We develop an analytical theoretical model for nonlinear hydrodynamic magnetotransport of two-dimensional (2D) electron fluids with strong pair correlations in electron dynamics. Within the classical kinetics of 2D electrons, such correlations are described as subsequent “extended” collisions of the same electrons, temporarily joined in pairs. Corresponding correlation-induced retarded terms in the fluid dynamic equations can be described for slow flows as the dependence of the electron fluid viscosity on the flow velocity gradient, that is, a non-Newtonian behavior of the fluid. We analytically calculate flow profiles in long samples in a stationary highly nonlinear regime and the corresponding magnetoresistance. Pair correlations lead to a characteristic nonmonotonic dependence of the differential resistance on the magnetic field. We compare our results with experimental data on nonlinear magnetotransport of high-purity GaAs quantum wells; we conclude that our model can be responsible for some of the observed features of the differential magnetoresistance.

The expressivity of quantum neural networks (QNNs) is a key issue in quantum machine learning (QML), which determines the capability to learn and represent complex functions. The recently proposed Randomness-Enhanced QNNs [Wu et al., Phys. Rev. Lett. 132, 010602 (2024)] use a mixed-unitary channel to accurately express arbitrary single observables. In this work, we generalize the mixed-unitary channel to a unital channel and prove that the unital channel can accurately express multiple arbitrary observables. We show that by training and implementing a unital quantum channel as a multiple-output QNN, we can accurately measure the expectation values of multiple incompatible observables simultaneously by Pauli-$Z$ measurements on distinct output qubits. We prove this accurate expressivity for multiple observables by computing the complete positivity of the unital quantum channel. An iterative algorithm is proposed to compute the theoretical maximal scaling factor of the QNNs' outcomes. Notably, our theoretical analysis shows that it requires fewer copies of state when measuring some incompatible observables by the multiple-output QNNs, which demonstrates a resource efficiency advantage over separately applying projective measurements.

We investigate a family of generalized ice models, employing Wang-Landau Monte Carlo sampling to characterize their residual entropies and thermodynamic behaviors. For the edge-sharing square-ice model, we derive an exact residual-entropy formula. Pauling's approximation yields semiquantitative agreement for corner-sharing systems, typically underestimating residual entropy, but notably overestimating it in the corner-sharing hexagonal-ice model. Thermodynamic analysis reveals that the models with extensive residual entropy exhibit Schottky-type specific heat, without indications of phase transitions, whereas the edge-sharing square-ice and face-sharing cubic-ice models show signatures of continuous and first-order finite-temperature phase transitions, respectively. These results demonstrate how ice-rule constraints give rise to diverse thermodynamic phenomena and offer insights into related frustrated systems.

We employ the stochastic series expansion quantum Monte Carlo method to investigate the $S=1/2$ antiferromagnetic Heisenberg model on a bilayer square lattice with diluted interlayer couplings. Both regular and random dilution patterns are considered. In systems with regular dilution, tuning the interlayer interaction drives a quantum phase transition from a Néel-ordered phase to a quantum disordered phase, consistent with the $O\left(3\right)$ universality class. In contrast, random dilution gives rise to a two-step transition: from the Néel phase to an intermediate Mott glass (MG) phase, followed by a transition to the quantum disordered phase. Within the MG phase, the uniform magnetic susceptibility exhibits a stretched-exponential temperature dependence ${\chi }_u\sim exp(-b/T^{\alpha }), 0<\alpha <1$. At the Néel-to-glass transition, the quenched disorder modifies the critical exponents in a manner consistent with the Harris criterion. These findings provide new insights into disorder-driven quantum phase transitions and the emergence of glassy phases in diluted bilayer quantum magnets.

We show that a three-dimensional (3D), fully gapped type-II superconductor can feature emergent in-gap Fermi surfaces of Caroli–de Gennes-Matricon (CdGM) quasiparticles in the presence of an Abrikosov vortex lattice. In particular, these CdGM Fermi surfaces manifest in the emergent 3D band structure enabled by the intervortex tunneling physics, and their stability is guaranteed by both ${\mathbb{Z}}_2$ and $2\mathbb{Z}$ topological charges. By developing an effective analytical theory, we find that each vortex line carrying a one-dimensional nodal dispersion is a sufficient condition for the vortex lattice to form CdGM Fermi surfaces. Following this prediction, in-gap CdGM Fermi surfaces are numerically confirmed in a microscopic vortex-lattice simulation of a superconducting Dirac semimetal with an $s$-wave spin-singlet pairing, which is directly applicable to a large class of type-II superconductors such as LiFeAs. Remarkably, the CdGM Fermi surfaces persist even when the normal state is deformed to a doped insulator of trivial band topology. Our work establishes the vortex lattice as an experimentally feasible control knob for emergent topological phenomena in superconductors.

