Fermi Surface of Metallic ${\mathrm{V}}_2{\mathrm{O}}_3$ from Angle-Resolved Photoemission: Mid-level Filling of $e_g^{\pi }$ Bands

Using angle resolved photoemission spectroscopy, we report the first band dispersions and distinct features of the bulk Fermi surface (FS) in the paramagnetic metallic phase of the prototypical metal-insulator transition material ${\mathrm{V}}_2{\mathrm{O}}_3$. Along the $c$ axis we observe both an electron pocket and a triangular holelike FS topology, showing that both V $3d$ $a_{1g}$ and $e_g^{\pi }$ states contribute to the FS. These results challenge the existing correlation-enhanced crystal field splitting theoretical explanation for the transition mechanism and pave the way for the solution of this mystery.

Figure 1

(a) Rhombohedral primitive cell containing two ${\mathrm{V}}_2{\mathrm{O}}_3$ formula units (four blue V atoms), surrounded by the nonprimitive hexagonal unit cell. The red hexagonal unit vectors measure $a=4.94\AA$ and $c=13.99\AA$. (b) Brillouin zone for the rhombohedral unit cell of ${\mathrm{V}}_2{\mathrm{O}}_3$ paramagnetic metallic phase. (c) Electronic structure of a ${\mathrm{V}}_2{\mathrm{O}}_3$ (0001) polished single crystal along normal emission for $T=200\mathrm{K}$. Wide Fermi surface slices in the plane at the upper half BZ height (360 eV); in the $\mathrm{\Gamma }$ plane (320 eV), $k_z=9.5{\AA }^{-1}$ but labeled as $k_z=0$ for simplicity; and in the plane at the lower half BZ height (280 eV), as indicated by dashed curves in (b).

Figure 2

Angle dependent $\mathrm{\Gamma }$ point electron pocket dispersion (a) image and (b) stack plot measured at $h\nu =88\mathrm{eV}$ for a (1000) surface. (c) Photon dependent $\mathrm{\Gamma }$ point electron pocket measured at $h\nu =670\mathrm{eV}$ for the (0001) surface. (d) ${\mathrm{V}}_2{\mathrm{O}}_3$ (0001) photon energy scan along normal emission, highlighting V $3d$ intensities down to $-2\mathrm{eV}$ and O $2p$ bands dispersing between $-4\mathrm{eV}$ and $-8\mathrm{eV}$. Vertical lines indicate locations of $\mathrm{\Gamma }$ points along the $c$ axis.

Figure 3

(a) Triangular feature measured at 180 eV showing three arclike pieces converging at the corners of the triangle. (b) Holelike energy dispersion cut through the triangular feature as indicated by the yellow dashed line in panel (a).

Figure 4

(a) Top view of the theoretical Fermi surface of a nonmagnetic $\mathrm{DFT}+U$ (6.5 eV) calculation including both electron (blue) and hole (purple) sheets. (b) $k_z=0.4{\AA }^{-1}$ image cut of Lorentzian $k$-broadened Fermi-edge contours. (c) V $3d$ band structure for the same calculation with highlighting of the $a_{1g}$ orbital character (fat line).