The nature of domain wall (DW) dynamics in synthetic ferrimagnetic multilayers composed of $\mathrm{Pt}\left|\mathrm{Co}\right|\mathrm{Tb}|\mathrm{Al}$ for different Tb thickness has been explored, focusing on the underlying pinning parameters, and on the different regimes of DW dynamics driven by spin-orbit torques (SOTs). We find that because of the AFM coupling between Co and Tb, the magnetic moment of Tb increases with Tb thickness resulting in a reduced saturation magnetization and an enhanced depinning field. The DW disorder interaction is found to vary weakly with the AFM coupling between Co and Tb, while the complete withdrawal of the Tb layer strongly increases the anisotropy and the DW pinning. Furthermore, we propose an approach to measure effective SOTs by comparing depinning transitions in current- and field-induced DW motion. This research reveals insights into DW dynamics in coupled AFM systems, highlighting enhancements in mobility through optimized SOTs and pinning landscapes.

We report the magnetic ground state, spin excitations, and spin Hamiltonian of the two-dimensional (2D) spin-1 trimerized Heisenberg antiferromagnet (AFM) $\mathrm{L}{\mathrm{i}}_2\mathrm{N}{\mathrm{i}}_3{\mathrm{P}}_4{\mathrm{O}}_{14}$. Below the magnetic ordering temperature $T_{\mathrm{N}}=14.5$ K, the compound exhibits a canted long-range antiferromagnetic order with a propagation vector $k$  = (0 0 0), consistent with the magnetic space group $P{2}_1/c.1$ (No. 14.75). The ground-state magnetic structure consists of ferromagnetic (FM) spin trimers of $\mathrm{N}{\mathrm{i}}^{2+}$ ions. The spin trimers are coupled antiferromagnetically along the $c$ axis and ferromagnetically along the $a$ axis. Inelastic neutron scattering (INS) reveals gapped and dispersive magnon excitations below the $T_{\mathrm{N}}$, and gapless quasielastic scatterings at higher temperature. The linear spin-wave theory simulations reveal the essential features of the excitation spectrum by a spin Hamiltonian composed of ferromagnetic intratrimer exchange interaction $J_1$ and intertrimer exchange interactions $J_2$ (FM) and $J_3$(AFM) within the $bc$ plane. The $J_2$ and $J_3$ are along the $b$ axis and $c$ axis, respectively, with strengths of $J_2/J_1=0.79$ and $J_3/J_1\sim =-0.91$. In addition, a weak interplanar ferromagnetic exchange interaction $J_4 \left(\right|J_4/J_1|\sim 0.12$ is found along the $a$ axis. The determined exchange constants reveal a 2D trimerized collinear-II spin lattice within the $bc$ plane. The analysis of INS spectra by linear spin-wave theory also yields a moderate single-ion anisotropy ($D/J_1=0.48$), which accounts for the observed spin gap below $T_{\mathrm{N}}$ as well as the metamagnetic transition near 44 kOe in dc magnetization ($M$ vs $H$) curves. These findings identify $\mathrm{L}{\mathrm{i}}_2\mathrm{N}{\mathrm{i}}_3{\mathrm{P}}_4{\mathrm{O}}_{14}$ as a rare realization of a two-dimensional trimerized spin system and offer the direct experimental confirmation of theoretically predicted magnon excitations, unveiling the fundamental characteristics of the expected excitation spectrum.

Stabilization of unusual spin-orbit-driven magnetic orderings are achieved for chains of Mn atoms deposited on a W(110) substrate. First-principles electronic structure calculations show that the ground-state spin configuration is noncollinear, forming chiral spiral-like structures, driven by competing nearest- and next-nearest-neighbor interactions. The orbital magnetic moments are also found to exhibit noncollinear ordering that, interestingly, tend to align in-plane for some systems with an orientation distinctly differently from that of the spin moment. We analyze the mechanism behind such behavior, and find that it is due to the competition between the spin-orbit interaction and crystal-field splitting. Model calculations based on this assumption reproduce the main findings observed in our first-principles calculations.

