The Berry curvature of molecular electronic wave function serves as an electron-spin-dependent effective magnetic field, which results in an effective magnetic force that can lead to electron-spin-dependent molecular dynamics. We propose an experimental scheme to observe this Berry curvature effect in molecular dynamics. We show that in ${\mathrm{CH}}_2\mathrm{OH}$ photodissociation process, the dissociation rates are different for molecules with opposite electronic spin directions, and the evolution of the electronic density of molecules with opposite spins can be observed with ultrafast x-ray diffraction using free electron lasers, which demonstrates the modified nuclear motion due to the electron-spin-dependent effective magnetic force. Our work paves the way to the direct observation of the Berry curvature effect in molecular systems and chemical reactions, and the Berry curvature effect has profound and wide applications in various areas of physics and chemistry.

Spin and charge pumping induced by a precessing magnetization has been instrumental to the development of spintronics. Nonetheless, most theoretical studies so far treat the spin-orbit coupling as a perturbation, which disregards the competition between exchange and spin-orbit fields. In this work, based on Keldysh formalism and Wigner expansion, we develop an adiabatic theory of spin and charge pumping adapted to systems with arbitrary spin-orbit coupling. We apply this theory to the magnetic Rashba gas and magnetic graphene cases and discuss the pumped ac and dc current. We show that the pumped current possesses both intrinsic (Berry curvature-driven) and extrinsic (Fermi surface breathing-driven) contributions, akin to magnetic damping. In addition, we find that higher harmonics can be generated under large-angle precession and we propose a couple of experimental setups where such an effect can be experimentally observed.

We use the spin functional renormalization group to investigate the $J_1\text{−}{J}_2$ quantum Heisenberg model on a square lattice. By incorporating sum rules associated with the fixed length of the spin operators as well as the nontrivial quantum dynamics implied by the spin algebra, we are able to compute the ground state phase diagram for arbitrary spin $S$, including the quantum paramagnetic phase at strong frustration. Our prediction for the extent of this paramagnetic region for $S=1/2$ agrees well with other approaches that are computationally more expensive. We find that the quantum paramagnetic phase disappears for $S\gtrsim 5$ due to the suppression of quantum fluctuations with increasing $S$.

Thermal switching materials, whose thermal conductivity can be controlled externally, show great potential in contemporary thermal management. The manipulation of thermal transport properties through magnetic fields has been accomplished in materials that exhibit a high magnetoresistance. However, it is generally understood that the lattice thermal conductivity attributed to phonons is not significantly impacted by the magnetic fields. In this study, we experimentally demonstrate the significant impact of phonon-magnon scattering on the thermal conductivity of the rare-earth metal gadolinium near room temperature, which can be controlled by a magnetic field to realize thermal switching. Using first-principles lattice dynamics and spin-lattice dynamics simulations, we attribute the observed change in phononic thermal conductivity to field-suppressed phonon-magnon scattering. This research suggests that phonon-magnon scattering in ferromagnetic materials is crucial to determine their thermal conductivity, opening the door to innovative magnetic-field-controlled thermal switching materials.

A conventional exchange bias manifests itself as a hysteresis loop shift in systems with an interface between a ferromagnet and an antiferromagnet after field cooling. Due to the complicated magnetic interactions at the interface, a spin glass with disordered and frustrated spin configurations is generated, resulting in the dependencies of the conventional exchange bias mechanism on a spin glass still being elusive. Here, we report that a spin glass, CuMn, exhibits a conventional exchange bias as in interface magnetic systems. More importantly, a spontaneous exchange bias is also observed in the spin glass after zero-field cooling, which is attributed to the response of ferromagnetic clusters embedded in a spin-glass matrix at high magnetic fields that form a unidirectional anisotropy through the interaction between the clusters and the spin-glass matrix. Our results show the relationship between the exchange bias and spin glasses, offering a foundational understanding for exchange bias research.

