1,505 research outputs found
High-magnetic field lattice length changes in URu2Si2
We report high magnetic field (up to 45 T) c-axis thermal expansion and
magnetostriction experiments on URu2Si2 single crystals. The sample length
change associated with the transition to the hidden order phase becomes
increasingly discontinous as the magnetic field is raised above 25 T. The
re-entrant ordered phase III is clearly observed in both the thermal expansion
and magnetostriction above 36 T, in good agreement with previous results. The
sample length is also discontinuous at the boundaries of this phase, mainly at
the upper boundary. A change in the sign of the coefficient of
thermal-expansion is observed at the metamagnetic transition (B_M = 38 T) which
is likely related to the existence of a quantum critical end point.Comment: 5 pages, 4 figures, to be published in PR
Magnetic field induced lattice anomaly inside the superconducting state of CeCoIn: evidence of the proposed Fulde-Ferrell-Larkin-Ovchinnikov state
We report high magnetic field linear magnetostriction experiments on
CeCoIn single crystals. Two features are remarkable: (i) a sharp
discontinuity in all the crystallographic axes associated with the upper
superconducting critical field that becomes less pronounced as the
temperature increases; (ii) a distinctive second order-like feature observed
only along the c-axis in the high field (10 T ) low
temperature ( 0.35 K) region. This second order transition is
observed only when the magnetic field lies within 20 of the ab-planes and
there is no signature of it above , which raises questions regarding
its interpretation as a field induced magnetically ordered phase. Good
agreement with previous results suggests that this anomaly is related to the
transition to the Fulde-Ferrel-Larkin-Ovchinnikov superconducting state.Comment: 3 figures, 5 page
Heavy holes: precursor to superconductivity in antiferromagnetic CeIn3
Numerous phenomenological parallels have been drawn between f- and d-
electron systems in an attempt to understand their display of unconventional
superconductivity. The microscopics of how electrons evolve from participation
in large moment antiferromagnetism to superconductivity in these systems,
however, remains a mystery. Knowing the origin of Cooper paired electrons in
momentum space is a crucial prerequisite for understanding the pairing
mechanism. Of especial interest are pressure-induced superconductors CeIn3 and
CeRhIn5 in which disparate magnetic and superconducting orders apparently
coexist - arising from within the same f-electron degrees of freedom. Here we
present ambient pressure quantum oscillation measurements on CeIn3 that
crucially identify the electronic structure - potentially similar to high
temperature superconductors. Heavy pockets of f-character are revealed in
CeIn3, undergoing an unexpected effective mass divergence well before the
antiferromagnetic critical field. We thus uncover the softening of a branch of
quasiparticle excitations located away from the traditional spin-fluctuation
dominated antiferromagnetic quantum critical point. The observed Fermi surface
of dispersive f-electrons in CeIn3 could potentially explain the emergence of
Cooper pairs from within a strong moment antiferromagnet.Comment: To appear in Proceedings of the National Academy of Science
A ferrofluid based neural network: design of an analogue associative memory
We analyse an associative memory based on a ferrofluid, consisting of a
system of magnetic nano-particles suspended in a carrier fluid of variable
viscosity subject to patterns of magnetic fields from an array of input and
output magnetic pads. The association relies on forming patterns in the
ferrofluid during a trainingdphase, in which the magnetic dipoles are free to
move and rotate to minimize the total energy of the system. Once equilibrated
in energy for a given input-output magnetic field pattern-pair the particles
are fully or partially immobilized by cooling the carrier liquid. Thus produced
particle distributions control the memory states, which are read out
magnetically using spin-valve sensors incorporated in the output pads. The
actual memory consists of spin distributions that is dynamic in nature,
realized only in response to the input patterns that the system has been
trained for. Two training algorithms for storing multiple patterns are
investigated. Using Monte Carlo simulations of the physical system we
demonstrate that the device is capable of storing and recalling two sets of