Extended and critical states are two common phenomena in quasiperiodic systems. In this paper, we first reveal the difference between the extended phase and the critical phase in the one-dimensional extended-critical system with off-diagonal quasiperiodic modulations from the perspectives of quantum transport and Wigner distribution. We reveal that in the extended phase, the quantum states exhibit ballistic or superdiffusion transport phenomena. While in the critical phase, the quantum states present subdiffusion transport phenomenon. Further, the transport conductance indicates that the extended-critical transition resembles a metallic-insulating transition. Moreover, the Wigner distributions show that the Wigner distribution of the extended wave function is localized in the momentum direction of the phase space, while that of the critical wave function is subextended in the momentum direction of the phase space. Based on the results of entanglement entropy, the extended-critical transition is a thermodynamic phase transition because it is accompanied by decreasing entropy. We engineer a quantum heat cycle engine with the extended-critical system as the working medium, and find that there are rich working modes in the engine, such as quantum accelerator, quantum heater, and quantum heat engine. Importantly, the extended phase is more conducive to the realization of quantum heat engines, while the critical phase is more conducive to the realization of quantum heaters. Our work is an important step toward exploring the rich thermodynamic applications of quasiperiodic systems.

We consider the dynamics in the one-dimensional quantum Ising model in which each spin coherently interacts with its phononic mode. The model is motivated by quantum simulators based on Rydberg atoms in tweezers or trapped ions. The configuration of two domain walls simulates the particle-antiparticle connecting string. We concentrate on the effect the local vibrations have on the dynamics of this initial state. Our study extends recent investigations of string breaking, traditionally studied within quantum chromodynamics, to quantum many-body systems. Two regimes are identified depending on the strength of the coupling with local vibrations. For weak coupling, the string breaking is slowed down compared to the dynamics in an isolated Ising string. Strong coupling leads to complicated dynamics in which the domain wall character of the excitation is dissolved among many coupled states.

Recent intriguing concepts have proposed that utilizing metal-organic frameworks (MOFs) as host matrixes can improve the crystallization of 9,10-diphenylanthracene (9,10-DPA) molecules in the solid film while also maintaining its high fluorescence quantum yield. Understanding the fundamental excited state dynamics is essential to the potential applications of these emerging materials, especially considering that photocarrier dynamics are expected to behave differently in the MOF structure due to the restricted degrees of freedom and long-range electronic couplings. Here, we have systematically investigated the carrier dynamics in highly crystalline and ordered DPA-MOF thin films employing transient absorption spectroscopy. Under photoexcitation, the constrained DPA molecules within the framework exhibit an ultrafast structural torsion in several hundred femtoseconds, which alters the energy positions of ${\mathrm{S}}_1$ states and blocks the ${\mathrm{S}}_0\to {\mathrm{S}}_1$ transition, enabling a strong localized excitation and the excimer formation. Sequentially, the localized photocarriers start to redistribute via the intramolecular singlet-to-triplet energy transfer and the interlayer singlet charge transfer. Furthermore, we have demonstrated that the photoinduced torsion and corresponding carrier dynamics can be effectively controlled by the excitation fluence.