Twisted nodal superconductors have been shown to exhibit chiral topological superconductivity under broken time-reversal symmetry. Here we show how a time-reversal preserving topological superconductivity can be induced in nodal triplet superconductor multilayers. For a bilayer system, the application of a Josephson spin current in triplet superconductors induces a nonzero spin Chern number per node in momentum space. However, we show that stabilizing a nontrivial global ${\mathbb{Z}}_2$ invariant requires an odd number of layers. As a specific example, we consider trilayers with three forms of twist: chiral, alternating, and single-layer. For chiral and single-layer case, we find that a gap opening in the dispersion leads to a nontrivial ${\mathbb{Z}}_2$ topological invariant. For single-layer twists, we show how this invariant is nontrivial when extended to an arbitrary odd number of layers.

We study the effective low-energy fermionic theory of the Kondo-Kitaev model to leading order in the Kondo coupling. Our main goal is to understand the nature of the superconducting instability induced in the proximate metal due to its coupling to spin fluctuations of the spin liquid. The special combination of the low-energy modes of a graphene-like metal and the form of the interaction induced by the Majorana excitations of the spin liquid furnish chiral superconducting order with $p_x+\mathrm{i}{p}_y$ symmetry. Computing its response to a $\mathrm{U}\left(1\right)$ gauge field moreover shows that this superconducting state is topologically nontrivial, characterized by a first Chern number of $\pm 2$.

We examine properties of the mean-field wave function of the one-dimensional Kitaev model supporting Majorana zero modes (MZMs) when restricted to a fixed number of particles. Such wave functions can, in fact, be realized as exact ground states of interacting number-conserving Hamiltonians and amount to a more realistic description of the finite isolated superconductors. Akin to their mean-field parent, the fixed-number wave functions encode a single electron spectral function at zero energy that decays exponentially away from the edges, with a localization length that agrees with the mean-field value. Based purely on the structure of the number-projected ground states, we construct the fixed particle number generalization of the MZM operators. They can be used to compute the edge tunneling conductance; however, notably the value of the zero-bias conductance remains the same as in the mean-field case, quantized to $2e^2/h$. We also compute the topological entanglement entropy for the number-projected wave functions and find that it contains a robust $ln\left(2\right)$ component as well as a logarithmic correction to the mean-field result, which depends on the precise partitioning used to compute it. The presence of the logarithmic term in the entanglement entropy indicates the absence of a spectral gap above the ground state; as one introduces fluctuations in the number of particles, the correction vanishes smoothly.

The valence band maximum (VBM) is an important quantity for semiconductors as it locates the Fermi level relative to the band edge. Accurate measurement of this quantity in near-surface regions of semiconductors by photoemission is a first step toward determining the electronic properties of heterostructures involving these materials. While extrapolating the leading edge of the valence band to the energy axis in photoemission spectra is a widely used way to find the VBM, this method can be ambiguous if the leading edge exhibits multiple slopes. Another way to determine the VBM is to fit the leading edge to an appropriately broadened, cross-section modulated theoretical density of states (DOS). Three kinds of broadening that should be included for maximum accuracy are those due to: (1) finite instrumental resolution, (2) valence hole lifetime, and (3) vibrational excitations. While steps (1) and (2) are straightforward to implement, (3) is more difficult because the appropriate amount of broadening is not known a priori. Here, we demonstrate that explicit inclusion of vibrational broadening using ab initio molecular dynamics facilitates accurate VBM determination for $n\text{−}\mathrm{SrTi}{\mathrm{O}}_3\left(001\right)$. The total DOS is constructed by summing time-averaged projections at elevated temperature onto s-, p-, and $d$ orbitals for the constituent atoms and modulating with the associated photoemission cross sections. Subsequent convolutions of the total DOS, first with a Gaussian of width equal to the experimental energy resolution and second with a Lorentzian to simulate valence hole lifetime effects, yield line shapes that reproduce the experimental leading edges rather well. The VBM is then given by the energy at which the vibrationally broadened total DOS (prior to the convolutions) goes to zero. The VBMs generated by this method quantitatively agree with those resulting from extrapolating from the middle of the measured leading edge for $\mathrm{SrTi}{\mathrm{O}}_3$.

