Strong diamagnetic response and specific heat anomaly above T_c in underdoped La_(2-x)Sr_xCuO_4

TL;DR

This study reveals a diamagnetic response and specific heat anomaly above T_c in underdoped La_(2-x)Sr_xCuO_4, indicating phase incoherent Cooper pairs exist between T_c and T*.

Contribution

It demonstrates the existence of diamagnetism and specific heat anomalies above T_c in underdoped LSCO, suggesting phase incoherent Cooper pairing in this temperature range.

Findings

Diamagnetism observed above T_c along the c-axis only.

Specific heat anomaly detected at T* via elastic constant measurements.

Diamagnetism is frequency independent between 0.1-10 kHz.

Abstract

By measuring AC susceptibility using a very low amplitude of the AC field (<1 mG) it is shown that underdoped samples of La_(2-x)Sr_xCuO_4 (LASCO), are diamagnetic in a temperature region above T_c up to a temperature T^*. This behavior is only observed with AC fields along the c-axis whereas for fields in the ab-plane no diamagnetism above Tc was detected. The diamagnetism is almost frequency independent in the frequency range 0.1-10 kHz. At T* a broad step anomaly in the specific heat is inferred through measurements of the elastic constant c33. We suggest that the observed diamagnetism and the anomaly in the elastic constant are associated with the existence of phase incoherent Cooper pairs between Tc and T*.