Pseudo-Goldstone Gaps and Order-by-Quantum Disorder in Frustrated Magnets.

@article{Rau2018PseudoGoldstoneGA,
  title={Pseudo-Goldstone Gaps and Order-by-Quantum Disorder in Frustrated Magnets.},
  author={Jeffrey G. Rau and Paul A. McClarty and Roderich Moessner},
  journal={Physical review letters},
  year={2018},
  volume={121 23},
  pages={
          237201
        }
}
In systems with competing interactions, continuous degeneracies can appear which are accidental, in that they are not related to any symmetry of the Hamiltonian. Accordingly, the pseudo-Goldstone modes associated with these degeneracies are also unprotected. Indeed, through a process known as "order-by-quantum disorder," quantum zero-point fluctuations can lift the degeneracy and induce a gap for these modes. We show that this gap can be exactly computed at leading order in 1/S in spin-wave… 

Figures and Tables from this paper

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

Anisotropic-Exchange Magnets on a Triangular Lattice: Spin Waves, Accidental Degeneracies, and Dual Spin Liquids

We present an extensive overview of the phase diagram, spin-wave excitations, and finite-temperature transitions of the anisotropic-exchange magnets on an ideal nearest-neighbor triangular lattice.

Order-by-disorder from bond-dependent exchange and intensity signature of nodal quasiparticles in a honeycomb cobaltate

High-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO3 revealing the presence of a finite energy gap is presented and it is shown that the gap implies the existence of a quantum order-by-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations.

Insights into the Anisotropic Spin-$S$ Kitaev Chain

Recently there has been a renewed interest in properties of the higher-spin Kitaev models, especially their low-dimensional analogues with additional interactions. These quasi-1D systems exhibit rich

Honeycomb-lattice Gamma model in a magnetic field: hidden N\'eel order and spin-flop transition

We show that a magnetic field in the high-symmetry direction lifts the macroscopic classical ground-state degeneracy of the honeycomb Γ model and induces a long-range magnetic order. While a simple

Quantum versus thermal fluctuations in the fcc antiferromagnet: Alternative routes to order by disorder

In frustrated magnetic systems with competing interactions fluctuations can lift the residual accidental degeneracy. We argue that the state selection may have different outcomes for quantum and

Pseudo-Goldstone excitations in a striped Bose-Einstein condensate

Significant experimental progress has been made recently for observing long-sought supersolid-like states in Bose-Einstein condensates, where spatial translational symmetry is spontaneously broken by

Pseudo-spontaneous U(1) symmetry breaking in hydrodynamics and holography

Abstract We investigate the low-energy dynamics of systems with pseudo-spontaneously broken U(1) symmetry and Goldstone phase relaxation. We construct a hydrodynamic framework which is able to

Precision Low Temperature Calorimetry and Susceptibility of Magnetic Pyrochlores

Spin-ice models feature the same statistical disorder as water ice, which is identified as the source of zero-point entropy. Gapped topological excitations with properties of monopoles are associated

Thermal Hall Effect of Magnons in Collinear Antiferromagnetic Insulators: Signatures of Magnetic and Topological Phase Transitions.

We demonstrate theoretically that the thermal Hall effect of magnons in collinear antiferromagnetic insulators is an indicator of magnetic and topological phase transitions in the magnon spectrum.

References

SHOWING 1-10 OF 146 REFERENCES

Quantum order by disorder in the Kitaev model on a triangular lattice

We identify and discuss the ground state of a quantum magnet on a triangular lattice with bond-dependent Ising-type spin couplings, that is, a triangular analog of the Kitaev honeycomb model. The

Kitaev materials beyond iridates: Order by quantum disorder and Weyl magnons in rare-earth double perovskites

Motivated by the experiments on the rare-earth double perovskites, we propose a generalized Kitaev-Heisenberg model to describe the generic interaction between the spin-orbit-entangled Kramers'

Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7.

The Order-by-Quantum-Disorder spin wave gap is measured at a zone center in Er2Ti2O7, using low incident energy neutrons and the time-of-flight inelastic scattering method, and is consistent with upper bounds placed on it from heat capacity measurements and roughly consistent with the theoretical estimate of ∼0.02  meV.

Spin dynamics in the presence of competing ferromagnetic and antiferromagnetic correlations inYb2Ti2O7

In this work, we show that the zero field excitation spectra in the quantum spin ice candidate pyrochlore compound \ybti\ is a continuum characterized by a very broad and almost flat dynamical

Effective Hamiltonians for large-S pyrochlore antiferromagnets

The pyrochlore lattice Heisenberg antiferromagnet has a massive classical ground-state degeneracy. We summarize three approximation schemes, valid for large spin length S, to capture the (partial)

Direct evidence for a gapless $Z_2$ spin liquid by frustrating Néel antiferromagnetism

By direct calculations of the spin gap in the frustrated Heisenberg model on the square lattice, with nearest- ($J_1$) and next-nearest-neighbor ($J_2$) super-exchange couplings, we provide a solid

LOW-TEMPERATURE PROPERTIES OF CLASSICAL GEOMETRICALLY FRUSTRATED ANTIFERROMAGNETS

We study the ground-state and low-energy properties of classical vector spin models with nearest-neighbor antiferromagnetic interactions on a class of geometrically frustrated lattices, which

Order by quantum disorder in Er2Ti2O7.

This work establishes the systematic existence of a U(1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level, and unambiguously shows that quantum fluctuations break the degeneracy in a way which is confirmed by experiment.

J1-J2 quantum Heisenberg antiferromagnet on the triangular lattice: A group-symmetry analysis of order by disorder.

The full symmetry analysis of the low-lying levels of the spin-1/2 Hamiltonian in the hypotheses of either a four- or a two-sublattice order is developed.

Frustration and Quantum Fluctuations in Heisenberg fcc Antiferromagnets

We consider the quantum Heisenberg antiferromagnet on a face-centered-cubic lattice in which J, the secondneighbor (intrasublattice) exchange constant, dominates J′, the first-neighbor
...