We utilize a glasslike structural transition in order to induce a Mott metal-insulator transition in the quasi-two-dimensional organic charge-transfer salt κ-(BEDT-TTF)2Cu[N(CN)2Br]. In this material, the terminal ethylene groups of the BEDT-TTF molecules can adopt two different structural orientations within the crystal structure, namely eclipsed (E) and staggered (S) with the relative orientation of the outer C-C bonds being parallel and canted, respectively. These two conformations are thermally disordered at room temperature and undergo a glasslike ordering transition at Tg∼75 K. When cooling through Tg, a small fraction that depends on the cooling rate remains frozen in the S configuration, which is of slightly higher energy, corresponding to a controllable degree of structural disorder. We demonstrate that, when thermally coupled to a lowerature heat bath, a pulsed heating current through the sample causes a very fast relaxation with cooling rates at Tg of the order of several 1000 K/min. The freezing of the structural degrees of freedom causes a decrease of the electronic bandwidth W with increasing cooling rate, and hence a Mott metal-insulator transition as the system crosses the critical ratio (W/U)c of bandwidth to on-site Coulomb repulsion U. Due to the glassy character of the transition, the effect is persistent below Tg and can be reversibly repeated by melting the frozen configuration upon warming above Tg. Both by exploiting the characteristics of slowly changing relaxation times close to this temperature and by controlling the heating power, the materials can be fine-tuned across the Mott transition. A simple model allows for an estimate of the energy difference between the E and S state as well as the accompanying degree of frozen disorder in the population of the two orientations.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2014 Nov 26|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics