Photothermal microscope for high-<i>T</i> <i>c</i> superconductors and charge density waves

Abstract

We have developed a new photothermal technique to investigate electronic phase transitions associated with high temperature superconductivity and charge density waves (CDW). The phase shift of the thermal wave yields the anisotropic thermal diffusivity coefficient of the sample. The amplitude of the photothermal signal is sensitive to electronic phase transitions of the second kind and measures directly the effect of thermodynamic fluctuations near the transitions. This noncontacting high-definition technique is well suited to measurements of small and fragile samples. Good comparisons between our experimental results and second-order phase transition theory are obtained on a high-Tc superconductor and a CDW sample.