266 research outputs found
Evidence for ferromagnetic spin-pairing superconductivity in UGe: A Ge-NQR study under pressure
We report that a novel type of superconducting order parameter has been
realized in the ferromagnetic states in UGe via Ge
nuclear-quadrupole-resonance (NQR) experiments performed under pressure ().
Measurements of the nuclear spin-lattice relaxation rate have
revealed an unconventional nature of superconductivity such that the up-spin
band is gapped with line nodes, but the down-spin band remains gapless at the
Fermi level. This result is consistent with that of a ferromagnetic
spin-pairing model in which Cooper pairs are formed among ferromagnetically
polarized electrons. The present experiment has shed new light on a possible
origin of ferromagnetic superconductivity, which is mediated by ferromagnetic
spin-density fluctuations relevant to the first-order transition inside the
ferromagnetic states.Comment: 5 pages, 5 figure
Metallic mean-field stripes, incommensurability and chemical potential in cuprates
We perform a systematic slave-boson mean-field analysis of the three-band
model for cuprates with first-principle parameters. Contrary to widespread
believe based on earlier mean-field computations low doping stripes have a
linear density close to 1/2 added hole per lattice constant. We find a
dimensional crossover from 1D to 2D at doping followed by a breaking
of particle-hole symmetry around doping 1/8 as doping increases. Our results
explain in a simple way the behavior of the chemical potential, the magnetic
incommensurability, and transport experiments as a function of doping. Bond
centered and site-centered stripes become degenerate for small overdoping.Comment: submitted to PR
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
de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2
We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al
doped crystals of MgB. We have measured crystals with % Al which
have a of 33.6 K, (% lower than pure MgB). dHvA frequencies
for the tube orbits in the doped samples are lower than in pure
MgB, implying a reduction in the number of holes in this sheet of
Fermi surface. The mass of the quasiparticles on the larger orbit is
lighter than the pure case indicating a reduction in electron-phonon coupling
constant . These observations are compared with band structure
calculations, and found to be in excellent agreement.Comment: 4 pages with figure
Catastrophic Fermi surface reconstruction in the shape-memory alloy AuZn
AuZn undergoes a shape-memory transition at 67 K. The de Haas van Alphen
effect persists to 100 K enabling the observation of a change in the quantum
oscillation spectrum indicative of a catastrophic Fermi surface reconstruction
at the transition. Coexistence of both Fermi surfaces at low temperatures is
suggestive of an intrinsic phase separation in the bulk of the material. In
addition, a Dingle analysis reveals a sharp change in the scattering mechanism
at a threshold cyclotron radius, which we suggest to be related to the
underlying microstructure that drives the shape-memory effect.Comment: 4 pages, 4 figure
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
Inelastic contribution of the resistivity in the hidden order in URu2Si2
In the hidden order of URu2Si2 the resistivity at very low temperature shows
no T^2 behavior above the transition to superconductivity. However, when
entering the antiferromagnetic phase, the Fermi liquid behavior is recovered.
We discuss the change of the inelastic term when entering the AF phase with
pressure considering the temperature dependence of the Grueneisen parameter at
ambient pressure and the influence of superconductivity by an extrapolation of
high field data.Comment: 5 pages, 2 figures, SCES conference proceedin
Behaviour of superconductivity energetic characteristics in electron-doped cuprates. A simple model
A simple model to describe the energetic phase diagram of electron-doped
cuprate superconductor is developed. Interband pairing operates between the UHB
and the defect states created by doping and supplied by both extincting HB-s.
Two defect subbands correspond to the () and () momentum
regions. Extended doping quenches the bare normal state gaps (pseudogaps).
Maximal transition temperature corresponds to overlapping bands ensemble
intersected by the chemical potential. Illustrative results for , pseudo-
and superconducting gaps are calculated on the whole doping scale. Major
characteristics features on the phase diagram are reproduced. Anticipated
manifestation of gaps doping dynamics is discussed.Comment: 10 pages, 3 figure
Transport properties of the heavy fermion superconductor PrOsSb
We have measured the electrical resistivity, thermoelectric power, Hall
coefficient, and magnetoresistance (MR) on single crystals of
PrOsSb, LaOsSb and NdOsSb. All the
transport properties in PrOsSb are similar to those in
LaOsSb and NdOsSb at high temperatures, indicating
the localized character of 4-electrons. The transverse MR both in
LaOsSb and PrOsSb tends to saturate for wide field
directions, indicating these compounds to be uncompensated metals with no open
orbit. We have determined the phase diagram of the field induced ordered phase
by the MR measurement for all the principle field directions, which indicates
an unambiguous evidence for the singlet crystalline electric
field ground state.Comment: 7 pages, 10 figures, to appear in Physical Review
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