First Principles Calculations of Charge and Spin Density Waves of sqr3-Adsorbates on Semiconductors

TL;DR

This study uses ab-initio calculations to explore charge and spin density waves on sqr3-adsorbed semiconductor surfaces, revealing instabilities driven by narrow surface bands and magnetic interactions.

Contribution

It provides new insights into the electronic instabilities and magnetic behaviors of sqr3-adsorbed surfaces, including the first theoretical prediction of SDW formation.

Findings

Sqr3 paramagnetic surface unstable towards SDW with 3x3 periodicity.

Narrow surface state bands are key to charge and spin density wave instabilities.

Preliminary calculations on Si/Si(111) suggest interplay between Fermi surface and electron correlations.

Abstract

We present ab-initio electronic structure results on the surface of sqr3 adsorbates. In particular, we address the issue of metal-insulator instabilities, charge-density-waves (CDWs) or spin-density-waves (SDWs), driven by partly filled surface states and their 2D Fermi surface, and/or by the onset of magnetic instabilities. The focus is both on the newly discovered commensurate CDW transitions in the Pb/Ge(111) and Sn/Ge(111) structures, and on the puzzling semiconducting behavior of the Pb/Ge(111), K/Si(111):B and SiC(0001) surfaces. In all cases, the main factor driving the instability appears to be an extremely narrow surface state band. We have carried out so far preliminary calculations for the Si/Si(111) surface, chosen as our model system, within the gradient corrected local density (LDA+GC) and local spin density (LSD+GC) approximations, with the aim of understanding the possible interplay between 2D Fermi surface and electron correlations in the surface + adsorbate system. Our spin- unrestricted results show that the sqr3 paramagnetic surface is unstable towards a commensurate SDW with periodicity 3x3 and magnetization 1/3.