271 research outputs found
Pair-Breaking in Rotating Fermi Gases
We study the pair-breaking effect of rotation on a cold Fermi gas in the
BCS-BEC crossover region. In the framework of BCS theory, which is supposed to
be qualitatively correct at zero temperature, we find that in a trap rotating
around a symmetry axis, three regions have to be distinguished: (A) a region
near the rotational axis where the superfluid stays at rest and where no pairs
are broken, (B) a region where the pairs are progressively broken with
increasing distance from the rotational axis, resulting in an increasing
rotational current, and (C) a normal-fluid region where all pairs are broken
and which rotates like a rigid body. Due to region B, density and current do
not exhibit any discontinuities.Comment: 4 pages, 2 figures; v2: discussion clarified, typos corrected, one
reference adde
Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure
New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.Comment: RevTeX, 4 figures, submitted to Physical Review Letters July 12, 200
Separable Structure of Many-Body Ground-State Wave Function
We have investigated a general structure of the ground-state wave function
for the Schr\"odinger equation for identical interacting particles (bosons
or fermions) confined in a harmonic anisotropic trap in the limit of large .
It is shown that the ground-state wave function can be written in a separable
form. As an example of its applications, this form is used to obtain the
ground-state wave function describing collective dynamics for trapped
bosons interacting via contact forces.Comment: J. Phys. B: At. Mol. Opt. Phys. 33 (2000) (accepted for publication
Charge-Doping driven Evolution of Magnetism and non-Fermi-Liquid Behavior in the Filled Skutterudite CePt4Ge12-xSbx
The filled-skutterudite compound CePt4Ge12 is situated close to the border
between intermediate-valence of Ce and heavy-fermion behavior. Substitution of
Ge by Sb drives the system into a strongly correlated and ultimately upon
further increasing the Sb concentration into an antiferromagnetically ordered
state. Our experiments evidence a delicate interplay of emerging Kondo physics
and the formation of a local 4f moment. An extended non-Fermi-liquid region,
which can be understood in the framework of a Kondo-disorder model, is
observed. Band-structure calculations support the conclusion that the physical
properties are governed by the interplay of electron supply via Sb substitution
and the concomitant volume effects.Comment: 5 pages, 3 Figur
Magnetic and transport properties of rare-earth-based half-Heusler phases RPdBi: prospective systems for topological quantum phenomena
RPdBi (R = Er, Ho, Gd, Dy, Y, Nd) compounds were studied by means of x-ray
diffraction, magnetic susceptibility, electrical resistivity,
magnetoresistivity, thermoelectric power and Hall effect measurements,
performed in the temperature range 1.5-300 K and in magnetic fields up to 12 T.
These ternaries, except diamagnetic YPdBi, exhibit localized magnetism of
ions, and order antiferromagnetically at low temperatures ( =
2-13 K). The transport measurements revealed behavior characteristic of
semimetals or narrow-band semiconductors. Both, electrons and holes contribute
to the conductivity with dominant role of p-type carriers. The Hall effect of
ErPdBi is strongly temperature and magnetic field dependent, reflecting complex
character of the underlying electronic structures with multiple electron and
hole bands. RPdBi, and especially DyPdBi, exhibit very good thermoelectric
properties with a power factor coefficient ranging from 6 to 20
WcmK.Comment: 6 pages, 5 figures; Accepted to Physical Review B (June 17, 2011
Evidence for time-reversal symmetry breaking in superconducting PrPt4Ge12
Zero and longitudinal field muon spin rotation (muSR) experiments were
performed on the superconductors PrPt4Ge12 and LaPt4Ge12. In PrPt4Ge12 below Tc
a spontaneous magnetization with a temperature variation resembling that of the
superfluid density appears. This observation implies time-reversal symmetry
(TRS) breaking in PrPt4Ge12 below Tc = 7.9 K. This remarkably high Tc for an
anomalous superconductor and the weak and gradual change of Tc and of the
related specific heat anomaly upon La substitution in La_(1-x)Pr_xPt_4Ge_(12)
suggests that the TRS breaking is due to orbital degrees of freedom of the
Cooper pairs.Comment: To appear in Phys. Rev. B. 5 pages, 3 figure
Electronic and Thermoelectric Properties of RuIn_{3-x}A_{x} (A = Sn, Zn)
Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)]
transport measurements on the semiconducting intermetallic system RuIn3 and its
substitution derivatives RuIn_{3-x}A_{x} (A = Sn, Zn). Higher values of the
thermoelectric figure of merit (zT = 0.45) compared to the parent compound were
achieved by chemical substitution. Here, using density functional theory based
calculations, we report on the microscopic picture behind the measured
phenomenon. We show in detail that the electronic structure of the substitution
variants of the intermetallic system RuIn_{3-x}A_{x} (A = Sn, Zn) changes in a
rigid-band like fashion. This behavior makes possible the fine tuning of the
substitution concentration to take advantage of the sharp peak-like features in
the density of states of the semiconducting parent compound. Trends in the
transport properties calculated using the semi-classical Boltzmann transport
equations within the constant scattering time approximation are in good
agreement with the former experimental results for RuIn_{3-x}Sn_{x}. Based on
the calculated thermopower for the p-doped systems, we reinvestigated the
Zn-substituted derivative and obtained ZnO-free RuIn_{3-x}Zn_{x}. The new
experimental results are consistent with the calculated trend in thermopower
and yield large zT value of 0.8.Comment: PRB Accepted, 11 pages, 10 figure
High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12
The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12
and NaFe4Sb12 is studied by point-contact Andreev reflection using
superconducting Nb and Pb tips. From these measurements an intrinsic transport
spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is
inferred which establishes these materials as a new class of highly spin
polarized ferromagnets. The results are in accord with band structure
calculations within the local spin density approximation (LSDA) that predict
nearly 100% spin polarization in the density of states. We discuss the impact
of calculated Fermi velocities and spin fluctuations on Pt.Comment: Pdf file with fi
Inertial parameters and superfluid-to-normal phase transition in superdeformed bands
The quasiclassically exact solution for the second inertial parameter is found in self-consistent way. It is shown that superdeformation and
nonuniform pairing arising from the rotation induced pair density significantly
reduce this inertial parameter. The different limiting cases for ,
which allow to study an interplay between rapid rotation, pairing correlations,
and mean field deformation, are considered. The new signature for the
transition from pairing to normal phase is suggested in terms of the variation
of versus spin. Experimental data indicate the existence of
such transition in the three superdeformed mass regions.Comment: 8 pages, LaTeX, 3 figure
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