2007/01/29 by Ol'ga Dimitrova, M. V. Feigel'man · 1 citation
Physics and Astronomy · #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.76.014522
23 pages, 14 figures
arxiv created 2007/01/29 · arxiv updated 2009/12/01
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) ∝ cos(Qr). 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≤ 0.4 Tc0 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) ∝ exp(i Qr) intervenes between the uniform BCS state and the LOFF-like state at gμB h ≈ 1.5 Tc0. The modulation vector Q in both phases is of the order of gμB h/vF. The superfluid density nsyy 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 Tc0τ≤ 0.11. However, once an account is made of the next-order term over the small parameter α/vF ≪ 1, a relatively long-wave helical modulation with Q ∼ gμB hα/vF2 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.