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TT: Fachverband Tiefe Temperaturen
TT 9: Poster Session: Correlated Electrons
TT 9.24: Poster
Dienstag, 28. September 2021, 13:30–16:00, P
Glass-like transitions in the frustrated charge system θ-(BEDT-TTF)2CsM(SCN)4 (M = Cs and Co) revealed by thermal expansion measurements — •Yohei Saito1, Tatjana Thomas1, Steffi Hartmann1, Tim Thyzel1, Yassine Agarmani1, Hungwei Sun1, Jens Müller1, Kenichiro Hashimoto2, Takahiko Sasaki2, Hiroshi Yamamoto3, and Michael Lang1 — 1Institute of Physics, Goethe University Frankfurt, Frankfurt (M), Germany — 2Institute for Materials Research, Tohoku University, Sendai, Japan — 3Institute for Molecular Science, Okazaki, Japan
Geometrical frustration causes degenerate states, giving rise to intriguing quantum phenomena such as a spin liquid. In addition to a frustrated spin system, a frustrated charge system is proposed in organic conductors called θ-type BEDT-TTF salts. It is expected that charge ordering is suppressed and is possibly replaced by a charge glass state. In organic charge-ordered salts, the charge order transition accompanies a structural transition. Therefore, investigating their elastic properties is of fundamental interest. We performed thermal expansion measurements on θ-(BEDT-TTF)2CsM(SCN)4 (M = Cs and Co) that does not show charge ordering. The thermal expansion coefficient exhibited a glassy transition at 90-100 K. This behavior is reminiscent of the freezing of the terminal ethylene end-groups on the BEDT-TTF molecules. We also found another glassy transition at 120-130 K for both salts where the development of a superlattice structure was reported. These results point to the importance of the lattice degrees of freedom in the frustrated charge system.