We apply the equations for the magnetization $\vec{M}$ and field $\vec{H}$ to study their coupled modes for a semi-infinite ferromagnet, conductor, or insulator with magnetization $M_0$ and field $H_0$ normal to the plane (perpendicular resonance) and wave vector normal to the plane, which makes the modes doubly degenerate. With dimensionless damping constant $\alpha$ and dimensionless transverse susceptibility ${\chi }_{\perp }=M_0/H_e(H_e\equiv H_0-M_0)$, we derive an analytic expression for the wave vector squared, showing that $\vec{M}$ and $\vec{H}$ are nearly decoupled only if $\alpha \gg {\chi }_{\perp }$. This is violated in the ferromagnetic regime, although a first correction is found to give good agreement away from resonance. Emphasizing the conductor permalloy as a function of $H_0$ we study the eigenvalues and eigenmodes and the dissipation rate due to absorption both from the total effective field and from the Joule heating. (We include the contribution of the nonuniform exchange energy term, needed for energy conservation.) Using these modes we then apply, for a semi-infinite ferromagnet, a range of boundary conditions (i.e., surface anisotropies) on $M_{\perp }$ to find the reflection coefficient $R$ and the reflectivity ${\left|R\right|}^2$. As a function of $H_0$, absorption is dominated by the the skin depth mode (primarily $\vec{H}$) except near the resonance and at a higher-field $H_d$ associated with a dip in the reflectivity, whose position above the main resonance varies quadratically with the surface anisotropy $K_s$. The dip is driven by the boundary condition on $\vec{M}$; the coefficient of the (primarily) $\vec{M}$ mode becomes very small at the dip, being compensated by an increase in the amplitude of the $\vec{M}$ mode, which has a Lorentzian line shape of height $\sim {\alpha }^{-1}$ and width $\sim \alpha$.

We propose utilizing the Cooper pair to induce magnetic frustration in systems of two-dimensional (2D) magnetic adatom lattices on $s$-wave superconducting surfaces. The competition between singlet electron correlations and the RKKY coupling is shown to lead to a variety of hidden-order states that break the point-group symmetry of the 2D adatom lattice at finite temperature. The phase diagram is constructed using a newly developed effective bond theory [M. Schecter et al., Phys. Rev. Lett. 119, 157202 (2017)], and exhibits broad regions of long-range vestigial nematic order.

We demonstrate a spin to charge current conversion via magnon-phonon coupling and an inverse Edelstein effect on the hybrid device ${\mathrm{Ni}/\mathrm{Cu}\left(\mathrm{Ag}\right)/\mathrm{Bi}}_2{\mathrm{O}}_3$. The generation of spin current $\left(J_s\approx {10}^8\text{A}/{\text{m}}^2\right)$ due to magnon-phonon coupling reveals the viability of acoustic spin pumping as a mechanism for the development of spintronic devices. A full in-plane magnetic field angle dependence of the power absorption and a combination of longitudinal and transverse voltage detection reveals the symmetric and asymmetric components of the inverse Edelstein effect voltage induced by Rayleigh-type surface acoustic waves. While the symmetric components are well studied, asymmetric components still need to be explored. We assign the asymmetric contributions to the interference between longitudinal and shear waves and an anisotropic charge distribution in our hybrid device.

We study the dynamics arising from a double quantum quench where the parameters of a given Hamiltonian are abruptly changed from being in an equilibrium phase A to a different phase B and back ($\mathrm{A}\to \mathrm{B}\to \mathrm{A}$). As prototype models, we consider the (integrable) transverse Ising field as well as the (nonintegrable) ANNNI model. The return amplitude features nonanalyticities after the first quench through the equilibrium quantum critical point ($\mathrm{A}\to \mathrm{B}$), which is routinely taken as a signature of passing through a so-called dynamical quantum phase transition. We demonstrate that nonanalyticities after the second quench ($\mathrm{B}\to \mathrm{A}$) can be avoided and reestablished in a recurring manner upon increasing the time $T$ spent in phase B. The system retains an infinite memory of its past state, and one has the intriguing opportunity to control at will whether or not dynamical quantum phase transitions appear after the second quench.

