Recent discovery of superconductivity at a transition temperature of $73\mathrm{K}$ in the doped layered compound ${\text{Ba}}_2{\mathrm{CuO}}_{3+x}$ for $x\sim 0.2$ has generated a lot of interest. Experiments in this alternately stacked oxygen octahedral and chain layered structure reveal that a compression of the octahedra causes the Cu-$d_{z^2}$ orbital to lie above the Cu-$d_{x^2-y^2}$ orbital unlike in the well-known cuprate superconducting materials. Our first-principles calculations and low-energy Hamiltonian studies on the $x$ = 0.25 system reveal that this energy ordering results in formation of $d_{z^2}$-dominated electron pockets. The strong nesting in the Fermi pockets leads to an AFM spin fluctuation mediated $d_{xy}$-wave superconducting state dominated by pairing among the $d_{z^2}$ orbitals. This is in contrast to the cuprate superconductors (e.g., YBCO) where both electron and hole pockets exist and the superconducting state with $B_{1g}$ symmetry are formed by the $d_{x^2-y^2}$ orbital electrons. Unlike the earlier reports we find the interlayer hybridization has an important contribution to the low-energy band structure and formation of the unconventional superconducting state.

The thermal properties of bilayer graphene (BLG) play a crucial role in the advancement of its promising electronic devices. However, the measurement of thermal conductivity using current techniques faces obstacles due to the low temperature gradient both in plane and across the interface in the sample. Here we present an approach to simultaneously explore the in-plane and interfacial thermal conductivity of chemical vapor deposited AB-stacked BLG by utilizing an isotope labeling assisted Raman spectroscopic technique. By applying the modified heat diffusion model, we acquire the interfacial thermal conductivity of isotopically labeled AB-stacked BLG of $105\pm 3\mathrm{MW}/\left({\mathrm{m}}^2\mathrm{K}\right)$, whereas we find the in-plane thermal conductivity of each layer is reduced compared with their monolayers. This technique demonstrates strong support for advancing the BLG thermal engineering research as well as a potential of extending to other two-dimensional systems.

The thickness-dependent atomic structures of two-dimensional (2D) few-layer (FL) ZnO are systematically investigated by the first-principles calculations. It is found that the structural transformation between thinner FL ZnO with graphitic structure $(\mathrm{FL} g\mathrm{ZnO})$ and thicker FL ZnO with wurtzite structure $(\mathrm{FL} w\mathrm{ZnO})$ takes place at the critical thickness of 9–12 Zn-O atomic layers. At the thickness of 9–12 layers, both graphitic and wurtzite structures can coexist at room temperature. In FL $g\mathrm{ZnO}$, the interlayer interaction is a long-range Coulomb interaction, and the charge population of Zn and O inside does not change during the structural transformation. Moreover, we demonstrate that the structural transformation of FL ZnO originates from the competition between the high energy of the O $2p_z$ orbital in the graphitic structure and the polar-surface-induced dipole energy in the wurtzite structure. Our microscopic understanding guides a clear direction of regulating the atomic structure of FL ZnO, further optimizing its electronic properties, which benefits developing function-advanced 2D stacked devices.

We analyze time evolution of spread complexity (SC) in an isolated interacting quantum many-body system when it is subjected to a sudden quench. Characteristics features of the time evolution of the SC after the quench are analyzed for different timescales, both in integrable and chaotic models. For a short time after the quench, the SC shows universal quadratic growth, irrespective of the initial state or the nature of the Hamiltonian, with the timescale of this growth being determined by the local density of states. The characteristics of the SC in the next phase depend on the nature of the system, and we show that, depending on whether the survival probability of an initial state is Gaussian or exponential, the SC can continue to grow quadratically, or it can show linear growth. To understand the behavior of the SC at late times, we consider sudden quenches in two models, a full random matrix in the Gaussian orthogonal ensemble, and a spin-$1/2$ system with disorder. We observe that, for the full random matrix model and the chaotic phase of the spin-$1/2$ system, the SC shows linear growth at early times and saturation at late times. The full random matrix case shows a peak in the intermediate-time region, whereas this feature is less prominent in the spin-$1/2$ system, as we explain.

