Modulation of superconductivity by quantum confinement in doped strontium titanate

Abstract

Quantum confinement in a thin-film geometry offers viable routes for tuning the critical properties of superconductors through modification of both density of states and pairing interaction. Low-density systems like doped strontium titanate are especially susceptible to these confinement-induced effects. In this paper, we show that the superconducting critical temperature $T_c$ is enhanced through quantum confinement in SrTiO${}_3$/SrTi${}_{1-x}$Nb${}_x$O${}_3$/SrTiO${}_3$ heterostructures at $x=1\%$ concentration, by measuring resistivity transitions and the Hall carrier density for different thicknesses of the doped layer. We observe a nonmonotonic raise of $T_c$ with decreasing layer thickness at constant carrier density as estimated from the Hall effect. We analyze the results by solving a two-band model with a pairing interaction reproducing the density-dependent $T_c$ of doped SrTiO${}_3$ in the bulk, that we confine to a potential well established self-consistently by the charged Nb dopants. The evolution of the theoretical $T_c$ with thickness agrees well with experiments. We point out the possible role of density inhomogeneities and suggest novel methods for engineering superconductivity in epitaxial thin films.

arXiv comment7 pages, 4 figures

References in corpus (20)

• Electric Field Control of the LaAlO${}_3$/SrTiO${}_3$ Interface Ground State
• A ferroelectric quantum phase transition inside the superconducting dome of Sr${}_{1-x}$Ca${}_x$TiO${}_{3-\delta }$
• Quantum critical origin of the superconducting dome in SrTiO${}_3$
• Common Fermi-liquid origin of T-squared resistivity and superconductivity in n-type SrTiO3
• Critical doping for the onset of a two-band superconducting ground state in SrTiO${}_{3-\delta }$
• Origin of the crossover from polarons to Fermi liquids in transition metal oxides
• Fermi surface of the most dilute superconductor
• Resonant and crossover phenomena in a multiband superconductor tuning the chemical potential near a band edge
• Enhanced Superconductivity and Suppression of Charge-density Wave Order in 2H-TaS${}_2$ in the Two-dimensional Limit
• Broadening of the Beresinkii-Kosterlitz-Thouless superconducting transition by inhomogeneity and finite-size effects
• Metallicity and superconductivity in doped strontium titanate
• Superconductivity at very low density: the case of strontium titanate
• Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms
• Intrinsic spin-orbit coupling in superconducting δ-doped SrTiO3 heterostructures
• Superconductivity at low density near a ferroelectric quantum critical point: doped SrTiO
• Unconventional multi-band superconductivity in bulk SrTiO${}_3$ and LaAlO${}_3$/SrTiO${}_3$ interfaces
• Superfluid density and carrier concentration across a superconducting dome: the case of SrTi${}_{1-x}$Nb${}_x$O${}_3$
• Shape Resonances in superconducting gaps in a 2DEG at oxide-oxide interface
• Localization and Superconductivity in Doped Semiconductors
• Impact of disorder on the superconducting transition temperature near a Lifshitz transition