82 research outputs found
Definitive Evidence for Order-by-Quantum-Disorder in Er2Ti2O7
Here we establish 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. By extracting the Hamiltonian of Er2Ti2O7 from
inelastic neutron scattering measurements, we then show that the
U(1)-degenerate states of Er2Ti2O7 are its classical ground states, and
unambiguously show that quantum fluctuations break the degeneracy in a way
which is confirmed by experiment. This is the first definitive observation of
order-by-disorder in any material. We provide further verifiable consequences
of this phenomenon, and several additional comparisons between theory and
experiment.Comment: 4.5 pages, 3 figures, 7.5 pages of Supplemental Material, 8
supplemental figure
Disorder raises the critical temperature of a cuprate superconductor
With the discovery of charge density waves (CDW) in most members of the
cuprate high temperature superconductors, the interplay between
superconductivity and CDW has become a key point in the debate on the origin of
high temperature superconductivity. Some experiments in cuprates point toward a
CDW state competing with superconductivity, but others raise the possibility of
a CDW-superconductivity intertwined order, or more elusive pair-density wave
(PDW). Here we have used proton irradiation to induce disorder in crystals of
LaBaCuO and observed a striking 50% increase of
accompanied by a suppression of the CDW. This is in clear
contradiction with the behaviour expected of a d-wave superconductor for which
both magnetic and non-magnetic defects should suppress . Our
results thus make an unambiguous case for the strong detrimental effect of the
CDW on bulk superconductivity in LaBaCuO. Using tunnel
diode oscillator (TDO) measurements, we find evidence for dynamic layer
decoupling in PDW phase. Our results establish irradiation-induced disorder as
a particularly relevant tuning parameter for the many families of
superconductors with coexisting density waves, which we demonstrate on
superconductors such as the dichalcogenides and LuIrSi.Comment: 10 pages, 7 figure
The dual nature of magnetism in a uranium heavy fermion system
The duality between localized and itinerant nature of magnetism in
electron systems has been a longstanding puzzle. Here, we report
inelastic neutron scattering measurements, which reveal both local and
itinerant aspects of magnetism in a single crystalline system of
UPtSi. In the antiferromagnetic state, we observe broad continuum
of diffuse magnetic scattering with a resonance-like gap of 7 meV,
and surprising absence of coherent spin-waves, suggestive of itinerant
magnetism. While the gap closes above the Neel temperature, strong dynamic spin
correlations persist to high temperature. Nevertheless, the size and
temperature dependence of the total magnetic spectral weight can be well
described by local moment with . Furthermore, polarized neutron
measurements reveal that the magnetic fluctuations are mostly transverse, with
little or none of the longitudinal component expected for itinerant moments.
These results suggest that a dual description of local and itinerant magnetism
is required to understand UPtSi, and by extension, other 5
systems in general.Comment: see supplementary material for more detail
Time-resolved one-dimensional detection of x-ray scattering in pulsed magnetic fields
We have developed an application of a one-dimensional micro-strip detector
for capturing x-ray diffraction data in pulsed magnetic fields. This detector
consists of a large array of 50 \mu m-wide Si strips with a full-frame read out
at 20 kHz. Its use substantially improves data-collection efficiency and
quality as compared to point detectors, because diffraction signals are
recorded along an arc in reciprocal space in a time-resolved manner. By
synchronizing with pulsed fields, the entire field dependence of a
two-dimensional swath of reciprocal space may be determined using a small
number of field pulses.Comment: Submitted to Rev. Sci. Instru
Fermi surface mapping and the nature of charge density wave order in the kagome superconductor CsVSb
The recently discovered family of AVSb (A: K, Rb Cs) kagome metals
possess a unique combination of nontrivial band topology, superconducting
ground states, and signatures of electron correlations manifest via competing
charge density wave order. Little is understood regarding the nature of the
charge density wave (CDW) instability inherent to these compounds and the
potential correlation with the accompanying onset of a large anomalous Hall
response. To understand the impact of the CDW order on the electronic structure
in these systems, we present quantum oscillation measurements on single
crystals of CsVSb. Our data provides direct evidence that the CDW
invokes a substantial reconstruction of the Fermi surface pockets associated
with the vanadium orbitals and the kagome lattice framework. In conjunction
with density functional theory modeling, we are able to identify split
oscillation frequencies originating from reconstructed pockets built from
vanadium orbitals and Dirac-like bands. Complementary diffraction measurements
are further able to demonstrate that the CDW instability has a correlated
phasing between neighboring VSb planes. These results provide critical
insights into the underlying CDW instability in AVSb kagome metals and
support minimal models of CDW order arising from within the vanadium-based
kagome lattice.Comment: 12 pages, 9 figure
A single-solenoid pulsed-magnet system for single-crystal scattering studies
We present a pulsed-magnet system that enables x-ray single-crystal
diffraction in addition to powder and spectroscopic studies with the magnetic
field applied on or close to the scattering plane. The apparatus consists of a
single large-bore solenoid, cooled by liquid nitrogen. A second independent
closed-cycle cryostat is used for cooling samples near liquid helium
temperatures. Pulsed magnetic fields close to T with a
zero-to-peak-field rise time of 2.9 ms are generated by discharging a 40
kJ capacitor bank into the magnet coil. The unique characteristic of this
instrument is the preservation of maximum scattering angle ()
on the entrance and exit sides of the magnet bore by virtue of a novel
double-funnel insert. This instrument will facilitate x-ray diffraction and
spectroscopic studies that are impractical, if not impossible, to perform using
split-pair and narrow-opening solenoid magnets, and offers a practical solution
for preserving optical access in future higher-field pulsed magnets.Comment: Accepted for publication in Rev. Sci. Instru
- …