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Optical investigation of (TMTT)2X under pressure

(TMTTF)2X[1] are organic conductors which show low-dimensional electronic properties due to strong anisotropy arising from the crystal structure. Because of the much stronger overlap of the molecular orbitals in the stacking direction these materials are assumed to be quasi one-dimensional. This leads to a very rich phase diagram with charge order, spin peierls, antiferromagnetic, charge density wave and superconducting phases (see figure). This phase diagram was established by different techniques, such as NMR [2] and DC transport [3], by applying external hydrostatic pressure and investigating compounds with various anions. For the first time, we present optical investigations on the compounds (TMTTF)2AsF6 and (TMTTF)2SbF6 under pressure. In this work we used a piston pressure cell [4] with diamond as optical window and daphne oil as the pressure medium (see figure). The accessible range of pressure is 11 kbar and the lowest reachable temperature is 7 K, which covers the highlighted range in the phase diagram. The biggest advantage of optical measurements is the possibility to directly access the amount of charge per molecule via polarization-dependent vibrational spectroscopy on charge-sensitive modes in the mid-infrared. [1] M. Dressel et al., Crystals 201, 2, 528-578 [2] F. Zamboroszky et al., Phys. Rev. B 66, (2022) 081103 [3] P. Auban-Senzier et al., J. Phys. IV France 114 (2004) 41 [4] R. Beyer, M. Dressel, to be published

infrared reflectivity; pressure; organic conductors

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