Motivated by recent experiments probing the wavefunctions of magic-angle twisted bilayer graphene (tBLG), we perform large-scale first-principles calculations of tBLG with full atomic relaxation across a wide range of twist angles down to $0.{99}^{\circ }$. Focusing on the magic angle, we compute wavefunctions of the low energy bands, resolving atomic-scale details and moiré-scale patterns that form triangular, honeycomb, and kagome lattices. By tuning the interlayer interactions, we illustrate the formation of the flat bands from isolated monolayers and the emergence of the band inversion and fragile topology at a sufficiently large interaction strength. We identify strong indicators of a new phase transition with increasing interlayer interaction strength, achievable with external pressure or a decrease in the twist angle. When this transition occurs, the upper and lower flat bands exchange their wavefunction character and symmetry eigenvalues, which may be correlated with the appearance of superconductivity with electron doping below the magic angle. Our study demonstrates the feasibility of using first-principles wavefunctions to help interpret experimental signatures of topological and correlated phases in tBLG.

As a type of energy carrier, polaritons can play a dominant role in the thermal conductivity of nano/microstructures. Here, we report an asymmetric thermal conductivity mediated by polaritons that break the Lorentz reciprocity. In contrast to existing approaches that rely on nonlinearity or time modulation, we leverage nonreciprocal polaritons induced by magnetic effects. We show that nonreciprocal surface plasmon polaritons in time-reversal symmetry-breaking systems, including magneto-optical materials and magnetic Weyl semimetals, can alter the symmetry of thermal conductivity in systems like thin films, resulting in direction-dependent thermal conductivity. Thermal conductivities of reciprocal material systems can also be made asymmetric through near-field coupling with these material systems. In accompaniment with the surging interest in nonreciprocal thermal radiation by polaritons, we extend the role of nonreciprocal polaritons from radiative heat transfer systems to conduction systems, paving the way for next-generation thermal devices and efficient energy management solutions.

The measurement-induced phase transition (MIPT) describes the nonanalytical change of the entanglement entropy resulting from the interplay between measurement and unitary evolution. In this paper, we investigate the relaxation critical dynamics near the MIPT for different initial states in a one-dimensional quantum circuit. Specifically, when the initial state is in the volume-law phase with vanishing measurement probability, we find that the half-chain entanglement entropy $S$ decays as $S\propto t^{-1}$ with the coefficients proportional to the size of the system in the short-time stage. In contrast, when the initial state is the product state, $S$ increases with time as $S\propto lnt$, consistent with the previous studies. Despite these contrasting behaviors, we develop a unified scaling form to describe these scaling behaviors for different initial states, where the off-critical-point effects can also be incorporated. We also confirm that this scaling form is applicable for other initial states. Possible experimental realizations are discussed.

We report an ultrafast Time-Resolved Raman scattering study of the out-of-equilibrium photoinduced dynamics across the superconducting to normal state phase transition of the cuprate ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$. Using the polarization-resolved momentum space selectivity of Raman scattering, we track the superconducting condensate destruction and recovery dynamics with subpicoseconds time resolution in the antinodal region of the Fermi surface where the superconducting gap is maximum. Leveraging ultrafast Raman thermometry, we find a significant dichotomy between the superconducting condensate and the quasiparticle temperature dynamics near the antinodes, which cannot be framed in terms of a single effective electron temperature. The present work demonstrates the ability of Time-Resolved Raman scattering to selectively probe out-of-equilibrium pathways of different electronic subdegrees of freedom during a photoinduced phase transition.

Intrinsic point defects in transition metal dichalcogenides (TMDs) significantly affect their crystal structure and optoelectronic properties. In this study, intrinsic point defects in the 2H and 1T phases of two-dimensional Janus WSSe were investigated in depth using first-principles methods, including vacancies, interstitials, antisites, and their effects on the atomic structure, thermodynamic stability, electronic, optical, and magnetic properties of the materials. The results show that the 1T phase of WSSe is more prone to lattice defects compared to the 2H phase, with vacancies (${\mathrm{V}}_{\mathrm{S}}, {\mathrm{V}}_{\mathrm{Se}}$) and interstitials (${\mathrm{S}}_{\mathrm{Se}}, {\mathrm{Se}}_{\mathrm{S}}$) between S and Se atoms being the most easily formed point defects. In the 2H phase, W atom vacancies (${\mathrm{V}}_{\mathrm{W}}$), interstitials (${\mathrm{W}}_{\mathrm{i}}$), and W atom substitutions for sulfur (${\mathrm{W}}_{\mathrm{S}}, {\mathrm{W}}_{\mathrm{Se}}$) are deep-level defects that easily form nonradiative recombination centers for carriers, affecting their lifetime. Additionally, ${\mathrm{W}}_{\mathrm{S}}$ and ${\mathrm{W}}_{\mathrm{Se}}$ defects in the 2H phase and ${\mathrm{W}}_{\mathrm{S}}$ defects in the 1T phase can induce local magnetic moments in the material, providing a feasible approach for generating magnetism in WSSe materials. Furthermore, the absorption characteristics of 2H WSSe with intrinsic defects exhibit stability within the visible light spectrum. These findings not only deepen the understanding of defect engineering in Janus-TMDs for tuning electronic and optical properties but also have important implications for the design and optimization of Janus MXY optoelectronic devices.

