STM/STS study on electronic superstructures in the superconducting state of high-T_c cuprate Bi_2Sr_2CaCu_2O_(8+δ)

摘要

We report STM/STS measurements at 8 K in underdoped Bi_2Sr_2CaCu_2O_(8+δ) crystals (T_c = 76 K and hole-doping level p ～ 0.12) whose energy spectra around the Fermi level are characterized by a two-gap structure consisting of spatially inhomogeneous pseudogap (PG) and comparatively homogeneous superconducting gap (SCG). Two electronic superstructures, checkerboard modulation (CBM) and Cu-O-Cu bond-centered modulation (BCM), are observed with mapping spectral weights at low energies within the SCG and the ratio of spectral weights at ±Δ_(PG) (PG energy), respectively. On the basis of the present findings, we suggest that the lower-energy scale CBM is an intrinsic property of Cu-O planes and can coexist with the BCM whose characteristic energy is ~Δ_(PG) in identical regions in real space.