We study magnetoelastic resonance phenomena in a monoaxial chiral helimagnet belonging to the hexagonal crystal class. By computing the spectrum of a coupled elastic wave and spin wave, it is demonstrated how hybridization occurs depending on their chirality. Specific features of the magnetoelastic resonance are discussed for the conical phase and the soliton lattice phase stabilized in the monoaxial chiral helimagnet. The former phase exhibits appreciable nonreciprocity of the spectrum, and the latter is characterized by a multiresonance behavior. We propose that the nonreciprocal spin wave around the forced-ferromagnetic state has potential capability to convert the linearly polarized elastic wave to a circularly polarized one with the chirality opposite to the spin-wave chirality.

We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U $4d-5f\left(N_{4,5}\right)$ and Co $2p-3d\left(L_{2,3}\right)$ absorption edges in order to investigate the magnetic properties of the U $5f$ and Co $3d$ electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co $3d$ electrons is unusually large. Through the systematic temperature $\left(T\right)$- and magnetic field $\left(H\right)$-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of $H$ and $T$ (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at $H_{\mathrm{M}}$. The value of the $H_{\mathrm{M}}$ and its $T$ dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co $3d$ electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.

In this work we propose a theory for the deconfined quantum critical point (DQCP) for spin-1/2 systems on a triangular lattice, which is a direct unfine-tuned quantum phase transition between the standard “$\sqrt{3}\times \sqrt{3}$” noncollinear antiferromagnetic order (or the so-called ${120}^{\circ }$ state) and the “$\sqrt{12}\times \sqrt{12}$” valence solid bond (VBS) order, both of which are very standard ordered phases often observed in numerical simulations. This transition is beyond the standard Landau-Ginzburg paradigm and is also fundamentally different from the original DQCP theory on the square lattice due to the very different structures of both the magnetic and VBS order on frustrated lattices. We first propose a topological term in the effective-field theory that captures the “intertwinement” between the $\sqrt{3}\times \sqrt{3}$ antiferromagnetic order and the $\sqrt{12}\times \sqrt{12}$ VBS order. Then using a controlled renormalization-group calculation, we demonstrate that an unfine-tuned direct continuous DQCP exists between the two ordered phases mentioned above. This DQCP is described by the $N_f=4$ quantum electrodynamics (QED) with an emergent PSU(4)=SU(4)/$Z_4$ symmetry only at the critical point. The aforementioned topological term is also naturally derived from the $N_f=4$ QED. We also point out that physics around this DQCP is analogous to the boundary of a $3d$ bosonic symmetry- protected topological state with only on-site symmetries.

We study the interplay between the electron-phonon $(e$-ph) and on-site electron-electron (e-e) interactions in a three-orbital Hubbard-Holstein model on an extended one-dimensional lattice using determinant quantum Monte Carlo. For weak e-e and $e$-ph interactions, we observe a competition between an orbital-selective Mott phase (OSMP) and a (multicomponent) charge-density-wave (CDW) insulating phase, with an intermediate metallic phase located between them. For large e-e and $e$-ph couplings, the OSMP and CDW phases persist, while the metallic phase develops short-range orbital correlations and becomes insulating when both the e-e and $e$-ph interactions are large but comparable. Many of our conclusions are in line with those drawn from a prior dynamical mean-field theory study of the two-orbital Hubbard-Holstein model [Phys. Rev. B 95, 121112(R) (2017)] in infinite dimension, suggesting that the competition between the $e$-ph and e-e interactions in multiorbital Hubbard-Holstein models leads to rich physics, regardless of the dimension of the system.