Unconventional magnetic orders usually interplay with superconductivity in intriguing ways. Here, we propose that a conventional superconductor in proximity to a compensated $p$-wave magnet exhibits behaviors analogous to those of Ising superconductivity found in transition-metal dichalcogenides, which we refer to as pseudo-Ising superconductivity. The pseudo-Ising superconductivity is characterized by several distinctive features: (i) it stays much more robust under strong $p$-wave magnetism than usual ferromagnetism or $d$-wave altermagnetism, owing to the apparent time-reversal symmetry in $p$-wave spin splitting; (ii) in the low-temperature regime, a second-order superconducting phase transition occurs at a significantly enhanced in-plane upper critical magnetic field $B_{c2}$; (iii) the supercurrent-carrying state establishes nonvanishing out-of-plane spin magnetization, which is forbidden by symmetry in Rashba and Ising superconductors. We further propose a spin-orbit-free scheme to realize Majorana zero modes by placing superconducting quantum wires on a $p$-wave magnet. Our work establishes another form of unconventional superconductivity generated by $p$-wave magnetism.

We investigate the necessary features of the pair interaction for the stabilization of self-assembled quantum quasicrystals in two-dimensional bosonic systems. Unlike the classical scenario, our results show that two-dimensional octagonal, decagonal, and dodecagonal aperiodic phases require a distinct number of properly tuned characteristic length scales for their stabilization. By using a mean-field spectral variational approach and Gross-Pitaevskii numerical calculations, we determine that the dodecagonal quasicrystal structure requires at least two characteristic length scales for its stabilization, while the decagonal and octagonal patterns need at least three and four length scales, respectively. The family of pair interaction potentials considered, albeit simple, is well justified in terms of a novel experimental platform based on laser-painted interactions in a cavity QED setup. Finally, we perform a structural characterization of the quasicrystal patterns obtained and show that these phases coexist with a finite superfluid fraction, forming what can be called a super quasicrystal phase.

We study the dynamic behavior of a Bose-Einstein condensate (BEC) with dipolar interactions when the influence of external electric fields affects the coherent tunneling properties. Here, we propose a tunable platform based on BECs where Josephson oscillations can be engineered and modulated through external electric fields. We develop a theoretical and numerical framework that reveals how electric fields affect intercondensate tunneling, phase dynamics, and collective excitations. By employing a coupled set of Gross-Pitaevskii equations with adiabatic elimination of excited states, we demonstrate field-induced tuning of Josephson frequencies and a transition from contact to dipole-dominated regimes. These findings corroborate theoretical predictions about the sensitivity of dipolar BECs to external fields and deepen our understanding of quantum coherence and tunneling in long-range interacting quantum systems.

Superconductivity in pure $\omega \text{−}\mathrm{Hf}$ under high pressures $(40-60\mathrm{G}\mathrm{Pa})$ was investigated using density functional theory (DFT) combined with the Migdal-Eliashberg theory. The results indicate that interstitial anionic electrons (IAE) in pure $\omega \text{−}\mathrm{Hf}$ exhibit both kagome and hexagonal electride structures, with interstitial electrons distributed across two distinct crystal planes. The results also show that spin-orbit coupling significantly modifies the conduction electronic band-structure, inducing a Van-Hove singularity at the Fermi level, which enhances the superconducting critical temperature $\left(T_c\right)$ from approximately $3.0\mathrm{K}$ to $5.3\mathrm{K}$ at $60\mathrm{G}\mathrm{Pa}$. In addition, interstitial electrons in the valence band at the Fermi level also contribute to superconductivity. These $T_c$ values agree well with previously reported experimental results. Furthermore, we demonstrate that crystal planes hosting anionic interstitial electrons exhibit anisotropy and low work function of $3.01\mathrm{e}\mathrm{V}$ along the [001] direction, consistent with the characteristics of electride materials.

