Two-gap s± -wave superconductivity at an oxide interface

Abstract

After half a century of debate, superconductivity in doped SrTiO 3 has come to the fore again with the discovery of interfacial superconductivity in the LaAlO 3 /SrTiO 3 heterostructures. While these interfaces share the interesting properties of bulk SrTiO 3 , quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping. Multigap superconductivity has been predicted to emerge in LaAlO 3 /SrTiO 3 at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field H c2 of superconducting (110)-oriented LaAlO 3 /SrTiO 3 heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional s ± -wave superconducting state with a repulsive coupling between the two condensates.

Multiband Effects in the Superconducting Phase Diagram of Oxide Interfaces

“…[37] Trevisan et al suggested that such mechanism could be responsible for the reduction of T c in the overdoped regime of (001)-oriented LaAlO 3 /SrTiO 3 interfaces. [13] The recent observation of single-gap to two-gap superconductivity transition associated to a decrease in T c in a (110)-oriented LaAlO 3 /SrTiO 3 interface, consistent with s ± -wave superconductivity, supports this proposal, [16,17] although this system has some significant differences in the band structure with respect to the conventional (001)-orientation discussed here. Following this approach, we interpret the optimal doping point c max T in LaAlO 3 /SrTiO 3 as the filling threshold of a new band, which accommodates a second superconducting gap repulsively coupled to the first one.…”

“…[ 13 ] and observed in (110)‐oriented interfaces. [ 16,17 ] We therefore expect T c to decrease in the overdoped region because of interband scattering (point C). In contrast, for Δ V TG > 0, the confining potential well becomes sharper as suggested in Figure 2a, and the $${d_{{\rm{xy}}}}$$ subband is repelled to higher energy (panel 5d).…”

“…Because of the coupling with the xz/yz d band, a second superconducting gap is likely to open in this band, prospectively leading to the formation of a s ± -wave superconducting state as proposed by Trevisan et al [13] and observed in (110)-oriented interfaces. [16,17] We therefore expect T c to decrease in the overdoped region because of interband scattering (point C). In contrast, for ΔV TG > 0, the confining potential well becomes sharper as suggested in Figure 2a, and the xy d subband is repelled to higher energy (panel 5d).…”

“…[ 15 ] More recently, signatures of two‐gap superconductivity consistent with a s ± ‐wave state were clearly observed in (110)‐oriented LaAlO 3 /SrTiO 4 interfaces in superfluid stiffness and critical field measurements. [ 16,17 ] Josephson experiments suggest that such state could also take place in the conventional (001)‐oriented LaAlO 3 /SrTiO 3 interfaces. [ 18,19 ]…”

A brief review of the physical properties of charge density wave superconductor LaPt2Si2

“…It is worth to try the effect of non-magnetic impurity on the superconducting transition temperature. It has been shown in [65][66][67] that T c suppresses drastically for s +− gap symmetry due to promoted pair breaking because of interband impurity scattering, whereas T c changes only slightly in case of s ++ symmetry.…”