The electric field dependence of the dielectric properties and the nonlinear conductance of $1T\text{−}{\mathrm{TaS}}_2$ below 50 K has been investigated. A large dielectric constant of about ${10}^4$ is obtained up to ${10}^7$ Hz, which cannot be attributed to hopping of the localized carriers alone, the collective excitations of the commensurate charge-density-wave must be another contributor. The dielectric spectra disperse slightly in our measured temperature and frequency range. At a moderate dc bias field, the real part of the dielectric constant ${\epsilon }_1\left(\omega \right)$ decreases. We propose that the separation of bound soliton-antisoliton pairs may be a contributor to the reduction of ${\epsilon }_1\left(\omega \right)$ and the accompanying nonlinear conductivity with increasing dc bias.

We study the entanglement entropy of gapped phases of matter in three spatial dimensions. We focus in particular on size-independent contributions to the entropy across entanglement surfaces of arbitrary topologies. We show that for low energy fixed-point theories, the constant part of the entanglement entropy across any surface can be reduced to a linear combination of the entropies across a sphere and a torus. We first derive our results using strong sub-additivity inequalities along with assumptions about the entanglement entropy of fixed-point models, and identify the topological contribution by considering the renormalization group flow; in this way we give an explicit definition of topological entanglement entropy $S_{\mathrm{topo}}$ in (3+1)D, which sharpens previous results. We illustrate our results using several concrete examples and independent calculations, and show adding “twist” terms to the Lagrangian can change $S_{\mathrm{topo}}$ in (3+1)D. For the generalized Walker-Wang models, we find that the ground state degeneracy on a 3-torus is given by $exp(-3S_{\mathrm{topo}}\left[T^2\right])$ in terms of the topological entanglement entropy across a 2-torus. We conjecture that a similar relationship holds for Abelian theories in $(d+1)$ dimensional spacetime, with the ground state degeneracy on the $d$-torus given by $exp(-d{S}_{\mathrm{topo}}\left[T^{d-1}\right])$.

The atomic-scale structure and vibrational properties of semiconductor alloys are determined by the energy required for stretching and bending the individual bonds. Using temperature-dependent extended x-ray absorption fine-structure spectroscopy, we have determined the element-specific In-As and Ga-As effective bond-stretching force constants in (In,Ga)As as a function of the alloy composition. The results reveal a striking inversion of the bond strength where the originally stiffer bond in the parent materials becomes the softer bond in the alloy and vice versa. Our findings clearly demonstrate that changes of both the individual bond length and the surrounding matrix affect the bond-stretching force constants. We thus show that the previously used common assumptions about the element-specific force constants in semiconductor alloys do not reproduce the composition dependence determined experimentally for (In,Ga)As.

We use density-functional theory to investigate the bulk and surface properties of ${\mathrm{MgB}}_2$. The unique bonding structure of ${\mathrm{MgB}}_2$ is investigated by Bader's atoms-in-molecules, charge density difference, and occupancy projected band structure analyses. Oxygen adsorption on the charge-depleted surfaces of ${\mathrm{MgB}}_2$ is studied by a surface potential energy mapping method, reporting a complete map including low-symmetry binding sites. The B-terminated ${\mathrm{MgB}}_2$(0001) demonstrates reconstruction of the graphenelike B layer, and the reconstructed geometry exposes a threefold site of the subsurface Mg, making it accessible from the surface. Detailed reconstruction mechanisms are studied by simulated annealing method based on ab initio molecular dynamics and nudged elastic band calculations. The surface clustering of B atoms significantly modifies the B $2p$ states to occupy low energy valence states. The present paper emphasizes that a thorough understanding of the surface phase may explain an apparent inconsistency in the experimental surface characterization of ${\mathrm{MgB}}_2$. Furthermore, these results suggest that the surface passivation can be an important technical challenge when it comes to development of a superconducting device using ${\mathrm{MgB}}_2$.

We use a symmetry approach to derive the coupling of lattice deformations to electronic excitations in three-dimensional Dirac and Weyl semimetals in the continuum low-energy model. We focus on the effects of rotational strain and show that it can drive transitions from Dirac to Weyl semimetals, gives rise to elastic gauge fields, tilts the cones, and generates pseudo-Zeeman couplings. It also can generate a deformation potential in volume-preserving deformations. The associated pseudoelectric field contributes to the chiral anomaly.

