Low Temperature Physics: 41, 965 (2015); https://doi.org/10.1063/1.4935694
Физика Низких Температур: Том 41, Выпуск 12 (Декабрь 2015), c. 1237-1242    ( к оглавлению , назад )

Complex conductance of ultrathin La2–xSrxCuO4 films and heterostructures

V.A. Gasparov

Institute of Solid State Physics RAS, Chernogolovka, Moscow district 142432, Russia
E-mail: vgasparo7@gmail.com

I. Božović

Brookhaven National Laboratory, Upton, NY 11973, USA
Applied Physics Department, Yale University, New Haven CT 06520, USA

Received June 11, 2015


We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (La1.55Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which each layer is just one unit cells thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films. Experiments have been carried out at frequencies between 2–50 MHz using the single-spiral coil technique. We found that: (i) the inductive response starts at ΔT = 3 K lower temperatures than Re σ(T), which in turn is characterized by a peak close to the transition, (ii) this shift is almost constant with magnetic field up to 14 mT; (iii) ΔT increases sharply up to 4 K at larger fields and becomes constant up to 8 T; (iv) the vortex diffusion constant D(T) is not linear with T at low temperatures as in the case of free vortices, but is rather exponential due to pinning of vortex cores, and (v) the dynamic Berezinski–Kosterlitz–Thouless (BKT) transition temperature occurs at the point where Y = (lω+)2 = 1. Our experimental results can be described well by the extended dynamic theory of the BKTtransition and dynamics of bound vortex–antivortex pairs with short separation lengths.

PACS: 74.78.Fk Multilayers, superlattices, heterostructures;
PACS: 74.72.Gh Hole-doped;
PACS: 74.40.−n Fluctuation phenomena.

Key words: superconducting heterostructures, high-frequency conductivity, Berezinski–Kosterlitz–Thouless transition.

Published online: Oсtober 23, 2015