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TT: Fachverband Tiefe Temperaturen

TT 75: Low Dimensional Systems

TT 75.1: Talk

Thursday, March 21, 2024, 15:00–15:15, H 3007

First-order electronic phase transition in α-(BEDT-TTF)₂I₃
revealed by temperature-dependent generalized ellipsometry — •Achyut Tiwari, Bruno Gompf, Dieter Schweitzer, and Martin Dressel — Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

The nature of correlation-driven metal-insulator transitions remains a longstanding puzzle in solid-state physics. While some theories suggest a second-order character, various experimental observations in these materials indicate first-order phase transitions. Despite considerable progress over the last decades in understanding the underlying driving mechanisms of metal-insulator transitions, in particular the phase coexistence remains poorly understood on a microscopic scale. Here, we employ Mueller matrix spectroscopic and temperature-dependent ellipsometry to determine the anisotropic dielectric functions of the two-dimensional charge-transfer salt α-(BEDT-TTF)₂I₃ across its charge-order metal-insulator transition. Our results offer valuable insights into temperature-dependent changes of the dielectric functions along the different crystallographic axes. Furthermore, we apply an effective-medium approximation to quantify the correlation between the metal-to-insulator transition and the volume fraction of the metallic phase embedded within the insulating phase. Through this comprehensive approach, generalized ellipsometry unravels the nature of the correlation-driven metal-insulator transition.

Keywords: Metal-insulator transition; Mueller matrix ellipsometry; first-order phase transition; effective medium approximation