Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-($\sqrt{3}\times \sqrt{3}$)-R30$^\textrm{o}$

TL;DR

This study reports the direct observation of a pseudogap in a modulation-doped Mott insulator using advanced microscopy, revealing its robustness and dependence on temperature and spatial confinement, and drawing parallels to cuprate superconductors.

Contribution

It provides the first experimental evidence of a pseudogap in a modulation-doped Mott insulator, highlighting its characteristics and relation to high-temperature superconductivity.

Findings

Universal pseudogap observed around the Fermi level in underdoped regions

Pseudogap remains stable under magnetic field and Sn vacancies

Pseudogap size varies with temperature and spatial confinement

Abstract

Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a combinatorial molecular beam epitaxy system integrated with cryogenic scanning tunneling microscopy, we investigate the electronic structure of a modulation-doped Mott insulator Sn/Si(111)-($\sqrt{3}\times \sqrt{3}$)-R30$^\textrm{o}$. In underdoped regions, we observe a universal pseudogap opening around the Fermi level, which changes little with the applied magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared out at elevated temperatures and alters in size with the spatial confinement of the Mott insulating phase. Our findings, along with the previously observed superconductivity at a higher doping level, are highly reminiscent of the electronic phase diagram in the doped copper oxide compounds.