348 research outputs found
Tomographic filtering of highâresolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95052/1/ggge1509.pd
Magnetoresistance of UPt3
We have performed measurements of the temperature dependence of the
magnetoresistance up to 9 T in bulk single crystals of UPt3 with the magnetic
field along the b axis, the easy magnetization axis. We have confirmed previous
results for transverse magnetoresistance with the current along the c axis, and
report measurements of the longitudinal magnetoresistance with the current
along the b axis. The presence of a linear term in both cases indicates broken
orientational symmetry associated with magnetic order. With the current along
the c axis the linear term appears near 5 K, increasing rapidly with decreasing
temperature. For current along the b axis the linear contribution is negative.Comment: 6 pages, 3 figures, submitted to Quantum Fluids and Solids Conference
(QFS 2006
New Electronic Phase Transitions in \alpha-(BEDT-TTF)2KHg(SCN)4
\alpha-(BEDT-TTF)2KHg(SCN)4 is considered to be in the charge-density-wave
(CDW) state below 8 K. We present new magnetoresistance data suggesting that
the material undergoes a series of field-induced CDW (FICDW) transitions at
pressures slightly exceeding the critical pressure Pc at which the zero-field
CDW state is destroyed. Further, we argue that a novel kind of FICDW
transitions, entirely determined by a superposition of the strong Pauli and
quantizing orbital effects of magnetic field on the CDW wavevector, arises when
the field is strongly tilted towards the conducting layers. These new
transitions can take place even in the case of a relatively well nested Fermi
surface. Finally we report on the superconducting (SC) state and its
coexistence with the CDW in the title compound under quasi-hydrostatic
pressure. Below Pc the material is most likely a heterogeneous SC/CDW mixture,
with the SC phase persisting down to ambient pressure. The SC onset temperature
appears to drastically increase upon entering the SC/CDW coexistence region.Comment: 7 pages, 6 figures; invited talk at ISCOM'2003, 21-26.09.2003, Port
Bourgenay, France to be published in J. Phys. IV Franc
Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCuSi versus YbRhSi
In this paper the low-temperature properties of two isostructural canonical
heavy-fermion compounds are contrasted with regards to the interplay between
antiferromagnetic (AF) quantum criticality and superconductivity. For
CeCuSi, fully-gapped d-wave superconductivity forms in the vicinity of
an itinerant three-dimensional heavy-fermion spin-density-wave (SDW) quantum
critical point (QCP). Inelastic neutron scattering results highlight that both
quantum critical SDW fluctuations as well as Mott-type fluctuations of local
magnetic moments contribute to the formation of Cooper pairs in CeCuSi.
In YbRhSi, superconductivity appears to be suppressed at
mK by AF order ( = 70 mK). Ultra-low temperature measurements reveal a
hybrid order between nuclear and 4f-electronic spins, which is dominated by the
Yb-derived nuclear spins, to develop at slightly above 2 mK. The hybrid
order turns out to strongly compete with the primary 4f-electronic order and to
push the material towards its QCP. Apparently, this paves the way for
heavy-fermion superconductivity to form at = 2 mK. Like the pressure -
induced QCP in CeRhIn, the magnetic field - induced one in YbRhSi
is of the local Kondo-destroying variety which corresponds to a Mott-type
transition at zero temperature. Therefore, these materials form the link
between the large family of about fifty low- unconventional heavy - fermion
superconductors and other families of unconventional superconductors with
higher s, notably the doped Mott insulators of the cuprates, organic
charge-transfer salts and some of the Fe-based superconductors. Our study
suggests that heavy-fermion superconductivity near an AF QCP is a robust
phenomenon.Comment: 30 pages, 7 Figures, Accepted for publication in Philosophical
Magazin
Growing the Grassroots or Backing Bandits? Dilemmas of Donor Support for Haitiâs (UN)Civil Society
Ye
Modeling and MEG evidence of early consonance processing in auditory cortex
Pitch is a fundamental attribute of auditory perception. The interaction of concurrentpitches gives rise to a sensation that can be characterized by its degree of consonance ordissonance. In this work, we propose that human auditory cortex (AC) processes pitchand consonance through a common neural network mechanism operating at earlycortical levels. First, we developed a new model of neural ensembles incorporatingrealistic neuronal and synaptic parameters to assess pitch processing mechanisms atearly stages of AC. Next, we designed a magnetoencephalography (MEG) experiment tomeasure the neuromagnetic activity evoked by dyads with varying degrees ofconsonance or dissonance. MEG results show that dissonant dyads evoke a pitch onsetFebruary 15, 20191/44
response (POR) with a latency up to 36 ms longer than consonant dyads. Additionally,we used the model to predict the processing time of concurrent pitches; here, consonantpitch combinations were decoded faster than dissonant combinations, in line with theexperimental observations. Specifically, we found a striking match between thepredicted and the observed latency of the POR as elicited by the dyads. These novelresults suggest that consonance processing starts early in human auditory cortex andmay share the network mechanisms that are responsible for (single) pitch processing
Superconductivity in the charge-density-wave state of the organic metal \alpha-(BEDT-TTF)2KHg(SCN)4
The superconducting transition in the layered organic compound
\alpha-(BEDT-TTF)_2KHg(SCN)_4 has been studied in the two hydrostatic pressure
regimes where a charge-density wave is either present or completely suppressed.
Within the charge-density-wave state the experimental results reveal a network
of weakly coupled superconducting regions. This is especially seen in a strong
enhancement of the measured critical field and the corresponding positive
curvature of its temperature dependence. Further, it is shown that on lowering
the pressure into the density-wave state traces of a superconducting phase
already start to appear at a much higher temperature.Comment: 8 pages, 9 figures, Phys. Rev. B, in pres
Low Temperature Properties of Anisotropic Superconductors with Kondo Impurities
We present a self-consistent theory of superconductors in the presence of
Kondo impurities, using large- slave-boson methods to treat the impurity
dynamics. The technique is tested on the s-wave case and shown to give good
results compared to other methods for . We calculate low temperature
thermodynamic and transport properties for various superconducting states,
including isotropic s-wave and representative anisotropic model states with
line and point nodes on the Fermi surface.Comment: 21 pages, RevTeX 3.0, 12 figures available upon request, UF preprin
Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2
We have performed elastic neutron-scattering experiments on the
heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found
that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly
enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at
1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m
increases slightly at a rate ~ 1 K/GPa, roughly following the transition
temperature T_o determined from macroscopic anomalies. We have also observed a
sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of
antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced
lattice constant.Comment: RevTeX, 4 pages, 4 eps figures, accepted for publication in Phys.
Rev. Let
- âŠ