Ferroelectric metal oxides are emerging as promising photocatalysts due to their efficient charge separation via a spontaneous polarization-induced built-in electric field. Such a spontaneous polarization is generally accompanied by some intrinsic defects, particularly oxygen vacancies (${\mathrm{O}}_{\mathrm{V}}$) confined on negatively polarized surfaces as active sites for the water oxidation reaction (WOR). However, the detailed WOR mechanism on the surface of ferroelectric metal oxides remains unclear; especially the impact of surface ${\mathrm{O}}_{\mathrm{V}}$ on WOR, which is far from fully understood. Herein, taking classic ferroelectric $\mathrm{PbTi}{\mathrm{O}}_3$ as an example, the WOR mechanism on a negatively polarized $\mathrm{PbTi}{\mathrm{O}}_3$ (001) surface has been comprehensively investigated by density functional theory (DFT) calculations. Our DFT results show that the WOR on a pristine surface follows the lattice oxygen oxidation mechanism (LOM) involving the participation of lattice oxygen species, and shifts to the adsorbate evolution mechanism (AEM) undergoing the evolution of a sequence of oxygen-containing intermediates (OH*, O*, and OOH*) on the defective surface with ${\mathrm{O}}_{\mathrm{V}}$. For both the LOM and AEM, the uphill energy demands for all potential determining steps can be overcome by photoexcited holes due to an extremely low-valence band edge (2.36 V vs NHE at $\mathrm{pH}=7$) of ferroelectric $\mathrm{PbTi}{\mathrm{O}}_3$. We have also found that surface ${\mathrm{O}}_{\mathrm{V}}$ can change the WOR from a $2{\mathrm{e}}^{-}$ path for yielding ${\mathrm{H}}_2{\mathrm{O}}_2$ to a $4{\mathrm{e}}^{-}$ path for ${\mathrm{O}}_2$ evolution, as a result of a stronger adsorption of key oxygen-containing intermediates (O*) on a defective surface with ${\mathrm{O}}_{\mathrm{V}}$. These results not only well explain the photocatalytic WOR activity of single-domain $\mathrm{PbTi}{\mathrm{O}}_3$ in the absence of cocatalyst, but also clearly uncover the essential role of surface ${\mathrm{O}}_{\mathrm{V}}$ in determining the reaction path of WOR, thus shedding light on developing other high-performance ferroelectric metal oxide photocatalysts.

For three-dimensional systems, discussing the possibility of implementing quantum Hall physics has been an enduring topic. Based on Weyl semimetals, pioneering works have proposed chiral Landau levels and three-dimensional quantum Hall effect. When the degenerate band extends from nodal points to nodal lines, the magnetic field can lead to various quantum Hall phenomena, such as the three-dimensional flat Landau levels. Usually, the above exotic phenomena are explored under a uniform magnetic field with a fixed direction and magnitude. Here, we obtain a momentum-dependent pseudomagnetic field in a nodal line semimetal by designing a gradient coupling. The resulting quantum Hall surface states exhibit momentum-dependent chiral and helical transport features. These findings are experimentally confirmed in the phononic crystal platform. The novel sound transport may pave the way for acoustic devices with unconventional functions.

We investigate the photoexcited states in potassium-tetracyanoquinodimethane (K-TCNQ) crystals using the first and second intramolecular charge excitations of the $\mathrm{TCN}{\mathrm{Q}}^{-}$ molecule. Infrared-light reflection measurements with these excitations reveal a photoinduced phase transition (PIPT) from the spin-Peierls to the Mott insulating phase. Femtosecond time-resolved photoluminescence and visible-light reflection measurements are used to investigate the origin of the PIPT. Our results show that the PIPT triggered by the first intramolecular charge excitation occurs via the relaxation to charge transfer excited state as proposed previously, while the PIPT by the second intramolecular charge excitation is caused by electron emission. It is expected that this mechanism will be effective in other charge transfer complexes.

Time modulation opens new avenues for light, heat control, and energy harvesting, yet the impact of nonequilibrium dynamics of microscopic particles remains largely unexplored. We develop a microscopic theory to describe radiative heat transfer in such Floquet systems. Significant heat transfer occurs due to differences in electronic properties between parallel metal plates, despite identical driving protocols and temperatures. This arises from a unique exponential-staircase distribution of radiative photons, induced by nonequilibrium electronic fluctuations, and can be tuned via both microscopic properties and driving parameters. Our work highlights the importance of nonequilibrium microscopic details, unlocking promising opportunities for active cooling, thermophotovoltaics, thermal imaging and manipulation, and carrier dynamics probing.