Real topological phases protected by the space-time inversion ($PT$) symmetry are a current research focus. The basis is that the $PT$ symmetry endows a real structure in momentum space, which leads to ${\mathbb{Z}}_2$ topological classifications in one and two dimensions ($1\mathrm{D}$ and $2\mathrm{D}$). Here, we provide solutions to two outstanding problems in the diagnosis of real topology. First, based on the stable equivalence in $K$ theory, we clarify that the 2D topological invariant remains well defined in the presence of nontrivial 1D invariant, and we develop a general numerical approach for its evaluation, which was hitherto unavailable. Second, under the unit-cell convention, noncentered $PT$ symmetries assume momentum dependence, which violates the presumption in previous methods for computing the topological invariants. We clarify the classifications for this case and formulate the invariants by introducing a twisted Wilson-loop operator for both $1\mathrm{D}$ and $2\mathrm{D}$. A simple model on a rectangular lattice is constructed to demonstrate our theory, which can be readily realized using artificial crystals.

Topological semimetal antiferromagnets provide a rich source of exotic topological states which can be controlled by manipulating the orientation of the Néel vector, or by modulating the lattice parameters through strain. We investigate via ab initio density functional theory calculations, the effects of shear strain on the bulk and surface states in two antiferromagnetic ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ phases with out-of-plane and in-plane spin configurations. When magnetic moments are along the $c$ axis, a 3% longitudinal or diagonal shear strain can tune the Dirac semimetal phase to an axion insulator phase, characterized by the parity-based invariant ${\eta }_{4I}=2$. For an in-plane magnetic order, the axion insulator phase remains robust under all shear strains. We further find that for both magnetic orders, the bulk gap increases, and a surface gap opens on the (001) surface up to 16 meV. Because of a nonzero ${\eta }_{4I}$ index and gapped states on the (001) surface, hinge modes are expected to happen on the side surface states between those gapped surface states. This result can provide valuable insight into the realization of the long-sought axion states.

The complicated ways in which electrons interact in many-body systems such as molecules and materials have long been viewed through the lens of local electron correlation and associated correlation functions. However, quantum information science has demonstrated that more global diagnostics of quantum states like the entanglement entropy can provide a complementary and clarifying lens on electronic behavior. One particularly useful measure that can be used to distinguish between quantum and classical sources of entanglement is the accessible entanglement, the entanglement available as a quantum resource for systems subject to conservation laws, such as fixed particle number, due to superselection rules. In this work, we introduce an algorithm and demonstrate how to compute accessible and symmetry-resolved entanglements for interacting fermion systems. This is accomplished by combining an incremental version of the swap algorithm with a recursive auxiliary field quantum Monte Carlo algorithm recently developed by the authors. We apply these tools to study the pairing and charge density waves exhibited in the paradigmatic attractive Hubbard model via entanglement. We find that the particle and spin symmetry-resolved entanglements and their related full probability distribution functions show very clear—and unique—signatures of the underlying electronic behavior even when those features are less pronounced in conventional correlation functions. Overall, this work provides a systematic means of characterizing the entanglement within quantum systems that can grant a deeper understanding of the complicated electronic behavior that underlies quantum phase transitions and crossovers in many-body systems.

One-dimensional (1D) van der Waals heterostructures (vdWHs) exhibit many properties, but many of these are difficult to understand because of their complicated structures and host-guest couplings that remain challenging to understand. Here, we observe a significant electron-phonon coupling (EPC) in 1D armchair graphene nanoribbons (AGNRs) confined in single-walled carbon nanotubes (SWNTs) via resonance Raman spectroscopy combined with theoretical calculation. A strong coupling between radial breathinglike mode (RBLM) phonons and the host nanotubes occurs due to the large vibration amplitude of RBLMs of the guest AGNRs. This results in unique deformation potential interactions in the heterostructure, contributing to the observed EPC enhancement. The EPC could be further modulated and strengthened by high pressure through tuning the RBLM-nanotube interactions. In this paper, we discover a mechanism governing the EPC in vdWHs and pave the way for manipulating the host-guest EPC for further control of the physical properties and potential device applications.