In general, the realization of strong optical pulling force on certain particle in a multiple particle system depends on the electromagnetic resonances of the particle. However, the accompanying resonant heat absorption of particle impairs the stable light traction. Moreover, the pulling force acting on an entire dimer is related to the configuration of its two constituent particles, yet the roles of the near-field interactions in mediating this force remain unclear. Here, we address these challenges by considering a silicon-silver heterodimer under normal illumination of a plane wave. The analytical results demonstrate that the pulling forces on two particles arise not only from electric dipolar interaction but also from near-field interactions such as electric-magnetic dipolar coupling and hybridization. Notably, the two large pulling forces can be independently achieved under an off-resonance condition because of the hybridization. Moreover, the coupling and hybridization can even dominate the pulling forces, respectively. In particular, the pulling forces depend on the particle sizes, wavelength, and gap between particles. Importantly, the optical pulling forces can be regulated by the polarization angle of the incident light. The presented theoretical approach is general for a dielectric-metal heterodimer within the electromagnetic dipolar approximation and the results provide insights for stable optical traction, sorting, separation, and delivery of particles and cells.

We develop a systematic projector-based Feynman diagram framework that intrinsically encodes quantum geometry for nonlinear optical responses. By explicitly incorporating geometric quantities such as the quantum geometric tensor, quantum hermitian connection, and triple-phase product, the method ensures componentwise gauge invariance and seamlessly extends to multiband systems, enabling accurate calculations of quantum geometry and nonlinear optical responses. We derive the projector formalism in the Wannier function basis and implement the ab initio calculations of shift current in GeS, demonstrating excellent agreement with the sum rule and Wilson loop approaches. This work extends projector-based representations within the Wannier functions basis, offering an efficient and reliable tool for investigating nonlinear light-matter interactions and quantum geometry in realistic materials.

We investigate transport phenomena and dynamical effects in flat bands where the band dispersion plays no role. We show that wave packets in geometrically nontrivial flat bands can display dynamics when inhomogeneous electric fields are present. This dynamics is revealed both for the wave-packet trajectory and for its variance, for which we derive semiclassical equations extended to the non-Abelian case. Our findings are tested in flat band models in one- and two-dimensional lattices where the dynamics is solely determined by geometric effects, in the absence of band dispersion. In particular, in the one-dimensional case, we show the existence of Bloch oscillations for the wave-packet position and for the wave-packet variance, whereas in the two-dimensional case we observe a transverse displacement of the wave packet in the absence of Berry curvature. This work paves the way for understanding quantum-geometry-induced dynamical effects in flat band materials and also opens the possibility for their observation with synthetic matter platforms.

Spin transport in time-reversal symmetric multichannel wire systems with only one propagating channel is known to be spin independent, with no spin polarization in the transmitted flux for unpolarized incident flux. In this work we show that out-of-plane resonant localized-spin polarization (RLSP) does occur, while the transport remains spin independent, in graphene nanoribbons with nonmagnetic adsorbate-induced spin-orbit interaction (SOI). This RLSP result is shown associated with evanescent subbands. Equally crucial, the most significant contribution is from the intrasubband interference, between the spin-dependent and the spin-independent parts of an evanescent subband in the scattering state. The resonance is enabled by (1) on-site potentials acted by the SOI adsorbates upon its surrounding carbon sites, and (2) large band-edge density-of-states effects from an evanescent subband. This resonance, with energies close to the evanescent-subband band edge, largely enhances the RLSP results. The sign of the spin polarization is determined by that of the SOI coupling parameter and the transport direction.

Conversion between two nuclear-spin isomers of water molecules has been extensively studied over many decades. A recent work on ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ single-molecule transistors (SMTs) suggested that water molecules may exhibit ortho-para fluctuation in a short timescale, when conduction electrons pass the ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ molecule. In this work, we have analyzed electron-tunneling spectra in ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ SMTs. We consider the selection rule for the ortho-para conversion (OPC), taking into account the angular momentum exchange among tunneling electrons, nuclear spins, and molecular rotations. Due to stringent parity conservation of the system, six OPC processes are accompanied by molecular rotation, while a tunneling electron provides only the transition energies. Furthermore, angular momentum exchange among an electron spin, a molecular rotation, and a nuclear spin gives rise to six more conversion channels, representing unique processes in a single-electron-tunneling system. In the Coulomb stability diagram, most of the OPC lines appear very close to the excited state lines of molecular rotation, except for the excited state line at 9.3 meV. The expected OPC energies are in good agreement with experiment. The findings provide strong support for the electron-induced OPC, linking transport measurements with nuclear-spin dynamics.

