229 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
One-Component Order Parameter in URuSi Uncovered by Resonant Ultrasound Spectroscopy and Machine Learning
The unusual correlated state that emerges in URuSi below T =
17.5 K is known as "hidden order" because even basic characteristics of the
order parameter, such as its dimensionality (whether it has one component or
two), are "hidden". We use resonant ultrasound spectroscopy to measure the
symmetry-resolved elastic anomalies across T. We observe no anomalies in
the shear elastic moduli, providing strong thermodynamic evidence for a
one-component order parameter. We develop a machine learning framework that
reaches this conclusion directly from the raw data, even in a crystal that is
too small for traditional resonant ultrasound. Our result rules out a broad
class of theories of hidden order based on two-component order parameters, and
constrains the nature of the fluctuations from which unconventional
superconductivity emerges at lower temperature. Our machine learning framework
is a powerful new tool for classifying the ubiquitous competing orders in
correlated electron systems
Quantum limit transport and destruction of the Weyl nodes in TaAs
Weyl fermions are a new ingredient for correlated states of electronic
matter. A key difficulty has been that real materials also contain non-Weyl
quasiparticles, and disentangling the experimental signatures has proven
challenging. We use magnetic fields up to 95 tesla to drive the Weyl semimetal
TaAs far into its quantum limit (QL), where only the purely chiral 0th Landau
levels (LLs) of the Weyl fermions are occupied. We find the electrical
resistivity to be nearly independent of magnetic field up to 50 tesla: unusual
for conventional metals but consistent with the chiral anomaly for Weyl
fermions. Above 50 tesla we observe a two-order-of-magnitude increase in
resistivity, indicating that a gap opens in the chiral LLs. Above 80 tesla we
observe strong ultrasonic attenuation below 2 kelvin, suggesting a
mesoscopically-textured state of matter. These results point the way to
inducing new correlated states of matter in the QL of Weyl semimetals
Scale-invariant magnetoresistance in a cuprate superconductor
The anomalous metallic state in high-temperature superconducting cuprates is
masked by the onset of superconductivity near a quantum critical point. Use of
high magnetic fields to suppress superconductivity has enabled a detailed study
of the ground state in these systems. Yet, the direct effect of strong magnetic
fields on the metallic behavior at low temperatures is poorly understood,
especially near critical doping, . Here we report a high-field
magnetoresistance study of thin films of \LSCO cuprates in close vicinity to
critical doping, . We find that the metallic state
exposed by suppressing superconductivity is characterized by a
magnetoresistance that is linear in magnetic field up to the highest measured
fields of T. The slope of the linear-in-field resistivity is
temperature-independent at very high fields. It mirrors the magnitude and
doping evolution of the linear-in-temperature resistivity that has been
ascribed to Planckian dissipation near a quantum critical point. This
establishes true scale-invariant conductivity as the signature of the strange
metal state in the high-temperature superconducting cuprates.Comment: 10 pages, 3 figure
Scale-invariant magnetic anisotropy in RuCl at high magnetic fields
In RuCl, inelastic neutron scattering and Raman spectroscopy reveal a
continuum of non-spin-wave excitations that persists to high temperature,
suggesting the presence of a spin liquid state on a honeycomb lattice. In the
context of the Kitaev model, magnetic fields introduce finite interactions
between the elementary excitations, and thus the effects of high magnetic
fields - comparable to the spin exchange energy scale - must be explored. Here
we report measurements of the magnetotropic coefficient - the second derivative
of the free energy with respect to magnetic field orientation - over a wide
range of magnetic fields and temperatures. We find that magnetic field and
temperature compete to determine the magnetic response in a way that is
independent of the large intrinsic exchange interaction energy. This emergent
scale-invariant magnetic anisotropy provides evidence for a high degree of
exchange frustration that favors the formation of a spin liquid state in
RuCl.Comment: arXiv admin note: substantial text overlap with arXiv:1901.09245.
Nature Physic
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