We study the nonequilibrium spin dynamics in the nonintegrable spin-1 XXZ chains, emerging from inhomogeneous quenches, with two halves initialized in distinct maximally polarized states. Employing the time-dependent variational principle (TDVP) we are able to reach times that are inaccessible by standard time-dependent density matrix renormalization group methods. We identify three distinct phases depending on the anisotropy of the chain, corresponding to diffusive, logarithmic superdiffusive, and insulating. In the easy-axis regime we observe a transient ballistic behavior with a crossover time that diverges as the isotropic point is approached. This leads us to the conclusion that on the intermediate-large timescales the spin dynamics is well described by the integrable Landau-Lifshitz classical differential equation.

The recent discovery of ferromagnetic two-dimensional material has moved the subject of 2D magnetism into the center of interest. Besides materials with intrinsic magnetic properties, nonmagnetic 2D materials in the proximity of bulk magnets or in heterostructures have been proposed as candidates. By breaking the time-reversal symmetry the energy degeneracy is lifted and allows for an independent manipulation of different valleys in the band structure. In contrast to these systems, magnetic adsorbates allow for an easy manipulation and a huge variety of molecular magnets has already been identified. In this work we study the interaction of magnetic molecules adsorbed on the transitions metal dichalcogenide monolayer ${\mathrm{MoS}}_2$ by performing first-principles $GW$ and Bethe-Salpeter equation calculations. For the (spin-polarized) triplet ${\mathrm{O}}_2$ on ${\mathrm{MoS}}_2$ we find that both the electronic band structure close to the band edges as well as the low-energy excitons localized at different valleys obtain a small splitting which should be measurable by circular polarized light. Its size ranges up to about 10 meV and can be controlled by different coverages or by the distance dependent overlap.

Driving a Mott insulator towards an orbital-selective metal with coexisting Mott localized and marginal Fermi liquid electronic states remains central to understanding various correlated emergent phenomena. Here, using density functional dynamical mean-field theory we explore correlation and hole-doping-induced electronic reconstruction in ${\mathrm{RbFe}}_2{\mathrm{Te}}_3$, a potential two-leg ladder system for hole carrier superconductivity under pressure. We stress the importance of multiorbital Coulomb interactions in concert with band structure calculations for a consistent understanding of intrinsic Mott localization at ambient pressure. We elucidate the nature of pressure-induced Mottness upon tuning the correlation to bandwidth ratio away from the Mott boundary. As a by-product of our analysis, a quantum critical phenomenon with coexisting Mott localized and marginal Fermi liquid electrons is predicted to exist in compressed ${\mathrm{RbFe}}_2{\mathrm{Te}}_3$ metal.

A number of rare-earth monopnictides have topologically nontrivial band structures together with magnetism and strong electronic correlations. In order to examine whether the antiferromagnetic (AFM) semimetal YbAs ($T_{\mathrm{N}}=0.5$ K) exhibits such a scenario, we have grown high-quality single crystals using a flux method, and characterized the magnetic properties and electronic structure using specific heat, magnetotransport, and angle-resolved photoemission spectroscopy (ARPES) measurements, together with density functional theory (DFT) calculations. Both ARPES and DFT calculations find no evidence for band inversions in YbAs, indicating a topologically trivial electronic structure. From low-temperature magnetotransport measurements, we map the field-temperature phase diagram, where we find the presence of a field stabilized phase distinct from the AFM phase at low temperatures. An extremely large magnetoresistance (XMR) for both YbAs and the nonmagnetic counterpart LuAs is also observed, which can consistently be accounted for by the presence of electron-hole compensation. Moreover, an angle-dependent study of the Shubnikov–de Haas effect oscillations reveals very similar Fermi surfaces between YbAs and LuAs, with light effective masses down to at least 0.5 K, indicating that the Yb-$4f$ electrons are well localized, and do not contribute to the Fermi surface. However, the influence of the localized Yb-$4f$ electrons on the magnetotransport of YbAs can be discerned from the distinct temperature dependence of the XMR compared to that of LuAs, which we attribute to the influence of short-ranged spin correlations that appear well above $T_{\mathrm{N}}$.