This study uses angle-resolved photoemission spectroscopy to examine the low-temperature electronic structure of $\mathrm{Cs}{\left({\mathrm{V}}_{0.95}{\mathrm{Nb}}_{0.05}\right)}_3{\mathrm{Sb}}_5$, demonstrating that partially substituting V atoms with isoelectronic Nb atoms results in an increase of the bandwidth and enhanced gap opening at the Dirac-like crossings due to the resulting chemical pressure. This increases the magnetic circular dichroism signal in the angular distribution compared to ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, enabling detailed analysis of magnetic circular dichroism in several bands near the Fermi level. These results substantiate the predicted coupling of orbital magnetic moments to three van Hove singularities near the Fermi level at $M$ points. Previous studies have observed that Nb doping lowers the charge density transition temperature and increases the critical temperature for superconductivity. This article demonstrates that Nb doping concomitantly increases the magnetic circular dichroism signal attributed to orbital moments.

Electronic band structures usually remain unaffected by doping via a chemical-potential shift or by increasing the temperature in conventional band insulators. In contrast, it has been shown that those of Mott and Kondo insulators can be altered by doping or by increasing the temperature: electronic modes are induced within the band gap, exhibiting momentum-shifted magnetic dispersion relations from the band edges. Here, this study demonstrates that the underlying mechanism of the remarkable strong-correlation effects can be generalized to the emergence of electronic modes caused by various spin and charge perturbations, including magnetization of spin-gapped Mott and Kondo insulators. These emergent modes can alter the band structure if a macroscopic number of spins or charges are excited by the perturbations at a given moment. The origins and dispersion relations of these emergent modes, particularly why and how the dispersion relations depend on the momentum and energy of the perturbations, are elucidated by investigating the selection rules and using the Bethe ansatz and the effective theory for weak inter-unit-cell hopping. The validity and generality of the theoretical results across different models and spatial dimensions are verified by numerical calculations for the one- and two-dimensional Hubbard models, periodic Anderson models, Kondo lattice models, and ladder and bilayer Hubbard models. This study provides crucial insights into why and how spin and charge perturbations can alter the band structure in strongly correlated insulators, thereby paving the way for band-structure engineering in strong-correlation electronics, which enables previously unexplored functionalities by exploiting the unconventional characteristics revealed in this paper.

Phonon decoherence determines the characteristic timescales over which coherent lattice vibrations decay, making it a crucial process for understanding the nonequilibrium dynamics of crystal lattices after excitation by a pump pulse. Here, we report a theoretical and computational investigation of the origin of phonon decoherence within a first-principles many-body framework. We derive quantum kinetic equations for the dynamics of coherent phonons by explicitly accounting for dissipation processes induced by electron-phonon and phonon-phonon interactions. The decoherence rate and frequency renormalization are formulated in terms of the nonequilibrium phonon self-energy, providing a framework amenable for ab initio calculations. To validate this approach, we conduct a first-principles study of phonon decoherence for the elemental semimetals antimony and bismuth. The robust agreement with available temperature- and fluence-dependent experimental data confirms the accuracy of our theoretical and computational framework. More generally, our findings reveal that either electron-phonon or phonon-phonon coupling can prevail in determining the decoherence time, depending on the temperature and driving conditions. Overall, this work fills a critical gap in the theoretical understanding of phonon decoherence, providing a predictive framework for determining the timescales of light-induced structural dynamics in driven solids.

Point-gap topological phases of non-Hermitian systems exhibit exotic boundary states that have no counterparts in Hermitian systems. Here, we develop a classification of second-order point-gap topological phases protected by reflection symmetry. Based on this classification, we propose exceptional second-order topological insulators, exhibiting second-order boundary states stabilized by point-gap topology. As an illustrative example, we uncover a two-dimensional exceptional second-order topological insulator with point-gapless corner states. Furthermore, we identify a three-dimensional exceptional second-order topological insulator that features hinge states with isolated exceptional points, representing second-order topological phases intrinsic to non-Hermitian systems. In this work, we enlarge the family of point-gap topological phases in non-Hermitian systems.

To understand the microscopic origins governing melting anisotropy, in situ x-ray diffraction (XRD) measurements were obtained in aluminum single crystals shocked along $\langle 100\rangle$ and $\langle 110\rangle$ to stresses below and above the melting threshold for each orientation. XRD results and analysis for the two orientations showed significant differences in the microstructure prior to the melting threshold stresses, demonstrating the key role of deformation induced microstructure—in addition to temperature and pressure—on the melting transition. Our findings make a strong case for reconsidering theoretical approaches to melting, specifically for dislocation mediated melting, in shock compressed solids.