A new mechanism of the magnetoelectric effect based on spin supercurrent is theoretically presented in terms a microscopic electronic model for noncollinear magnets. The electric polarization P(ij) produced between two magnetic moments S(i) and S(j) given by P proportional e(ij) X (S(i) S(j)) with being unit vector connecting sites i j. Applications to spiral structure gauge theoretical interpretation are discussed.

We report the theoretical discovery of a class 2D tight-binding models containing nearly flatbands with nonzero Chern numbers. In contrast previous studies, where nonlocal hoppings are usually required, Hamiltonians our only require short-range hopping and have potential to be realized in cold atomic gases. Because similarity continuum Landau levels, these topologically nontrivial may lead realization fractional anomalous quantum Hall states topological insulators real materials. Among we...

The Hall effect usually occurs when the Lorentz force acts on a charge current in conductor presence of perpendicular magnetic field. On other hand, neutral quasi-particles such as phonons and spins can carry heat potentially show without resorting to force. We report experimental evidence for anomalous thermal caused by spin excitations (magnons) an insulating ferromagnet with pyrochlore lattice structure. Our theoretical analysis indicates that propagation wave is influenced...

We present a theory of the thermal Hall effect in insulating quantum magnets, where heat current is totally carried by charge-neutral objects such as magnons and spinons. Two distinct types responses are identified. For ordered intrinsic for arises when certain conditions satisfied lattice geometry underlying magnetic order. The other type allowed spin liquid which novel state since there no order even at zero temperature. this case, deconfined spinons contribute to response due Lorentz...

We study theoretically the electronic states in a 5d transition metal oxide Na2IrO3, which both spin-orbit interaction and electron correlation play crucial roles. A tight-binding model analysis together with first-principles band structure calculation predicts that this material is layered quantum spin Hall system. Because of correlation, an antiferromagnetic order first develops at edge, later inside bulk low temperatures.

We consider (2+1)-dimensional topological quantum states which possess edge described by a chiral (1+1)-dimensional conformal field theory, such as, e.g., general Hall state. demonstrate that for the reduced density matrix of finite spatial region gapped state is thermal theory would appear at boundary region. obtain this result applying physical instantaneous cut to system and viewing cutting process as sudden "quantum quench" into using tools theory. thus provide demonstration observation...

Nonequilibrium open systems effectively described by non-Hermitian Hamiltonians with parity-time ($P\phantom{\rule{0}{0ex}}T$) symmetry have recently attracted considerable attention due to their properties no Hermitian counterparts. In particular, there exists a growing interest in topological phases of matter. Here, the authors show that $P\phantom{\rule{0}{0ex}}T$-symmetric superconducting wire possesses two distinct types unconventional edge modes, those complex energies and...

We propose a class of non-integrable quantum spin chain models that exhibit many-body scars even in the presence disorder. With use so-called Onsager symmetry, we construct such scarred for arbitrary number $ S $. There are two types scar states, namely, coherent states associated to an Onsager-algebra element and one-magnon states. While both them highly-excited they have area-law entanglement can be written as matrix product state. Therefore, explicitly violate eigenstate thermalization...

We introduce two disorder-free variants of the Sachdev-Ye-Kitaev (SYK) model, demonstrate their integrability, and study static dynamical properties. Unlike diagrammatic techniques, integrability these models allows us to obtain correlation functions even when number Majorana fermions is finite. From solutions, we find that out-of-time-order correlators (OTOCs) in exhibit exponential growth at early times, resembling many-body quantum chaotic systems, such as those with disorder or external...

Collective mode dynamics of the helical magnets coupled to electric polarization via spin-orbit interaction is studied theoretically. The soft modes associated with ferroelectricity are not transverse optical phonons, as expected from Lyddane-Sachs-Teller relation, but spin waves hybridized polarization. This leads Drude-like dielectric function $\epsilon(\omega)$ in limit zero magnetic anisotropy. There two more low-lying modes; phason spiral and rotation plane along axis. roles these...

We have investigated the thermal Hall effect of magnons for various ferromagnetic insulators. For pyrochlore insulators Lu${}_{2}$V${}_{2}$O${}_{7}$, Ho${}_{2}$V${}_{2}$O${}_{7}$, and In${}_{2}$Mn${}_{2}$O${}_{7}$, finite conductivities been observed below Curie temperature ${T}_{C}$. From magnetic-field dependencies, it is concluded that are responsible effect. The can be well explained by theory based on Berry curvature in momentum space induced Dzyaloshinskii-Moriya (DM) interaction....

We study a system of interacting spinless fermions in one dimension which, the absence interactions, reduces to Kitaev chain [A. Yu Kitaev, Phys.-Usp. \textbf{44}, 131 (2001)]. In non-interacting case, signal topological order appears as zero-energy modes localized near edges. show that exact ground states can be obtained analytically even presence nearest-neighbor repulsive interactions when on-site (chemical) potential is tuned particular function other parameters. As with are two-fold...