The thermoelectric performance of the BaCaSn compound is systematically investigated through first-principles calculations and Boltzmann transport theory in the current work. The BaCaSn compound features a ${{\left[\mathrm{Ca}\text{−}\mathrm{Sn}\right]}^2}^{-}$ anionic framework interlaced with $\mathrm{B}{\mathrm{a}}^{2+}$ cation. The intricate bond lengths and distorted bond angles within the anionic framework facilitate efficient carrier transport while simultaneously enhancing the anharmonic lattice dynamics. Electronic structure analysis reveals that the BaCaSn compound is an indirect semiconductor with a bandgap of 0.71 eV. The sharp conduction band distribution improves electron mobility, while the multivalley nature of the valence band increases the hole effective mass, significantly enhancing the Seebeck coefficient. In terms of thermal transport, the weak interaction between $\mathrm{B}{\mathrm{a}}^{2+}$ cation and the ${{\left[\mathrm{Ca}\text{−}\mathrm{Sn}\right]}^2}^{-}$ anionic framework leads to pronounced rattling dissipation behavior, which significantly enhances phonon scattering and reduces phonon group velocity, thus exhibiting typical phonon glass behavior. Notably, the $p$-type doping strategy significantly increases the power factor due to the multivalley effect, thereby resulting in an excellent thermoelectric performance. The BaCaSn compound demonstrated figure of merit values of 1.1 and 0.8 under $p$-type and $n$-type doping conditions at 700 K, respectively. This work not only elucidates the fundamental physicochemical mechanisms governing the coupled electron-phonon transport in the BaCaSn compound, but also provides critical theoretical insights for the rational design of advanced thermoelectric materials.

Two-dimensional spin-spiral magnets provide promising building blocks for van der Waals heterostructures due to their tunable spin textures and potential for novel functionalities for quantum devices. However, due to its vanishing magnetization and two-dimensional nature, it is challenging to detect the existence of its noncollinear magnetization. Here, we show that a van der Waals junction based on a spin-spiral magnet and a quantum spin Hall insulator enables obtaining signatures of noncollinear magnetization directly from electrical measurements. Our strategy exploits the sensitivity of helical states to local breaking of time-reversal symmetry, potentially enabling the detection of local magnetic orders even in the absence of net magnetization. We show that the combination of spin-spiral order and nonmagnetic disorder gives rise to scattering in the helical channels that can be directly associated with the spiral exchange coupling and residual nonmagnetic disorder strength. Our results show how electrical transport measurement may offer a way to detect spin-spiral magnets by leveraging helical states in van der Waals heterostructures.

Two-dimensional (2D) boron-based materials are promising candidates for high-temperature superconductors. Authors of most studies have focused on stabilizing honeycomb and kagome boron layers by intercalating metals to tune σ- and π-electron states at the Fermi level. However, the specific roles of these electrons in superconductivity remain unclear. Here, we propose a structural resonance strategy to stabilize 2D boron-based materials, exemplified by ${\mathrm{B}}_6{X}_4$ ($X$ = S, Se, and Te) monolayers. These structures, composed of ${\mathrm{B}}_6$ hexagonal rings and ${\mathrm{B}}_3{X}_2$ trigonal bipyramidal units, enforce exclusive σ bonding within ${\mathrm{B}}_6$ rings due to the tetrahedral bonding configuration of boron. Meanwhile, variations in the electronegativity of $X$ elements modulate the electron occupancy of B–B bonds, thereby altering the Fermi-level electronic states. First-principles calculations confirm that these structures exhibit high cohesive energy and strong dynamical stability. Among them, ${\mathrm{B}}_6{\mathrm{S}}_4$, which has the largest B–B σ-orbital electron contribution at the Fermi level, displays the highest superconducting transition temperature ($T_{\mathrm{c}}\approx 33$ K). This sharply contrasts with the lower $T_{\mathrm{c}}$ values of ${\mathrm{B}}_6{\mathrm{Se}}_4$ (24 K) and ${\mathrm{B}}_6\mathrm{T}{\mathrm{e}}_4$ (1.71 K), which correspond to a reduced B–B σ-electron contribution. Additionally, ${\mathrm{B}}_6{\mathrm{S}}_4$ exhibits single-gap superconductivity dominated by B-B σ electrons, which is different from multigap boron-based superconductors that rely on both σ and π electrons. These findings highlight the critical role of B–B σ-orbital electrons in superconductivity and provide insights into the design of 2D boron-based superconductors with tunable electronic properties.

