A low temperature disordered phase of alpha-Pb/Ge(111)

TL;DR

This paper reports the discovery of a new disordered phase in alpha-Pb/Ge(111) at low temperatures, challenging previous assumptions about its ground state and linking the transition mechanism to frustrated antiferromagnetic models.

Contribution

It identifies a novel disordered phase at ~76 K in alpha-Pb/Ge(111) and maps its transition mechanism onto a frustrated spin Ising model.

Findings

Disordered phase appears at ~76 K

Transition incompatible with previous ground state assumptions

Mechanism linked to geometric frustration in triangular lattice

Abstract

A new structural phase transition has been observed at low temperatures for the one third of a monolayer (alpha phase) of Pb on Ge(111) using a variable-temperature scanning tunneling microscope. The well-known (r3xr3)R30 to (3x3) transition is accompanied by a new structural phase transition from (3x3) to a disordered phase at ~76 K. The formation of the new disordered phase is incompatible with the belief that the (3x3) phase is the ground state. The mechanism of the phase transition in this triangular lattice can be mapped onto antiferromagnetic spin Ising model, with the geometric frustration.