562 research outputs found
Enhanced thermoelectric properties by Ir doping of PtSb2 with pyrite structure
The effects of Ir doping on the thermoelectric properties of Pt1-xIrxSb2 (x =
0, 0.01, 0.03, and 0.1) with pyrite structure were studied. Measurements of
electrical resistivity rho, Seebeck coefficient S, and thermal conductivity
kappa were conducted. The results showed an abrupt change from semiconducting
behavior without Ir (x = 0) to metallic behavior at x = 0.01. The sample with x
= 0.01 exhibited large S and low rho, resulting in a maximum power factor
(S^2/rho) of 43 muW/cmK^2 at 400 K. The peculiar "pudding mold"-type electronic
band dispersion could explain the enhanced thermoelectric properties in the
metallic state.Comment: 3 pages, 2 figure
Fulde-Ferrell-Larkin-Ovchinnikov state in a perpendicular field of quasi two-dimensional CeCoIn5
A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the
quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to
the ab-plane. Here, we conduct 115^In NMR studies of this material in a
PERPENDICULAR field, and provide strong evidence for FFLO in this case as well.
Although the topology of the phase transition lines in the H-T phase diagram is
identical for both configurations, there are several remarkable differences
between them. Compared to H//ab, the FFLO region for H perpendicular to the
ab-plane shows a sizable decrease, and the critical field separating the FFLO
and non-FFLO superconducting states almost ceases to have a temperature
dependence. Moreover, directing H perpendicular to the ab-plane results in a
notable change in the quasiparticle excitation spectrum within the planar node
associated with the FFLO transition.Comment: 5 pages, 3 figure
ARPES and NMTO Wannier Orbital Theory of LiMoO - Implications for Unusually Robust Quasi-One Dimensional Behavior
We present the results of a combined study by band theory and angle resolved
photoemission spectroscopy (ARPES) of the purple bronze,
LiMoO. Structural and electronic origins of its unusually
robust quasi-one dimensional (quasi-1D) behavior are investigated in detail.
The band structure, in a large energy window around the Fermi energy, is
basically 2D and formed by three Mo -like extended Wannier orbitals,
each one giving rise to a 1D band running at a 120 angle to the two
others. A structural "dimerization" from to gaps
the and bands while leaving the bands metallic in the gap, but
resonantly coupled to the gap edges and, hence, to the other directions. The
resulting complex shape of the quasi-1D Fermi surface (FS), verified by our
ARPES, thus depends strongly on the Fermi energy position in the gap, implying
a great sensitivity to Li stoichiometry of properties dependent on the FS, such
as FS nesting or superconductivity. The strong resonances prevent either a
two-band tight-binding model or a related real-space ladder picture from giving
a valid description of the low-energy electronic structure. We use our extended
knowledge of the electronic structure to newly advocate for framing
LiMoO as a weak-coupling material and in that framework can
rationalize both the robustness of its quasi-1D behavior and the rather large
value of its Luttinger liquid (LL) exponent . Down to a temperature of
6K we find no evidence for a theoretically expected downward
renormalization of perpendicular single particle hopping due to LL fluctuations
in the quasi-1D chains.Comment: 53 pages, 17 Figures, 6 year
Quasiparticle spectrum of the hybrid s+g-wave superconductors YNi_2B_2C and LuNi_2B_2C
Recent experiments on single crystals of YNiBC have revealed the
presence of point nodes in the superconducting energy gap Delta(k} at k =
(1,0,0), (0,1,0), (-1,0,0), and (0,-1,0). In this paper we investigate the
effects of impurity scattering on the quasiparticle spectrum in the vortex
state of s+g-wave superconductors, which is found to be strongly modified in
the presence of disorder. In particular, a gap in the quasiparticle energy
spectrum is found to open even for infinitesimal impurity scattering, giving
rise to exponentially activated thermodynamic response functions, such as the
specific heat, the spin susceptibility, the superfluid density, and the nuclear
spin lattice relaxation. Predictions derived from this study can be verified by
measurements of the angular dependent magnetospecific heat and the
magnetothermal conductivity.Comment: 8 pages, RevTex, 4 figure
Dispersive Gap Mode of Phonons in Anisotropic Superconductors
We estimate the effect of the superconducting gap anisotropy in the
dispersive gap mode of phonons, which is observed by the neutron scattering on
borocarbide superconductors. We numerically analyze the phonon spectrum
considering the electron-phonon coupling, and examine contributions coming from
the gap suppression and the sign change of the pairing function on the Fermi
surface. When the sign of the pairing function is changed by the nesting
translation, the gap mode does not appear. We also discuss the suppression of
the phonon softening of the Kohn anomaly due to the onset of superconductivity.
We demonstrate that observation of the gap dispersive mode is useful for
sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp
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