Fluctuation, insulation and superconductivity: the pressuredependent phase-diagram of Rb2Mo6Se6
Résumé
The quasi-one-dimensional (q1D) material Rb2Mo6Se6 has been proposed to display a nontrivial combination of low-dimensional fluctuations and a dynamical charge density wave (CDW) at ambient pressure. This may lead to a progressive metal to insulator cross over at low temperature. To explore the link between the crystal dimensionality and this insulating instability, we have performed hydrostatic pressure-dependent electrical transport measurements on single crystals of Rb2Mo6Se6. At low pressure, we observe thermally-activated behavior consistent with a temperature-dependent gap Eg(T) opening below a characteristic temperature TRmin. Upon increasing the pressure TRmin initially rises, indicating a reinforcement of the low temperature insulating state despite a continuous reduction in Eg(P). We interpret this as a signature of suppressed fluctuations as the dimensionality of the electronic structure rises. However, TRmin drops above 8.8 GPa and superconductivity emerges at 12 GPa. Between 12-24.2 GPa the superconducting and insulating instabilities coexist, with superconductivity surviving up to the maximum attained pressure (52.8 GPa). Analysis of the magneto transport reveals two distinct regions: at high pressures the anisotropy gradually falls and the superconducting state appears unremarkable. In contrast, coexistence with the gapped insulating phase creates a superconducting dome. The emergence of a peak in the critical temperature Tc despite the depleted density of states is indicative of enhanced coupling. Our journey from the extreme 1D to 3D limits in this prototypical q1D metal reveals an intriguing relationship between superconducting and insulating ground states which is simultaneously competitive and symbiotic.
Domaines
Physique [physics]
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