SKM 2023 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 51: Correlated Electrons: Charge Order
TT 51.9: Vortrag
Donnerstag, 30. März 2023, 17:15–17:30, HSZ 103
Glass-like transitions in the frustrated charge system θ-(BEDT-TTF)2MM′(SCN)4 (MM′ = CsZn, CsCo, and RbZn) revealed by thermal expansion measurements — •Yohei Saito1, Tatjana Thomas1, Yassine Agarmani1, Tim Thyzel1, Kenichiro Hashimoto2, Takahiko Sasaki2, 3, Jens Müller1, and Michael Lang1 — 1Goethe University Frankfurt, Frankfurt (M), Germany — 2University of Tokyo, Chiba, Japan — 3Tohoku University, Sendai, Japan
Geometrical frustration causes degenerate states and a frustrated charge system is proposed in organic conductors. It is expected that charge order (CO) is suppressed and is possibly replaced by a charge glass state. In organic condutors, the CO transition accompanies a structural transition. Therefore, investigating their elastic properties is of fundamental interest. We performed thermal expansion measurements on θ-(BEDT-TTF)2MM′(SCN)4 (MM′ = CsZn, CsCo, and RbZn) : whereas the CsZn and CsCo salts exhibit no CO transition, slowly-cooled RbZn salt shows the transition. The thermal expansion coefficient of no-CO salts 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. For the RbZn salt we observe a CO transition at 210 K and also an ethylene-group related glass-like transition at 80-100 K. Therefore, the glass-like anomaly around 90 K appears as a common feature in θ-type salts regardless of whether long-range CO exists. These results point to the importance of the lattice degrees of freedom in the frustrated charge system.