19 research outputs found
Topological phase diagrams of in-plane field polarized Kitaev magnets
While the existence of a magnetic field induced quantum spin liquid in Kitaev
magnets remains under debate, its topological properties often extend to
proximal phases where they can lead to unusual behaviors of both fundamental
and applied interests. Subjecting a generic nearest neighbor spin model of
Kitaev magnets to a sufficiently strong in-plane magnetic field, we study the
resulting polarized phase and the associated magnon excitations. In contrast to
the case of an out-of-plane magnetic field where the magnon band topology is
enforced by a three-fold symmetry, we find that it is possible for
topologically trivial and nontrivial parameter regimes to coexist under
in-plane magnetic fields. We map out the topological phase diagrams of the
magnon bands, revealing a rich pattern of variation of the Chern number over
the parameter space and the field angle. We further compute the magnon thermal
Hall conductivity as a weighted summation of Berry curvatures, and discuss
experimental implications of our results to planar thermal Hall effects in
Kitaev magnets.Comment: 8+7 pages, 5+1 figures, 1+0 tabl
Symmetry fractionalization in the gauge mean-field theory of quantum spin ice
Symmetry fractionalization is a ubiquitous feature of topologically ordered
states that can be used to classify different symmetry-enriched topological
phases and reveal some of their unique experimental signatures. Despite its
vast popularity, there is currently no available framework to study symmetry
fractionalization of quantum spin ice (QSI) -- a quantum spin liquid
(QSL) on the pyrochlore lattice supporting emergent photons -- within the most
widely used theoretical framework to describe it, gauge mean-field theory
(GMFT). In this work, we provide an extension of GMFT that allows for the
classification of space-time symmetry fractionalization. The construction
classifies all GMFT Ans\"atze that yield physical wavefunctions invariant under
given symmetries and a specific low-energy gauge structure. As an application
of the framework, we first show that the only two Ans\"atze with emergent
gauge fields that respect all space-group symmetries are the well-known
0- and -flux states. We then showcase how the framework may describe QSLs
beyond the currently known ones by classifying chiral QSI. We find two
new states described by - and -fluxes of the emergent gauge
field threading the hexagonal plaquettes of the pyrochlore lattice. We finally
discuss how the different ways translation symmetries fractionalize for all
these states lead to unique experimentally relevant signatures and compute
their respective inelastic neutron scattering cross-section to illustrate the
argument.Comment: 12+10 pages, 4+1 figure
Emergence of a nematic paramagnet via quantum order-by-disorder and pseudo-Goldstone modes in Kitaev magnets
The appearance of nontrivial phases in Kitaev materials exposed to an
external magnetic field has recently been a subject of intensive studies. Here,
we elucidate the relation between the field-induced ground states of the
classical and quantum spin models proposed for such materials, by using the
infinite density matrix renormalization group (iDMRG) and the linear spin wave
theory (LSWT). We consider the model, where and
are off-diagonal spin exchanges on top of the dominant Kitaev
interaction . Focusing on the magnetic field along the direction, we
explain the origin of the nematic paramagnet, which breaks the
lattice-rotational symmetry and exists in an extended window of magnetic field,
in the quantum model. This phenomenon can be understood as the effect of
quantum order-by-disorder in the frustrated ferromagnet with a continuous
manifold of degenerate ground states discovered in the corresponding classical
model. We compute the dynamical spin structure factors using a matrix operator
based time evolution and compare them with the predictions from LSWT. We, thus,
provide predictions for future inelastic neutron scattering experiments on
Kitaev materials in an external magnetic field along the direction. In
particular, the nematic paramagnet exhibits a characteristic pseudo-Goldstone
mode which results from the lifting of a continuous degeneracy via quantum
fluctuations.Comment: 14 pages, 9 figur
Emergence of nematic paramagnet via quantum order-by-disorder and pseudo-Goldstone modes in Kitaev magnets
The appearance of nontrivial phases in Kitaev materials exposed to an external magnetic field has recently been a subject of intensive studies. Here, we elucidate the relation between the field-induced ground states of the classical and quantum spin models proposed for such materials, by using the infinite density matrix renormalization group (iDMRG) and the linear spin wave theory (LSWT). We consider the KΓΓ′ model, where Γ and Γ′ are off-diagonal spin exchanges on top of the dominant Kitaev interaction K. Focusing on the magnetic field along the [111] direction, we explain the origin of the nematic paramagnet, which breaks the lattice-rotational symmetry and exists in an extended window of magnetic field, in the quantum model. This phenomenon can be understood as the effect of quantum order-by-disorder in the frustrated ferromagnet with a continuous manifold of degenerate ground states discovered in the corresponding classical model. We compute the dynamical spin structure factors using a matrix operator based time evolution and compare them with the predictions from LSWT. We, thus, provide predictions for future inelastic neutron scattering experiments on Kitaev materials in an external magnetic field along the [111] direction. In particular, the nematic paramagnet exhibits a characteristic pseudo-Goldstone mode, which results from the lifting of a continuous degeneracy via quantum fluctuations
Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in -RuCl
-RuCl is drawing much attention as a promising candidate Kitaev
quantum spin liquid. However, despite intensive research efforts, controversy
remains about the form of the basic interactions governing the physics of this
material. Even the sign of the Kitaev interaction (the bond-dependent
anisotropic interaction responsible for Kitaev physics) is still under debate,
with conflicting results from theoretical and experimental studies. The
significance of the symmetric off-diagonal exchange interaction (referred to as
the term) is another contentious question. Here, we present resonant
elastic x-ray scattering data that provides unambiguous experimental
constraints to the two leading terms in the magnetic interaction Hamiltonian.
We show that the Kitaev interaction () is ferromagnetic, and that the
term is antiferromagnetic and comparable in size to the Kitaev
interaction. Our findings also provide a natural explanation for the large
anisotropy of the magnetic susceptibility in -RuCl as arising from
the large term. We therefore provide a crucial foundation for
understanding the interactions underpinning the exotic magnetic behaviours
observed in -RuCl.Comment: 5 pages, two-column, 3 figure