A defining property of particles is their behavior under exchange. In two dimensions anyons can exist which, opposed to fermions and bosons, gain arbitrary relative phase factors or even undergo a change type. the latter case one speaks non-Abelian - particularly simple aesthetic example which are Fibonacci anyons. They have been studied in context fractional quantum Hall physics where they occur as quasiparticles $k=3$ Read-Rezayi state, conjectured describe state at filling fraction...

We derive exact results for the Lindblad equation a quantum spin chain (one-dimensional compass model) with dephasing noise. The system possesses doubly degenerate nonequilibrium steady states due to presence of conserved charge commuting Hamiltonian and operators. show that can be mapped non-Hermitian Kitaev model on two-leg ladder, which is solvable by representing spins in terms Majorana fermions. This allows us study Liouvillian gap, inverse relaxation time, detail. find gap increases...

We introduce and study a class of discrete-time quantum walks on one-dimensional lattice. In contrast to the standard homogeneous walks, coin operators are inhomogeneous depend their positions in this models. The models shown be self-dual with respect Fourier transform, which is analogous Aubry-Andr\'e model describing tight-binding quasi-periodic potential. When period incommensurate lattice spacing, we rigorously show that limit distribution walk localized at origin. also numerically...

We report a thorough theoretical study of the low temperature phase diagram ${\mathrm{Cs}}_{2}\mathrm{Cu}{\mathrm{Cl}}_{4}$, spatially anisotropic spin $S=1∕2$ triangular lattice antiferromagnet, in magnetic field. Our results, obtained quasi-one-dimensional limit which system is regarded as set weakly coupled Heisenberg chains, are excellent agreement with experiment. The analysis reveals some surprising physics. First, we find that when field oriented within layer, spins actually most...

To explore superfluidity in flat-band systems, we consider a Bose-Hubbard model on cross-linked ladder with $\ensuremath{\pi}$ flux, which has flat band gap between the other for noninteracting particles, where study effect of on-site repulsion nonperturbatively. For low densities, find exact degenerate ground states, each is Wigner solid nonoverlapping Wannier states band. At higher many-body system, when projected onto lower band, can be mapped to spin-chain model. This mapping enables us...

We study solvable spin chains, one-dimensional massless Dirac fermions and conformal field theories (CFTs) with sine-square deformation (SSD), in which the Hamiltonian density is modulated by function f(x) = sin 2(πx/ℓ), where x position ℓ length of system. For XY chain transverse Ising at criticality, it shown that ground state an open system SSD identical to a uniform periodic boundary conditions. The same holds for SSD, corresponding continuum limit gapless chain. general CFTs, we find...

Understanding the phases of a model usually requires knowledge their characteristic features, which are nonlocal in topologically ordered systems. Here, authors reframe phase classification problem disordered topological superconductors as data-driven task, motivated by recent surge interest application machine-learning techniques including deep learning. It is demonstrated that an artificial neural network learns to extract essence clean system and successfully distinguishes even under...

We propose a definition of ${\mathbb Z}_2$ topological invariant for magnon spin Hall systems which are the bosonic analog two-dimensional insulators in class AII. The existence "Kramers pairs" these is guaranteed by pseudo-time-reversal symmetry same as time-reversal up to some unitary transformation. index each Kramers pair bands expressed terms counterparts Berry connection and curvature. construct explicit examples demonstrate that our precisely characterizes presence or absence helical...

We study a quantum Ising chain with tailored bulk dissipation, which can be mapped onto non-Hermitian Ashkin-Teller model. By exploiting the Kohmoto-den Nijs-Kadanoff transformation, we further map it to staggered XXZ spin pure-imaginary anisotropy parameters. This allows us eigenstates of original Liouvillian in great detail. show that steady state each parity sector is completely mixed state. The uniqueness proved rigorously. then decay modes on self-dual line corresponding uniform and...

In quantum spin-1 chains, there is a nonlocal unitary transformation known as the Kennedy-Tasaki ${U}_{\mathrm{KT}}$, which defines duality between Haldane phase and ${\mathbb{Z}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathbb{Z}}_{2}$ symmetry-breaking phase. this paper, we find that ${U}_{\mathrm{KT}}$ also topological Ising critical trivial phase, provides ``hidden symmetry breaking'' interpretation of criticality. Moreover, since relates different phases matter, argue model with...

We characterize several phases of gapped spin systems by local order parameters defined quantized Berry [Y. Hatsugai, J. Phys. Soc. Jpn. 75, 123601 (2006)]. This characterization is topologically stable against any small perturbation as long the energy gap remains finite. The models we pick up are $S=1,2$ dimerized Heisenberg chains and $S=2$ with uniaxial single-ion-type anisotropy. Analytically, also evaluate topological for generalized Affleck-Kennedy-Lieb-Tasaki model. relation between...

We introduce and study two classes of Hubbard models with magnetic flux or spin-orbit coupling, which have a flat lowest band separated from other bands by non-zero gap. the Chern number bands, find that it is zero for first class but can be non-trivial in second. also prove introduction on-site Coulomb repulsion leads to ferromagnetism both classes.