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Register a new userEffect of Born and unitary impurity scattering on the Kramer-Pesch shrinkage of a vortex core in an s-wave superconductor
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We theoretically investigate a non-magnetic impurity effect on the temperature dependence of the vortex core shrinkage (Kramer-Pesch effect) in a single-band s-wave superconductor. The Born limit and the unitary limit scattering are compared within the framework of the quasiclassical theory of superconductivity. We find that the impurity effect inside a vortex core in the unitary limit is weaker than in the Born one when a system is in the moderately clean regime, which results in a stronger core shrinkage in the unitary limit than in the Born one.
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The low-temperature shrinking of the vortex core (Kramer-Pesch effect) is studied for an isolated single vortex for chiral p-wave and s-wave superconducting phases. The effect of nonmagnetic impurities on the vortex core radius is numerically investigated in the Born limit by means of a quasiclassical approach. It is shown that in the chiral p-wave phase the Kramer-Pesch effect displays a certain robustness against impurities owing to a specific quantum effect, while the s-wave phase reacts more sensitively to impurity scattering. This suggests chiral p-wave superconductors as promising candidates for the experimental observation of the Kramer-Pesch effect.
The size of the vortex core in a clean superconductor is strongly temperature dependent and shrinks with decreasing temperature, decreasing to zero for T -> 0. We study this so-called Kramer-Pesch effect both for a single gap superconductor and for the case of a two gap superconductor using parameters appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both bands of a two gap superconductor even if only one of the two bands is in the clean limit and the other band in the dirty limit, a case appropriate for MgB2. In this case an induced Kramer-Pesch effect appears in the dirty band. Besides numerical results we also present an analytical model for the spatial variation of the pairing potential in the vicinity of the vortex center that allows a simple calculation of the vortex core radius even in the limit T -> 0.
As a model for the vortex core in MgB2 we study a two band model with a clean sigma band and a dirty pi band. We present calculations of the vortex core size in both bands as a function of temperature and show that there exists a Kramer-Pesch effect in both bands even though only one of the bands is in the clean limit. We present calculations for different pi band diffusivities and coherence lengths.
We study the effects of non-magnetic impurity scattering on the Andreev bound states (ABS) in an isolated vortex in a two-dimensional chiral p-wave superconductor numerically. We incorporate the impurity scattering effects into the quasiclassical Eilenberger formulation through the self-consistent $t$-matrix approximation. Within this scheme, we calculate the local density of states (LDOS) around two types of vortices: parallel (anti-parallel) vortex where the phase winding of the pair-potential coming from vorticity and that coming from chirality have the same (opposite) sign. When the scattering phase-shift $delta_0$ of each impurity is small, we find that impurities affect differently low energy quasiparticle spectrum around the two types of vortex in a way similar to that in the Born limit ($delta_0rightarrow 0$). For a larger $delta_0(leq pi/2)$ however we find that ABS in the vortex is strongly suppressed by impurities for both types of vortex. We found that there are some correlations between the suppression of ABS near vortex cores and the low energy density of states due to impurity bands in the bulk.
We theoretically study a non-magnetic impurity effect on the vortex bound states of a multi-quantum vortex. The zero-energy peak of the local density of states is investigated for vortex cores with the winding numbers 2 and 4 within the framework of the quasiclassical theory of superconductivity. We find that the zero-energy peaks, which appear away from the vortex center in the clean limit, move towards the vortex center with increasing the impurity scattering rate, resolving a contradiction between an experimental result and previous theoretical predictions.
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