Periodic DOS modulation in underdoped Bi2223

TL;DR

This study uses STM/STS to investigate underdoped Bi2223 crystals, revealing a new periodic LDOS modulation likely linked to charge/spin order, and showing doping-dependent homogeneity of the superconducting gap.

Contribution

It reports the discovery of a new periodic LDOS modulation in underdoped Bi2223 and analyzes its relation to doping levels and layer decoupling.

Findings

Homogeneous superconducting gap in optimally doped Bi2223

Inhomogeneous gap increases with underdoping

Observation of a 2a0 periodic LDOS modulation in underdoped samples

Abstract

In this report, we show the results of the STM/STS study on the Bi2223 single crystals whose doping levels were ranging from an optimally doped to an underdoped region. Bi2223 single crystals were grown by a TSFZ method and their doping levels were adjusted with annealing in an oxygen deficient atmosphere. Single crystals were cleaved in an UHV at around 77 K and STM/STS measurements were carried out in the same conditions. We successfully obtained the tunneling spectrum maps as well as topographic images. We found that the superconducting gap was much more homogeneous than in the case of the Bi2212 in optimal doping, but becomes inhomogeneous with decreasing a doping level. This suggests the decoupling of the three Cu-O layers in terms of the SC correlation. More importantly, we found a new periodic modulation in the LDOS map with periods about 2a0, which was almost dispersion-less and observed only in the underdoped TC=85 K sample. This modulation is possibly related to the charge/spin order in the inner plane, which is supposed to be highly undrerdoped.