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Register a new userEffect of anisotropic Fermi surface on the flux-flow resistivity under rotating magnetic field
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We numerically investigate the effect of in-plane anisotropic Fermi surface (FS) on the flux-flow resistivity $rho_{rm f}$ under rotating magnetic field on the basis of the quasiclassical Greens function method. We demonstrate that one can detect the phase in pairing potential of Cooper pair through the field-angular dependence of $rho_{rm f}$ even if the FS has in-plane anisotropy. In addition, we point out one can detect the gap-node directions irrespective of the FS anisotropy by measuring $rho_{rm f}$ under rotating field.
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We theoretically investigate the magnetic-field-angle dependence of the flux-flow resistivity $rho_{rm f}$ in unconventional superconductors. Two contributions to $rho_{rm f}$ are considered: one is the quasiparticle (QP) relaxation time $tau(bm{k}_{rm F})$ and the other is $omega_0(bm{k}_{rm F})$, which is a counterpart to the interlevel spacing of the QP bound states in the quasiclassical approach. Here, $bm{k}_{rm F}$ denotes the position on a Fermi surface. Numerical calculations are conducted for a line-node s-wave and a d-wave pair potential with the same anisotropy of their amplitudes, but with a sign change only for a d-wave one. We show that the field-angle dependence of $rho_{rm f}$ differs prominently between s-wave and d-wave pairs, reflecting the phase of the pair potentials. We also discuss the case where $tau$ is constant and compare it with the more general case where $tau$ depends on $bm{k}_{rm F}$.
We theoretically investigate the applied magnetic field-angle dependence of the flux-flow resistivity $rho_{rm f}(alpha_{rm M})$ for an uniaxially anisotropic Fermi surface. $rho_{rm f}$ is related to the quasiparticle scattering rate $varGamma$ inside a vortex core, which reflects the sign change in the superconducting pair potential. We find that $rho_{rm f}(alpha_{rm M})$ is sensitive to the sign-change in the pair potential and has its maximum when the magnetic field is parallel to the gap-node direction. We propose the measurement of the field-angle dependent oscillation of $rho_{rm f}(alpha_{rm M})$ as a phase-sensitive field-angle resolved experiment.
The flux flow resistivity associated with purely viscous motion of vortices in high-quality MgB_2 was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different flux flow resistivity slopes was clearly observed in H//ab-plane. The unusual H-dependence indicates that two very differently sized superconducting gaps in MgB_2 manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat capacity and thermal conductivity results.
We theoretically study the dependence of the quasiparticle (QP) scattering rate $varGamma$ on the uniaxial anisotropy of a Fermi surface with changing the magnetic field angle $alpha_{rm M}$. We consider the QP scattering due to the non-magnetic impurities inside a single vortex core. The field-angle dependence of the quasiparticle scattering rate $varGamma(alpha_{rm M})$ is sensitive to the sign-change of the pair potential. We show that with increasing the two dimensionality of the system, $varGamma(alpha_{rm M})$ reflects more clearly whether there is the sign-change in the pair potential.
We report resistivity and the Hall effect measurements in the normal and superconducting states of MgB2 single crystal. The resistivity has been found to be anisotropic with slightly temperature dependent resistivity ratio of about 3.5. The Hall constant, with a magnetic field parallel to the Mg and B sheets is negative in contrast to the hole-like Hall response with a field directed along the c-axis indicating presence of both types of charge carriers and, thus, multi-band electronic structure of MgB2. The Hall effect in the mixed state shows no sign change anomaly reproducing the Hall effect behavior in clean limit type-II superconductors.
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