A method is proposed for calculating the surface energy density ${\gamma }_B$ of ${180}^{\circ }$ Bloch domain walls in uniaxial ferromagnetic crystals over the entire range of magnetic ordering temperatures. This method enables the determination of ${\gamma }_B$ for an arbitrary number of anisotropy constants $K_i\left(T\right)$ in the expansion of the magnetocrystalline anisotropy (MCA) energy and for various types of MCA. The method is tested using the intermetallic compound ${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$, which undergoes a spin-reorientation transition (SRT) at $T_{\text{SRT}}=135$ K from a high-temperature easy-axis MCA type to a low-temperature easy-cone type. The energy of ${180}^{\circ }$ Bloch domain walls in ${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$ was calculated in the temperature range of 78–293 K, taking into account sixth-order MCA constants. It is shown that using standard MCA expansions truncated at fourth-order terms is insufficient for accurately evaluating ${\gamma }_B$ near the SRT or in temperature ranges where the MCA type deviates from the easy-axis configuration.

We theoretically study the dynamics of gain-driven magnon-polaritons (MPs), which characterizes auto-oscillation of MPs, across the strong coupling (SC) and ultrastrong coupling (USC) regimes. Taking into account the magnon dynamics via the magnetic flux, we present an effective circuit model of gain-driven MPs, which allows us to manipulate the coupling strength of MPs by tuning the size of a ferromagnet and incorporates the self-Kerr nonlinearity of magnons due to the shape magnetic anisotropy. In the SC regime, we find that the self-Kerr nonlinearity generates a frequency shift and reduces the coherent magnon-photon coupling. In contrast, in the USC regime, we find that the coherent magnon-photon coupling not only overcomes the self-Kerr nonlinearity but also effectively couples to gain via the imaginary part of complex eigenfrequencies, resulting in magnonlike auto-oscillations. Subsequently, the USC enables one to widely tune the auto-oscillation frequency by means of an external magnetic field. These findings indicate that there is a trade-off relation between the coupling strength of MPs and the self-Kerr nonlinearity of magnons. This work contributes to the understanding of the interplay between gain-loss and USC in nonlinear polariton dynamics, offering a novel principle for frequency-tunable maserlike devices based on gain-driven MPs.

We study a time-reversal invariant vortex, namely, a spin vortex, in helical superconductors by focusing on its emergent gravitational structure. The topology of the time-reversal invariant vortex is classified by a ${\mathbb{Z}}_2$ invariant: a zero-energy Majorana Kramers pair appears at the vortex core when the winding number is odd, while no such zero modes exist when it is even. We provide a formal mapping to the theory of gravity to describe this ${\mathbb{Z}}_2$ topological structure. Identifying a superconducting order parameter as a vielbein in the theory of gravity, we explicitly convert the Bogoliubov–de Gennes Hamiltonian into the Dirac Hamiltonian coupled to a nontrivial gravitational field. Then we find that a gravitational curvature is induced at the vortex core, with its total flux quantized in integer multiples of $\pi$, reflecting the ${\mathbb{Z}}_2$ topology. Although the curvature vanishes everywhere except at the vortex core, the energy spectrum remains sensitive to the total curvature flux, owing to the gravitational Aharonov-Bohm effect. We further demonstrate that our gravitational framework can be applied to the topological phase transition driven by the vortex-linking precess in three-dimensional helical superconductors such as the He-B phase.

