Evidence of Coherent C-Axis Charge Transport in Underdoped La2-xSrxCuO4 Superconductors

TL;DR

This study provides evidence that c-axis charge transport in underdoped La2-xSrxCuO4 superconductors is intrinsically coherent, based on far-infrared reflectivity measurements revealing a plasma edge at specific doping levels.

Contribution

The paper demonstrates the presence of coherent c-axis charge transport in underdoped LSCO, challenging previous assumptions of incoherence in this regime.

Findings

Plasma edge observed at x=0.07 doping level

C-axis scattering rate is small and nearly temperature independent

Coherent charge transport persists in the underdoped regime

Abstract

We have observed the plasma edge in the normal state c-axis far-infrared (far-IR) reflectivity of La2-xSrxCuO4 (LSCO) single crystals at an unlikely Sr-doping concentration x = 0.07 but not in x = 0.09. We find that the c-axis scattering rate (Gc) is surprisingly small, Gc = 13 (+_) 2 cm-1 for x = 0.07 and Gc = 24 (+_) 1 cm-1 for x = 0.09 and nearly temperature independent but increases linearly with doping up to x = 0.16. We suggest that the apparent absence of the normal state plasma edge in the previous measurements is due to the larger Gc than the screened plasma frequency of the coherent free carriers. We conclude that the c-axis charge transport in LSCO in the underdoped regime is intrinsically coherent.