Intrinsic Tunneling Spectra of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ near Optimal Doping

Abstract

We report tunneling spectra of near optimally doped Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ intrinsic Josephson junctions with area of 0.09 $\mu$m${}^2$, which avoid some fundamental difficulties in the previous tunneling experiments and allow a stable temperature-dependent measurement. A d-wave Eliashberg analysis shows that the spectrum at 4.2 K can be well fitted by considering electron couplings to a bosonic magnetic resonance mode and a broad high-energy continuum. Above $T_c$, the spectra show a clear pseudogap that persists up to 230 K, and a crossover can be seen indicating two different pseudogap phases existing above $T_c$. The intrinsic electron tunneling nature is discussed in the analysis.

4 pages, 4 figures, 1 table