Doping Dependence of Two Energy Scales in the Tunneling Spectra of Superconducting La$_{2-x}$Sr$_{x}$CuO$_{4}$

TL;DR

This study uses scanning tunneling microscopy to investigate how doping levels affect two distinct energy scales in the superconducting La$_{2-x}$Sr$_{x}$CuO$_{4}$, revealing spatial variations in the energy gap and uniformity of the kink energy.

Contribution

It provides new insights into the doping dependence of two energy scales in La$_{2-x}$Sr$_{x}$CuO$_{4}$ using high-resolution tunneling spectroscopy.

Findings

Energy gap varies with doping and spatially fluctuates.

Kink energy remains spatially uniform and doping-independent.

Two energy scales are identified in the tunneling spectra.

Abstract

Scanning tunneling microscopy and spectroscopy have been performed on superconducting La$_{2-x}$Sr$_{x}$CuO$_{4}$ ($x=0.06, 0.12, 0.16$, and 0.21) at 4.2 K. Atomically resolved surface topography has been observed on the $ab$ surface, which exhibits a one-dimensional structure corresponding to the buckling pattern of the orthorhombic phase. The tunneling spectra of all samples exhibit kinks at about $\pm 5$ meV in addition to the energy gap, indicating the existence of two energy scales. While the gap magnitude varies on the length scale of a few nm and steadily increases upon underdoping, the kink energy is spatially uniform on the surface and almost independent of the doping level.