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Register a new userEffect of Delocalized Vortex Core States on the Specific Heat of Nb
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The magnetic field (B) dependence of the electronic specific heat for a simple BCS type-II superconductor has been determined from measurements on pure niobium (Nb). Contrary to expectations, the electronic specific heat coefficient gamma(T,B) is observed to be a sublinear function of B at fields above the lower critical field H_{c1}. This behavior is attributed to the delocalization of quasiparticles bound to the vortex cores. The results underscore the ambiguity of interpretation that arises in specific heat studies of this kind on newly discovered type-II superconductors, and also emphasize the need to such measurements under field-cooled conditions.
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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.
High resolution measurements of the specific heat of liquid $^{3}$He in the presence of a silver surface have been performed at temperatures near the superfluid transition in the pressure range of 1 to 29 bar. The surface contribution to the heat capacity is identified with Andreev bound states of $^{3}$He quasiparticles that have a range of half a coherence length.
The specific heat of single crystal hole-doped Ca0.33Na0.67Fe2As2, Tc(onset)=33.7 K, was measured from 0.4 to 40 K. The discontinuity in the specific heat at Tc, deltaC, divided by Tc is 105 +- 5 mJ/molK2, consistent with values found previously for hole-doped Ba0.6K0.4Fe2As2 and somewhat above the general trend for deltaC/Tc vs Tc for the iron based superconductors established by Budko, Ni and Canfield. The usefulness of measured valued of deltaC/Tc as an important metric for the quality of samples is discussed.
The vortex dynamics and the specific heat of a type II superconducting system with quasi-periodic geometry is studied theoretically for different values of interaction parameters using the numerical simulation technique, where the vortex-vortex interaction potential is considered in the form of the modified Bessels function of first kind. The dynamics of the system is analysed by phase space trajectories of the vortex for both high and low values as well as for both high and low mismatch of vortex-vortex and vortex-pinning interaction parameters. The specific heat variation with temperature is analysed statistically for different values of interaction parameters. It is observed that for low values and lower mismatch of interaction parameters, the system is highly chaotic and shows a bifurcation pattern similar to Hopf bifurcation. The specific heat also shows a highly divergent character in this situation. However for high values and higher mismatch, the superconducting system tends to be a very regular one. The trajectory of the vortices will also be very stable in this situation. Similar situations are also observed respectively for low and high values of the quasi-periodic parameter.
The discoveries of superconductivity in the heavily-boron doped semiconductors diamond (C:B) in 2004 and silicon (Si:B) in 2006 have renewed the interest in the physics of the superconducting state of doped semiconductors. Recently, we discovered superconductivity in the closely related mixed system heavily boron-doped silcon carbide (SiC:B). Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type-II. In this paper we present an extensive analysis of our recent specific-heat study, as well as the band structure and expected Fermi surfaces. We observe an apparent quadratic temperature dependence of the electronic specific heat in the superconducting state. Possible reasons are a nodal gap structure or a residual density of states due to non-superconducting parts of the sample. The basic superconducting parameters are estimated in a Ginzburg-Landau framework. We compare and discuss our results with those reported for C:B and Si:B. Finally, we comment on possible origins of the difference in the superconductivity of SiC:B compared to the two parent materials C:B and Si:B.
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