Title: Potential for High-temperature Superconductivity on a Silicon Platform.
When: Tuesday, June 13, 2017, at 12:00.
Place: Sala de Grados, Módulo 08, Facultad de Ciencias, Universidad Autónoma de Madrid.
Speaker: Hanno H. Weitering, The University of Tennessee, USA.
Mott insulators are an important class of materials that are supposed to be metallic according to the band theory of solids. However, band theory fails if the motion of the valence electrons in the crystal is strongly correlated. When Coulomb repulsions are strong, electrons may choose to ‘stay at home’ and the material ends up being non-conducting and often antiferromagnetic at low temperature. Carrier doping via e.g. chemical substitution can restore the metallicity but destroys magnetic order.
The rich physics of doped Mott insulators is at the heart of high-temperature superconductivity in complex oxide compounds, although the precise mechanism for high temperature superconductivity is still up for debate. Advances in this field would greatly benefit from the availability of new material systems with similar richness of physical phenomena, ideally those that are much less complex in structure and composition, and easier to model theoretically. Here we show that such a system could potentially be realized on a silicon surface. Adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half-filled dangling bonds. Modulation hole-doping of these dangling bonds unveils clear hallmarks of Mott physics, and additionally produces a sharp ‘van Hove’ singularity in the density of states just below the Fermi level. At a critical doping level, we observe a strong zero-bias anomaly in the local density of states, possibly signaling the formation of a magnetic or superconducting gap. These observations are remarkably similar to those made in complex oxide materials, including the high-temperature superconductors, but highly extraordinary within the realm of conventional sp-bonded semiconductor materials.