We examine the near-field radiative heat transfer between finite-thickness planar fused silica slabs covered with graphene gratings, through the utilization of the Fourier modal method augmented with local basis functions (FMM-LBF), with a focus on the lateral shift effect (LSE). To do so, we propose and validate a minor modification of the FMM-LBF theory to account for the lateral shift. This approach goes far beyond the effective medium approximation, which cannot account for the lateral shift. We show that the heat flux can exhibit significant oscillations with the lateral shift, and at short separation, it can experience up to a 60–70% reduction compared with the aligned case. Such an LSE is found to be sensitive to the geometric factor $d/D$ (separation distance to grating period ratio). When $d/D>1$ (realized through large separation or small grating period), the two graphene gratings see each other as an effective whole rather than in detail, and thus, the LSE on heat transfer becomes less important. Therefore, we can clearly distinguish two asymptotic regimes for radiative heat transfer: the LSE regime, where a significant LSE is observed, and the non-LSE regime, where this effect is negligible. Furthermore, regardless of the lateral shift, the radiative heat flux shows a nonmonotonic dependence on the graphene chemical potential. That is, we can get an optimal radiative heat flux (peaking at $\sim 0.3$ eV chemical potential) by modulating the chemical potential in situ. This paper has the potential to unveil avenues for harnessing the LSE on radiative heat transfer in graphene-based nanodevices.

Studies of the formation of Landau levels based on the Schrödinger equation for electrons constrained to curved surfaces have a long history. These include as prime examples surfaces with constant negative curvature, like the pseudosphere [A. Comtet, Ann. Phys. 173, 85 (1987)]. Now, topological insulators, hosting Dirac-type surface states, provide a unique platform to experimentally examine such quantum Hall physics in curved space. Hence, extending previous work we consider solutions of the Dirac equation for the pseudosphere for both the case of an overall perpendicular magnetic field and a homogeneous coaxial, thereby locally varying, magnetic field. For both magnetic-field configurations, we provide analytical solutions for spectra and eigenstates. For the experimentally relevant case of a coaxial magnetic field we find that the Landau levels split and one class shows a peculiar scaling $\propto B^{1/4}$, thereby characteristically differing from the usual linear $B$ and $B^{1/2}$ dependence of the planar Schrödinger and Dirac case, respectively. We compare our analytical findings to numerical results that we also extend to the case of the Minding surface.

Ab initio quantum Monte Carlo (QMC) is a state-of-the-art numerical approach for evaluating accurate expectation values of many-body wave functions. However, one of the major drawbacks that still hinders widespread QMC applications is the lack of an affordable scheme to compute unbiased atomic forces. In this study, we propose an efficient method to obtain unbiased atomic forces and pressures in the variational Monte Carlo (VMC) framework with the Jastrow-correlated Slater determinant ansatz or the Jastrow antisymmetrized geminal power ansatz, exploiting the gauge-invariant and locality properties of their geminal representation. We demonstrate the effectiveness of our method for ${\mathrm{H}}_2$ and ${\mathrm{Cl}}_2$ molecules and for the cubic boron nitride crystal. Our framework has a better algorithmic scaling with the system size than the traditional finite-difference method and, in practical applications, is as efficient as single-point VMC calculations. Thus, it paves the way to study dynamical properties of materials, such as phonons, and is beneficial for pursuing more reliable machine-learning interatomic potentials based on unbiased VMC forces.

We present electrical resistivity measurements on the prototypical heavy-fermion metal ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ (YRS) under $a$-axis tensile and compressive strain and focus on the evolution of the resistivity maximum near 136 K that arises from the interplay of the Kondo effect and the crystal electric field (CEF) splitting. While compressive strain reduces $T_{\max }$, similar as previously reported for hydrostatic pressure, $T_{\max }$ is enhanced up to 145 K for 0.13% tensile strain. Model calculations for the strain effect on CEF splitting in YRS reveal a negligible shift of the levels. Instead, the enhancement of the resistivity maximum indicates a 20% increase of the Kondo temperature. This opens the perspective to access the hidden zero-field quantum critical point in pure YRS.

