1,161 research outputs found
Strain dependence of bonding and hybridization across the metal-insulator transition of VO2
Soft x-ray spectroscopy is used to investigate the strain dependence of the
metal-insulator transition of VO2. Changes in the strength of the V 3d - O 2p
hybridization are observed across the transition, and are linked to the
structural distortion. Furthermore, although the V-V dimerization is
well-described by dynamical mean-field theory, the V-O hybridization is found
to have an unexpectedly strong dependence on strain that is not predicted by
band theory, emphasizing the relevance of the O ion to the physics of VO2
Recommended from our members
Analysis of potential impacts of Flaming Gorge Dam hydropower operations on archaeological sites
An archaeological field study was conducted along the Green River in the areas of Little Hole and Browns Park in Utah and Colorado. The purpose of the study was to measure the potential for hydropower operations at Flaming Gorge Dam to directly or indirectly affect archaeological sites in the study area. Thirty-four known sites were relocated, and six new sites were recorded. Information was collected at each site regarding location, description, geomorphic setting, sedimentary context, vegetation, slope, distance from river, elevation above river level, and site condition. Matching the hydrologic projections of river level and sediment load with the geomorphic and sedimentary context at specific site locations indicated that eight sites were in areas with a high potential for erosion
Unifying the Phase Diagrams of the Magnetic and Transport Properties of La_(2-x)Sr_xCuO_4, 0 < x < 0.05
An extensive experimental and theoretical effort has led to a largely
complete mapping of the magnetic phase diagram of La_(2-x)Sr_xCuO_4, and a
microscopic model of the spin textures produced in the x < 0.05 regime has been
shown to be in agreement with this phase diagram. Here we use this same model
to derive a theory of the impurity-dominated, low temperature transport. Then,
we present an analysis of previously published data for two samples: x = 0.002
data from Chen et. al., and x = 0.04 data from Keimer et. al. We show that the
transport mechanisms in the two systems are the same, even though they are on
opposite sides of the observed insulator-to-metal transition. Our model of
impurity effects on the impurity band conduction, variable-range hopping
conduction, and coulomb gap conduction, is similar to that used to describe
doped semiconductors. However, for La_(2-x)Sr_xCuO_4 we find that in addition
to impurity-generated disorder effects, strong correlations are important and
must be treated on a equal level with disorder. On the basis of this work we
propose a phase diagram that is consistent with available magnetic and
transport experiments, and which connects the undoped parent compound with the
lowest x value for which La_(2-x)Sr_xCuO_4 is found to be superconducting, x
about 0.06.Comment: 7 pages revtex with one .ps figur
Demagnetization of Quantum Dot Nuclear Spins: Breakdown of the Nuclear Spin Temperature Approach
The physics of interacting nuclear spins arranged in a crystalline lattice is
typically described using a thermodynamic framework: a variety of experimental
studies in bulk solid-state systems have proven the concept of a spin
temperature to be not only correct but also vital for the understanding of
experimental observations. Using demagnetization experiments we demonstrate
that the mesoscopic nuclear spin ensemble of a quantum dot (QD) can in general
not be described by a spin temperature. We associate the observed deviations
from a thermal spin state with the presence of strong quadrupolar interactions
within the QD that cause significant anharmonicity in the spectrum of the
nuclear spins. Strain-induced, inhomogeneous quadrupolar shifts also lead to a
complete suppression of angular momentum exchange between the nuclear spin
ensemble and its environment, resulting in nuclear spin relaxation times
exceeding an hour. Remarkably, the position dependent axes of quadrupolar
interactions render magnetic field sweeps inherently non-adiabatic, thereby
causing an irreversible loss of nuclear spin polarization.Comment: 15 pages, 3 figure
Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor
We introduce Cryoscope, a method for sampling on-chip baseband pulses used to
dynamically control qubit frequency in a quantum processor. We specifically use
Cryoscope to measure the step response of the dedicated flux control lines of
two-junction transmon qubits in circuit QED processors with the temporal
resolution of the room-temperature arbitrary waveform generator producing the
control pulses. As a first application, we iteratively improve this step
response using optimized real-time digital filters to counter the
linear-dynamical distortion in the control line, as needed for high-fidelity,
repeatable one- and two-qubit gates based on dynamical control of qubit
frequency
Entropy of vortex cores on the border of the superconductor-to-insulator transition in an underdoped cuprate
We present a study of Nernst effect in underdoped in
magnetic fields as high as 28T. At high fields, a sizeable Nernst signal was
found to persist in presence of a field-induced non-metallic resistivity. By
simultaneously measuring resistivity and the Nernst coefficient, we extract the
entropy of vortex cores in the vicinity of this field-induced
superconductor-insulator transition. Moreover, the temperature dependence of
the thermo-electric Hall angle provides strong constraints on the possible
origins of the finite Nernst signal above , as recently discovered by Xu
et al.Comment: 5 Pages inculding 4 figure
Behavior of the Quantum Critical Point and the Fermi-liquid Domain in the Heavy Fermion Superconductor CeCoIn5 studied by resistivity
We report detailed very low temperature resistivity measurements on the heavy
fermion compounds Ce_{1-x}La_{x}CoIn5 (x=0 and x=0.01), with current applied in
two crystallographic directions [100] (basal plane) and [001] (perpendicular to
the basal plane) under magnetic field applied in the [001] or [011] direction.
We found a Fermi liquid (\rho \propto T^{2}) ground state, in all cases, for
fields above the superconducting upper critical field. We discuss the possible
location of a field induced quantum critical point with respect to Hc2(0), and
compare our measurements with the previous reports in order to give a clear
picture of the experimental status on this long debated issue.Comment: 17 pages, 7 figures accepted for publication in JPS
- …