Eur. Phys. J. Special Topics 222, 1217-1221 (2013)
https://doi.org/10.1140/epjst/e2013-01916-x

Review

On field effect studies and superconductor-insulator transition in high-T_c cuprates

¹ Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
² Laboratory for Physics of Complex Matter, CREAM-ICMP–FSB, station 3, École Polytechnique Fédérale de Lausanne, 1015 Lausanne EPFL, Switzerland

Received: 18 March 2013
Revised: 12 May 2013
Published online: 15 July 2013

Abstract

We summarize previous field effect studies in high-T_c cuprates and then discuss our method to smoothly tune the carrier concentration of a cuprate film over a wide range using an applied electric field. We synthesized epitaxial one-unit-cell thick films of La_2−xSr_xCuO₄ and from them fabricated electric double layer transistor devices utilizing various gate electrolytes. We were able to vary the carrier density by about 0.08 carriers per Cu atom, with the resulting change in T_c of 30 K. The superconductor-insulator transition occurred at the critical resistance very close to the quantum resistance for pairs, R_Q = h/(2e)² = 6.5 kΩ. This is suggestive of a quantum phase transition, possibly driven by quantum phase fluctuations, between a “Bose insulator” and a high-T_c superconductor state.