It is well known that non-Hermitian systems can be extremely sensitive to boundary conditions owing to non-Hermitian skin effect (NHSE). Analogously, we investigate two boundary-sensitive $\text{U}\left(1\right)$-symmetric Lindbladians: one carries current in the steady state, and the other does not. The numerical results indicate significant change of the Liouvillian spectrum, eigenmodes, and relaxation time for both Lindbladians when the boundary conditions are altered. This phenomenon is found to be triggered by the Liouvillian skin effect (LSE), specifically the localization of eigenmodes, which stems from the NHSE of the non-Hermitian effective Hamiltonian. In addition, these two Lindbladians manifest different LSE, ultimately resulting in distinct relaxation behaviors.

Frustration-induced strong quantum fluctuations accompanied by spin-orbit coupling and crystal electric field can give rise to rich and diverse magnetic phenomena associated with unconventional low-energy excitations in rare-earth-based quantum magnets. Herein, we present crystal structure, magnetic susceptibility, specific heat, muon spin relaxation ($\mu \mathrm{SR}$), and electron spin resonance (ESR) studies on polycrystalline samples of ${\mathrm{Ba}}_6{\mathrm{Yb}}_2{\mathrm{Ti}}_4{\mathrm{O}}_{17}$, in which ${\mathrm{Yb}}^{3+}$ ions constitute a perfect triangular lattice in the $ab$ plane without detectable antisite disorder between atomic sites. The Curie-Weiss fit of the low-temperature magnetic susceptibility data suggests spin-orbit driven effective pseudospin $J_{\mathrm{eff}}=\frac{1}{2}$ degrees of freedom of ${\mathrm{Yb}}^{3+}$ spin with weak antiferromagnetic exchange interactions in the Kramers doublet ground state. The zero-field specific heat data reveal the presence of long-range magnetic order at Néel temperature $T_{\mathrm{N}}=77\mathrm{mK}$ which is suppressed in a magnetic field ${\mu }_{0}H\ge 1\mathrm{T}$. The broad maximum in specific heat is attributed to the Schottky anomaly implying the Zeeman splitting of the Kramers doublet ground state in a magnetic field. The ESR measurements suggest the presence of anisotropic exchange interaction between the moments of ${\mathrm{Yb}}^{3+}$ spins. The $\mu \mathrm{SR}$ experiments reveal a fluctuating state of ${\mathrm{Yb}}^{3+}$ spins in the temperature range $0.1\mathrm{K}\le T\le 10\mathrm{K}$ owing to depopulation of crystal electric field levels, which suggests that the lowest Kramers doublets with $J_{\mathrm{eff}}=\frac{1}{2}$ are well separated, and the low-temperature physics of this frustrated magnet is dominated by $J_{\mathrm{eff}}=\frac{1}{2}$ moments. In addition to the intraplane nearest-neighbor superexchange interaction, the interplane exchange interaction and anisotropy are expected to stabilize the long-range ordered state in this triangular lattice antiferromagnet.

We conducted a comparative study of the rare-earth infinite-layer nickelate films, $R{\mathrm{NiO}}_2$ ($R$ = La, Pr, and Nd), using resonant inelastic x-ray scattering (RIXS). We found that the gross features of the orbital configurations are essentially the same, with minor variations in the detailed hybridization. For low-energy excitations, we unambiguously confirm the presence of damped magnetic excitations in all three compounds. By fitting to a linear spin-wave theory, comparable spin exchange coupling strengths and damping coefficients are extracted, indicating a universal magnetic structure in the infinite-layer nickelates. Interestingly, while signatures of a charge order are observed in ${\mathrm{LaNiO}}_2$ in the quasielastic region of the RIXS spectrum, it is absent in ${\mathrm{NdNiO}}_2$ and ${\mathrm{PrNiO}}_2$. This prompts further investigation into the universality and the origins of charge order within the infinite-layer nickelates.

