Measurement of low energy charge correlations in underdoped spin-glass La-based cuprates using impedance spectroscopy

Abstract

We report on the charge kinetics of ${\text{La}}_{2}{\text{CuO}}_{4}$ lightly doped with Li and Sr. Impedance spectroscopy measurements down to 25 mK and from 20 Hz to 500 kHz reveal evidence for low energy charge dynamics, which slow down with decreasing temperature. Both systems are acutely sensitive to stoichiometry. In the case of Sr substitution, which at higher carrier concentration evolves to a high-temperature superconductor, the ground state in the pseudogap-doping regime is one of spatially segregated, dynamic charge domains. The charge carriers slow down at substantially lower temperatures than their spin counterparts and the dynamics are particularly sensitive to crystallographic direction. This is contrasted with the case of Li doping.