Absence of metallicity in K-doped picene: Importance of electronic correlations

TL;DR

This study combines experimental photoelectron spectroscopy and advanced theoretical calculations to show that potassium-doped picene remains an insulator at certain doping levels, challenging previous claims of superconductivity.

Contribution

The paper provides the first combined experimental and theoretical evidence that K-doped picene is a Mott insulator at specific doping levels, emphasizing the importance of electronic correlations.

Findings

K-doped picene is a Mott insulator at x=1, 2, 3

Spectra always show a finite energy gap, indicating insulating behavior

Discrepancies with previous reports of superconductivity are discussed

Abstract

Potassium-doped picene (K$_x$picene) has recently been reported to be a superconductor at $x=3$ with critical temperatures up to 18 K. Here we study the electronic structure of K-doped picene films by photoelectron spectroscopy and {\it ab initio} density functional theory combined with dynamical mean-field theory (DFT+DMFT). Experimentally we observe that, except for spurious spectral weight due to the lack of a homogeneous chemical potential at low K-concentrations ($x \approx 1$), the spectra always display a finite energy gap. This result is supported by our DFT+DMFT calculations which provide clear evidence that K$_x$picene is a Mott insulator for integer doping concentrations $x=1$, 2, and 3. We discuss various scenarios to understand the discrepancies with previous reports of superconductivity and metallic behavior.