Organic charge transfer salts are ideal model systems to investigate exotic physical phenomena. Our samples are quasi one- and two-dimensional crystals with a ½- or ¼-filled conduction band, typically. However, due to strong electron-electron repulsion the ground state is not metallic but insulating, exhibiting magnetic or charge order. Changing these electronic interactions, e.g., by varying the hydrostatic or chemical pressure, reveals a phase diagram with a similar structure as that of other strongly correlated materials (high temperature superconductivity, heavy fermions, …). Compression enhances the effective wave-function overlap, causing a suppression of the ordered state, eventually making the compound metallic - as expected from the original band structure. Between the insulating and conducting phases one finds - at low temperatures - unconventional superconductivity.
At the 1st Physics Institute we specialize in studying optical characteristics in the infrared spectral range at low temperatures. We are particularly interested in collective excitations and lattice vibrations as well as how these change at phase transitions.