37 research outputs found
Dipolar spin ice regime proximate to an all-in-all-out N\'{e}el ground state in the dipolar-octupolar pyrochlore CeSnO
The dipolar-octupolar (DO) pyrochlores, RMO (R = Ce, Sm, Nd), are
key players in the search for realizable novel quantum spin liquid (QSL) states
as a large parameter space within the DO pyrochlore phase diagram is theorized
to host QSL states of both dipolar and octupolar nature. We present neutron
diffraction measurements on newly synthesized hydrothermally-grown
CeSnO powders that show a broad signal at low scattering vectors,
reminiscent of a dipolar spin ice. This is strikingly different from previous
neutron diffraction on powder samples grown from solid-state synthesis, which
found diffuse scattering at high scattering vectors associated with magnetic
octupoles. This raises the question about subtle crystalline structural
differences and in particular the potential role of disorder that is present in
the different samples. We quantify any differences through complementary
neutron structure refinement and atomic PDF measurements but detect no
oxidation or other crystallographic disorder in the hydrothermally-grown
samples. To interpret the new diffuse scattering, we characterize the exchange
interaction parameters in the near-neighbor XYZ model Hamiltonian associated
with DO pyrochlores by fitting quantum numerical linked cluster expansions
(NLCE) to heat capacity and magnetic susceptibility measurements, and classical
Monte Carlo calculations to the diffuse neutron diffraction of the newly
synthesized CeSnO samples. This places CeSnO's ground
state within the ordered dipolar all-in-all-out (AIAO) N\'{e}el phase with
quantum Monte-Carlo calculations showing a transition to long-range order at
temperatures below those accessed experimentally. We conclude that new
hydrothermally-grown CeSnO samples host a finite-temperature
proximate dipolar spin ice phase, above the expected transition to AIAO
N\'{e}el order.Comment: 11 pages, 11 figure
Quantum Spin Ice Response to a Magnetic Field in the Dipole-Octupole Pyrochlore CeZrO
We report new heat capacity measurements on single crystal CeZrO
down to 0.1 K in a magnetic field along the direction.
These new measurements show that the broad hump in the zero-field heat capacity
moves higher in temperature with increasing field strength and is split into
two humps by the field at 2 T. These separate features
are due to the decomposition of the pyrochlore lattice into effectively
decoupled chains for fields in this direction: one set of chains
(-chains) is polarized by the field while the other (-chains)
remains free. Our theoretical modelling suggests that the -chains are
close to a critical state, with nearly-gapless excitations. We also report new
elastic and inelastic neutron scattering measurements on single crystal
CeZrO in and magnetic fields at
temperatures down to 0.03 K. The elastic scattering behaves consistently with
the formation of independent chains for a field, while the
field produces a single field-induced magnetic Bragg peak at and equivalent wavevectors, indicating a polarized spin ice for fields
above 3 T. For both and fields, our
inelastic neutron scattering results show an approximately-dispersionless
continuum of scattering that increases in both energy and intensity with
increasing field strength. By modelling the complete set of experimental data
using numerical linked cluster and semiclassical molecular dynamics
calculations, we demonstrate the dominantly multipolar nature of the exchange
interactions in CeZrO and the smallness of the parameter
which controls the mixing between dipolar and octupolar degrees of freedom.
These results support previous estimates of the microscopic exchange
parameters.Comment: 20 pages, 10 figure
Reply to "Comment on: 'Case for a U(1) Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore ' "
In his comment [arXiv:2209.03235], S. W. Lovesey argues that our analysis of
neutron scattering experiments performed on CeZrO is invalid.
Lovesey argues that we have not properly accounted for the higher-order
multipolar contributions to the magnetic scattering and that our use of
pseudospin- operators to describe the scattering is inappropriate. In this
reply, we show that the multipolar corrections discussed by Lovesey only become
significant at scattering wavevectors exceeding those accessed in our
experiments. This in no way contradicts or undermines our work, which never
claimed a direct observation of scattering from higher-order multipoles. We
further show that Lovesey's objections to our use of pseudospins are unfounded,
and that the pseudospin operators are able to describe all magnetic scattering
processes at the energy scale of our experiments, far below the crystal field
gap. Finally, we comment on certain assumptions in Lovesey's calculations of
the scattering amplitude which are inconsistent with experiment.Comment: 6 pages, 1 figur
Measurement of the Spectral Shape of the beta-decay of 137Xe to the Ground State of 137Cs in EXO-200 and Comparison with Theory
We report on a comparison between the theoretically predicted and
experimentally measured spectra of the first-forbidden non-unique -decay
transition ^{137}\textrm{Xe}(7/2^-)\to\,^{137}\textrm{Cs}(7/2^+). The
experimental data were acquired by the EXO-200 experiment during a deployment
of an AmBe neutron source. The ultra-low background environment of EXO-200,
together with dedicated source deployment and analysis procedures, allowed for
collection of a pure sample of the decays, with an estimated
signal-to-background ratio of more than 99-to-1 in the energy range from 1075
to 4175 keV. In addition to providing a rare and accurate measurement of the
first-forbidden non-unique -decay shape, this work constitutes a novel
test of the calculated electron spectral shapes in the context of the reactor
antineutrino anomaly and spectral bump.Comment: Version as accepted by PR