A detailed high-resolution, variable temperature powder diffraction study of the fluoro-perovskites ${\mathrm{NaFeF}}_3$ and ${\mathrm{NaCoF}}_3$ is performed to probe their orbital ordering transitions. Through analysis of the symmetry adapted macrostrains and atomic distortions, we show that ${\mathrm{NaFeF}}_3$ undergoes a C-type orbital order transition associated with the $t_{2g}^4$ states of ${\mathrm{Fe}}^{2+}$. Counterintuitively, the phase transition leading to the orbital order appears second-order-like, which contradicts the thermodynamic requirements for electronic and isosymmeric phase transitions, implying that there must be an associated hidden symmetry breaking. On the other hand, for ${\mathrm{NaCoF}}_3$, consideration of the symmetry adapted strains allows us to confidently rule out the occurrence of any long-range orbital orders down to 4 K. Since ${\mathrm{NaCoF}}_3$ is an insulator with quenched orbital angular momentum at this temperature, our findings point towards a novel kind of orbital disorder associated to the $t_{2g}^5$ electronic degeneracy.

The ${\mathrm{BaAl}}_4$-type structure family is home to a vast landscape of interesting and exotic properties, with descendant crystal structures hosting a variety of electronic ground states including magnetic, superconducting, and strongly correlated electron phenomena. ${\mathrm{BaAl}}_4$ itself hosts a nontrivial topological band structure, but is otherwise a paramagnetic metal. However, the other members of the $A{\mathrm{Al}}_4$ family ($A$ = alkali earth), including ${\mathrm{SrAl}}_4$ and ${\mathrm{EuAl}}_4$, exhibit symmetry-breaking ground states including charge density wave (CDW) and magnetic orders. Here we investigate the properties of the solid solution series ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Al}}_4$ and ${\mathrm{Ba}}_{1-y}{\mathrm{Eu}}_y{\mathrm{Al}}_4$ using transport, thermodynamic, and scattering experiments to study the evolution of the charge-ordered state as it is suppressed with Ba substitution to zero near 50% substitution in both systems. Neutron and x-ray diffraction measurements reveal an incommensurate CDW state in ${\mathrm{SrAl}}_4$ with $c$-axis-oriented ordering vector (0, 0, 0.097) that evolves with Ba substitution toward a shorter wavelength. A similar progression is observed in the ${\mathrm{Ba}}_{1-y}{\mathrm{Eu}}_y{\mathrm{Al}}_4$ series that also scales with the ordering temperature, revealing a universal correlation between charge-order transition temperature and ordering vector that points to a critical wave vector that stabilizes CDW order in both systems. We study the evolution of the phonon band structure in the ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Al}}_4$ system, revealing that the suppression of the CDW phase matches the suppression of a phonon instability at precisely the same momentum as observed in experiments, confirming the electron-phonon origin of charge order in this system.

Light-current conversion in single phase materials has been widely-studied. One of its main mechanisms is the bulk photovoltaic (BPV) effect. Other than electric charge current, generating pure spin current under light irradiation in a single material that only carries spin angular momentum without net electric currents is beneficial for high-performance spintronic devices. As both electric BPV and spin-resolved BPV require the breaking of inversion symmetry, they often emerge simultaneously. Hence, it is intriguing to design materials that could only host the spin BPV effect, while the electric charge current is completely suppressed, so that the Joule heating can be greatly eliminated. Furthermore, in order to increase spin lifetime and reduce spin decoherence, one promising route is the realization of a persistent spin helix in the momentum space. In this work, we scrutinize the point groups that could simultaneously host persistent spin helix in the momentum space and pure spin BPV generation, while the electric BPV process is symmetrically forbidden. We perform tight-binding model calculations and show that these requirements can be realized in a topological screw dislocation of centrosymmetric $\mathrm{BaBi}{\mathrm{O}}_3$ crystal. We also evaluate orbital moment BPV generation that follows the same symmetry arguments with spin moment. As both spin and orbital angular momenta are not good quantum numbers, they would be subject to torque effects during transport. This has been largely overlooked in most previous works. Our calculations suggest that these angular momentum torques are significant and cannot be omitted. Moreover, we show that the topological gapless states and spin (orbital) BPV from the screw dislocation line defects can be manipulated through defect-defect interactions.

