Identification of the crystal structures of two superconducting phases for potassium-doped picene

TL;DR

This study uses first principles calculations and X-ray diffraction simulations to identify the crystal structures of two superconducting phases in potassium-doped picene, explaining their different transition temperatures and electronic properties.

Contribution

It systematically determines the crystal structures of two superconducting phases in potassium-doped picene, linking structure to superconducting behavior.

Findings

K2picene is a semiconducting phase with T_c of 7 K.

K3picene is a metallic phase with T_c of 18 K.

Distinct structures explain the two superconducting phases.

Abstract

By the first principles calculations and X-ray diffraction simulations, we perform a systematic study of multiple superconducting phases of potassium-doped picene [Nature {\bf464} 76, 2010]. The combination of optimized lattice parameters, formation energy, and simulated X-ray diffraction spectra indicates that the superconducting phase with transition temperature (T$_c$) of 7 K corresponds to a charge doped K$_2$picene, which is semiconducting with a 0.1 eV energy gap, while the superconducting phase with T$_c$=18 K corresponds to a metallic K$_3$picene. The distinct crystal and electronic structures of K$_2$picene and K$_3$picene provide a reasonable explanation of two superconducting phases in potassium-doped picene.