Fabrication of mesa structures on superconducting Bi2Sr2CaCu2O8+& single crystals

Abstract

There have been tremendous efforts to understand the relatively much more sophisticated mechanism of superconductivity in high temperature superconductors (HTSC). In order to investigate the inherent features and tunneling characteristics just only peculiar to HTSC, micron-sized mesa structures were fabricated on the surfaces of both pristine optimally doped and HgBr2 intercalated Bi2Sr2CaCu2O8+& (Bi-2212) single crystals using photolithography and Argon ion beam etching techniques. The surface topography and heights of the mesas were examined with atomic force microscopy.Hysteretic I-V curves with multiple branches and temperature dependence of tunneling characteristics were investigated by means of a novel technique, point contact tunneling (PCT) and experiments were carried out in a large range of temperatures from 4.2 K to 300 K. The results of SIN single junctions and SIS break junctions obtained by tunneling measurements using PCT technique on bulk crystals were compared withtunneling measurements using PCT technique on bulk crystals were compared with intrinsic Josephson junction quasiparticle spectra generally showing sharp peaks at the gap voltages and no dip/hump structures; which are reconciled with overheating in the mesa. The IJJ measurements performed with HgBr2 intercalated Bi-2212 samples showed far more enhanced characteristics indicating less heating. The zero bias conductance versus temperature plots were examined to scrutinize the existence of pseudogap in electronic excitation spectra of investigated samples. Besides, the normalized gap voltages were plotted against normalized temperature to show the deviation from BCS fit, which displays the novelty of HTSC.