images, each with an accuracy approaching 100%.Comment: submitted to Neural Network
Time-resolved dynamics of electron wave packets in chaotic and regular quantum billiards with leads
We perform numerical studies of the wave packet propagation through open
quantum billiards whose classical counterparts exhibit regular and chaotic
dynamics. We show that for t less or similar to tau (tau being the Heisenberg
time), the features in the transmitted and reflected currents are directly
related to specific classical trajectories connecting the billiard leads. In
contrast, the long-time asymptotics of the wave packet dynamics is
qualitatively different for classical and quantum billiards. In particularly,
the decay of the quantum system obeys a power law that depends on the number of
decay channels, and is not sensitive to the nature of classical dynamics
(chaotic or regular).Comment: 5 pages, 4 figure
A versatile and compact capacitive dilatometer
We describe the design, construction, calibration, and operation of a
relatively simple differential capacitive dilatometer suitable for measurements
of thermal expansion and magnetostriction from 300 K to below 1 K with a
low-temperature resolution of about 0.05 angstroms. The design is characterized
by an open architecture permitting measurements on small samples with a variety
of shapes. Dilatometers of this design have operated successfully with a
commercial physical property measurement system, with several types of
cryogenic refrigeration systems, in vacuum, in helium exchange gas, and while
immersed in liquid helium (magnetostriction only) to temperatures of 30 mK and
in magnetic fields to 45 T.Comment: 8 pages, incorporating 6 figures, submitted to Rev. Sci. Instru
A de Haas-van Alphen study of the filled skutterudite compounds PrOsAs and LaOsAs
Comprehensive magnetic-field-orientation dependent studies of the
susceptibility and de Haas-van Alphen effect have been carried out on single
crystals of the filled skutterudites PrOsAs and LaOsAs
using magnetic fields of up to 40~T. Several peaks are observed in the
low-field susceptibility of PrOsAs, corresponding to cascades of
metamagnetic transitions separating the low-field antiferromagnetic and
high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments
show that the Fermi-surface topologies of PrOsAs in its PMM phase
and LaOsAs are very similar. In addition, they are in reasonable
agreement with the predictions of bandstructure calculations for
LaOsAs on the PrOsAs lattice. Both observations suggest
that the Pr 4 electrons contribute little to the number of itinerant
quasiparticles in the PMM phase. However, whilst the properties of
LaOsAs suggest a conventional nonmagnetic Fermi liquid, the effects
of direct exchange and electron correlations are detected in the PMM phase of
PrOsAs. For example, the quasiparticle effective masses in
PrOsAs are found to decrease with increasing field, probably
reflecting the gradual suppression of magnetic fluctuations associated with
proximity to the low-temperature, low-field antiferromagnetic state
Field-Orientation Dependent Heat Capacity Measurements at Low Temperatures with a Vector Magnet System
We describe a heat capacity measurement system for the study of the
field-orientation dependence for temperatures down to 50 mK. A "Vector Magnet"
combined with a mechanical rotator for the dewar enables the rotation of the
magnetic field without mechanical heating in the cryostat by friction. High
reproducibility of the field direction, as well as an angular resolution of
better than 0.01 degree, is obtained. This system is applicable to other kinds
of measurements which require a large sample space or an adiabatic sample
environment, and can also be used with multiple refrigerator inserts
interchangeably.Comment: 7 pages, 8 figure
Fermi Surface Measurements on the Low Carrier Density Ferromagnet Ca1-xLaxB6 and SrB6
Recently it has been discovered that weak ferromagnetism of a dilute 3D
electron gas develops on the energy scale of the Fermi temperature in some of
the hexaborides; that is, the Curie temperature approximately equals the Fermi
temperature. We report the results of de Haas-van Alphen experiments on two
concentrations of La-doped CaB6 as well as Ca-deficient Ca1-dB6 and
Sr-deficient Sr1-dB6. The results show that a Fermi surface exists in each case
and that there are significant electron-electron interactions in the low
density electron gas.Comment: 4 pages, 5 figures, submitted to PR
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