Zero-bias anomaly in nano-scale hole-doped Mott insulators on a triangular silicon surface

TL;DR

This study investigates the zero-bias anomaly in nanoscale hole-doped Mott insulators on a silicon surface, revealing that the anomaly is mainly caused by a dynamical Coulomb blockade effect rather than superconductivity.

Contribution

It demonstrates that the zero-bias anomaly in nanoscale Mott insulators is primarily due to Coulomb blockade effects, with minimal influence from superconducting phenomena.

Findings

Zero-bias anomaly increases as domain size decreases.

Dynamical Coulomb blockade model fits the data better than superconductivity.

Oscillatory Coulomb staircase behavior observed in lightly-doped substrates.

Abstract

Adsorption of 1/3 monolayer of Sn on a heavily-doped p-type Si(111) substrate results in the formation of a hole-doped Mott insulator, with electronic properties that are remarkably similar to those of the high-Tc copper oxide compounds. In this work, we show that the maximum hole-density of this system increases with decreasing domain size as the area of the Mott insulating domains approaches the nanoscale regime. Concomitantly, scanning tunneling spectroscopy data at 4.4 K reveal an increasingly prominent zero bias anomaly (ZBA). We consider two different scenarios as potential mechanisms for this ZBA: chiral d_(x^2 -y^2 )+ id_xy wave superconductivity and a dynamical Coulomb blockade (DCB) effect. The latter arises due to the formation of a resistive depletion layer between the nano-domains and the substrate. Both models fit the tunneling spectra with weaker ZBAs, while the DCB model clearly fits better to spectra recorded at higher temperatures or from the smallest domains with the strongest ZBA. Consistently, STS spectra from the lightly-doped substrates display oscillatory behavior that can be attributed to conventional Coulomb staircase behavior, which becomes stronger for smaller sized domains. We conclude that the ZBA is predominantly due to a DCB effect, while a superconducting instability is absent or a minor contributing factor.