Checkerboard stripe electronic state on cleaved surface of NdO$_{0.7}$F$_{0.3}$BiS$_{2}$ probed by scanning tunneling microscope

摘要

We present scanning tunneling microscopy measurements on a cleaved surface ofthe recently discovered superconductor NdO$_{0.7}$F$_{0.3}$BiS$_{2}$ with atransition temperature ($T_{\mathrm{c}}$) of 5.1 K.Tunneling spectra at 4.2 K(below $T_{\mathrm{c}}$) and 22 K (above $T_{\mathrm{c}}$) show a largespectroscopic gap ($\sim$40 mV), which is inconsistent with the metallic naturedemonstrated in bulk measurements. Moreover, we find two interesting real-spaceelectronic features. The first feature is a `checkerboard stripe' electronicstate characterized by an alternating arrangement of two types of nanocluster.In one cluster, one-dimensional electronic stripes run along one Bi-Bidirection, whereas, in the other cluster, the stripes run along the other Bi-Bidirection. The second feature is a nanoscale electronic inhomogeneity whosemicroscopic source seems to be atomic defects on the cleaved surface or dopantF atoms.