Combining the long-coherence of spin qubits and the capability to transmit information and entanglement through photons, spin-photon interfaces (SPIs) are a promising platform for networked quantum computation and long-distance quantum communication. SPIs that possess local ‘memory’ qubits in addition to the optically coupled ‘communication’ qubit can improve remote entanglement fidelities through brokered entanglement schemes and entanglement purification. In these schemes, it is critical to protect the memory qubit from decoherence during entanglement operations on the communications qubit. Silicon, a platform with mature microelectronic and nanophotonic fabrication, is host to the $T$-center, an SPI with emission in the telecommunications O-band that directly integrates with silicon nanophotonics. Cavity-coupled $T$-centers are a platform for brokered entanglement distribution in silicon photonic circuits and over long-distance optical fiber links. The $T$-center's electron and nuclear spin qubits are an intrinsic register of communication and memory qubits respectively, with anisotropic hyperfine coupling. In this work we determine the $T$-center's hydrogen hyperfine coupling tensor. We also introduce schemes to protect against dephasing or eliminate relaxation of the $T$-center's hydrogen memory qubit during optical excitation. These results address a key challenge for practical $T$-center quantum networks.

We theoretically investigate the superconducting phase and perpendicular Josephson supercurrent in twisted three-dimensional (3D) superconductors, where two layered 3D materials are stacked with a relative twist. We formulate the Bogoliubov–de Gennes Hamiltonian and develop a self-consistent method to calculate the superconducting order parameter and the resulting supercurrent. Applying this framework to a toy model with Fermi surfaces located near the Brillouin zone corners, we demonstrate a phase discontinuity at the twisted interface, indicating that a Josephson junction is formed purely by the twist. Our calculations reveal that the interface supports a finite critical current even when the Fermi surfaces of the two superconductors are completely separated, unlike in the case of a twisted normal-metal interface. We further show that the critical current can be effectively controlled by the twist angle, transitioning from a high-transparency regime at small angles to a low-transparency regime at larger angles.

Multipole moments serve as order parameters for characterizing higher-order magnetic effects in momentum space, providing a framework to describe diverse magnetic responses by extending the concept of magnetism. In this paper, we introduce a methodology to quantitatively determine the multipole moment contributions in anomalous Hall effect through angle-dependent anomalous Hall current, with explicit incorporation of discrete crystal symmetries. Our technique uniquely enables the investigation of octupole contribution in nonperiodic systems, particularly at interfaces and surfaces. Typically, in (${\mathrm{Ag}}_2{\mathrm{Fe}}_5{)}_n$ multilayers with quantum-well-engineered $k$-point selectivity, we observe an octupole-dominated anomalous Hall effect in conventional ferromagnetic materials, through first-principles calculations. These results fundamentally challenge the existing theoretical understanding of the anomalous Hall effect, showing that even the conventional contribution arises not only from the dipole moment (net magnetization). Furthermore, we establish practical control over the octupole contribution through two distinct approaches: interface engineering and magnetic ordering reconfiguration, opening new possibilities for manipulating higher-order transport effects.

Leveraging the rapid development of quantum simulators, the intriguing phenomena of quantum strings are observed across various quantum simulation platforms. However, the complex interplay between the quantum strings cannot be well analyzed due to the limited system size in real quantum simulators. Here, with the help of a recently developed quantum Monte Carlo method, we can simulate a larger-scale Kagome Rydberg atom array, providing an ideal playground for studying quantum strings. By introducing an edge pinning method, the ends of a quantum string can be attached to the edges so that the flexible manipulation of the quantum string becomes possible. Due to the geometric constraint, the quantum strings are unidirectional, which strongly complicates their interplay. To quantitatively describe the quantum string, we built a one-dimensional effective model. With both analytic and numerical methods, rich physics can be found, including “geometric breaking,” a heartlike superposition state of quantum strings, and attractive interstring interactions. This work can benefit the comprehension of quantum strings and may also shed light on the simulation of high-energy physics.

Thorium-doped ${\mathrm{LiCaAlF}}_6$ and ${\mathrm{LiSrAlF}}_6$ (Th:LiCAF and Th:LiSAF) are promising crystals for a solid-state nuclear clock based on the 8 eV transition in ${}^{229}\mathrm{Th}$; however, their complex crystal structures complicate understanding the atomic arrangement of the thorium defects. In this work, density functional theory simulations are employed to systematically investigate these systems, including temperature-dependent effects and environmental conditions of fluorine saturation and deficiency. By examining 20 distinct charge compensation schemes for each material, we found that experimental conditions have a significant impact on the energies of charge compensation pathways. This has important implications for selectively favoring defect geometries with desirable properties, such as enhanced quenching rates, to improve the nuclear clock performance. In addition, we found lower defect formation energies in Th:LiSAF than in Th:LiCAF, suggesting that the former may attain a higher concentration of thorium nuclei. Furthermore, we calculated the electric field gradient for the lowest-energy structure associated with each compensation scheme, enabling the experimental identification of some crystal defect structures through nuclear quadrupole splittings.