Motivated by the rich physics of honeycomb magnetic materials, we obtain the phase diagram and analyze magnetic properties of the spin-$1/2$ and spin-$1J_1\text{−}{J}_2\text{−}{J}_3$ Heisenberg model on the honeycomb lattice. Based on the SU(2) and SU(3) symmetry representations of the Schwinger boson approach, which treats disordered spin liquids and magnetically ordered phases on an equal footing, we obtain the complete phase diagrams in the $(J_2,J_3)$ plane. This is achieved using a fully unrestricted approach which does not assume any pre-defined Ansätze. For $S=1/2$, we find a quantum spin liquid (QSL) stabilized between the Néel, spiral, and collinear antiferromagnetic phases in agreement with previous theoretical work. However, by increasing $S$ from $1/2$ to 1, the QSL is quickly destroyed due to the weakening of quantum fluctuations indicating that the model already behaves as a quasiclassical system. The dynamical structure factors and temperature dependence of the magnetic susceptibility are obtained in order to characterize all phases in the phase diagrams. Moreover, motivated by the relevance of the single-ion anisotropy, $D$, to various $S=1$ honeycomb compounds, we have analyzed the destruction of magnetic order based on an SU(3) representation of the Schwinger bosons. Our analysis provides a unified understanding of the magnetic properties of honeycomb materials realizing the $J_1\text{−}{J}_2\text{−}{J}_3$ Heisenberg model from the strong quantum spin regime at $S=1/2$ to the $S=1$ case. Neutron scattering and magnetic susceptibility experiments can be used to test the destruction of the QSL phase when replacing $S=1/2$ by $S=1$ localized moments in certain honeycomb compounds.

We have grown the phase-homogeneous ternary compound with composition ${\mathrm{Bi}}_2{\mathrm{Te}}_{1.85}{\mathrm{S}}_{1.15}$ very close to the stoichiometric ${\mathrm{Bi}}_2{\mathrm{Te}}_2\mathrm{S}$. The measurements performed with spin- and angle-resolved photoelectron spectroscopy as well as density functional theory and $GW$ calculations revealed a wide-band-gap three-dimensional topological insulator phase. The surface electronic spectrum is characterized by the topological surface state (TSS) with Dirac point located above the valence band and Fermi level lying in the band gap. TSS band dispersion and constant energy contour manifest a weak warping effect near the Fermi level along with in-plane and out-of-plane spin polarization along the $\overline{\mathrm{\Gamma }}\text{−}\overline{K}$ line. We identified four additional states at deeper binding energies with high in-plane spin polarization.

Using generalized gradient approximation+dynamical mean-field theory, we provide a microscopic description of orbital-selective spin ordering in the tetragonal manganese pnictide ${\mathrm{BaMn}}_2{\mathrm{As}}_2$. We demonstrate the coexistence of local moments and small band-gap electronic states in the parent compound. We also explore the role played by electron/hole doping, showing that the Mott insulating state is rather robust to small removal of electron charge carriers similar to cuprate oxide superconductors. Good qualitative accord between theory and angle-resolved photoemission as well as electrical transport provides support to our view of orbital-selective spin ordering in ${\mathrm{BaMn}}_2{\mathrm{As}}_2$. Our proposal is expected to be an important step to understanding the emergent correlated electronic structure of materials with persisting ordered localized moments coexisting with Coulomb reconstructed nonmagnetic electronic states.

