Linear resistivity at van Hove singularities in twisted bilayer WSe₂.

Abstract

Different mechanisms driving a linear temperature dependence of the resistivity <i>ρ</i> ∼ <i>T</i> at van Hove singularities (VHSs) or metal-insulator transitions when doping a Mott insulator are being debated intensively with competing theoretical proposals. We experimentally investigate this using the exceptional tunability of twisted bilayer (TB) WSe₂ by tracking the parameter regions where linear-in-<i>T</i> resistivity is found in dependency of displacement fields, filling, and magnetic fields. We find that even when the VHSs are tuned rather far away from the half-filling point and the Mott insulating transition is absent, the <i>T</i>-linear resistivity persists at the VHSs. When doping away from the VHSs, the <i>T</i>-linear behavior quickly transitions into a Fermi liquid behavior with a <i>T</i>² relation. No apparent dependency of the linear-in-<i>T</i> resistivity, besides a rather strong change of prefactor, is found when applying displacement fields as long as the filling is tuned to the VHSs, including D ∼ 0.28 V/nm where a high-order VHS is expected. Intriguingly, such non-Fermi liquid linear-in-<i>T</i> resistivity persists even when magnetic fields break the spin-degeneracy of the VHSs at which point two linear in <i>T</i> regions emerge, for each of the split VHSs separately. This points to a mechanism of enhanced scattering at generic VHSs rather than only at high-order VHSs or by a quantum critical point during a Mott transition. Our findings provide insights into the many-body consequences arising out of VHSs, especially the non-Fermi liquid behavior found in moiré materials.