in ${\mathrm{Na}}_3{\mathrm{RuO}}_4$ and suggest an effective description in terms of the spatially anisotropic triangular lattice if the tetramers are treated as single sites.

We theoretically study the current-phase relation in a Josephson junction comprising the Zeeman-split superconductors (ZSs) and a normal metal (N). We show that at low temperatures the Josephson current in the ZS/N/ZS junctions exhibits a supercurrent reversal at a certain phase difference ${\phi }_c\in (0,\pi )$. By calculating the spectral Josephson current, we demonstrate that the band splitting due to the Zeeman interaction causes the level crossing in the spectra of the Andreev bound states and the sign reversal of the Josephson current. Additionally, we propose an alternative method to observe the supercurrent reversal. Tuning the Rashba spin-orbit coupling electrically, one can control the critical phase difference ${\phi }_c$, eliminating the need for manipulating two magnetizations independently.

An antiferromagnetic insulator (AFMI) bearing a compensated interface to an adjacent conventional superconductor (S) has recently been predicted to generate Néel triplet Cooper pairs, whose amplitude alternates sign in space. Here, we theoretically demonstrate that such Néel triplets enable control of the superconducting critical temperature in an S layer via the angle between the Néel vectors of two enclosing AFMI layers. This angle dependence changes sign with the number of S monolayers providing a distinct signature of the Néel triplets. Furthermore, we show that the latter mediate a similarly distinct exchange interaction between the two AFMIs' Néel vectors.

We consider a two-dimensional Wigner crystal coupled to a quasi-one-dimensional asymmetric potential under ac or dc driving. As a function of electron density, substrate strength, and ac amplitude, we find that the system exhibits ordered and disordered pinned and dynamical states. Ratchet effects can appear under an applied ac drive and can be associated with pronounced structural changes from a disordered state to a one-dimensional smecticlike state. We observe a pinned phase, a diodelike ratchet where motion only occurs along the easy direction of the substrate asymmetry, a plastic ratchet where motion occurs in both directions but there is only a net drift in the easy direction, and an elastic ratchet where the system forms a crystal without plastic deformation that can still undergo ratcheting. At high filling, we find that there can be a ratchet reversal in which the net drift is along the hard direction of the substrate asymmetry. For weak disorder, there is an Aubry transition to a floating phase where the ratchet effects are lost. We map out the different dynamical phases as a function of substrate strength, filling, ac amplitude, and ac frequency. The ratchet effect on strong substrates is enhanced by thermal fluctuations, but is destroyed when the fluctuations become too large. Based on our results, we suggest other ways to detect Wigner crystals as well as methods for creating different types of devices to control disordered charge flow.

The planar Hall effect (PHE), the appearance of an in-plane transverse voltage in the presence of coplanar electric and magnetic fields, has been ascribed to the chiral anomaly and Berry curvature effects in Weyl semimetals. In the presence of position- and time-dependent perturbations, such as strain, Weyl semimetals react as if they would be subjected to emergent electromagnetic fields, known as pseudofields. In this paper we investigate the possibility of inducing nonlinear phenomena, including the PHE, in strained Weyl semimetals. Using the chiral kinetic theory in the presence of pseudofields, we derive general expressions for the magnetoconductivity tensor by considering the simultaneous effects of the Berry curvature and orbital magnetic moment of carriers, which are indeed of the same order of magnitude. Since pseudofields couple to the Weyl fermions of opposite chirality with opposite signs, we study chirality-dependent phenomena, including the longitudinal magnetoconductivity and the planar Hall effect. We discuss our results in terms of the chiral anomaly with pseudofields. These may open possibilities in chiralitytronics.

Since the 1960s and the first observations of radiation-induced disruption of electronic devices in space, the study of the effects of ionizing radiation on electronics has grown into an extensive field of its own. The present paper is concerned with studying accurately the energy-loss processes that control the thermalization of hot carriers (electrons, holes, and/or electron-hole pairs) that are generated by high-energy radiation in wurtzite GaN, using an ab initio approach. Current physical models of the nuclear/particle physics community cover thermalization in the high-energy range (kinetic energies exceeding $\sim 100\mathrm{eV}$), and the electronic-device community has studied extensively carrier transport in the low-energy range (below $\sim 10\mathrm{eV}$). However, the processes that control the energy losses and thermalization of electrons and holes in the intermediate energy range of about 10–100 eV (which we define as the “10–100 eV gap”) are poorly known. The aim of this research is to close this gap. To this end, we utilize density functional theory (DFT) to obtain the band structure and dielectric function of GaN for energies up to about 100 eV. We also calculate charge-carrier scattering rates for the major charge-carrier interactions (phonon scattering, impact ionization, and plasmon emission), using the DFT results and first-order perturbation theory (Fermi's golden rule/first Born approximation). With this information, we study the thermalization of electrons starting at 100 eV using the Monte Carlo method to solve the semiclassical Boltzmann transport equation. Full thermalization of electrons and holes is complete within $\sim 1$ and 0.5 ps, respectively. Hot electrons dissipate about 90% of their initial kinetic energy to the electron-hole gas (90 eV) during the first $\sim 0.1\mathrm{fs}$, due to rapid plasmon emission and impact ionization at high energies. The remaining energy is lost more slowly as phonon emission dominates at lower energies (below $\sim 10\mathrm{eV}$). During the thermalization, hot electrons generate pairs with an average energy of $\sim 8.9\mathrm{eV}/\mathrm{pair}$ (11–12 pairs per hot electron). Additionally, during the thermalization, the maximum electron displacement from its original position is found to be on the order of 100 nm.

