Scaling between Superfluid Density and Tc in Overdoped La2−xSrxCuO4 Films

Evandro V L De Mello

doi:10.3390/condmat4020052

Abstract

We used an electronic phase separation approach to interpret the scaling between the low-temperature superfluid density average ρ sc ( 0 ) and the superconducting critical temperature T c on overdoped La 2 − x Sr x CuO 4 films. Guided by the observed nematic and incommensurate charge ordering (CO), we performed simulations with a free energy that reproduces charge domains with wavelength λ C O and provides a scale to local superconducting interactions. Under these conditions a complex order parameter with amplitude Δ d ( r i ) and phase θ ( r i ) may develop at a domain i. We assumed that these domains are coupled by Josephson energy E J ( r i j ) , proportional to the local superfluid density ρ sc ( r i j ) . Long-range order occured when the average E J ( T c ) is ∼ k B T c . The linear ρ s c ( 0 ) vs. T c relation was satisfied whenever CO was present, even with almost vanishing charge amplitudes.

Highlights

Overdoped high-temperature cuprate superconductors have been widely believed to be described by the physics of d-wave BCS-like superconductivity
Competing broken symmetry states in cuprates arising from a nanoscale electronic phase separation have been predicted by many different microscopic models using Hubbard, Holstein, t-J Hamiltonians, and with many different techniques [10,11,12,13]
We verified that LSCO films are well-described by mesoscopic grains with charge modulation λCO, similar to a granular superconductor

Summary

Introduction

Overdoped high-temperature cuprate superconductors have been widely believed to be described by the physics of d-wave BCS-like superconductivity. The authors in [1] developed a technique to grow homogeneous overdoped La2−xSrxCuO4 (LSCO) films and measured the penetration depth from which ρsc(0) is derived, establishing a new unforeseen scaling law: ρsc(p, T ∼ 0 K) is directly proportional to Tc(p), both being maximum at p = 0.16 and vanishing near the superconducting (SC) limiting phase at p = 0.26. Their films displayed homogeneous properties with less than 1% variations in Tc [1,2], but the induction of an anisotropic transverse voltage [3] indicates some intrinsic electronic disorder. The very low normal state residual resistance measured in the same experiment [1] and subsequent time-domain THz spectroscopy [8] ruled out an approach based on the dirty BCS scenario [9]

Results

Discussion

Conclusion