Peierls transition in two-dimensional metallic monophosphate tungsten bronzes

摘要

The two-dimensional metallic bronzes made of ReO_3-type layers of MoO_6 or WO_6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t_(2g) transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2k_F critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D band structures out of three. The Peierls transition is achieved through a periodic lattice distortion (PLD), that we analyse, in the present work, for the monophosphate tungsten bronzes. The Peierls critical temperature decreases in presence of disorder, which breaks the electron-hole pairs forming the CDW condensate, and in presence of misfit between the PLD wave vector and the 2k_F nesting wave vector. The pair breaking effect accounts for the drop of the Peierls transition in the Na_xP_4W_(12)O_(44) (x<1) bronzes while the misfit effect, associated to a variation of the band filling, explains quantitatively the phase diagram of the K_xP_4W_8O_(32) (1