Charge density wave and metallic state coexistence in the multiband conductorTTF[Ni(dmit)2]2

Abstract

We have established a pressure-temperature phase diagram of $\mathrm{TTF}{[\mathrm{Ni}{(\mathrm{dmit})}_{2}]}_{2}$ based on spin susceptibility at ambient pressure as well as longitudinal and transverse resistivity measurements under pressure up to 30 kbar. The data were analyzed on the basis of first-principles density functional theory calculations. We were able to find several phase transitions and identify three different charge density wave (CDW) states which all coexist with a metallic state in a wide temperature range and superconductivity at the lowest temperatures. This metallicity arises from the development, upon cooling, of a two-dimensional band associated to the $\mathrm{Ni}{(\mathrm{dmit})}_{2}$ chains. At low pressure, two successive CDW transitions have been clearly identified and are associated to the successive nesting of two strongly one-dimensional bands: The LUMO and ${\mathrm{HOMO}}_{\mathrm{I}}$ of the $\mathrm{Ni}{(\mathrm{dmit})}_{2}$ chains. These two transitions merge into a single one at 12 kbar which probably corresponds to the partial nesting of a bunch of LUMOs into the ${\mathrm{HOMO}}_{\mathrm{I}}$'s. A maximum of this unique CDW transition temperature is observed at 19 kbar. The CDW instability associated to the LUMO band is announced by an important regime of Peierls-like fluctuations in the metallic state which give rise to the progressive development of a pseudogap in the spin susceptibility which has been quantitatively analyzed using the Lee-Rice-Anderson theory.