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Non-centrosymmetric Superconductors

27 Oct 2021

Reading time ~2 minutes

Bachelor thesis report on superconductivity.

Abstract

Lack of inversion symmetry in a crystal can have very profound impact on its superconducting properties. The free-energy functionals describing these, so-called non-centrosymmetric systems (NCS), can have new terms which are absent in ordinary superconductors on account of symmetry. While externally applied field decays monotonically for usual BCS, in NCS it can have a spiral decay (imagine \(\vec{B}\) rotating and decaying, much like a
helix). Moreover, these materials also feature vortex bound states, and an admixture of singlet-triplet pairings. I studied one such model (PhysRevB.102.184517, Babaev et al.) and looked at the effect of “spin-orbit coupling” on superconductivity. Specifically, I investigated SOC’s effect on observables both below and above \(T_c\) (when the system is non-superconducting). For the latter, mean field predicts a vanishing order parameter (and thus a normal state), but thermal fluctuations atop this mean field can still contribute to thermodynamic measurables (in some cases, their contribution can overpower normal “metallic” state answer, see larkin’s paper below). Using regularization, I calculated these effects and finally presented my findings to a committee.

Presentation (v3)

Presentation (v2)

Presentation (v1)

Final Report

References

  1. Albert Samoilenka and Egor Babaev. “Spiral magnetic field and bound states of vor- tices in noncentrosymmetric superconductors”. In: Physical Review B 102.18 (2020), p. 184517.

  2. E. Bauer et al. “Heavy Fermion Superconductivity and Magnetic Order in Non- centrosymmetric CePt3Si”. In: Phys. Rev. Lett. 92 (2 Jan. 2004), p. 027003. doi: 10.1103/PhysRevLett.92.027003. url: https://link.aps.org/doi/10.1103/ PhysRevLett.92.027003.

  3. AI Larkin and AA Varlamov. “Fluctuation phenomena in superconductors”. In: Su- perconductivity. Springer, 2008, pp. 369–458.

  4. M Smidman et al. “Superconductivity and spin–orbit coupling in non-centrosymmetric materials: a review”. In: Reports on Progress in Physics 80.3 (Jan. 2017), p. 036501. issn: 1361-6633. doi: 10.1088/1361-6633/80/3/036501. url: http://dx.doi. org/10.1088/1361-6633/80/3/036501.

  5. Albert Schmid. “Diamagnetic Susceptibility at the Transition to the Superconduct- ing State”. In: Phys. Rev. 180 (2 Apr. 1969), pp. 527–529. doi: 10.1103/PhysRev. 180.527. url: https://link.aps.org/doi/10.1103/PhysRev.180.527.

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