Intrinsic tunneling spectroscopy: A look from the inside at HTSC

Layered structure of Bi-2212 high $T_c$ superconductor (HTSC), provides a unique opportunity to probe quasiparticle density of states inside a bulk single crystal by means of intrinsic (interlayer) tunneling spectroscopy. Here I present a systematic study of intrinsic tunneling characteristics of Bi-2212 as a function of doping, temperature, magnetic field and intercalation. An improved resolution made it possible to simultaneously trace the superconducting gap (SG) and the normal state pseudo-gap (PG) in a close vicinity of $T_c$ and to analyze closing of the PG at $T^*$. The obtained doping phase diagram exhibits a critical doping point for appearance of the PG and a characteristic crossing of the SG and the PG close to the optimal doping. All this points towards coexistence of two different and competing order parameters in Bi-2212.