Quantum-dot circuit quantum electrodynamics (QD-cQED) offers an important platform for achieving photon-to-electron conversion in the linear regime, but it has been challenging to efficiently control the photocurrent. Here, we propose a nonlinear QD-cQED setup of a double quantum dot system capacitively coupled to a microwave resonator containing Kerr nonlinearity. By means of the quantum master equation, we derive a general formulation to establish the connection between photon excitation and generated photocurrent. It is revealed that the excitation of photons undergoes a first-order quantum phase transition, which provides a mechanism to adjust the photon-assisted electron transport and leads to an increase in the photocurrent. In contrast to the linear QD-cQED setups, the enhancement in photocurrent benefits from the enhanced energy transfer from photon to electron systems near the phase transition. Our results establish the quantum phase transition as an invaluable tool for optimizing the photon-to-electron conversion in QD-cQED devices.

Altermagnets are a new class of magnetic materials, which exhibit large spin splitting, but due to the combined spin and real space group symmetry protection maintain zero net macroscopic magnetization. Such a characteristic may prove them to be superior in applications in superconducting heterostructures and thus here we investigate the Andreev reflection at the altermagnet/superconductor interface. We compare and contrast altermagnets to other magnetic materials, revealing qualitative differences in the behavior of altermagnetic junction depending on the Fermi surface orientation. We study the resonant states arising in setups with strong tunneling barriers and show that sensitivity to nonmagnetic disorder is also dependent on the orientation. Our results provide a building block for altermagnetic superconducting heterostructures such as Josephson $\pi$ junctions with superior properties.

There is no doubt that the information hidden in entanglement entropy (EE), for example, the $n\mathrm{th}$ order Rényi EE, i.e., $S_n^A=\frac{1}{1-n}ln\mathrm{Tr}\left({\rho }_A^n\right)$, where ${\rho }_A={\mathrm{Tr}}_{\overline{A}}\rho$ is the reduced density matrix, can be used to infer the organizing principle of two-dimensional (2D) interacting fermion systems, ranging from spontaneous symmetry-breaking phases and quantum critical points to topologically ordered states. It is far from clear, however, whether EE can be obtained with the precision required to observe these fundamental features—usually in the form of universal finite-sized scaling behavior. Even for the prototypical 2D interacting fermion model—the Hubbard model—to all existing numerical algorithms, the computation of EE has not been successful with reliable data from which the universal scaling regime can be accessed. Here, we explain the reason for these unsuccessful attempts of EE computations in quantum Monte Carlo simulations in the past decades and, more importantly, show how to overcome the conceptual and computational barrier with the incremental algorithm, such that the stable computation of EE in 2D interacting fermion systems can be achieved and universal scaling information can be extracted. Relevance toward experimental 2D interacting fermion systems is discussed.

We study the spectral form factor (SFF) for hydrodynamic systems with a sound pole, a large class including any fluid with momentum conservation and energy conservation, or any extended system with spontaneously broken continuous symmetry. We study such systems in a finite volume cavity and find that the logarithm of the hydrodynamic enhancement to the SFF is closely related to the spectral form factor of a quantum particle moving in the selfsame cavity. Depending upon the dimensionality and nature of the effective single-particle physics, these systems exhibit a range of behaviors including an intricate resonance phenomenon, emergent integrability in the SFF, and anomalously large fluctuations of the SFF.

Within density functional theory, we have studied self-sustained, deformable, rotating liquid He cylinders subject to planar deformations. In the normal fluid ${}^3\mathrm{He}$ case, the kinetic energy has been incorporated in a semiclassical Thomas-Fermi approximation. In the ${}^4\mathrm{He}$ case, our approach takes into account its superfluid character. For this study, we have chosen to limit our investigation to vortex-free configurations where angular momentum is exclusively stored in capillary waves on a deformed cross-section cylinder. Only planar deformations leading to noncircular cross sections have been considered, as they aim to represent the cross section of the very large deformed He drops discussed in the experiments. Axisymmetric Rayleigh instabilities, always present in fluid columns, have been set aside. The calculations allow us to carry out a comparison between the rotational behavior of a normal, rotational fluid $\left({}^3\mathrm{He}\right)$ and a superfluid, irrotational fluid $\left({}^4\mathrm{He}\right)$.