We investigate the superconducting (SC), charge-density wave (CDW), and antiferromagnetic (AFM) phases in the extended Hubbard model at zero temperature and half filling. We employ the iterated equations of motion approach to compute the two-particle Green's functions and their spectral densities. This renders a comprehensive analysis of the behavior of collective excitations possible as the model's parameters are tuned across phase transitions. We identify the well-known amplitude (Higgs) and phase (Anderson-Bogoliubov) modes within the superconducting phase and observe a similar excitation (cooperon) in the CDW phase which shifts towards zero energy as the system approaches the phase transition to the SC phase. In the CDW phase, close to the phase transition to the AFM phase, we find a collective mode, an exciton, that does not change significantly and another mode, a longitudinal magnon, that emerges from the two-particle continuum as the system approaches the phase transition to the AFM phase. It becomes identical with the former at the transition. In the AFM phase, their roles are reversed. Additionally, we find a transversal Goldstone magnon located at zero energy.

The discovery of superconductivity in $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ has sparked significant research interest in the field of nickelate superconductors. Despite extensive studies on pristine $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$, the role of oxygen vacancies ($V_{\mathrm{O}}$), a common type of intrinsic defect in oxides, on electronic structures and superconductivity in $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ remains unclear. In this paper, we identify that the loss of intrabilayer apical oxygen is the most energetically favorable. The electronic structure undergoes notable changes, particularly for the Ni-$d_{z2}$ and Ni-$d_{x2-y2}$ orbitals. The $d_{z2}$ orbital shifts downward, substantially reducing its proportion at the Fermi level. Conversely, the proportion of the $d_{x2-y2}$ state increases due to the orbital localization. Applying the two-band model, the hopping strength between intrabilayer $d_{z2}$ functions is observed to increase significantly but with opposite signs, which deviates from the previous understanding. The interorbital hopping between $d_{z2}$ and $d_{x2-y2}$ functions decreases in the presence of $V_{\mathrm{O}}$. Our results indicate that the formation of $V_{\mathrm{O}}$ could be harmful to the superconductivity in $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$, considering the general assumption regarding the critical role of $d_{z2}$ in superconductivity generation. Additionally, we propose that $\mathrm{C}{\mathrm{e}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$, possessing similar electronic structures to $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$, could be a promising nickelate superconductor with a potential low concentration of $V_{\mathrm{O}}$.

It is an outstanding goal to unveil the key features of quantum dynamics at eigenstate transitions. Focusing on quadratic fermionic Hamiltonians that exhibit localization transitions, we identify physical observables that exhibit scale-invariant critical dynamics at the transition when quenched from the initially localized charge-density-wave states. The identification is based on two ingredients: (a) a relationship between the time evolution of observables in a many-body state and the transition probabilities of single-particle states, and (b) scale invariance of transition probabilities, which generalizes the corresponding recent result for survival probabilities [M. Hopjan and L. Vidmar, Phys. Rev. Lett. 131, 060404 (2023); Phys. Rev. Res. 5, 043301 (2023)]. These properties suggest that the scale-invariant critical dynamics in the quantum-quench dynamics is also exhibited by the observables, which share the common eigenbasis with the Hamiltonian before the quench. Focusing on experimentally relevant observables such as site occupations and the particle imbalance, we numerically demonstrate their critical behavior at the eigenstate transitions in the three-dimensional Anderson model and the one-dimensional Aubry-André model.

New radiative transitions in undoped and Mn-doped ${\mathrm{CdGeP}}_2$ crystals have been detected by low-temperature photoluminescence and excitation at different wavelengths. ${\mathrm{CdGeP}}_2$ is a direct-band-gap semiconductor with good luminescent properties due to intrinsic point defects, mainly ${\mathrm{V}}_{\mathrm{Cd}}$ and ${\mathrm{V}}_{\mathrm{P}}$ vacancies, ${\mathrm{Cd}}_{\mathrm{Ge}}$, ${\mathrm{Ge}}_{\mathrm{Cd}}$, and ${\mathrm{Ge}}_{\mathrm{P}}$ cation antisites, and defect pairs. Doping with manganese does not significantly affect the intrinsic defects but cardinally changes the emission at energies above the band gap. Optical transitions occur due to redistribution of optical energy channels through Mn ions embedded in the tetragonal lattice, which allows observation of previously unobserved interband transitions in ${\mathrm{CdGeP}}_2$ crystal. The emission at energies of 2.5–3.5 eV becomes even stronger than the emission through intrinsic point defects, especially when deep levels are excited by violet (325 nm) and blue (458 nm) lasers compared to green (514, 532 nm) lasers.

