Persistent electrical doping of Bi2Sr2CaCu2O8+x mesa structures

TL;DR

This study demonstrates that applying a large bias voltage to Bi2Sr2CaCu2O8+x mesas induces persistent, reversible doping, enabling detailed analysis of doping effects on superconductivity and electronic spectra without chemical modification.

Contribution

It introduces a method for controllably and reversibly doping Bi-2212 crystals electrically, revealing doping-dependent superconducting properties and mechanisms of persistent electric doping.

Findings

Overdoping reduces critical temperature and superconducting gap.

Underdoping increases pseudogap and decreases interlayer tunneling coherence.

Electric doping mechanisms involve charge transfer and oxygen impurity reordering.

Abstract

Application of a significantly large bias voltage to small Bi2Sr2CaCu2O8+x mesa structures leads to persistent doping of the mesas. Here we employ this effect for analysis of the doping dependence of the electronic spectra of Bi-2212 single crystals by means of intrinsic tunneling spectroscopy. We are able to controllably and reversibly change the doping state of the same single crystal from underdoped to overdoped state, without changing its chemical composition. It is observed that such physical doping is affecting superconductivity in Bi-2212 similar to chemical doping by oxygen impurities: with overdoping the critical temperature and the superconducting gap decrease, with underdoping the c-axis critical current rapidly decreases due to progressively more incoherent interlayer tunneling and the pseudogap rapidly increases, indicative for the presence of the critical doping point. We distinguish two main mechanisms of persistent electric doping: (i) even in voltage contribution, attributed to a charge transfer effect, and (ii) odd in voltage contribution, attributed to reordering of oxygen impurities.