Anomalous Thermoelectric power of over-doped Bi2Sr2CaCu2O8 superconductor

TL;DR

This study investigates the temperature-dependent thermoelectric power of Bi2Sr2CaCu2O8 superconductors with different doping levels, revealing anomalous negative thermopower in over-doped samples linked to electronic band structure effects.

Contribution

It provides new insights into the thermoelectric behavior of over-doped Bi2212 superconductors and correlates experimental results with recent band structure calculations.

Findings

Optimally doped samples show positive thermoelectric power across all temperatures.

Over-doped sample exhibits negative thermopower above TcS=0.

Results align with recent ARPES studies on split Fermi surfaces.

Abstract

Temperature dependence of thermoelectric power S(T) of three differently processed Bi2Sr2CaCu2O8 (Bi2212) samples, viz. as-processed melt quenched (Bi2212-MQ), 6000C N2-annealed (Bi2212-N2) and 6000C O2-annealed (Bi2212-O2) is reported here. All the samples possess single-phase character and their superconducting transition temperatures (TcR=0) are 85 K, 90 K and 72 K respectively for Bi2212-MQ, Bi2212-N2 and Bi2212-O2. While Bi2212-MQ and Bi2212-N2 samples are in near optimum doping regime, Bi2212-O2 is an over-doped sample. TcS=0 values obtained through S(T) data are also in line with those deduced from the temperature dependence of resistance and DC magnetization. Interestingly, S(T) behaviour of the optimally-doped Bi2212-MQ and Bi2212-N2 samples is seen to be positive in whole temperature range, it is found negative for the over-doped Bi2212-O2 sample above TcS=0. These results have been seen in the light of the recent band structure calculations and the ensuing split Fermi surface as determined by angle-resolved photoelectron spectroscopy (ARPES).