In general, the photoelectric properties of $\mathrm{Ti}{\mathrm{O}}_2$ are highly dependent on its crystal directions and facets. However, the impact of initial momentum distributions, group velocity distributions, and spatial transport properties of photoexcited carriers on the anisotropic photoelectric properties needs more study. In this work, we have thoroughly investigated these issues at the atomic and electronic scales for anatase and rutile $\mathrm{Ti}{\mathrm{O}}_2$ with homemade code. It is meaningful to find that anatase and rutile $\mathrm{Ti}{\mathrm{O}}_2$ mainly produce high-energy electrons and holes upon photoexcitation, respectively, which is beneficial for the efficient separation of carriers in the heterojunction system of anatase and rutile $\mathrm{Ti}{\mathrm{O}}_2$. In addition, it is found that for both anatase and rutile $\mathrm{Ti}{\mathrm{O}}_2$, the initial momentum and group velocity distribution of the photoexcited carriers is highly anisotropic, and anatase $\mathrm{Ti}{\mathrm{O}}_2$ has a better directionality than rutile as a whole. Moreover, the transport properties of carriers in group velocity space also exhibit high anisotropy. Notably, the crystal directions with excellent transport properties are consistent with the group velocity distribution of carriers in anatase $\mathrm{Ti}{\mathrm{O}}_2$, which indicates the beneficial transport and accumulation of photoexcited carriers. In contrast, the crystal directions with excellent transport properties are inconsistent with the preferable group velocity distribution of carriers in rutile $\mathrm{Ti}{\mathrm{O}}_2$, which may result in unfavorable carrier transport and accumulation properties. These results provide not only valuable thoughts for understanding related experimental phenomena but also theoretical guidance for effectively collecting carriers in $\mathrm{Ti}{\mathrm{O}}_2$.

In analogy with superfluidity, nonequilibrium polariton condensation can be phenomenologically described in terms of separated condensed and normal fractions. Under the assumption of a significantly shorter characteristic timescale, the incoherent part is frequently traced out adiabatically. In this work, we stress the importance of accounting for the time-resolved coupling between the condensed and normal fractions. Even in the case of a significant mismatch in the evolution rates, the coupling with the normal fraction drastically alters the condensate dynamics and leads to a variety of previously overlooked phases in a confined configuration. Focusing on the case of annular optically induced traps for polaritons, we elaborate on the nonadiabatic model of polariton condensation. Using the two-mode approximation, accounting for a couple of quantized polariton vortices with opposite angular momenta, we identify the range of validity for the adiabatic elimination of the incoherent reservoir. Beyond this range, the nonadiabatic interaction with a circularly symmetric trapping reservoir supports multistability, limit cycle dynamics, and the formation of a neutral equilibrium standing-wave phase featuring spontaneous breaking of the continuous radial symmetry. In the presence of a weak trap asymmetry, the nonadiabaticity prevents the formation of giant polariton vortices. We argue that our detailed description provides an interpretation of the dominance of the standing-wave phase over the persistent vortex phase in experimental observations.

