Kinetic energy change with doping upon superfluid condensation in high temperature superconductors

TL;DR

This paper investigates how the electronic kinetic energy change during superfluid condensation varies with doping in high-temperature superconductors, revealing a transition from conventional to unconventional behavior as doping decreases.

Contribution

It demonstrates the doping-dependent crossover of kinetic energy change in high-Tc superconductors, suggesting a unified mechanism across different doping regimes.

Findings

Kinetic energy change is positive in optimally doped Bi-2212.

Kinetic energy change becomes negative in underdoped regimes.

A smooth transition in behavior occurs around optimal doping.

Abstract

In conventional BCS superconductors, the electronic kinetic energy increases upon superfluid condensation (the change DEkin is positive). Here we show that in the high critical temperature superconductor Bi-2212, DEkin crosses over from a fully compatible conventional BCS behavior (DEkin>0) to an unconventional behavior (DEkin<0) as the free carrier density decreases. If a single mechanism is responsible for superconductivity across the whole phase diagram of high critical temperature superconductors, this mechanism should allow for a smooth transition between such two regimes around optimal doping.