Conformal symmetry governs the behavior of closed systems near second-order phase transitions and is expected to emerge in open systems going through dissipative phase transitions. We propose a framework allowing for a manifest description of conformal symmetry in open Markovian systems. The key difference from the closed case is that both conformal algebra and the algebra of local fields are realized on the space of superoperators. We illustrate the framework by a series of examples featuring systems with quadratic Hamiltonians and linear jump operators, where the Liouvillian dynamics can be efficiently analyzed using the formalism of third quantization. We expect that our framework can be extended to interacting systems using an appropriate generalization of the conformal bootstrap.

${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type ${\mathrm{NdMn}}_2{\mathrm{Ge}}_2$ was recently proposed to be a magnetic skyrmion candidate exhibiting the topological Hall effect. In this work, we report magnetic, electronic, and thermoelectric measurements for ${\mathrm{NdMn}}_2{\mathrm{Ge}}_2$ single crystals. We show that, in the canted antiferromagnetic phase and the conical magnetic phase with a large out-of-plane ferromagnetic component, this system exhibits both an anomalous Nernst effect and a topological Nernst effect. We argue that ${\mathrm{NdMn}}_2{\mathrm{Ge}}_2$ is a unique magnetic material, with its topological characteristics associated with the Berry phases in both real space and momentum space.

The two most interesting properties of Fe-based superconductors (FeSCs), high-temperature superconductivity and nematicity, are widely believed to come from spin fluctuations (SF). One of the least studied aspects of SF are their frequency spectrum, albeit it is generally believed that SF in FeSCs can be roughly separated into (1) fast SF in the spin space which preserve the local nematic correlations, (2) slow SF in the real space, where the sense of the local nematic order fluctuates, and (3) the high-energy SF which break the local nematic order. Although, the latter are probably irrelevant in the entire observable temperature range. Nuclear quadrupolar interactions, as opposed to magnetic interactions, are sensitive only to SF in the real space, and only to those slower than its characteristic timescale. We combine existing nuclear magnetic resonance data on electric field gradient anisotropy with first-principles calculations to access the amplitude of the real-space (nematic) SF on the timescale above the actual nematic transition in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ as a function of Co doping. This demonstrates exceptionally slow dynamics of nematic fluctuations even in the formally tetragonal phase.

The real Chern insulator state, featuring a nontrivial real Chern number and second-order boundary modes, has been revealed in a few two-dimensional systems. The concept can be extended to three dimensions, but a proper material realization is still lacking. Here, based on first-principles calculations and theoretical analysis, we identify the recently synthesized bulk $\gamma$-graphyne as a three-dimensional real Chern insulator. Its nontrivial bulk topology leads to topological hinge modes spreading across the one-dimensional edge Brillouin zone. Under compression of the interlayer distance, the system can undergo a topological phase transition into a real nodal-line semimetal, which hosts three bulk nodal rings and topological boundary modes on both surfaces and hinges. We also develop a minimal model which captures the essential physics of the system.

In topological phase transitions involving a change in topological invariants such as the Chern number and the ${\mathbb{Z}}_2$ topological invariant, the gap closes, and the electric polarization becomes undefined at the transition. In this paper, we show that the jump of polarization across such topological phase transitions in two dimensions is described in terms of positions and monopole charges of Weyl points in the intermediate Weyl semimetal phase. We find that the jump of polarization is described by the Weyl dipole at ${\mathbb{Z}}_2$ topological phase transitions and at phase transitions without any change in the value of the Chern number. Meanwhile, when the Chern number changes at the phase transition, the jump is expressed in terms of the relative positions of Weyl points measured from a reference point in the reciprocal space.