Theory predicts that double-layer systems realize “two-component composite fermions,” which are formed when electrons capture both intra- and interlayer vortices, to produce a wide variety of new strongly correlated liquid and crystal states as a function of the layer separation. Recent experiments in double-layer graphene have revealed a large number of layer-correlated fractional quantum Hall states in the lowest Landau level, many of which have not been studied quantitatively in previous theoretical works. We consider the competition between various liquid and crystal states at several of these filling factors (specifically, the states at total filling factors $\nu =3/7, 4/9, 6/11, 4/7, 3/5, 2/3$, and $4/5$) to determine the theoretical phase diagram as a function of the layer separation. We compare our results with experiments and identify various observed states. In particular, we show that at small layer separations the states at total fillings $\nu =3/7$ and $\nu =3/5$ are partially pseudospin polarized, where pseudospin refers to the layer index. For certain fractions, such as $\nu =3/7$, interlayer correlations are predicted to survive to surprisingly large interlayer separations.

Locally, the atomic structure in well-annealed amorphous silicon appears similar to that of crystalline silicon. We address here the question whether a point defect, specifically a vacancy, in amorphous silicon also resembles that in the crystal. From density-functional theory calculations of a large number of nearly defect-free configurations, relaxed after an atom has been removed, we conclude that there is little similarity. The analysis is based on formation energy, relaxation energy, bond lengths, bond angles, Voronoï volume, coordination, atomic charge, and electronic gap states. All these quantities span a large and continuous range in amorphous silicon and while the removal of an atom leads to the formation of one to two bond defects and to a lowering of the local atomic density, the relaxation of the bonding network is highly effective, and the signature of the vacancy generally unlike that of a vacancy in the crystal.

We demonstrate that both the magnitude and sign of the Dzyaloshinskii-Moriya interaction can be tuned by modifying the type and thickness of an oxide layer adjacent to a ferromagnet. We focus on $\mathrm{Ti}/\mathrm{Cu}/\mathrm{C}{\mathrm{o}}_{90}\mathrm{F}{\mathrm{e}}_{10}/\mathrm{Ta}\left(d_{\mathrm{Ta}}\right)/\mathrm{Oxide}/\mathrm{Ta}$ structures, where the Ta interlayer thickness $d_{\mathrm{Ta}}$ ranged from 0 nm to 3 nm, followed by an exposure to oxygen and “Oxide” can mean $\mathrm{CoFe}{\mathrm{O}}_{\mathrm{x}}$ and/or $\mathrm{Ta}{\mathrm{O}}_{\mathrm{x}}$. We used Brillouin light scattering spectroscopy to directly determine the volume-averaged Dzyaloshinskii-Moriya interaction from the nonreciprocity of the spin-wave frequency. The magnitude of the interfacial Dzyaloshinskii-Moriya interaction, $D_{\mathrm{DMI}}$, ranges from $-0.17$ to $+0.09\left(\pm 0.02\right)\mathrm{mJ}/{\mathrm{m}}^2$, clearly showing a change in both sign and magnitude, with an increase of Ta interlayer thickness. The modification of the oxide interface allows us to systematically change the hybridization of the $3d-\mathrm{CoFe}$ orbitals from $3d-5d$ to $3d-2p$ and analyze the influence on the Dzyaloshinskii-Moriya interaction. Importantly, we can vary the Dzyaloshinskii-Moriya interaction while maintaining a relatively small value of the damping parameter.

