Counterintuitive Consequence of Heating in Strongly-Driven Intrinsic-Junctions of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ Mesas

TL;DR

This study reveals that the sharp conductance peaks in Bi2212 intrinsic Josephson junctions, previously attributed to superconducting gaps, are actually caused by heating effects leading to a nonequilibrium two-phase state, challenging conventional interpretations.

Contribution

It demonstrates that the conductance peaks are due to heating-induced instabilities, not superconducting gaps, providing a new understanding of tunneling spectra in these junctions.

Findings

Conductance peaks are caused by heating, not superconducting gaps.

Peak sharpening correlates with increased power and number of junctions.

The observed phenomena match predictions of a nonequilibrium two-phase state.

Abstract

Anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ (Bi2212) mesas have been universally interpreted as superconducting energy gaps, but here we show they are a result of heating. This interpretation follows from a direct comparison to the equilibrium gap, $\mathit \Delta$, measured in break junctions on similar Bi2212 crystals. As the dissipated power increases with a greater number of junctions in the mesa, the conductance peak abruptly sharpens and its voltage decreases to well below 2$\mathit \Delta$. This sharpening, found in our experimental data, defies conventional intuition of heating effects on tunneling spectra, but it can be understood as an instability into a nonequilibrium two-phase coexistent state. The measured peak positions occur accurately within the voltage range that an S-shaped backbending is found in the {\it calculated} current-voltage curves for spatially {\it uniform} self-heating and that S-shape implies the potential for the uniform state to be unstable.