Materials that break time-reversal or inversion symmetry possess nondegenerate electronic bands, which can touch at so-called Weyl points. The spinor eigenstates in the vicinity of a Weyl point exhibit a well-defined chirality $\pm 1$. Numerous works have studied the consequences of this chirality, for example, in unconventional magnetoelectric transport. However, even a Weyl point with isotropic dispersion is not only characterized by its chirality but also by the momentum dependence of the spinor eigenstates. For a single Weyl point, this momentum-space spin structure can be brought into standard “hedgehog” form by a unitary transformation, but for two or more Weyl points, this is not possible. In this work, we show that the relative spin structure of a pair of Weyl points has strong qualitative signatures in the electromagnetic response. Specifically, we investigate the Friedel oscillations in the induced charge density due to a test charge for a centrosymmetric system consisting of two Weyl points with isotropic dispersion. The most pronounced signature is that the amplitude of the Friedel oscillations falls off as $1/r^4$ in directions in which both Weyl points exhibit the same spin structure, while for directions with inverted spin structures, the amplitude of the Friedel oscillations decreases as $1/r^3$.

We demonstrate that the fidelity between a pure state trivial insulator and the mixed state density matrix of a Chern insulator generated from decoherence or measurement can be mapped to a variety of two-dimensional conformal field theories (CFTs); more specifically, the quantity $\mathcal{Z}=\mathrm{tr}\left\{{\widehat{\rho }}_c^D{\widehat{\rho }}_{\mathrm{\Omega }}\right\}$ is mapped to the partition function of the desired CFT, where ${\widehat{\rho }}_{\mathrm{\Omega }}$ and ${\widehat{\rho }}_c^D$ are respectively the density matrix of a pure state trivial insulator and the mixed state density matrix generated from the Chern insulator. For a pure state Chern insulator with Chern number $2N$, the fidelity $\mathcal{Z}$ is mapped to the partition function of the $\mathrm{U}{\left(2N\right)}_1$ CFT; under decoherence or measurement, the Chern insulator density matrix can experience a certain instability, and the “partition function” $\mathcal{Z}$ can flow to other interacting CFTs with smaller central charges. The Rényi relative entropy $\mathcal{F}=-ln\mathrm{tr}\left\{{\widehat{\rho }}_c^D{\widehat{\rho }}_{\mathrm{\Omega }}\right\}$ is mapped to the free energy of the CFT, and we demonstrate that the central charge of the CFT can be extracted from the finite-size scaling of $\mathcal{F}$, analogous to the well-known finite-size scaling of $2d$ CFT.

High-harmonic generation (HHG) has emerged as a pivotal process in strong-field physics, yielding extreme ultraviolet radiation and attosecond pulses for a wide range of applications. Furthermore, its emergent connection with the field of quantum optics has revealed its potential for generating nonclassical states of light. Here, we investigate the process of high-harmonic generation in semiconductors under a quantum optical perspective while using a Bloch-based solid-state description. Through the implementation of quantum operations based on the measurement of high-order harmonics, we demonstrate the generation of nonclassical light states similar to those found when driving atomic systems. These states are characterized using diverse quantum optical observables and quantum information measures, showing the influence of electron dynamics on their properties. Additionally, we analyze the dependence of their features on solid characteristics such as the dephasing time and crystal orientation, while also assessing their sensitivity to changes in driving field strength. This paper provides insights into HHG in semiconductors and its potential for generating nonclassical light sources.

Graphene has garnered tremendous interest in the last decade due to its great potential for applications in almost every scientific and engineering discipline. The adsorption of molecules onto graphene is itself also of significant interest, including in catalysis and trace molecule detection. However, density functional theory has traditionally struggled to accurately model surface adsorption involving long-range dispersion interactions between a molecule and a substrate, accentuating the need for comprehensive benchmarking and analysis. Here, we test the accuracy of several functionals in describing the adsorption energy of graphene–molecule adsorption complexes, including several van der Waals density functionals as well as the nonlocal correlation functional rVV10 and the dispersion-corrected PBE-D3. We find that the highest accuracy is provided by vdW–DF2 and the two realizations of vdW–DF3, the most recent generations of the van der Waals density functional family. In addition, we use a reduced-gradient analysis technique to examine the material's exchange energy. This analysis resolves contributions to the exchange interaction energy as a function of the reduced-gradient $s$, revealing regimes of $s$ that are important components of the interaction energy of these systems. In doing so, we identify the best functionals currently available and initiate discussion on desirable traits of each functional for modeling surface adsorption.