The Hartree-Fock (HF) approximation with charge-density-wave (CDW) instability is used to examine ground-state properties of the spinless Falicov-Kimball model extended by $f$-electron hopping and nonlocal hybridization with inversion symmetry in two and three dimensions. Particular attention is paid to the effects of hybridization on the electronic ferroelectricity, valence transitions, and metal-insulator transitions. It is shown that inhomogeneous HF solutions exist for both the CDW and excitonic order parameters, but generally they are suppressed with increasing nonlocal hybridization $V$. The effects of $V$ are very strong, and even relatively small values of $V$ ($V<1$) completely destroy the ferroelectric state. Strong, but positive, effects on excitonic correlations are exhibited by the interband $d\text{−}f$ Coulomb interaction $U$, which significantly enhances the stability region of the homogeneous excitonic phase. Unlike the nonlocal hybridization $V$ and the Coulomb interaction $U$, the $f\text{−}f$-electron hopping only renormalizes the phase boundaries between different phases in the $V\text{−}{E}_f$ phase diagrams (with $E_f$ being the $f$-level position) and does not generate any new phases. In addition, a comparative HF study of the influence of hydrostatic pressure $p$ on valence and metal-insulator transitions within $p\text{−}{E}_f$ and $p\text{−}V$ parametrizations shows that the $p\text{−}V$ parametrization describes much better the relevant aspects of real experiments in mixed-valence systems (e.g., ${\mathrm{SmB}}_6$), where a nice qualitative accordance between theoretical predictions and experimental measurements is found for both pressure-induced valence transitions and metal-insulator transitions. This opens a route for the description of pressure-induced transitions in mixed-valence systems.

In one-dimensional disordered systems with a chiral symmetry it is well known that electrons at energy $E=0$ avoid localization and simultaneously exhibit a diverging density of states (DOS). For $N$ coupled chains with zero-correlation-length disorder, the diverging DOS remains for odd $N$, but a vanishing DOS is found for even $N$. We use a thin spinless graphene nanotube with disordered Semenoff mass and disordered Haldane coupling to construct $N=2$ chiral chain models which at low energy have two linear band crossings at different momenta $\pm K$ (two valleys) and disorder with an arbitrary correlation length $\xi$ in units of lattice constant $a$. We find that the finite momentum $\pm K$ forces the disorder in one valley to depend on the disorder in the other valley, thus departing from known analytical results which assume having $N$ independent disorders (whatever their spatial correlation lengths). Our main numerical results show that for this interdependent mass disorder the DOS is also suppressed in the limit of strongly coupled valleys (lattice white-noise limit, $\xi /a=0$) and exhibits a nontrivial crossover as the valleys decouple ($\xi /a\gtrsim 5$) into the DOS shapes of the $N=1$ continuum model with finite correlation length $\xi$. We also show that changing the intra-unit-cell geometry of the disordered Haldane coupling can tune the amount of intervalley scattering yet at lowest energies it produces the decoupled-valley behavior ($N=1$) all the way down to lattice white noise.

Transition metal dichalcogenide devices are composed of a two-dimensional (2D) sheet connected to metallic electrodes. The interface between the 2D material and metallic junction significantly affects the performance of the device. Herein, we investigate the equilibrium and nonequilibrium thermoelectric performance of a device composed of ${\mathrm{MoSe}}_2$ as the central region and Au(111) as the electrode by combining density functional theory and Green's function formalism. In the linear response regime, the maximum of the thermopower is directly related to the length of the ${\mathrm{MoSe}}_2$, and the figure of merit increases linearly with temperature so it is more than one at 600 K. In the nonequilibrium regime, the differential thermopower is strongly dependent on the external potential difference. In addition, thermoelectric efficiency approaches one when the electrochemical potential of the colder electrode is higher than that of the hotter one and the temperature difference is tuned. Findings unveil that the thermopower of the TMD-based junctions can be significantly tuned under nonequilibrium conditions, demonstrating their potential for thermoelectric applications.

Three-dimensional obstructed atomic insulators (OAIs) are characterized by the appearance of floating surface states (FSSs) at specific surfaces. Benefiting from this feature, our study here shows the presence of abundant surface-semimetal phases in 3D OAIs. The symmetries of obstructed Wannier charge centers ensure the degeneracy of such FSSs at high-symmetry points or invariant lines in the surface Brillouin zone. Utilizing topological quantum chemistry theory, we identify a carbon allotrope with a body-centered tetragonal structure, named $\mathrm{bct}\text{−}{\mathrm{C}}_{20}$, as an ideal candidate for realizing different kinds of surface-semimetal phases. For the (001) surface of $\mathrm{bct}\text{−}{\mathrm{C}}_{20}$, there are four in-gap FSSs, and these four FSSs form two kinds of surface Dirac cones, i.e., topological Dirac cones with linear dispersion and symmetry-enforced quadratic Dirac cones. The band topology of a surface Dirac cone is captured by the effective surface Hamiltonian and the emergence of hinge states. Moreover, the existence of the surface-nodal-line state is also discussed. This work reports an approach to obtain $d$-dimensional semimetal phases from the surface states of $(d+1)$-dimensional systems, which is of great significance for the studies in revealing topological states and their practical applications in high-dimensional crystals.

