123 research outputs found
Giant Carrier Mobility in Single Crystals of FeSb2
We report the giant carrier mobility in single crystals of FeSb2. Nonlinear
field dependence of Hall resistivity is well described with the two-carrier
model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8
K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class
of materials with promising potential for applications in solid state
electronics.Comment: 5 pages, 3 figures. Applied Physics Letters (in press
Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2
We have investigated anisotropy in magnetic and electrical transport
properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground
state of the system evolves from paramagnetic to antiferromagnetic with gradual
substitution of Fe with Cr. Anisotropy in electrical transport diminishes with
increased Cr substitution and fades away by x=0.5. We find that the variable
range hopping (VRH) conduction mechanism dominates at low temperatures for
0.4<= x <=0.75.Comment: 5 pages, 6 figure
Anisotropy in magnetic and transport properties of Fe1-xCoxSb2
Anisotropic magnetic and electronic transport measurements were carried out
on large single crystals of Fe1-xCoxSb2 (0<= x <=1). The semiconducting state
of FeSb2 evolves into metallic and weakly ferromagnetic by substitution of Fe
with Co for x<0.5. Further doping induces structural transformation from
orthorhombic Pnnm structure of FeSb2 to monoclinic P21/c structure of CoSb2
where semiconducting and diamagnetic ground state is restored again. Large
magnetoresistance and anisotropy in electronic transport were observed.Comment: 7 pages, 6 figure
Comment on ``Texture in the Superconducting Order Parameter of CeCoIn Revealed by Nuclear Magnetic Resonance''
The study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been of
considerable recent interest. Below the temperature which is believed to
be the transition temperature () to the FFLO phase in CeCoIn, K.
Kakuyanagi et al. (Phys. Rev. Lett. 94, 047602 (2005)) reported a composite NMR
spectrum with a tiny component observed at frequencies corresponding to the
normal state signal. The results were interpreted as evidence for the emergence
of an FFLO state. This result is inconsistent with two other NMR studies of V.
F. Mitrovi{\'c} et al. (Phys. Rev. Lett. 97, 117002 (2006)) and B.-L. Young et
al. (Phys. Rev. Lett. 98, 036402 (2007)). In this comment we show that the
findings of K. Kakuyanagi et al. do not reflect the true nature of the FFLO
state but result from excess RF excitation power used in that experiment.Comment: 1 page, to appear in PR
Optical investigation of the metal-insulator transition in FeSb2
Abstract.: We present a comprehensive optical study of the narrow gap FeSb2 semiconductor. From the optical reflectivity, measured from the far infrared up to the ultraviolet spectral range, we extract the complete absorption spectrum, represented by the real part σ1(ω) of the complex optical conductivity. With decreasing temperature below 80K, we find a progressive depletion of σ1(ω) below Eg∼300 cm-1, the semiconducting optical gap. The suppressed (Drude) spectral weight within the gap is transferred at energies ω>Eg and also partially piles up over a continuum of excitations extending in the spectral range between zero and Eg. Moreover, the interaction of one phonon mode with this continuum leads to an asymmetric phonon shape. Even though several analogies between FeSb2 and FeSi were claimed and a Kondo-insulator scenario was also invoked for both systems, our data on FeSb2 differ in several aspects from those of FeSi. The relevance of our findings with respect to the Kondo insulator description will be addresse
Properties of the superconducting state in a two-band model
Eliashberg theory is used to investigate the range of thermodynamic
properties possible within a two-band model for s-wave superconductivity and to
identify signatures of its two-band nature. We emphasize dimensionless BCS
ratios (those for the energy gaps, the specific heat jump and the negative of
its slope near Tc, the thermodynamic critical field Hc(0), and the normalized
slopes of the critical field and the penetration depth near Tc), which are no
longer universal even in weak coupling. We also give results for
temperature-dependent quantities, such as the penetration depth and the energy
gap. Results are presented both for microscopic parameters appropriate to MgB2
and for variations away from these. Strong coupling corrections are identified
and found to be significant. Analytic formulas are provided which show the role
played by the anisotropy in coupling in some special limits. Particular
emphasis is placed on small interband coupling and on the opposite limit of no
diagonal coupling. The effect of impurity scattering is considered,
particularly for the interband case.Comment: 20 pages, 14 figures, final version accepted in PR
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