Observation of a Mott insulating ground state for Sn/Ge(111) at low temperature

TL;DR

This study demonstrates that Sn/Ge(111) exhibits a low-temperature Mott insulating ground state, characterized by a structural phase transition and a metal-insulator transition, confirming theoretical predictions for a 2D triangular lattice system.

Contribution

First experimental observation of a Mott insulator in Sn/Ge(111) at low temperatures, validating theoretical models of correlated electron behavior in 2D lattices.

Findings

Transition from (3x3) to (root-3xroot-3)R30 phase below 30 K

Loss of vertical distortion across the phase transition

Metal-insulator transition observed at low temperature

Abstract

We report an investigation on the properties of 0.33 ML of Sn on Ge(111) at temperatures down to 5 K. Low-energy electron diffraction and scanning tunneling microscopy show that the (3x3) phase formed at 200 K, reverts to a new (root-3xroot-3)R30 phase below 30 K. The vertical distortion characteristic of the (3x3) phase is lost across the phase transition. Angle-resolved photoemission experiments show that concomitantly with the structural phase transition, a metal-insulator phase transition takes place. In agreement with theoretical predictions, the (root-3xroot-3)R30 ground state is interpreted as the experimental realization of a Mott insulator for a narrow half-filled band in a two-dimensional triangular lattice.