Spectroscopic Signatures of a Bandwidth-Controlled Mott Transition at the Surface of $1T\mathrm{\text{−}}{\mathrm{T}\mathrm{a}\mathrm{S}\mathrm{e}}_2$

High-resolution angle-resolved photoemission data show that a metal-insulator Mott transition occurs at the surface of the quasi-two-dimensional compound $1T\mathrm{\text{−}}{\mathrm{T}\mathrm{a}\mathrm{S}\mathrm{e}}_2$. The transition is driven by the narrowing of the Ta $5d$ band induced by a temperature-dependent modulation of the atomic positions. A dynamical mean-field theory calculation of the spectral function of the half-filled Hubbard model captures the main qualitative feature of the data, namely, the rapid transfer of spectral weight from the observed quasiparticle peak at the Fermi surface to the Hubbard bands, as the correlation gap opens up.

Figure 1

ARPES intensity maps of $1T\mathrm{\text{−}}{\mathrm{T}\mathrm{a}\mathrm{S}\mathrm{e}}_2$ at $T=300\mathrm{K}$ (left) and $T=70\mathrm{K}$ (right) measured along the $\Gamma M$ high-symmetry direction ($h\nu =21\mathrm{e}\mathrm{V}$). The arrows mark Fermi level crossings by the Ta “$d$” band at 300 K.

Figure 2

(a) ARPES spectra measured at $k=k_{F_1}$ between 300 and 70 K; (b) temperature dependence of the ARPES signal at the Fermi surface, showing a sharp break and a large hysteresis.

Figure 3

Temperature-dependent ARPES spectral function at $k=k_{F_1}$ ($h\nu =21\mathrm{e}\mathrm{V}$). The spectra have been obtained from the raw spectra $I(E)$ by symmetrization around $E_F$: $I*(E)=I(E)+I(-E)$.

Figure 4

Temperature-dependent spectral function $A(k_F,\omega )$ of the half-filled Hubbard model calculated within DMFT for the temperatures of Fig. 4. $U$ was fixed at $U=0.52\mathrm{e}\mathrm{V}$, and the bandwidth is chosen as $W=0.50\mathrm{e}\mathrm{V}$ at 300 K (solid line); 0.48 eV at 260 K (dashed line); 0.44 eV at 220 K (dash-dotted line); and 0.36 eV at 70 K (dotted line).