Route to high-temperature superconductivity in composite systems

Abstract

Apparently, some form of local superconducting pairing persists up to temperatures well above the maximum observed ${T}_{c}$ in underdoped cuprates; i.e., ${T}_{c}$ is suppressed due to the small phase stiffness. With this in mind, we consider the following question: Given a system with a high pairing scale ${\ensuremath{\Delta}}_{0}$ but with ${T}_{c}$ reduced by phase fluctuations, can one design a composite system in which ${T}_{c}$ approaches its mean-field value, ${T}_{c}\ensuremath{\rightarrow}{T}_{\text{MF}}\ensuremath{\approx}{\ensuremath{\Delta}}_{0}/2$? Here, we study a simple two-component model in which a ``metallic layer'' with ${\ensuremath{\Delta}}_{0}=0$ is coupled by single-particle tunneling to a ``pairing layer'' with ${\ensuremath{\Delta}}_{0}>0$ but zero phase stiffness. We show that in the limit where the bandwidth of the metal is much larger than ${\ensuremath{\Delta}}_{0}$, the ${T}_{c}$ of the composite system can reach the upper limit ${T}_{c}\ensuremath{\approx}{\ensuremath{\Delta}}_{0}/2$.