Orbital hybridization within the $d$-band model has been widely recognized as an important factor affecting the catalytic properties of materials. Separately, the spin degrees of freedom have also been gaining increasing attention in catalytic processes on magnetic substrates. Here, using first-principles calculations based on density functional theory, we systematically investigate the catalytic activity of ferromagnetic $M{X}_2$ ($M$ = V, Cr, Mn; $X$ = Se, Te) in the $1T$ phase, focusing on water splitting. Our studies show that $\mathrm{1T}\text{−}{\mathrm{VSe}}_2$ and $\mathrm{1T}\text{−}{\mathrm{VTe}}_2$ are excellent catalysts for the crucial constituent steps of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The enhanced reactivities in these two systems over the other four counterparts can be traced to the synergistic effects of magnetism and strong hybridization between the $p$ orbitals of $X$ and $d$ orbitals of V. We also propose a modified descriptor of ${\mathrm{\Delta }}_{\sigma {\sigma }^{*}}$ to characterize the HER activity, defined by the bonding and antibonding energy splitting, and further demonstrate that the magnetic properties of the catalysts should be explicitly accounted for in both reactions. The present findings may shed light on a microscopic understanding of the physical mechanisms of various catalytic reactions on two-dimensional magnets.

Fundamental understanding of the interaction between atoms and molecules with the surfaces of oxides including semiconducting oxides is crucial for the development of several thermo-, photo-, and electrocatalytic reactions as well as any application where surfaces are exposed to an environment beyond vacuum. While previous studies have postulated material features (descriptors) that to some extent suggest the adsorption energy trends on semiconducting oxides, a physics based model to describe the interaction of atoms and molecules with the surfaces of these materials is still lacking. In this study, we perform a series of controlled in silico experiments involving doping of quintessential semiconducting oxides (${\mathrm{SrTiO}}_3, {\mathrm{SrZrO}}_3$, and ${\mathrm{TiO}}_2$) to identify the perturbation by the dopant to the electronic structure of the host oxide and its resultant effect on the adsorption energies of simple atoms and molecules. We identify that a combination of three surface features: unique surface resonance states of the host-metal and lattice oxygen atoms of the terminating surface oxide layer as well as the gap states dominated by the introduced dopants contribute to the adsorption energy in a concerted fashion. We find that this intricate interplay between on the one hand host-metal and on the other hand oxygen surface resonance states with the adsorbate, respectively, results in a deviation from the well-established adsorbate scaling relations seen for ${\mathrm{NH}}_x$ ($x=0$–2) and ${\mathrm{CH}}_x$ ($x=0$–3) but not ${\mathrm{OH}}_x$ and ${\mathrm{SH}}_x$. Through this lens, we develop a physics based adsorption model hitherto referred as the generalized concerted coupling model (GCC model). The introduced model provides a physical understanding with an associated electronic structure descriptor rooted in the unique surfaces resonances that accurately captures the adsorption energy trends on doped semiconducting oxides. This paves the way for the atomistic design of doped semiconducting oxides for different catalytic applications, including sustainable energy applications such as electrochemical water splitting.

We report a study of the Fermi surface of the chiral semimetal CoSi and its relationship to a network of multifold topological crossing points, Weyl points, and topological nodal planes in the electronic band structure. Combining quantum oscillations in the Hall resistivity, magnetization, and torque magnetization with ab initio electronic structure calculations, we identify two groups of Fermi-surface sheets, one centered at the $R$ point and the other centered at the $\mathrm{\Gamma }$ point. The presence of topological nodal planes at the Brillouin zone boundary enforces topological protectorates on the Fermi-surface sheets centered at the $R$ point. In addition, Weyl points exist close to the Fermi-surface sheets centered at the $R$ and the $\mathrm{\Gamma }$ points. In contrast, topological crossing points at the $R$ point and the $\mathrm{\Gamma }$ point, which have been advertised to feature exceptionally large Chern numbers, are located at a larger distance to the Fermi level. Representing a unique example in which the multitude of topological band crossings has been shown to form a complex network, our observations in CoSi highlight the need for detailed numerical calculations of the Berry curvature at the Fermi level, regardless of the putative existence and the possible character of topological band crossings in the band structure.

