Fermi-surface analysis of a quasi-two-dimensional monophosphate tungsten bronze

The ${\mathrm{P}}_4{\mathrm{W}}_8{\mathrm{O}}_{32}$ compound is a member of the low-dimensional monophosphate tungsten bronzes family whose reduced dimensionality induces electronic instabilities such as charge-density waves (CDWs). We report here the direct mapping of the Fermi surface (FS) of this compound at room temperature using synchrotron-radiation angle-resolved photoemission. The recorded FS images confirm the superimposition of three nested sheets, as proposed by the hidden-nesting model. We found two well defined parallel stripes along the $\overline{\Gamma \mathrm{Y}}$ direction as well as a crosslike feature. Moreover, the small FS splitting predicted by ab initio calculations was distinguished in the experimental data. To extract quantitative information on the CDW phase transitions, the values of the nesting vectors were also determined from the FS topology. The obtained values were in excellent agreement with existing tight-binding calculations, although the accord was even better with the recently published ab initio theoretical predictions.