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Seminar | Materials Science Division

Non-Uniform Superconducting Phases in the Presence of Magnetic Fields

MSD Seminar

Abstract: I will talk about two forms of interplay: between a magnetic field and disorder in an s-wave superconductor (SC); and between a magnetic field and strong electronic correlations in a d-wave SC.

As a first case, I will present the results of our study on a type-II s-wave SC in a simultaneous presence of orbital magnetic field and disorder, both of which are conventionally considered to weaken superconductivity when they are strong. Within a framework of mean-field theory, we find the effect of disorder is intriguing in an s-wave vortex lattice. At weak disorder strengths, the superfluid density and the superconducting energy gap collapse simultaneously. However, as the disorder strength increases, the two critical fields corresponding to the vanishing of the superfluid density and collapsing of the energy gap, start diverging from each other. Our results also have important consequences for the strong magneto-resistance peak observed in  disordered In2O3 film. We illustrate this by calculating the dynamical conductivity and analyzing its low-frequency behavior.

As a second case, I will discuss our findings on the Zeeman effects of  magnetic field in a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in strongly correlated d-wave SC. Within a consolidated framework of Hartree-Fock-Bogoliubov theory and Gutzwiller approximation, we find that the crucial effects of strong correlations lie in shifting the BCS-FFLO phase boundary towards a lower Zeeman field and thereby enlarging the window of the FFLO phase. In the FFLO state, our calculation features a sharp midgap peak in the density of states, indicating the formation of strongly localized Andreev bound states. We also find that the signatures of the FFLO phase survive even in the presence of a competing spin-density wave order, often found in unconventional SCs.

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Anushree Datta, Indian Institute of Science Education and Research, Kolkata

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