Anomalous thermal expansion behavior of the YBaCuO superconductor. Indirect evidence of polaron formation

Abstract

A simple-minded semiclassical method is used to study the thermal expansion data of YBa2Cu3O7-δ (δ = 0.15) both in the normal and superconducting phases. It is shown that there is an anomaly in the temperature variation of the thermal expansion which begins to show up at a temperature somewhat higher than Tc. We argue that this anomaly can be attributed to the phenomenon of polaron formation. This might give an indirect support to the bipolaronic mechanism of high-temperature superconductivity. © 1994.