Electric field control of magnetic susceptibility in laminate magnetostrictive/piezoelectric composites promises to create a new class of magnetoelectric elements, voltage tunable inductors. To elucidate the underlying mechanism of electric field modulated magnetic susceptibility at the domain level, phase-field modeling, and computer simulation are employed to systematically study the laminate magnetoelectric composites of Terfenol-D and PZT, where polycrystalline Terfenol-D can provide a giant magnetoelectric coupling that is important for high-tunability voltage tunable inductors. The simulations focus on the interplay between magnetocrystalline anisotropy and stress-induced anisotropy that is induced by electric field and reveal three regimes of magnetic susceptibility behaviors: constant (regime I), fast-varying (regime II), and reciprocal linear (regime III), where regimes II and III can give rise to a high tunability. Such three regimes are attributed to different magnetization distribution and evolution mechanisms that are modulated by the stress-induced anisotropy. To further characterize the electric field control of magnetic susceptibility behaviors, a general theoretical model of laminate magnetoelectric (ME) composites based on polycrystalline magnetostrictive materials is developed, which reproduces the three regimes of susceptibility behaviors for polycrystalline Terfenol-D material. The general theoretical model for this specific system can also be extended to other laminate polycrystalline ME composites.

We examine driven skyrmion dynamics in systems with inhomogeneous pinning where a strip of strong pinning coexists with a region containing no pinning. For driving parallel to the strip, we find that the initial skyrmion motion is confined to the unpinned region and the skyrmion Hall angle is zero. At larger drives, a transition occurs to a phase in which motion also appears within the pinned region, creating a shear band in the skyrmion velocity, while the skyrmion Hall angle is still zero. As the drive increases further, the flow becomes disordered and the skyrmion Hall angle increases with drive until saturating at the highest drives when the system transitions into a moving crystal phase. The different dynamic phases are associated with velocity and density gradients across the pinning boundaries. We map out the dynamic phases as a function of pinning strength, skyrmion density, and Magnus force strength, and correlate the phase boundaries with features in the velocity-force curves and changes in the local and global ordering of the skyrmion structure. For large Magnus forces, the shear banding instability is replaced by large-scale intermittent flow in the pinned region accompanied by simultaneous motion perpendicular to the direction of the drive, which appears as oscillations in the transport curves. We also examine the case of a drive applied perpendicular to the strip, where we find a jamming effect in which the skyrmion flow is blocked by skyrmion-skyrmion interactions until the drive is large enough to induce plastic flow.

We calculate magnon dispersions and damping in the Kitaev-Heisenberg model with an off-diagonal exchange $\mathrm{\Gamma }$ and isotropic third-nearest-neighbor interact ion $J_3$ on a honeycomb lattice. This model is relevant to a description of the magnetic properties of iridium oxides $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ and ${\mathrm{Na}}_2{\mathrm{IrO}}_3$, and Ru-based materials such as $\alpha \text{−}{\mathrm{RuCl}}_3$. We use an unconventional parametrization of the spin-wave expansion, in which each Holstein-Primakoff boson is represented by two conjugate Hermitian operators. This approach gives us an advantage over the conventional one in identifying parameter regimes where calculations can be performed analytically. Focusing on the parameter regime with the zigzag spin pattern in the ground state that is consistent with experiments, we demonstrate that one such region is $\mathrm{\Gamma }=K>0$, where $K$ is the Kitaev coupling. Within our approach, we are able to obtain explicit analytical expressions for magnon energies and eigenstates and go beyond the standard linear spin-wave theory approximation by calculating magnon damping and demonstrating its role in the dynamical structure factor. We show that the magnon damping effects in both Born and self-consistent approximations are very significant, underscoring the importance of nonlinear magnon coupling in interpreting broad features in the neutron-scattering spectra.

We report ${}^{51}\mathrm{V}$ NMR, muon spin rotation, and zero-applied-field ${}^{63,65}\mathrm{Cu}$ NMR measurements on powder samples of Sr-vesignieite, ${\mathrm{SrCu}}_3{\mathrm{V}}_2{\mathrm{O}}_8{\left(\mathrm{OH}\right)}_2$, a $S=1/2$ nearly kagome Heisenberg antiferromagnet. Our results demonstrate that the ground state is a $\mathit{q}=\mathit{0}$ magnetic structure with spins canting either in or out of the kagome plane, giving rise to weak ferromagnetism. We determine the size of ordered moments and the angle of canting for different possible $\mathit{q}=\mathit{0}$ structures and orbital scenarios, thereby providing insight into the role of the Dzyaloshinskii-Moriya interaction in this material.

