1,068 research outputs found
Evidence for the band broadening across the ferromagnetic transition in CrNbSe
The electronic structure of CrNbSe is studied via optical
spectroscopy. We observe two low-energy interband transitions in the
paramagnetic phase, which split into four peaks as the compound enters the
ferromagnetic state. The band structure calculation indicates the four peaks
are interband transitions to the spin up Cr e states. We show that the peak
splitting below the Curie temperature is \emph{not} due to the exchange
splitting of spin up and down bands, but directly reflects a band broadening
effect in Cr-derived states upon the spontaneous ferromagnetic ordering.Comment: 6 pages, 5 figures, to be published in Phys. Rev.
Data for Modeling of Positron Collisions and Transport in Gases
We review the current status of positron cross sections for collisions with atoms and molecules from the viewpoint of their use in studies of positron transport processes in gases, liquids and human tissue. The data include cross sections for positron scaThis work is supported by MNPRS Projects ON171037 and III41011 and the Australian Research Council’s Centre of Excellence Program
Wilson ratio in Yb-substituted CeCoIn5
We have investigated the effect of Yb substitution on the Pauli limited,
heavy fermion superconductor, CeCoIn. Yb acts as a non-magnetic divalent
substituent for Ce throughout the entire doping range, equivalent to hole
doping on the rare earth site. We found that the upper critical field in
(Ce,Yb)CoIn is Pauli limited, yet the reduced (H,T) phase diagram is
insensitive to disorder, as expected in the purely orbitally limited case. We
use the Pauli limiting field, the superconducting condensation energy and the
electronic specific heat coefficient to determine the Wilson ratio (),
the ratio of the specific heat coefficient to the Pauli susceptibility in
CeCoIn. The method is applicable to any Pauli limited superconductor in the
clean limit.Comment: 5 pages, 1 table, 4 figure
Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn_5
Point-contact spectroscopy was performed on single crystals of the
heavy-fermion superconductor CeCoIn_5 between 150 mK and 2.5 K. A pulsed
measurement technique ensured minimal Joule heating over a wide voltage range.
The spectra show Andreev-reflection characteristics with multiple structures
which depend on junction impedance. Spectral analysis using the generalized
Blonder-Tinkham-Klapwijk formalism for d-wave pairing revealed two coexisting
order parameter components, with amplitudes Delta_1 = 0.95 +/- 0.15 meV and
Delta_2 = 2.4 +/- 0.3 meV, which evolve differently with temperature. Our
observations indicate a highly unconventional pairing mechanism, possibly
involving multiple bands.Comment: 4 pages, 3 figure
Coexistence of magnetism and superconductivity in CeRh1-xIrxIn5
We report a thermodynamic and transport study of the phase diagram of
CeRh1-xIrxIn5. Superconductivity is observed over a broad range of doping, 0.3
< x < 1, including a substantial range of concentration (0.3 < x <0.6) over
which it coexists with magnetic order (which is observed for 0 < x < 0.6). The
anomalous transition to zero resistance that is observed in CeIrIn5 is robust
against Rh substitution. In fact, the observed bulk Tc in CeRh0.5Ir0.5In5 is
more than double that of CeIrIn5, whereas the zero-resistance transition
temperature is relatively unchanged for 0.5 < x < 1
Quasiparticles and quantum phase transition in universal low-temperature properties of heavy-fermion metals
We demonstrate, that the main universal features of the low temperature
experimental phase diagram of CeCoIn5 and other heavy-fermion metals can
be well explained using Landau paradigm of quasiparticles. The main point of
our theory is that above quasiparticles form so-called fermion-condensate
state, achieved by a fermion condensation quantum phase transition (FCQPT).
When a heavy fermion liquid undergoes FCQPT, the fluctuations accompanying
above quantum critical point are strongly suppressed and cannot destroy the
quasiparticles. The comparison of our theoretical results with experimental
data on CeCoIn5 have shown that the electronic system of above substance
provides a unique opportunity to study the relationship between quasiparticles
properties and non-Fermi liquid behavior.Comment: 7 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:cond-mat/060260
Positrons in gas filled traps and their transport in molecular gases
In this paper we give a review of two recent developments in positron transport, calculation of transport coefficients for a relatively complete set of collision cross sections for water vapour and for application of they Monte Carlo technique to model gas filled subexcitation positron traps such as Penning Malmberg Surko (Surko) trap. Calculated transport coefficients, very much like those for argon and other molecular gases show several new kinetic phenomena. The most important is the negative differential conductivity (NDC) for the bulk drift velocity when the flux drift velocity shows no sign of NDC. These results in water vapour are similar to the results in argon or hydrogen. The same technique that has been used for positron (and previously electron) transport may be applied to model development of particles in a Surko trap. We have provided calculation of the ensemble of positrons in the trap from an initial beam like distribution to the fully thermalised distribution. This model, however, does not include plasma effects (interaction between charged particles) and may be applied for lower positron densities
Unpaired Electrons in the Heavy-Fermion Superconductor CeCoIn_{5}
Thermal conductivity and specific heat were measured in the superconducting
state of the heavy fermion material Ce_{1-x}La_{x}CoIn_{5}. With increasing
impurity concentration x, the suppression of T_{c} is accompanied by the
increase in the residual electronic specific heat expected of a d-wave
superconductor, but it occurs in parallel with a decrease in residual
electronic thermal conductivity. This contrasting behavior reveals the presence
of uncondensed electrons coexisting with nodal quasiparticles. An extreme
multiband scenario is proposed, with a d-wave superconducting gap on the
heavy-electron sheets of the Fermi surface and a negligible gap on the light,
three-dimensional pockets.Comment: 4 pages, 3 figure
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