We report on single-crystal growth, single-crystal x-ray diffraction, physical properties, and density functional theory (DFT) electronic structure as well as Fermi surface calculations for two ternary carbides, ${\mathrm{LuCoC}}_2$ and ${\mathrm{LuNiC}}_2$. Electrical resistivity measurements reveal for ${\mathrm{LuNiC}}_2$ a charge density wave (CDW) transition at $T_{\mathrm{CDW}}\simeq 450$ K and, for $T>T_{\mathrm{CDW}}$, a significant anisotropy of the electrical resistivity, which is lowest along the orthorhombic $a$ axis. The analysis of x-ray superstructure reflections suggest a commensurate CDW state with a Peierls-type distortion of the Ni atom periodicity along the orthorhombic $a$ axis. DFT calculations based on the CDW modulated monoclinic structure model of ${\mathrm{LuNiC}}_2$ as compared to results of the orthorhombic parent type reveal the formation of a partial CDW gap at the Fermi level which reduces the electronic density of states from $N\left(E_{\mathrm{F}}\right)=1.03$ states/eV f.u. without CDW to $N\left(E_{\mathrm{F}}\right)=0.46$ states/eV f.u. in the CDW state. The corresponding bare DFT Sommerfeld value of the latter, ${\gamma }_{\mathrm{DFT}}^{\mathrm{CDW}}=0.90$ mJ/mol ${\mathrm{K}}^2$, reaches reasonable agreement with the experimental value $\gamma =0.83\left(5\right)$ mJ/mol ${\mathrm{K}}^2$ of ${\mathrm{LuNiC}}_2$. ${\mathrm{LuCoC}}_2$ displays a simple metallic behavior with neither CDW ordering nor superconductivity above 0.4 K. Its experimental Sommerfeld coefficient, $\gamma =5.9$(1) mJ/mol ${\mathrm{K}}^2$, is in realistic correspondence with the calculated, bare Sommerfeld coefficient, ${\gamma }_{\mathrm{DFT}}=3.82$ mJ/mol ${\mathrm{K}}^2$, of orthorhombic ${\mathrm{LuCoC}}_2$.

In the present article we investigate the heat and momentum fluxes radiated by a hot magneto-optical nanoparticle in its surroundings under the action of an external magnetic field. We show that the flux lines circulate in a confined region at a nanometric distance from the particle around the axis of the magnetic field in a vortexlike configuration. Moreover we prove that the spatial orientation of these vortices (clockwise or counterclockwise) is associated with the contribution of optical resonances with topological charges $m=+1$ or $m=-1$ to the thermal emission. This work paves the way for a geometric description of heat and momentum transport in lattices of magneto-optical particles. Moreover it could have important applications in the field of energy storage as well as in thermal management at nanoscale.

We study a particle which propagates in a one-dimensional strong random potential and is coupled to a bosonic bath. We independently test various properties of bosons (hopping term, hard-core effects, and generic boson-boson interaction) and show that bosonic itineracy is the essential ingredient governing the dynamics of the particle. Coupling of the particle to itinerant phonons or hard-core bosons alike leads to delocalization of the particle by virtue of a subdiffusive (or diffusive) spread from the initially localized state. Delocalization remains in effect even when the boson frequency and the bandwidth of itinerant bosons remain an order of magnitude smaller than the magnitude of the random potential. When the particle is coupled to localized bosons, its spread remains logarithmic or even sublogarithmic. The latter result together with the survival probability shows that the particle remains localized despite being coupled to bosons.

In the quest for materials with emergent or improved properties, an effective route is to create artificial superstructures. Novel properties emerge from the coupling between the phases, but the strength of this coupling depends on the quality of the interfaces. Atomic control of crystalline interfaces is notoriously complicated and to elude that obstacle, we suggest here an all-amorphous design. Starting from a model amorphous iron alloy, we locally tune the magnetic behavior by creating boron-doped regions by means of ion implantation through a lithographic mask. This process preserves the amorphous environment, creating a non-topographic magnetic superstructure with smooth interfaces and no structural discontinuities. The absence of inhomogeneities acting as pinning centers for the magnetization reversal is demonstrated by the formation of magnetic vortexes for ferromagnetic disks as large as 20 µm in diameter embedded within a paramagnetic matrix. Rigid exchange coupling between two amorphous ferromagnetic phases in a microstructured sample is evidenced by an investigation involving first-order reversal curves. The sample consists of a soft matrix with embedded elements constituting a hard phase where the anisotropy originates from an elongated shape of the elements. We provide an intuitive explanation for the micrometer-range exchange coupling mechanism and discuss how to tailor the properties of all-amorphous superstructures.