Layered Monophosphate Tungsten Bronzes [Ba(PO₄)₂]W_mO_{3m-3: 2D Metals with Locked Charge-Density-Wave Instabilities}

Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge-density-wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO4)(2)][WmO3m-3] (m=3, 4 and 5) denominated ' layered monophosphate tungsten bronzes ' (L-MPTB). It results from thick [Ba(PO4)(2)](4-) spacer layers disrupting the cationic metal-oxide 2D units and enforcing an overall trigonal structure. Their symmetries are preserved down to 1.8 K and the compounds show metallic behaviour with no clear anomaly as a function of temperature. However, their electronic structure displays the characteristic Fermi surface of previous bronzes derived from 5d W states with hidden nesting properties. By analogy with previous bronzes, such a Fermi surface should result into CDW order. Evidence of CDW order was only indirectly observed in the low-temperature specific heat, giving an exotic context at the crossover between stable 2D metals and CDW order.