Investigation on synthesis and physical properties of metal doped picene solids

TL;DR

This study investigates the electronic structure, synthesis, and pressure effects of metal-doped picene, revealing a new synthesis method for K3picene with an 18 K superconducting transition and analyzing its properties.

Contribution

It introduces a selective synthesis method for K3picene with 18 K superconductivity and examines its pressure dependence and electron transfer characteristics.

Findings

Three electrons transferred per picene molecule in superconducting phase

Pressure dependence of Tc varies between phases, indicating complex mechanisms

New solution-based synthesis method for K3picene with 18 K transition

Abstract

We report electronic structure and physical properties of metal doped picene as well as selective synthesis of the phase exhibiting 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules. The charge transfer leads to a softening of Raman scattering peaks, which enables us to determine the number of transferred electrons. From this we have identified that three electrons are transferred to each picene molecule in the superconducting doped-picene solids. Second, we report the pressure dependence of Tc in 7 and 18 K phases of K3picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K3picene by a solution process with monomethylamine, CH3NH2. This method enables one to prepare selectively the K3picene sample exhibiting 18 K superconducting transition. The discovery of suitable way for preparing K3picene with Tc = 18 K may facilitate clarification of the mechanism of superconductivity.