Defects and interfaces are essential to understand the properties of matter. However, studying their dynamics in the quantum regime remains a challenge, in particular concerning the regime of two spatial dimensions. Recently, it has been shown that a quantum counterpart of the hard-disk problem on a lattice yields defects and interfaces, which are stable just due to quantum effects while they delocalize and dissolve in an analogous classical stochastic process. Here, we study in more detail the properties of defects and interfaces in this quantum hard-disk problem with a particular emphasis on the stability of these quantum effects upon including perturbations. Specifically, we introduce short-range soft-core interactions between the hard disks. From both analytical arguments and numerical simulations we find that large classes of defects and interfaces remain stable even under such perturbations suggesting that the quantum nature of the dynamics exhibits a large range of robustness. Our findings demonstrate the stability and nonclassical behavior of quantum interface dynamics, offering insights into the dynamics of two-dimensional quantum matter and establishing the quantum hard-disk model as a platform for studying unconventional constrained quantum dynamics.

Many-body localization (MBL) represents a unique physical phenomenon, providing a testing ground for exploring thermalization, or more precisely its failure. Here we characterize the MBL regime geometrically by the many-body quantum metric (MBQM), defined in the parameter space of twist boundary, and the localization parameter as defined in the modern theory of polarization and insulators. First, we demonstrate that the quantum metric can be used to characterize disordered insulating states by applying this theoretical framework to excited states of the one-dimensional (1D) Anderson insulator. There we observe that the MBQM and localization parameter are related in finite realizations despite the states being gapless in the thermodynamic limit. Then, we consider a disordered 1D Bose-Hubbard model and find that we can characterize the ergodic-MBL crossover by comparing the MBQM and localization parameter. We find that we can extract a natural localization length in the MBL regime that characterizes the real space spread of the wave function and can be measured by extracting the quantum metric. Our analysis provides complementary insight into the MBL regime focusing on its insulating properties and providing a localization length whose definition is consistent across a range of insulating phases.

Strain exerted by a ferroelectric substrate on a thin ferromagnetic multilayer film with an interfacial Dzyaloshinskii-Moriya interaction is a promising method of manipulating chiral magnetic spin textures. Here, we report on the strain coupling between magnetic domains in a Pt/CoFeB/Ir multilayer and ferroelectric domains in a ${\mathrm{BaTiO}}_3\left(001\right)$ substrate. Using wide-field Kerr microscopy to image the demagnetized domain pattern, at room temperature (RT), we observe magnetic stripe domains aligned with the underlying ferroelectric domain pattern. Cooling to 13 K and subsequently warming back up to RT, there are irreversible changes to the ferroelectric domain pattern associated with structural phase transitions, and we find that magnetic stripe domains reorient to match the new ferroelectric domain structure in each phase. These results open a route to electric field manipulation of the domain morphology and chiral spin textures in thin multilayer films.

Altermagnetism is an unconventional form of antiferromagnetism characterized by momentum-dependent spin polarization of electronic states and zero net magnetization, arising from specific crystalline symmetries. In the presence of spin-orbit coupling (SOC), altermagnets can exhibit finite net magnetization and anomalous Hall effect (AHE), phenomena typically associated with ferromagnets. As AHE is closely linked to weak ferromagnetism, clarifying its microscopic origin in terms of spin and orbital contributions to magnetization is crucial for interpreting experiments and designing altermagnetic devices. In this work, we use density functional theory to explore the intrinsic spin and orbital magnetization of the magnetic ground state of the prototypical altermagnet $\alpha$-MnTe. We find that SOC induces weak ferromagnetism through spin canting, accompanied by a slight in-plane rotation of the Néel vector. Notably, we identify a significant net orbital magnetization of 0.176 ${\mu }_B$ per unit cell oriented along the $z$ axis, whereas the spin magnetization in the same direction is much smaller, at only 0.002 ${\mu }_B$. By varying the chemical potential, we show that the spin magnetization can be tuned through hole doping, whereas the orbital magnetization remains robust against carrier concentration changes. These results highlight the important role of orbital magnetization and establish its relevance for orbital-based phenomena in altermagnets.