Confinement is a prominent phenomenon in condensed-matter and high-energy physics that has recently become the focus of quantum-simulation experiments of lattice gauge theories (LGTs). As such, a theoretical understanding of the effect of confinement on LGT dynamics is not only of fundamental importance but also can lend itself to upcoming experiments. Here we show how confinement in a ${\mathbb{Z}}_2$ LGT can be locally avoided by proximity to a resonance between the fermion mass and the electric field strength. Furthermore, we show that this local deconfinement can become global for certain initial conditions, where information transport occurs over the entire chain. In addition, we show how this can lead to strong quantum many-body scarring starting in different initial states. Our findings provide deeper insights into the nature of confinement in ${\mathbb{Z}}_2$ LGTs and can be tested on current and near-term quantum devices.

It is believed that an isolated and far-from-equilibrium quantum many-body system will approach equilibrium via a mechanism whereby any given subsystem acts as an open quantum system that is coupled to an environment—the complementary part of the full system—and undergoes a complicated equilibration process such that all the subsystems in the long-time limit attain equilibrium states compatible with the global equilibrium state. This picture prompts the question whether the dynamics of any given subsystem is Markovian (monotonic loss of information and memory) or non-Markovian. In this work, by numerically probing the dynamical behavior of the quantum distances between temporally separated states of small subsystems, we reveal the telltale signatures of (non-)Markovianity of the dynamics of subsystems of an isolated quantum spin system brought into the far-from-equilibrium regime, exemplified with the mixed-field Ising spin chain quenched between parameter regimes deep inside its magnetically ordered and disordered regimes. Additionally, remarkably systematic behavior is seen in a measure of classical distances between the quantum states of the considered subsystems. These features strongly depend on the direction of quenching in the parameter space, with paramagnetic-to-ferromagnetic quenches offering considerably stronger signatures of subsystem non-Markovianity, for which we offer heuristic arguments.

Modulating the magnetic properties of two-dimensional materials is crucial for advancing spintronic applications. Here, we explore the enhancement effect of perpendicular magnetocrystalline anisotropy (PMA) in $M\mathrm{T}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$ ($M$ = Pd, Pt) van der Waals heterostructures using first-principles calculations. The PMA in $\mathrm{PdT}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$ and $\mathrm{PtT}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$ is enhanced to 3.14 and 2.63 meV, respectively, more than doubling that of monolayer $\mathrm{Cr}{\mathrm{I}}_3$. This enhancement originates from three distinct mechanisms: reduced ${\left(p_{x/y}\uparrow \right)}^1\text{−}{\left(p_{x/y}\uparrow \right)}^0$ interaction gap of I atoms, magnetic proximity effect at the interface, and Rashba effect-induced modulation. Notably, $\mathrm{PdT}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$ exhibits stronger interfacial charge transfer and Rashba splitting, leading to enhanced Dzyaloshinskii-Moriya interaction. Micromagnetic simulations reveal the formation of Néel-type skyrmions under external magnetic fields, with sizes tunable from 9 nm to complete collapse at the field of 2.5 T. For trilayers, $\mathrm{PtT}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$/$\mathrm{PtT}{\mathrm{e}}_2$ shows further strengthened PMA (5.84 meV), while $\mathrm{PdT}{\mathrm{e}}_2/\mathrm{Cr}{\mathrm{I}}_3$/$\mathrm{PdT}{\mathrm{e}}_2$ exhibits spin reorientation phenomenon. Our findings provide insights into interfacial engineering of magnetic properties and demonstrate potential applications in spintronic devices.

Motivated by theoretical and experimental studies of the compound ($o\text{−}\mathrm{MePy}\text{−}\mathrm{V}){\mathrm{PF}}_6$ reported by Yamaguchi et al. [Phys. Rev. B 98, 094402 (2018)], we performed a cluster mean-field analysis of an anisotropic Heisenberg model with six competing exchange interactions. We study the ground and thermal states by tuning the spin anisotropy, magnetic field, and temperature. Our results show that an external magnetic field induces quantum fluctuations, suppressing local moments and leading to the occurrence of a magnetization plateaulike state. When weak spin anisotropy is considered, the competing interactions are affected, and the field-induced fluctuations can lead to a well-defined magnetization plateau within a field range, in which an exotic quantum state can emerge. This state exhibits the coexistence of ferromagnetic and dimerized chains driven by the relation between frustration and the external field. Moreover, we identify a phase transition from a collinear antiferromagnetic order to a disordered state at a finite temperature. Our findings reveal unconventional magnetic properties at low temperatures that can guide future experimental studies of verdazyl-based compounds with anisotropic exchange interactions.