Transition metal oxides in the (111) orientation have been predicted to harbor topological phases and unconventional quantum states because of their hexagonal crystal symmetry and strong interactions between charge, spin, and orbital degrees of freedom. We report Shubnikov–de Haas oscillations into the quantum limit at magnetic fields up to 35 T in high-mobility (>20 000 $\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) two-dimensional electron liquids at (111)-oriented $\mathrm{SrTi}{\mathrm{O}}_3$ interfaces with controllable carrier densities. Spin splitting is observed at low Landau levels, which is attributed to the interplay between the Zeeman splitting and Rashba spin-orbit coupling according to our theoretical modeling, yielding Landé factor $g=0.29$ and Rashba coefficient $\alpha =0.6\mathrm{meV}\mathrm{nm}$. At high magnetic field after the system reaches the lowest Landau level, the temperature dependence of the resistance shows a metallic to insulating state transition with the magnetoresistance changing significantly from a primarily quadratic to a large linear field dependence.

The higher Berry curvature was introduced by Kapustin and Spodyneiko as an extension of the Berry curvature in quantum mechanical systems with finite degrees of freedom to quantum many-body systems in finite spatial dimensions. In this paper, we propose an alternative formulation of the higher Berry curvature using translationally invariant matrix product states. They are the ground states of a set of gapped Hamiltonians, which are evolved adiabatically through a discretized parameter space. Because matrix product states transform under a projective representation, evaluating the Berry curvature on a closed loop through parameter space is not sufficient to fix all the gauge degrees of freedom. To obtain a gauge-invariant real quantity, the higher-dimensional Berry curvature is evaluated on small tetrahedra in parameter space. Our numerical calculations confirm that the higher Berry curvature varies continuously throughout an adiabatic evolution and becomes quantized over a closed three-dimensional parameter space.

In the last years, kagome materials have received massive attention by virtue of being candidate hosts for a large variety of quantum phases: spin liquids, unconventional superconductivity, and topological phases of matter, to name the more exotic. One of the most interesting features is tunability: changing the filling, the noninteracting band structure can be tuned from flat bands to conventional metallic phases as well as to semimetals. In this paper, we concentrate on the latter. At specific lattice filling, the electronic bands have a semimetallic structure, hosting Dirac, massless quasiparticles, such as in graphene or other layered two dimensional materials. Specifically, we determine what terms can be added to the nearest-neighbor hopping that opens at the gap at the said Dirac point. These terms can, in principle, arise through external perturbations, interactions, or collective instabilities. We classify the 16 possible gap-opening terms according to the broken symmetries. Furthermore, we identify concrete microscopic realizations, allowing for an interpretation of these phases.

Photoelectron satellites—the structures appearing on the low kinetic or high binding-energy side of the “main” or “elastic” photopeak—betray the complex many-body interactions set in motion by the sudden creation of the core hole. In this work, we demonstrate, using the technologically important ferromagnetic half-metal ${\mathrm{CrO}}_2$, how such satellites can manifest themselves in other core-level spectroscopies of the material and how they can reveal important details pertinent to its electronic structure. Specifically, we identify a fluorescence satellite in the Cr $L_3$ resonant x-ray-emission spectra that radiates at a constant emission energy across the Cr $L_3$ x-ray edge with energy ≈1.3 eV above the ordinary valence fluorescence. We provide evidence that this feature arises from the valence recombination of the Cr $2p$ core hole “dressed” by the same shakeup charge-transfer process present in both the Cr x-ray photoelectron and the Cr x-ray absorption spectra with its energy uniquely measuring the exchange splitting of the Cr $3d$ level. Further analysis of the x-ray emission data reveals three additional features that radiate at constant loss energy that are attributed to combinations of Cr $3d\left(t_{2g}\right)$ → Cr $3d\left(t_{2g}\right)$, charge-transfer O $2p\to \mathrm{Cr}$ $3d$, and crystal-field $\mathrm{Cr}3d\left(t_{2g}\right)\to \mathrm{Cr}3d\left(e_g\right)$ excitations. These assignments and their energies are supported by density-functional theory calculations, the accuracy of which we demonstrate by hard x-ray valence-photoemission measurements. Atomic multiplet calculations, which include crystal-field effects, help interpret x-ray photoelectron and x-ray absorption spectra of the covalently mixed Cr ion. Resonant Cr K-$L_{2,3}{L}_{2,3}$ Auger-electron emission spectra support a ligand-to-metal nature of the charge-transfer process while highlighting the charge sensitivity differences between photon-in/electron-out and photon-in/photon-out spectroscopies.

