117 research outputs found
Superfluid Phase Stability of He in Axially Anisotropic Aerogel
Measurements of superfluid He in 98% aerogel demonstrate the existence of
a metastable \emph{A}-like phase and a stable \emph{B}-like phase. It has been
suggested that the relative stability of these two phases is controlled by
anisotropic quasiparticle scattering in the aerogel. Anisotropic scattering
produced by axial compression of the aerogel has been predicted to stabilize
the axial state of superfluid He. To explore this possiblity, we used
transverse acoustic impedance to map out the phase diagram of superfluid He
in a % porous silica aerogel subjected to 17% axial compression. We
have previously shown that axial anisotropy in aerogel leads to optical
birefringence and that optical cross-polarization studies can be used to
characterize such anisotropy. Consequently, we have performed optical
cross-polarization experiments to verify the presence and uniformity of the
axial anisotropy in our aerogel sample. We find that uniform axial anisotropy
introduced by 17% compression does not stabilize the \emph{A}-like phase. We
also find an increase in the supercooling of the \emph{A}-like phase at lower
pressure, indicating a modification to \emph{B}-like phase nucleation in
\emph{globally} anisotropic aerogels.Comment: 4 pages, 4 figures, submitted to LT25 (25th International Conference
on Low Temperature Physics
Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5
Electronic nematics are exotic states of matter where electronic interactions
break a rotational symmetry of the underlying lattice, in analogy to the
directional alignment without translational order in nematic liquid crystals.
Intriguingly such phases appear in the copper- and iron-based superconductors,
and their role in establishing high-temperature superconductivity remains an
open question. Nematicity may take an active part, cooperating or competing
with superconductivity, or may appear accidentally in such systems. Here we
present experimental evidence for a phase of nematic character in the heavy
fermion superconductor CeRhIn5. We observe a field-induced breaking of the
electronic tetragonal symmetry of in the vicinity of an antiferromagnetic (AFM)
quantum phase transition at Hc~50T. This phase appears in out-of-plane fields
of H*~28T and is characterized by substantial in-plane resistivity anisotropy.
The anisotropy can be aligned by a small in-plane field component, with no
apparent connection to the underlying crystal structure. Furthermore no
anomalies are observed in the magnetic torque, suggesting the absence of
metamagnetic transitions in this field range. These observations are indicative
of an electronic nematic character of the high field state in CeRhIn5. The
appearance of nematic behavior in a phenotypical heavy fermion superconductor
highlights the interrelation of nematicity and unconventional
superconductivity, suggesting nematicity to be a commonality in such materials
Second order Zeeman interaction and ferroquadrupolar order in TmVO
TmVO exhibits ferroquadrupolar order of the Tm 4f electronic orbitals
at low temperatures, and is a model system for Ising nematicity that can be
tuned continuously to a quantum phase transition via magnetic fields along the
-axis. Here we present V nuclear magnetic resonance data in magnetic
fields perpendicular to the -axis in a single crystal that has been
carefully cut by a plasma focused ion beam to an ellipsoidal shape to minimize
the inhomogeneity of the internal demagnetization field. The resulting dramatic
increase in spectral resolution enabled us to resolve the anisotropy of the
electric field gradient and to measure the magnetic and quadrupolar relaxation
channels separately. Perpendicular magnetic fields nominally do not couple to
the low energy degrees of freedom, but we find a significant nonlinear
contribution for sufficiently large fields that give rise to a rich phase
diagram. The in-plane magnetic field can act either as an effective transverse
or longitudinal field to the Ising nematic order, depending on the orientation
relative to the principle axes of the quadrupole order, and leads to a marked
in-plane anisotropy in both relaxation channels. We find that the small
in-plane transverse fields initially enhance the ferroquadrupolar ordering
temperature but eventually suppress the long-range order. We tentatively
ascribe this behavior to the competing effects of field-induced mixing of
higher energy crystal field states and the destabilizing effects of
field-induced quantum fluctuations.Comment: 15 pages, 13 figure
Stability of the A-like Phase of Superfluid 3He in Aerogel with Globally Anisotropic Scattering
It has been suggested that anisotropic quasiparticle scattering will
stabilize anisotropic phases of superfluid He contained within highly
porous silica aerogel. For example, global anisotropy introduced via uniaxial
compression of aerogel might stabilize the axial state, which is called the
A-phase in bulk superfluid 3He. Here we present measurements of the phase
diagram of superfluid 3He in a 98% porous silica aerogel using transverse
acoustic impedance methods. We show that uniaxial compression of the aerogel by
17% does not stabilize an axial phase.Comment: 3 pages, 4 figures, Submitted to PR Rapid Communication
NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors
We present As nuclear magnetic resonance spin-lattice and spin-spin
relaxation rate data in Ba(FeCo)As and
Ba(FeCu)As as a function of temperature, doping and
magnetic field. The relaxation curves exhibit a broad distribution of
relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K.
The doping and temperature response of the width of the dynamical heterogeneity
is similar to that of the nematic susceptibility measured by elastoresistance
measurements. We argue that quenched random fields which couple to the nematic
order give rise to a nematic glass that is reflected in the spin dynamics.Comment: Accepted to Physical Review
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