The transverse current $\left({\mathbf{j}}_H\right)$ due to the anomalous Hall effect (AHE) is usually assumed to be perpendicular to the magnetization $\left(\mathbf{m}\right)$ in ferromagnetic materials, which governs experiments in spintronics. Generally, this assumption is derived from a continuum model, where the discrete symmetry of the crystal is effectively represented by the concept of an effective mass from the band structure. In this paper, we calculate the spin transport through the nonmagnetic metal $|$ ferromagnetic metal interfaces and find that the corresponding Hall current is generally not perpendicular to $\mathbf{m}$ with only a few exceptions at high-symmetry crystal orientations. The calculation illustrates the breakdown of ${\mathbf{j}}_H=\mathrm{\Theta }\mathbf{m}\times {\mathbf{j}}_c$, where $\mathrm{\Theta }$ denotes the anomalous Hall angle and ${\mathbf{j}}_c$ represents the injecting charge current. An analytical formula based on the discrete symmetry of the solid can describe this effect well. In this framework, the leading order corresponds to the conventional AHE, while higher-order terms account for deviations in the Hall current. Additionally, we identify the presence of a chiral AHE at the interface with odd rotational symmetry (e.g., $C_{3v}$), and the higher-order terms can even dominate the AHE by constructing superlattices. The general existence of hidden chirality in spin transport is also revealed, with a specific focus on interface chirality. Our results highlight the significance of discrete atomic positions in solids for spin transport, which extends beyond the conventional continuum model. Moreover, considering the important application of the AHE in spintronics and the wide existence of the interfaces in the devices, the breakdown of ${\mathbf{j}}_H=\mathrm{\Theta }\mathbf{m}\times {\mathbf{j}}_c$ suggests that all experimental measurements related to the AHE should be re-evaluated, with particular focus on the high-quality van der Waals heterostructures.

The Abrikosov fermion representation of the spin-1/2 degree of freedom allows for auxiliary-field quantum Monte Carlo simulations of frustrated spin systems. This approach provides a manifold of equivalent actions over which the negative sign problem can be optimized. As a result, we can reach temperature scales well below the magnetic scale. Here, we show how to generalize this algorithm to spin-Peierls systems. In contrast to exact diagonalization approaches, Monte Carlo methods are not Hilbert space bound such that the computational effort per sweep remains invariant when adding phonons. However, the computational effort required to generate independent configurations increases in the presence of phonons. We also show that, for the specific case of the Kitaev-Heisenberg model, the inclusion of phonons does not render the negative sign problem more severe. This new algorithm hence allows us to investigate the interplay between phonon degrees of freedom and magnetic frustration. We present results for frustrated and nonfrustrated spin systems.

Misfit layered compounds, naturally occurring bulk heterostructures, present a compelling alternative to artificially engineered ones, offering a unique platform for exploring correlated phases and quantum phenomena. This study investigates the magnetotransport and superconducting properties of the misfit compound $({\mathrm{PbS})}_{1.13}{\mathrm{TaS}}_2$, comprising alternating PbS and $1H\text{−}{\mathrm{TaS}}_2$ layers. It exhibits distinctive transport properties, including a prominent planar Hall effect and a fourfold oscillatory butterfly-shaped anisotropic magnetoresistance. Moreover, it shows multigap two-dimensional superconductivity with a high in-plane upper critical field, exceeding the Pauli limit. The coexistence of multigap superconductivity and anomalous transport within the same material firmly positions misfit compounds as an ideal platform for realizing quantum effects in the two-dimensional limit of bulk crystals. This opens the door to the development of quantum devices with less complexity and enhanced tunability.

