What does intrinsic tunnelling spectroscopy really examine?

Abstract

The out-of-plane current-voltage (I-V) characteristics of Bi2212 are studied in experimental environments of different heat transfer efficiency, allowing practical separation of intrinsic and extrinsic phenomena. {\it Intrinsic} (heating-free) response is Ohmic in the normal state of Bi2212, while its resistance, R=V/I, is found to be a good practical measure of the mean temperature of the sample in the overheated case. A self-heating model proposed for the latter case provides a qualitative and quantitative description of key findings of intrinsic tunnelling spectroscopy including (pseudo)gaps, quasiparticle and normal state resistances. The model also naturally explains the `superconducting' gap closure well below $T_c$ of the material as well as its survival at a magnetic field significantly exceeding $H_{c2}$. The generic shape of the individual branches of the brush-like part of I-V established under conditions of negligible overheating suggests a phase-slip origin of the so-called `intrinsic Josephson effect' (IJE).