The minimally entangled typical thermal states (METTS) are an ensemble of pure states, equivalent to the Gibbs thermal state, designed with an efficient tensor network representation in mind. In this article, we use the projected entangled pair states (PEPS) as their representation on a two-dimensional (2D) lattice. Unlike matrix product states (MPS), which for 2D systems are limited by an exponential computational barrier in the lattice size, PEPS provides a more tractable approach. To substantiate the prowess of PEPS in modeling METTS (dubbed PEPS-METTS), we benchmark it against the purification method in the context of the 2D quantum Ising model at its critical temperature. Our analysis reveals that PEPS-METTS achieves accurate results with significantly lower bond dimensions. We further corroborate this finding in the 2D Fermi-Hubbard model. At a technical level, we introduce an efficient zipper method to obtain PEPS boundary MPS needed to compute expectation values and perform sampling. The imaginary time evolution is done with the neighborhood tensor update.

Transverse plasma polaritons and longitudinal plasmons describe the propagation of light-matter modes in an isotropic metal. However, in a layered metal the anisotropy of the bare electromagnetic response mixes the longitudinal and transverse excitations, making the distinction between polariton and plasmon blurred at small wave vectors, where retardation effects of the electromagnetic interactions become quantitatively relevant. In the usual Kubo approach for the linear response, this effect appears as a mixing between the density and the transverse current fluctuations, that requires to revise the standard random phase approximation (RPA) approach for density correlations where only the instantaneous Coulomb potential is included. In this paper we derive the general expression for the density and current correlation functions at long wavelength in a layered metal, showing that below a crossover scale set by the anisotropy of the plasma frequencies retardation effects make the dispersion of the generalized plasma modes different from the standard RPA result. In addition, the mixed longitudinal and transverse nature of these excitations reflects in a double-peak structure for the density response, that can be eventually accessed by means of high-momentum resolution electron-energy-loss or x-ray spectroscopies.

Metal-organic frameworks (MOFs) have often been used for gas storage owing to their high surface areas and nanoscale pores, where they are packed in the tank. The concomitant exothermicity and endothermicity during the gas storage process strongly affect their storage capacity. Understanding the thermal transport in MOFs under mechanical strain is critical to maximizing the gas uptake capacity of MOFs. Here, we systematically investigate the thermal transport in a typical MOF (i.e., HKUST-1 or equivalently MOF-199) considering the external mechanical strain using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases with compressive strain and increases with tensile strain, which is contradictory to the classical Liebfried and Schlömann theory, i.e., the thermal conductivity of crystals should increase with applied compression. Our spectral analysis further shows that the abnormal strain-dependent thermal conductivity can be well explained by the phonon-gas theory. We find that the relaxation time of vibrations in HKUST-1 decreases when compressive strain is applied. This is because the anharmonicity of compressed HKUST-1 increases compared with that of pristine HKUST-1. The anharmonicity of HKUST-1 decreases when tensile strain is applied, and thus, the corresponding vibrational relaxation time increases. Meanwhile, the vibrational group velocity decreases or increases for compressed or tensile HKUST-1, respectively. This is due to the compression- or stretch-induced shift of vibrational branches caused by the structural softening and hardening. Therefore, the thermal conductivity of HKUST-1 decreases with compressive strain even though the volumetric heat capacity of compressed HKUST-1 increases. The thermal conductivity of HKUST-1 increases with tensile strain, though the corresponding volumetric heat capacity decreases. Here, we provide a fundamental understanding of the thermal transport mechanisms in MOFs considering mechanical strain, which offers guidance for the thermal management design in these corresponding gas storage applications.