This study investigates the impact of exchange-correlation functional choices on the predictive accuracy of multiscale models for charge transport in organic semiconductors (OSCs). A hybrid functional approach is applied to analyze uncertainties in key parameters influencing charge mobility, focusing on the Hartree–Fock exchange fraction. Using 2-methyl-9,10-bis(naphthalen-2-yl)anthracene as a test system, molecular dynamics and density functional theory are combined to compute reorganization energies, site energies, and electronic coupling elements. Monte Carlo sampling quantifies the uncertainty propagation, revealing that site-energy variations dominate transport property uncertainties, while coupling elements contribute minimally. The findings underscore the need for accurate parameter determination and functional selection, with implications for enhancing the reliability of first-principles-based multiscale modeling frameworks in OSC design.

Altermagnets (AMs) constitute a novel class of spin-compensated materials in which the symmetry connecting opposite-spin sublattices involves a spatial rotation. Here, we uncover a set of unique nonlinear, light-driven properties that set AMs apart from traditional ferro- and antiferromagnets. We demonstrate theoretically that the polarization of an electromagnetic pulse that photo-excites electrons and holes in an AM, controls the spin orientation of these nonequilibrium charge carriers. For a $d$-wave AM model and a prototype material, a ${\mathrm{RuO}}_2$ bilayer, we show that very large post-pump spin polarizations may be attained by exploiting resonances. We show that this protocol also allows, in an AM, to directly probe the spin splitting of the electronic states in energy and momentum space. Thus, it can be used to identify and characterize altermagnetic materials via ultrafast pump-probe Kerr/Faraday spectroscopy or spin- and time-resolved ARPES. This opens up the possibility of devising ultrafast optical switches of nonequilibrium spin-polarization, finely tunable by adjusting the pump-pulse characteristics.

We consider the $S=1/2$ antiferromagnetic Heisenberg model on a frustrated kagome-lattice bilayer with strong nearest-neighbor interlayer coupling and examine its low-temperature magnetothermodynamics using a mapping onto a rhombi gas on the kagome lattice. Besides, we use finite-size numerics to illustrate the validity of the classical lattice-gas description. Among our findings there are (i) the absence of an order-disorder phase transition and (ii) the sensitivity of the specific heat at low temperatures to the shape of the system just below the saturation magnetic field even in the thermodynamic limit.

The BCS theory has achieved widespread success in describing conventional superconductivity. However, when the length scale reaches the atomic limit, the reduced dimensionality may lead to the quantum breakdown resulting in unpredictable superconducting behaviors. It has been experimentally evidenced that the critical temperature is strongly enhanced in the monolayer films of FeSe/STO and epitaxial aluminum. Here, we propose the exciton mechanism of superconductivity as a possible reason for the enhanced superconductivity in hybrid superconductor-semiconductor structures. The exciton-induced Cooper pairing may lead to the larger energy gaps and higher critical temperatures as compared to those caused by the phonon induced superconductivity. A detailed comparison of the theory and experimental results reveals the possibility of exciton-induced superconductivity in thin films of aluminum near the monolayer limit.

This research introduces an improved framework for constructing matrix product operators and tree tensor network operators (TTNOs), crucial tools in quantum simulations. A given (Hamiltonian) operator typically has a known symbolic “sum of operator strings” form that can be translated into a tensor network structure. Combining the existing bipartite-graph-based approach and a newly introduced symbolic Gaussian elimination preprocessing step, our proposed method improves upon earlier algorithms in cases when Hamiltonian terms share the same prefactors. We test the performance of our method against established ones for benchmarking purposes. Finally, we apply our methodology to the model of a cavity filled with molecules in a solvent. This open quantum system is cast into the hierarchical equation of motion setting to obtain an effective Hamiltonian. Construction of the corresponding TTNO demonstrates a sublinear increase of the maximum bond dimension.

SnTe materials are know to be a platform for realization of various strong and symmetry protected topological phases in one, two, and three spatial dimensions. We study symmetry-protected topological states in [110] SnTe nanowires in the presence of various combinations of Zeeman field, $s\text{−}\mathrm{wave}$ superconductivity, inversion-symmetry-breaking field, and the thickness of the wire. In the normal state we find a Weyl semimetal phase protected by a twofold screw axis symmetry and a topological insulating phase characterized by a $\mathbb{Z}$ invariant protected by a mirror symmetry. In the presence of superconductivity, we find inversion-symmetry-protected gapless phase which becomes fully gapped and topologically nontrivial by introducing an inversion-symmetry-breaking field. Consequently, we find topologically protected localized Majorana zero modes appear at the ends of the wire. We find that this Majorana phase is much easier to achieve in a [110] SnTe nanowire than in a [001] one.