Assuming a logarithmic interaction between constituent particles, compact and locally accurate wave functions that describe bound states of the two-particle neutral, and three-particle charged complexes in two dimensions are designed. Prime examples of these complexes are excitons and trions that appear in monolayers of transition-metal dichalcogenides (TMDCs). In the case of excitons, these wave functions led to five to six correct decimal digits in the energy and the diamagnetic shifts. In addition, it is demonstrated that they can be used as zero-order approximations to study magnetoexcitons via perturbation theory in powers of the magnetic field strength. For the trion, making a comparison with experimental data for concrete TMDCs, we established that the logarithmic potential leads to binding energies $\lesssim 30$% greater than experimental ones. Finally, the structure of the wave function at small and large distances was established for excitons whose carriers interact via the Rytova-Keldysh potential.

We establish the Hatsugai-Kohmoto model as a stable quartic fixed point (distinct from Wilson-Fisher) by computing the $\beta$ function in the presence of perturbing local interactions. In vicinity of the half-filled doped Mott state, the $\beta$ function vanishes for all local interactions regardless of their sign. The only flow away from the HK model is through the superconducting channel which lifts the spin degeneracy as does any ordering tendency. The superconducting instability is identical to that established previously [Phillips et al., Nat. Phys. 16, 1175 (2020)]. A corollary of this work is that any system in which the spectral weight bifurcates into lower and upper bands such as the Hubbard model with repulsive interactions flows into the HK stable fixed point in the vicinity of half-filling. Consequently, although the HK model has all-to-all interactions, the bifurcation of the spectral weight is stable as nothing local destroys it. The consilience with Hubbard arises because both models break the $Z_2$ symmetry on a Fermi surface, the HK model being the simplest to do so. Indeed, the simplicity of the HK model belies its robustness and generality.

Recently, models with long-range interactions—known as Hatsugai-Kohmoto (HK) models—have emerged as a promising tool to study the emergence of superconductivity and topology in strongly correlated systems. Two obstacles, however, have made it difficult to understand the applicability of these models, especially to topological features: they have thermodynamically large ground state degeneracies and they tacitly assume spin conservation. We show that neither are essential to HK models and that both can be avoided by introducing interactions between tight-binding states in the orbital basis rather than between energy eigenstates. To solve these orbital models, we introduce a general technique for solving HK models and show that previous models appear as special cases. We illustrate our method by exactly solving graphene and the Kane-Mele model with HK interactions. Both realize Mott insulating phases with finite magnetic susceptibility; the graphene model has a fourfold degenerate ground state while the Kane-Mele model has a nondegenerate ground state in the presence of interactions. Our technique then allows us to study the effect of strong interactions on symmetry-enforced degeneracy in spin-orbit coupled double-Dirac semimetals. We show that adding HK interactions to a double Dirac semimetal leads to a Mott-insulating, spin-liquid phase. We then use a Schrieffer-Wolff transformation to express the low-energy Hamiltonian in terms of the spin degrees of freedom, making the spin-charge separation explicit. Finally, we enumerate a broader class of symmetry-preserving HK interactions and show how they can violate insulating filling constraints derived from space-group symmetries. This suggest that additional care is needed to study topological order in the presence of long-range interactions of the HK type.

Within the method of spectral moments it is possible to construct the spectral function of a many-electron system from the first $2P$ spectral moments ($P=1,2,3,\cdots$). The case $P=1$ corresponds to standard Kohn-Sham density functional theory (KS-DFT). Taking $P>1$ allows us to consider additional important properties of the uniform electron gas (UEG) in the construction of suitable moment potentials for moment-functional-based spectral density functional theory (MFbSDFT). For example, the quasiparticle renormalization factor $Z$, which is not explicitly considered in KS-DFT, can be included easily. In the four-pole approximation of the spectral function of the UEG (corresponding to $P=4$) we can reproduce the momentum distribution, the second spectral moment, and the charge response acceptably well, while a treatment of the UEG by KS-DFT reproduces from these properties only the charge response. For weakly and moderately correlated systems we can reproduce the most important aspects of the four-pole approximation by an optimized two-pole model, which leaves out the low-energy satellite band. From the optimized two-pole model we extract parameter-free universal moment potentials for MFbSDFT, which improve the description of the band gaps in Si, SiC, BN, MgO, CaO, and ZnO significantly.