The antisymmetrized geminal power (AGP), a wave function equivalent to number-projected Hartree-Fock-Bogoliubov (HFB), and number-projected Bardeen-Cooper-Schrieffer (BCS) when working in the paired (natural orbitals) basis, has proven to be an excellent reference for strong pairing interactions. Several correlation methods have also been applied on top of AGP. In this work, we show how AGP can also be applied to spin systems by simply basing its formulation on a spin $su\left(2\right)$ algebra. We here implement spin AGP and spin AGP-based correlation techniques and benchmark them on the XXZ and ${\mathrm{J}}_1\text{−}{\mathrm{J}}_2$ Heisenberg models, both in one and two dimensions. Our results indicate that spin AGP is a promising starting point for modeling spin systems.

We investigate the $\mathrm{Cu}/\mathrm{Ni}\text{−}{\mathrm{O}}_2$ bilayer multiorbital Hubbard model with a Cu/Ni impurity approximation embedded in the O lattice by incorporating the $3d^8$ multiplet structure coupled to a full $\mathrm{O}\text{−}2p$ band. For this simplified model of describing the local electronic structure of hole doped homobilayer $\mathrm{Cu}\left(\mathrm{Ni}\right){\mathrm{O}}_2\text{−}\mathrm{Cu}\left(\mathrm{Ni}\right){\mathrm{O}}_2$ and heterobilayer $\mathrm{Cu}{\mathrm{O}}_2\text{−}\mathrm{Ni}{\mathrm{O}}_2$, we demonstrate that the homobilayer system hosts a rich phase diagram with inversion symmetry breaking between two layers at strong enough interlayer hybridization, especially the coexistence of two-hole singlet and triplet states in opposite layers. Additionally, we show that the interlayer hybridization in heterobilayer systems destabilizes the Zhang-Rice singlets or $3d^8$ triplets within each layer via charge transfer between layers. The relevance of these electronic redistributions to the bilayer or interface systems of cuprates and/or nickelates is discussed.

The construction of Hilbert spaces that are characterized by local constraints as the low-energy sectors of microscopic models is an important step towards the realization of a wide range of quantum phases with long-range entanglement and emergent gauge fields. Here we show that planar structures of trapped atoms in the Rydberg blockade regime are functionally complete: Their ground-state manifold can realize any Hilbert space that can be characterized by local constraints in the product basis. We introduce a versatile framework, together with a set of provably minimal logic primitives as building blocks, to implement these constraints. As examples, we present lattice realizations of the string-net Hilbert spaces that underlie the surface code and the Fibonacci anyon model. We discuss possible optimizations of planar Rydberg structures to increase their geometrical robustness.

Chemical vapor deposition (CVD) is one of the prominent techniques to realize the device-grade monolayer ${\mathrm{MoS}}_2$ (1L-${\mathrm{MoS}}_2$). Thus, it is important to understand the defects in CVD grown 1L-${\mathrm{MoS}}_2$ to develop the 1L-${\mathrm{MoS}}_2$–based optoelectronic devices. In this work, we established the origin of defect-bound exciton emission in CVD-grown 1L-${\mathrm{MoS}}_2$ using low-temperature photoluminescence (PL) spectroscopy. So far, the role of substrate in bound exciton emission of 1L-${\mathrm{MoS}}_2$ has largely been overlooked. Here, we adopted an innovative dry detachment method to delineate the effect of substrate-borne impurities on bound exciton emission. The bound exciton emission was completely absent in the detached 1L-${\mathrm{MoS}}_2$ flake. The role of substrate-borne impurities was established using the Raman and PL spectroscopies by qualitatively analyzing the carrier density in the film before and after detachment. Kelvin probe force microscopy was employed to gauge surface-potential change after detachment. The work function of 1L-${\mathrm{MoS}}_2$ was found to be increased by 90 meV after the detachment. In addition, the bound exciton emission of as-grown 1L-${\mathrm{MoS}}_2$ was compared for wet- and surface-energy assisted transferred 1L-${\mathrm{MoS}}_2$ flakes. We also found that the strength of the bound exciton emission is dependent on the heat-dissipating area of the 1L-${\mathrm{MoS}}_2$ flake.