Theory of 2D superconductor with broken inversion symmetry

Ol'ga Dimitrova; M. V. Feigel'man

doi:10.1103/PhysRevB.76.014522

paper

Theory of 2D superconductor with broken inversion symmetry

arXiv:cond-mat/0701698 · doi:10.1103/PhysRevB.76.014522

Abstract

A detailed theory of a phase diagram of a 2D surface superconductor in a parallel magnetic field is presented. A spin-orbital interaction of the Rashba type is known to produce at a high magnetic field $h$ (and in the absence of impurities) an inhomogeneous superconductive phase similar to the Larkin-Ovchinnikov-Fulde-Ferrel (LOFF) state with an order parameter $Δ (r) \propto cos (Q r)$ . We consider the case of a strong Rashba interaction with the spin-orbital splitting much larger than the superconductive gap $Δ$ , and show that at low temperatures $T \leq 0.4 T_{c 0}$ the LOFF-type state is separated from the usual homogeneous state by a first-order phase transition line. At higher temperatures another inhomogeneous state with $Δ (r) \propto exp (i Q r)$ intervenes between the uniform BCS state and the LOFF-like state at $g μ_{B} h \approx 1.5 T_{c 0}$ . The modulation vector $Q$ in both phases is of the order of $g μ_{B} h / v_{F}$ . The superfluid density $n_{s}^{y y}$ vanishes in the region around the second-order transition line between the BCS state and the new ``helical'' state. Non-magnetic impurities suppress both inhomogeneous states, and eliminate them completely at $T_{c 0} τ \leq 0.11$ . However, once an account is made of the next-order term over the small parameter $α / v_{F} ≪ 1$ , a relatively long-wave helical modulation with $Q \sim g μ_{B} h α / v_{F}^{2}$ is found to develop from the BCS state. This long-wave modulation is stable with respect to disorder. In addition, we predict that unusual vortex defects with a continuous core exist near the phase boundary between the helical and the LOFF-like states. In particular, in the LOFF-like state these defects may carry a half-integer flux.

23 pages, 14 figures

Theory of 2D superconductor with broken inversion symmetry

Abstract

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