Browsing by Author "Choudhury, Sourav Sen"
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Item Thermal transport in superconductors with coexisting spin density wave order(Montana State University - Bozeman, College of Letters & Science, 2021) Choudhury, Sourav Sen; Chairperson, Graduate Committee: Anton Vorontsov; This is a manuscript style paper that includes co-authored chapters.In this thesis we study thermal transport in a two-dimensional system with coexisting s- or d-wave Superconducting (SC) and Spin Density Wave (SDW) orders. We analyse the nature of coexistence phase in a tight-binding square lattice with Q = (pi, pi) SDW ordering. The electronic thermal conductivity is computed within the framework of the Boltzmann kinetic theory, using Born approximation for the impurity scattering collision integral. We describe the influence of the Fermi surface (FS) topology, the competition between the SC and SDW order parameters, the presence or absence of zero energy excitations in the coexistence phase, on the low temperature behavior of thermal conductivity of the various paring states. We present qualitative analytical, and fully numerical results that show that the heat transport signatures of various SC states emerging from collinear SDW order are quite distinct, and depend on the symmetry properties of the SC order parameter under translation by the SDW nesting vector Q. A combination of (pi, pi)-SDW and the d x 2-y 2 pairing state results in fully gapped excitations, whereas (pi, pi)-SDW co-existing with either d xy or s-wave pairing states may always have gapless excitations. There appear special stable Dirac nodal points that are not gapped by the SC order in the coexistence phase, resulting in finite residual heat conductivity.Item Thermal transport in two-dimensional nematic superconductors(American Physical Society, 2022-06) Choudhury, Sourav Sen; Peterson, Sean; Idzerda, YvesWe study the thermal transport in a two-dimensional system with coexisting superconducting (SC) and nematic orders. We analyze the nature of the coexistence phase in a tight-binding square lattice where the nematic state is modelled as a d-wave Pomeranchuk-type instability and the feedback of the symmetry breaking nematic state on the SC order is accounted for by mixing of the s, d paring interaction. The electronic thermal conductivity is computed within the framework of Boltzmann kinetic theory where the impurity scattering collision integral is treated in the Born and unitary limits. We present qualitative, analytical, and numerical results that show that the heat transport properties of SC states emerging from a nematic background are quite distinct and depend on the degree of anisotropy of the SC gap induced by nematicity. We describe the influence of the Fermi surface topology, the van Hove singularities, and the presence or absence of zero-energy excitations in the coexistence phase on the the low-temperature behavior of the thermal conductivity. Our main conclusion is that the interplay of nematic and SC orders has visible signatures in the thermal transport, which can be used to infer SC gap structure in the coexistence phase.