The quantum robustness of fracton phases is investigated by studying the influence of quantum fluctuations on the X-Cube model and Haah's code, which realize a type-I and type-II fracton phase, respectively. To this end, a finite uniform magnetic field is applied to induce quantum fluctuations in the fracton phase, resulting in zero-temperature phase transitions between fracton phases and polarized phases. Using high-order series expansions and a variational approach, all phase transitions are classified as strongly first order, which turns out to be a consequence of the (partial) immobility of fracton excitations. Indeed, single fractons as well as few-fracton composites can hardly lower their excitation energy by delocalization due to the intriguing properties of fracton phases, as demonstrated in this work explicitly in terms of fracton quasiparticles.

We describe boundary effects in superconducting systems with Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting instability, using Bogoliubov-de-Gennes and Ginzburg-Landau (GL) formalisms. First, we show that in dimensions larger than one the standard GL functional formalism for FFLO superconductors is unbounded from below. This is demonstrated by finding solutions with zero Laplacian terms near boundaries. We generalize the GL formalism for these systems by retaining higher order terms. Next, we demonstrate that a cuboid sample of a superconductor with imbalanced fermions at a mean-field level has a sequence of the phase transitions. At low temperatures it forms Larkin-Ovchinnikov state in the bulk but has a different modulation pattern close to the boundaries. When temperature is increased the first phase transition occurs when the bulk of the material becomes normal while the faces remain superconducting. The second transition occurs at higher temperature where the system retains superconductivity on the edges. The third transition is associated with the loss of edge superconductivity while retaining superconducting gap in the vertices. We obtain the same sequence of phase transition by numerically solving the Bogoliubov-de Gennes model.

The chemical potentials of atoms and molecules in condensed matter are fundamental properties that allow one to predict a wide variety of thermodynamic properties. However, predictions using first principles are challenging. Here, an efficient and accurate method using machine-learned force fields is presented. A key point is that it requires training only at the end points of the thermodynamic pathway, rendering the training simple and efficient. Applications to liquid Si, and Li and F ions hydrated by water show that the method can predict accurate chemical potentials at low computational cost.

We present an ab initio based theoretical framework which elucidates the origin of the spin-orbit torque (SOT) in normal-metal (NM)/ferromagnet (FM) heterostructures. The SOT is decomposed into two contributions, namely, spin-Hall and the spin-orbital components. We find that (i) the fieldlike (FL) SOT is dominated by the spin-orbital component and (ii) both components contribute to the dampinglike (DL) torque with comparable magnitude in the limit of thick Pt film. The contribution of the spin-orbital component to the DL-SOT is present only for NMs with strong SOC coupling strength. We demonstrate that the FL-SOT can be expressed in terms of the nonequilibrium spin-resolved orbital moment accumulation. The calculations reveal that the experimentally reported oxygen-induced sign reversal of the FL-SOT in Pt/Co bilayers is due to the significant reduction of the majority-spin orbital moment accumulation on the interfacial NM atoms.

We report results of the time-resolved x-ray structure analysis of a relaxor ferroelectric single crystal under an alternating electric field. The time dependence of the lattice strain, atomic displacements, and ferroelectric domain volumes in a $0.955\mathrm{Pb}\left(\mathrm{Z}{\mathrm{n}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_3-0.045\mathrm{PbTi}{\mathrm{O}}_3$ (PZN-4.5PT) single crystal during piezoelectric lattice straining and ferroelectric domain switching is revealed. The lattice strain induced by an electric field is consistent with that expected from the piezoelectric constants. The crystal mosaicity is momentarily increased by a nucleation of nanosized ferroelectric domains when the polarization switching starts. The nucleated ferroelectric domains grow with the time constant of $\tau =14\mu \mathrm{s}$. An intersite displacement of the disordered Pb atoms observed in those site occupancies suggests that a rotational intersite displacement of Pb atoms is easily induced by an electric field and causes continuous rotation of the spontaneous polarization. The rotational intersite displacement of Pb atoms is essential for the large piezoelectric lattice strain and fatigue-free ferroelectric domain switching.