This paper investigates the bulk and boundary dynamics of Laughlin states, which are modeled using composite boson theory within a fluid dynamics framework. In this work, we adopt an alternative starting point based on a hydrodynamic action with topological terms, which fleshes out the fluid aspects of the Laughlin state manifestly. For a particular choice of the velocity field, the fluid equation for this action is akin to first-order hydrodynamic equations, supplemented with an additional constitutive equation known as the Hall constraint. When a hard wall boundary is present, one of the topological terms in the fluid action triggers anomaly inflow, indicating the presence of gauge anomaly at the edge. The first-order hydrodynamic equations require a second boundary condition, which, in the absence of dissipation, can be either a no-slip or a no-stress condition. We find that the no-slip condition, where the fluid adheres to the wall, is incompatible with the chiral edge dynamics. On the other hand, the no-stress condition, which allows the fluid to move along the wall without friction, is consistent with the expected chiral edge dynamics of the Laughlin state. Furthermore, our work derives this modified no-stress boundary condition within a variational principle. This is accomplished by incorporating a chiral boson action within the boundary action that is nonlinearly coupled to the edge density, thus systematically extending the edge chiral Luttinger liquid theory.

We consider two-dimensional (2d) quantum many-body systems with long-range orders, where the only gapless excitations in the spectrum are Goldstone modes of spontaneously broken continuous symmetries. To understand the interplay between classical long-range order of local order parameters and quantum order of long-range entanglement in the ground states, we study the topological point defects and textures of order parameters in such systems. We show that the universal properties of point defects and textures are determined by the remnant symmetry enriched topological order in the symmetry-breaking ground states with a nonfluctuating order parameter, and provide a classification for their properties based on the inflation-restriction exact sequence. We highlight a few phenomena revealed by our theory framework. First, in the absence of intrinsic topological orders, we show a connection between the symmetry properties of point defects and textures to deconfined quantum criticality. Second, when the symmetry-breaking ground state has intrinsic topological orders, we show that the point defects can permute different anyons when braided around. They can also obey projective fusion rules in the sense that multiple vortices can fuse into an Abelian anyon, a phenomenon for which we coin “defect fractionalization.” Finally, we provide a formula to compute the fractional statistics and fractional quantum numbers carried by textures (skyrmions) in Abelian topological orders.

In the absence of vortices or phase slips, the phase dynamics of exciton-polariton condensates was shown to map onto the Kardar-Parisi-Zhang (KPZ) equation, which describes the stochastic growth of a classical interface. This implies that the coherence of such nonequilibrium quasicondensates decays in space and time following stretched exponentials, characterized by KPZ universal critical exponents. In this work, we focus on the time evolution of the average phase of a one-dimensional exciton-polariton condensate in the KPZ regime and determine the frequency of its evolution, which is given by the blueshift, i.e., the nonequilibrium analog of the chemical potential. We determine the stochastic corrections to the blueshift within Bogoliubov linearized theory and find that while this correction physically originates from short scale effects, and depends both on density and phase fluctuations, it can still be related to the effective large-scale KPZ parameters. Using numerical simulations of the full dynamics, we investigate the dependence of these blueshift corrections on both noise and interaction strength, and compare the results to the Bogoliubov prediction. Our finding contributes both to the close comparison between equilibrium and nonequilibrium condensates, and to the theoretical understanding of the KPZ mapping.

In this work, we propose a many-body model for cooperative Jahn-Teller/orbital ordering in crystals containing unpaired electrons in locally degenerate e-shells (${\mathrm{KCuF}}_3$, CuO, ${\mathrm{CuCl}}_2$, $\cdots$) that moves away from the usual Heisenberg-like expressions for solids and that is closely related to the usual local Jahn-Teller formulation for molecules and impurities. In particular, we show that the crystal problem can be expressed as a $[E_g\left(\mathrm{\Gamma }\right)+E_g\left(R\right)]\otimes [e_g^{\text{st}}\left(\mathrm{\Gamma }\right)+e_g^{\text{ph}}\left(R\right)]$ combined Jahn-Teller and pseudo-Jahn-Teller problem where the involved distortion modes $e_g^{\text{st}}\left(\mathrm{\Gamma }\right)$ and $e_g^{\text{ph}}\left(R\right)$ are, respectively, a ferrodistortive strain mode and a phonon (ferro- or antiferrodistortive) mode that are strongly coupled among themselves. This model, fully consistent with experimental data, allows us to predict new phases that are separated by only a few meV from the ground state, and to propose ways to observe them. First-principles simulations fully support these findings. Comparison of our model with previous orbital ordering models shows subtle yet significant differences in the way orbital degrees of freedom work. We finally show that many orbital ordering models and density functional theory simulations yield solutions that are not consistent with Bloch's theorem and should be regarded with caution.