We compare the acoustic Su–Schrieffer–Heeger (SSH) model with two of its optical variants where the phonons are defined on either on the sites or bonds of the system. First, we discuss how to make fair comparisons between these models in any dimension by ensuring their dimensionless coupling $\lambda$ and relevant phonon energies are the same. We then use determinant quantum Monte Carlo to perform nonperturbative and sign-problem-free simulations of all three models on one-dimensional chains at and away from half-filling. By comparing the results obtained from each model, we demonstrate that the optical and acoustic models produce near identical results within error bars for suitably chosen phonon energies and $\lambda$ at half-filling. In contrast, the bond model has quantitatively different behavior due to its coupling to the $\mathbf{q}=0$ phonon mode. These differences also manifest in the total length of the chain, which shrinks for the bond model but not for the acoustic and optical models when $\lambda \ne 0$. Our results have important implications for quantum Monte Carlo modeling of SSH-like interactions, where these models are sometimes regarded as being interchangeable.

Phosphorene, a monolayer of black phosphorus, is a two-dimensional material that lacks a multivalley structure in the Brillouin zone and has negligible spin-orbit coupling. This makes it a promising candidate for investigating the orbital Hall effect independently of the valley or spin Hall effects. To model phosphorene, we utilized a density-functional-theory-derived tight-binding Hamiltonian, which is constructed with the pseudoatomic orbital projection method. For that purpose, we use the paoflow code with a newly implemented internal basis that provides a fairly good description of the phosphorene conduction bands. By employing linear response theory, we show that phosphorene exhibits a sizable orbital Hall effect with strong anisotropy in the orbital Hall conductivity for the out-of-plane orbital angular momentum component. The magnitude and sign of the conductivity depend on the in-plane direction of the applied electric field. These distinctive features enable the observation of the orbital Hall effect in this material unambiguously. The effects of strain and of a perpendicularly applied electric field on the phosphorene orbital Hall response are also explored. We show that a supplementary electric field applied perpendicular to the phosphorene layer in its conductive regime gives rise to an induced in-plane orbital magnetization.

In this work, we report a meta-layer consisting of subwavelength local resonators to achieve low-frequency isolation of elastic waves. Apart from its distinctive low-dimensional configuration with a thickness of $\frac{1}{7}$ the wavelength, the meta-layer differs from bandgap-based metamaterials in that its optimally isolating frequency is higher than the eigenfrequency. We demonstrate theoretically, numerically, and experimentally that the isolating frequency shift arises from the coupling effect between the resonators and the load-carrying plate or beam. As a further step, to demonstrate the universality of our theory, we predict and design a meta-layer with an opposite-frequency shift. The proposed meta-layer, along with its corresponding theory, can precisely guide the development of compact low-frequency wave isolation devices.

We propose emergent time-reversal switching responses in antiferromagnets, which are triggered by an accompanying magnetic toroidal monopole, i.e., a time-reversal odd scalar distinct from electric and magnetic monopoles. We show that simple collinear antiferromagnets exhibit unconventional responses to external electric and/or magnetic fields once magnetic symmetry accommodates the magnetic toroidal monopole. We specifically demonstrate that the emergence of the magnetic toroidal monopole in antiferromagnets enables us to control rotational distortion by an external magnetic field, switch vortex-type antiferromagnetic structure by an external electric field, and convert right-handedness/left-handedness in chirality by a composite electromagnetic field. We also present the symmetry conditions to induce the magnetic toroidal monopole and exhibit candidate materials including noncollinear antiferromagnets in order to stimulate experimental observations.

Helium (He) plays a critical role in numerous areas ranging from the study of celestial objects like brown dwarfs and gas giants to modern-day technologies like nuclear energy and rocket propulsion. For many of these applications, it is essential to have a reliable equation of state (EOS) for He that yields an accurate representation of its thermodynamic behavior. To help constrain and develop such EOS models, we have performed a series of shock-compression experiments on cryogenic liquid He to pressures exceeding 100 GPa using a magnetically accelerated flyer plate on Sandia National Laboratories' Z-machine. We have also performed quantum molecular dynamics simulations that are consistent with our shock measurements. None of the previously available EOSs agree with our experimental and simulation results, motivating the development of a fluid-phase He EOS that we present in this study. We show that our EOS yields good agreement with published data that span temperatures and pressures encountered across a diverse array of applications.