Manganese oxide is a prototype of an antiferromagnetic Mott insulator. Here, we investigate the interplay of magnetic ordering and lattice distortion across the Néel temperature $T_N$ under pressure using neutron and x-ray diffraction. We find an increase in $T_N$ with a rate of $d{T}_N/dP=+4.5\left(5\right)\mathrm{K}/\mathrm{GPa}$, an increase in the rhombohedral distortion $\alpha$ by $d\alpha /dP=+0.{018}^{\circ }/\mathrm{GPa}$, as well as a volume striction which is insensitive to pressure. These results allow retrieving the dependence of the coupling constants $J_1$ and $J_2$ on interatomic distances and compare it to first-principles predictions. Antiferromagnetic diffuse scattering was observed up to $\approx 1.2T_N$, and long-range magnetic order appears at room temperature at 42 GPa.

Dynamic heterogeneity is an intrinsic characteristic of amorphous materials that is closely related to the mysterious glass transition. However, there is seldom an intuitive physical parameter characterizing the degree of dynamic heterogeneity and linking it quantitatively to the dynamic arrest phenomenon at the glass transition. Here, we propose a general theoretical protocol to explain the glass transition via a statistical parameter quantifying the dynamic heterogeneity of glass-forming systems. The parameter can be calculated using the concept of the Shannon information entropy associated with the variation in the activation barriers to local structural excitations on the underlying potential energy landscape, which can be explored extensively using the recently developed activation-relaxation technique in inherent structures spanning a wide range of configurational space. The concept is demonstrated successfully in a model of a prototypical glass-forming system ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$. The Shannon entropy and statistical variation in the activation barriers are found to change dramatically at the glass-to-liquid transition and, therefore, can be treated as a novel signature of the glass transition, beyond the conventional thermodynamic indicators, such as the volume, potential energy, enthalpy, and heat capacity. The temperature-dependent Shannon entropy coincides with the evolution of the experimentally available stretching exponent during the glass-to-liquid transition and provides an intuitive explanation for the obscure decrease in dynamic heterogeneity from a metastable glass to an equilibrium liquid. Finally, possible relationships among structures, thermodynamics, and dynamics are discussed in terms of quantitative correlations among the structural Shannon entropy, excess total entropy, and dynamic Shannon entropy, respectively.

We report on the impact of magnetoelastic coupling on the magnetocaloric properties of ${\mathrm{LaFe}}_{11.4}{\mathrm{Si}}_{1.6}{\mathrm{H}}_{1.6}$ in terms of the vibrational (phonon) density of states (VDOS), which we determined with ${}^{57}\mathrm{Fe}$ nuclear resonant inelastic x-ray scattering (NRIXS) measurements and with density functional theory (DFT) based first-principles calculations in the ferromagnetic (FM) low-temperature and paramagnetic (PM) high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between nonhydrogenated and hydrogenated samples. This shows that hydrogen not only shifts the temperature of the first-order phase transition, but also affects the elastic response of the Fe subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. As a consequence, the change in the Fe-specific vibrational entropy $\mathrm{\Delta }{S}_{\mathrm{lat}}$ across the phase transition has the same sign as the magnetic and electronic contribution. DFT calculations show that the same mechanism, which is a consequence of the itinerant electron metamagnetism associated with the Fe subsystem, is effective in both the hydrogenated and the hydrogen-free compounds. Although reduced by 50% as compared to the hydrogen-free system, the measured change $\mathrm{\Delta }{S}_{\mathrm{lat}}$ of $(3.2\pm 1.9)\frac{\mathrm{J}}{\mathrm{kg}\mathrm{K}}$ across the FM-to-PM transition contributes with $\sim 35$% significantly and cooperatively to the total isothermal entropy change $\mathrm{\Delta }{S}_{\mathrm{iso}}$. Hydrogenation is observed to induce an overall blueshift of the Fe VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of ${\mathrm{LaFe}}_{11.4}{\mathrm{Si}}_{1.6}{\mathrm{H}}_{1.6}$ was determined from the NRIXS and the DFT data.