Topological magnon insulators support chiral edge excitations, whose lack of electric charge makes them notoriously difficult to detect experimentally. We show that relativistic magnetoelectric coupling universally renders chiral edge magnons electrically active, thereby facilitating electrical probes of magnon topology. Considering a two-dimensional out-of-plane magnetized topological magnon insulator, we predict a fluctuation-activated electric polarization perpendicular to the sample edges. Furthermore, the chiral topological electromagnons give rise to a unique in-gap signal in electrical absorption experiments. These results suggest THz spectroscopy as a promising probe for topological magnons.

The isotope effect with a large coefficient $\alpha =-\partial ln{T}_c/\partial lnM$ is usually taken as evidence of phonon-mediated superconductors in the Bardeen-Cooper-Schrieffer (BCS) theory. However, in cuprates which are now widely believed to be strong correlation-induced $d$-wave superconductors, $\alpha$ is experimentally observed to be quite small at optimal doping, but keeps growing with decreasing $T_c$ upon doping, even after exceeding the BCS value $1/2$. Such an anomalous isotope effect seems to challenge the nonphonon picture and still leave room for the phonon-dominated mechanism. In this Letter, we show that the anomalous dependence of $\alpha$ on $T_c$ can actually be obtained in spin-fluctuation-induced $d$-wave superconductors by studying the Hubbard model on square lattices with functional renormalization group. We have considered two types of electron-phonon couplings (EPCs). The first type couples to electron densities, including the Holstein, breathing, and buckling phonons, called Holstein-like. For all these EPCs, $\alpha$ is negative and drops down towards $-\infty$ with decreasing $T_c$ upon doping. On the opposite, for the other type of Peierls-like EPC coupling to electron hoppings on the nearest bonds, also called Su-Schrieffer-Heeger phonon, $\alpha$ is positive, grows with decreasing $T_c$, and tends to diverge as $T_c\to 0$, in qualitative agreement with the experiments. The difference between these two types of EPCs can be understood by their isotope effects on spin fluctuations. From this study, we conclude that the SSH phonon can explain the anomalous isotope effect in cuprates, although it is not the leading pairing mechanism.

To clarify the nature of high-temperature superconductivity in the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under pressure, we investigate, using the density-matrix renormalization group method, the pair correlations in the two-orbital $t\text{−}J$ ladder model. While the interchain-intraorbital pair correlations exhibit a slow power-law decay in both orbitals, the interorbital pair correlation also develops strongly enough to be comparable with the intraorbital correlations. These intra and interorbital pair correlations are enhanced by Hund's coupling, but more importantly, the interorbital pair correlation develops even when interorbital pairing glue mediated by Hund's coupling is absent. Our finding suggests that the pair correlation in the present system develops as a hybridized two-orbital entity, which may have some implications on the superconductivity in the bilayer nickelate.

Generating a pure spin current using electrons, which have degrees of freedom beyond spin, such as electric charge and valley index, presents challenges. In response, we propose a mechanism based on intervalley exciton dynamics in arc-shaped strained transition metal dichalcogenides (TMDs) to achieve the exciton spin Hall effect in an electrically insulating regime, without the need for an external electric field. The interplay between strain gradients and strain-induced pseudomagnetic fields results in a net Lorentz force on long-lived intervalley excitons in ${\mathrm{WSe}}_2$, carrying nonzero spin angular momentum. This process generates an exciton-mediated pure spin Hall current, resulting in opposite-sign spin accumulations and local magnetization on the two sides of the single-layer arc-shaped TMD. We demonstrate that the magnetic field induced by spin accumulation, at approximately $\sim \mathrm{mT}$, can be detected using techniques such as superconducting quantum interference magnetometry or spatially resolved magneto-optical Faraday and Kerr rotations.