Non-charge-transfer origin of Tc Enhancement in a Surface Superconductor Si(111)-(root7xroot3)-In with Adsorbed Organic Molecules

TL;DR

This study demonstrates that organic molecule adsorption can enhance surface superconductor Tc without charge transfer, likely due to physical effects like push-back, expanding understanding of surface superconductivity modulation.

Contribution

It reveals a non-charge-transfer mechanism for Tc enhancement in a surface superconductor via organic molecule adsorption, supported by experimental and theoretical evidence.

Findings

ZnPc increases Tc by 11% without significant charge transfer.

Charge transfer is ruled out as the cause of Tc enhancement.

Push-back effect is proposed as a possible mechanism.

Abstract

The effects of adsorption of Zn-phthalocyanine (ZnPc) molecules on the superconductivity of the Si(111)-(root7xroot3)-In surface are studied through transport measurements under ultrahigh vacuum environment. The ZnPc molecules are found to increase the transition temperature Tc by 11% at maximum, which is about 2.7 times the Tc increase previously reported using CuPc. By contrast, angle-resolved photoemission spectroscopy measurements and ab initio calculations show that charge transfer from the In atomic layers to ZnPc is substantially smaller than that to CuPc. This clearly shows that charge transfer should be excluded as the origin of the increase in Tc. The push-back effect induced by physical adsorption of molecules is discussed as a possible mechanism for the Tc enhancement.