Among the most sought-after chalcogenides, Hg-based diamondlike semiconductors have recently been realized for ultralow low heat conduction and potential thermoelectric devices. We present a less well-known but promising quaternary Hg-based chalcogenide, ${\mathrm{Cu}}_2{\mathrm{HgSnS}}_4$ (CHTS), for its electrical and thermal transport properties and compare it to its parent compound ${\mathrm{Cu}}_2{\mathrm{ZnSnS}}_4$ (CZTS) for better insight. CHTS is observed with distinct Hg-S and other bond pair strengths, but CZTS has similar cation-anion bond strengths, signifying anharmonicity caused by the heavy element Hg. Phonon dispersion in the Hg-dominated top acoustic frequency zone is nearly flat, indicating reduced phonon group velocity. The avoided-crossing characteristic, a sign of coupling in both high-frequency acoustic and lower-frequency optical modes, is also evident in the same region. The Hg atom's weak binding and considerable vibration with avoided crossing resemble cagelike skutterudite rattling. An ultralow glasslike average lattice thermal conductivity (${\kappa }_l$) of $\sim 0.53\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 300 K is noticed and associated with overall lower phonon group velocity, mild anharmonicity, and a lower avoided-crossing frequency. At higher temperatures, ${\kappa }_l$ decreases to $0.23\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 573 K, comparable to typical Hg-based tellurides such as ${\mathrm{Cu}}_2{\mathrm{HgGeTe}}_4$ and ${\mathrm{Cu}}_2{\mathrm{HgSnTe}}_4$ (${\kappa }_l<0.25\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) and noticeably smaller than the ${\kappa }_l$ of known ${\mathrm{Cu}}_2{\mathrm{HgSnSe}}_4$ nanoparticles. A large power factor for $p$-type doped structures is ascribed to an increased Seebeck coefficient because of the high-density-of-state effective mass close to the valence-band edge. The isoelectronic environment of CZTS and CHTS band edges should make them conduct similarly. This is further confirmed while comparing the estimated electrical conductivity of CHTS with the experimental data of CZTS for moderate doping concentration. Furthermore, in modest concentrations, holes with Ionized impurity scattering as their principal limiter have lifetimes of $\sim 10$ fs. A $p$-type Figure of Merit (ZT) value $>2.0$ is obtained with moderate doping of $\sim {10}^{18}$ to ${10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$ at 700 K. These remarkable ZT and ultralow lattice thermal conductivity characteristics suggest CHTS's promise for intermediate-temperature thermoelectricity, making it easier to implement devices using the same material.

Bound states in the continuum (BICs) are of special interest in photonics due to their theoretically infinite radiative lifetime. In this work, we take a specific example (a structure composed of GaN and a ${\mathrm{TiO}}_2$ photonic crystal slab), showcasing how the interactions affect BICs. The photonic BIC hosted by the photonic crystal slab couples with the excitons of GaN to form a polaritonic BIC with a negative mass. This allows condensation to be reached with a low threshold in a structure suitable for electrical injection, paving the way for room-temperature polariton microdevices. We study in detail how the repulsive interaction between exciton-polaritons affects the condensate distribution in reciprocal space and, consequently, the condensate's overlap with the BIC resonance and, therefore, the condensate lifetime. We study an intrinsic contribution related to the formation of a bright soliton and the extrinsic contribution related to the interaction with an excitonic reservoir induced by spatially focused nonresonant pumping. We then study the peculiar dynamics of the condensation process in a BIC state for interacting particles using Boltzmann equations and hybrid Boltzmann–Gross-Pitaevskii equations. We find optimal conditions allowing one to benefit from the long lifetime of the BIC for polariton condensation in a real structure.

We consider Josephson junctions formed by multiple superconductors with distinct phases and explore the formation of nonlocal or intersuperconductor pair correlations. We find that the multiple superconductor nature offers an additional degree of freedom that broadens the classification of pair symmetries, enabling nonlocal even- and odd-frequency pairings that can be highly controlled by the superconducting phases and the energy of the superconductors. Specially, when the phase difference between two superconductors is $\pi$, their associated nonlocal odd-frequency pairing is the only type of intersuperconductor pair correlations. Finally, we show that these nonlocal odd-frequency Cooper pairs dominate the nonlocal conductance via crossed Andreev reflections, which constitutes a direct evidence of odd-frequency pairing.