484 research outputs found
Chiral spin-order in some purported Kitaev spin-liquid compounds
We examine recent magnetic torque measurements in two compounds,
-LiIrO and RuCl, which have been discussed as possible
realizations of the Kitaev model. The analysis of the reported discontinuity in
torque, as an external magnetic field is rotated across the axis in both
crystals, suggests that they have a translationally-invariant chiral spin-order
of the from in the ground
state and persisting over a very wide range of magnetic field and temperature.
An extra-ordinary dependence of the torque for small fields, beside
the usual part, is predicted due to the chiral spin-order, and found to
be consistent with experiments upon further analysis of the data. Other
experiments such as inelastic scattering and thermal Hall effect and several
questions raised by the discovery of chiral spin-order, including its
topological consequences are discussed.Comment: Clearer figures of the experimental data provided. Also clearer
exposition and comment on related recent wor
Thermodynamic constraints on the amplitude of quantum oscillations
Magneto-quantum oscillation experiments in high temperature superconductors
show a strong thermally-induced suppression of the oscillation amplitude
approaching critical dopings---in support of a quantum critical origin of their
phase diagrams. We suggest that, in addition to a thermodynamic mass
enhancement, these experiments may directly indicate the increasing role of
quantum fluctuations that suppress the oscillation amplitude through inelastic
scattering. We show that the traditional theoretical approaches beyond
Lifshitz-Kosevich to calculate the oscillation amplitude in correlated metals
result in a contradiction with the third law of thermodynamics and suggest a
way to rectify this problem.Comment: PRB Rapid commun. (2017
Rapid Method for Computing the Mechanical Resonances of Irregular Objects
A solid object's geometry, density, and elastic moduli completely determine
its spectrum of normal modes. Solving the inverse problem - determining a
material's elastic moduli given a set of resonance frequencies and sample
geometry - relies on the ability to compute resonance spectra accurately and
efficiently. Established methods for calculating these spectra are either fast
but limited to simple geometries, or are applicable to arbitrarily shaped
samples at the cost of being prohibitively slow. Here, we describe a method to
rapidly compute the normal modes of irregularly shaped objects using entirely
open-source software. Our method's accuracy compares favorably with existing
methods for simple geometries and shows a significant improvement in speed over
existing methods for irregular geometries.Comment: 16 pages, 3 figure
Extent of Fermi-surface reconstruction in the high-temperature superconductor HgBaCuO
High magnetic fields have revealed a surprisingly small Fermi-surface in
underdoped cuprates, possibly resulting from Fermi-surface reconstruction due
to an order parameter that breaks translational symmetry of the crystal
lattice. A crucial issue concerns the doping extent of this state and its
relationship to the principal pseudogap and superconducting phases. We employ
pulsed magnetic field measurements on the cuprate HgBaCuO to
identify signatures of Fermi surface reconstruction from a sign change of the
Hall effect and a peak in the temperature-dependent planar resistivity. We
trace the termination of Fermi-surface reconstruction to two hole
concentrations where the superconducting upper critical fields are found to be
enhanced. One of these points is associated with the pseudogap end-point near
optimal doping. These results connect the Fermi-surface reconstruction to both
superconductivity and the pseudogap phenomena.Comment: 5 pages. 3 Figures. PNAS (2020
Langevin equations with multiplicative noise: resolution of time discretization ambiguities for equilibrium systems
A Langevin equation with multiplicative noise is an equation schematically of
the form dq/dt = -F(q) + e(q) xi, where e(q) xi is Gaussian white noise whose
amplitude e(q) depends on q itself. Such equations are ambiguous, and depend on
the details of one's convention for discretizing time when solving them. I show
that these ambiguities are uniquely resolved if the system has a known
equilibrium distribution exp[-V(q)/T] and if, at some more fundamental level,
the physics of the system is reversible. I also discuss a simple example where
this happens, which is the small frequency limit of Newton's equation d^2q/dt^2
+ e^2(q) dq/dt = - grad V(q) + e^{-1}(q) xi with noise and a q-dependent
damping term. The resolution does not correspond to simply interpreting naive
continuum equations in a standard convention, such as Stratanovich or Ito. [One
application of Langevin equations with multiplicative noise is to certain
effective theories for hot, non-Abelian plasmas.]Comment: 15 pages, 2 figures [further corrections to Appendix A
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