The substrate-adsorbate interaction can significantly influence the adsorbate's electronic structure, stability, reactivity, and topological properties. In this study, we investigate the emergence of non-Hermitian physics in the Su-Schrieffer-Heeger (SSH) model when coupled to a substrate, focusing on the impact of substrate interaction on the electronic states of the adsorbate. We demonstrate how the coupling between the SSH chain and the underlying substrate induces non-Hermitian effects, which manifest as amplification or attenuation of zero-energy electronic states. Furthermore, inspired by experimental techniques such as using a scanning tunneling microscope tip to lift part of the nanomaterial, we present simulations of scenarios where a segment of the SSH chain is decoupled from the substrate. By examining various configurations, including cases with odd or even numbers of sites coupled to the substrate, we demonstrate that tuning the coupling strength induces phenomena such as the emergence of a zero-energy monomode or additional zero-energy states localized at the boundary between on-surface and suspended chain segments. Our results reveal the role of substrate coupling in shaping the topological properties of non-Hermitian SSH chains, offering insights into tunable non-Hermitian effects and their potential applications in quantum technologies and nanodevices.

Dissociative chemisorption is a key process in hydrogen-metal surface chemistry, where nonadiabatic effects caused by low-lying electron-hole-pair excitations may affect reaction outcomes. Molecular dynamics with electronic friction simulations can capture weak nonadiabatic effects at metal surfaces, but require energy landscapes and electronic friction tensors as input. Here, we present full-dimensional machine learning surrogate models of the electronic friction tensor to study reactive hydrogen chemistry at the low-index surface facets Cu(100), Cu(110), Cu(111), and Cu(211). We combine these surrogate models with machine learning interatomic potentials to simulate quantum-state-resolved ${\mathrm{H}}_2$ reactive scattering on pristine copper surfaces. The predicted sticking coefficient and survival probabilities are in excellent agreement with experiments. Comparison between adiabatic and nonadiabatic simulations reveals that the influence of electron-hole pair excitations on the scattering dynamics is weak, and that the probability for dissociative adsorption is dominated by the shape of the underlying potential energy surface and the initial vibrational quantum state. Nonadiabatic effects only lead to subtle changes in rovibrationally inelastic state-to-state scattering probabilities. The differences between jellium-based isotropic local density friction and full ab initio response-theory-based orbital-dependent friction are even more subtle. The presented machine learning models represent the most accurate publicly available, full-dimensional models for ${\mathrm{H}}_2$ on copper to date.

A sensible application of the hybrid Monte Carlo (HMC) method is often hindered by the presence of large—or even infinite—potential barriers. These potential barriers separate the configuration space into distinct sectors and can lead to ergodicity violations that bias measurements. In this work, we address this problem by augmenting HMC with a multiplicative Metropolis-Hastings update in a “radial direction” of the fields which enables crossing the potential barriers and ensures ergodicity of the sampling algorithm at comparably low computational cost. We demonstrate the algorithm on a simple toy model and show how it can be applied to the fermionic Hubbard model describing physics ranging from an exactly solvable two-site system to the ${\mathrm{C}}_{20}{\mathrm{H}}_{12}$ perylene molecule. Our numerical results show that the radial updates successfully remove ergodicity violations, while simultaneously reducing autocorrelation times.