Energy gap of the high-Tc superconductor HgBa2Ca2Cu3O8+ delta determined by point-contact spectroscopy.

Abstract

Tunneling spectra of a polycrystalline bulk ${\mathrm{HgBa}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ with ${\mathit{T}}_{\mathit{c}}$=132 K have been measured by point-contact spectroscopy using a low-temperature scanning tunneling microscope. Unlike other high-${\mathit{T}}_{\mathit{c}}$ superconductors, the conductance of this material shows a BCS-like gap structure with a relatively small smearing parameter \ensuremath{\Gamma}. Conductances with a linear density of states for \ensuremath{\Vert}eV\ensuremath{\Vert}a small cusp at the gap are also observed. From a simple calculation based on the assumption that the surface is covered with a normal layer, we explained the linear dI/dV for \ensuremath{\Vert}eV\ensuremath{\Vert}obtained two distinctively different energy gaps \ensuremath{\Delta}=48 meV and 22 meV with the resultant 2\ensuremath{\Delta}/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$=8.5 and 3.9, respectively.