We consider the nearest-neighbor lattice tight-binding model of graphene with slowly spatially varying hopping functions. We develop a systematic low-energy approximation as a derivative expansion in a Dirac spinor field that is perturbative in the strength of the hopping function deformation. The well-known leading description in both the derivative and perturbative expansions is the Dirac equation in flat $2+1$-dimensional spacetime with magnetic (strain-)gauge field. Prior work has considered subleading corrections written as nontrivial frame and spin connection terms. We have argued previously that such corrections cannot be considered consistently without taking all the terms at the same order of approximation, which due to the unconventional power counting originating from the large gauge field, involve also higher covariant derivative terms. Here we confirm this, explicitly computing subleading terms in this approximation. To the order we explore, the theory is elegantly determined by the nontrivial gauge field and frame, both given by the slowly varying hopping functions, the torsion free spin connection of the frame, together with coefficients for the higher derivative terms derived from lattice invariants. We stress the importance of the local frame and gauge symmetries that are inherited from matching to the lattice model. For the first time we compute the metric that the Dirac field sees—the “electrometric”—to quadratic order in the hopping function deformation. This allows us to describe the subleading corrections to the dispersion relation for inhomogeneous deformations that originate from corrections to the frame. Focussing on purely in-plane inhomogeneous strain, we use a simple model to relate the hopping functions to the strain field, finding the electrometric becomes curved at this quadratic order. Thus, this lattice model yields an effective “analog gravity” description as a curved space Dirac theory, with large magnetic field, and Lorentz violating higher covariant derivative terms. We check our calculations by a simple numerical diagonalization of the lattice model for a periodic arm-chair deformation, confirming that frame corrections contribute at the same order of approximation as higher covariant derivative terms. Finally, based on our lattice model derivation, we conjecture a form for the effective theory for monolayer graphene, written in terms of the strain tensor, and consistent up to quadratic order in the electrometric deformation.

The current-dipole conductivity formula for doped three-dimensional Dirac semimetals is derived by using a modified gauge-invariant tight-binding approach. In a heavily doped regime, the effective number of charge carriers $n_{\alpha \alpha }^{\mathrm{eff}}$ in the Drude contribution is found to be by a factor of 4 larger than the nominal electron concentration $n$. However, its structure is the same as in standard Fermi liquid theory. In a lightly doped regime, on the other hand, the ratio $n_{\alpha \alpha }^{\mathrm{eff}}/n$ is much larger, with much more complex structure of $n_{\alpha \alpha }^{\mathrm{eff}}$. It is shown that the dc resistivity and reflectivity date measured in two TlBiSSe samples can be easily understood, even in the relaxation-time approximation, provided that finite quasiparticle lifetime effects in the momentum distribution functions are properly taken into account.

We predict a complete delocalization of the localized states following the localization transition in a one-dimensional non-Hermitian Aubry-André model with a generalized quasiperiodic potential. We show that the system first undergoes a transition from the delocalized phase to the localized phase and then to the delocalized phase as a function of the complex phase of the quasiperiodic potential of fixed strength revealing a reentrant delocalization transition. We further identify the localized region as topological in nature exhibiting a well-defined spectral winding number which vanishes in the delocalized phases resulting in a reentrant spectral topological transition. Moreover, we find that these two transitions occur through intermediate regions hosting both delocalized and localized states which also possess nontrivial winding numbers that are different from that of the localized phase.

The nature of the superfluid-to-Bose-glass (SF-BG) quantum phase transition, occurring in systems of interacting bosons immersed in a disordered environment, remains elusive. One fundamental open question is whether or not the transition obeys conventional scaling at quantum critical points (QCPs): this scaling would lock the value of the crossover exponent $\varphi$—dictating the vanishing of the superfluid critical temperature upon approaching the QCP—to the value of quantum critical exponents for the ground-state transition. Yet such a relation between exponents has been called into question by several numerical as well as experimental results on the SF-BG transition. Here we revisit this issue in the case of the $S=1/2$ Heisenberg antiferromagnet on a site-diluted cubic lattice, which lends itself to efficient quantum Monte Carlo simulations. Our results show that the model exhibits a percolation transition in zero applied field, with the correlation length exponent $\nu =0.87\left(8\right)$ and $\varphi =1.1\left(1\right)$ consistent with $3d$ percolation. When applying a sufficiently strong magnetic field, the dilution-induced transition decouples from geometric percolation, and it becomes a SF-BG transition; nonetheless, the $\nu$ and $\varphi$ exponents maintain values consistent with those of the percolation transition. These results contradict the conventional scaling, which predicts $\varphi ⩾2$; and they suggest a possible relationship between the SF-BG transition and percolation of phase coherence.

We induce and study a topological dynamical phase transition between two planar superconducting phases. Using the Lindblad equation to account for the interactions of Bogoliubov quasiparticles among themselves and with the fluctuations of the superconducting order parameter, we derive the relaxation dynamics of the order parameter. To characterize the phase transition, we compute the fidelity and the spin-Hall conductance of the open system. Our approach provides crucial information for experimental implementations, such as the dependence of the critical time on the system-bath coupling.