Enhanced Superconductivity by Rare-earth Metal-doping in Phenanthrene

TL;DR

This study reports the synthesis of La- and Sm-doped phenanthrene, discovering superconductivity around 6 K, with evidence suggesting unconventional pairing mechanisms and charge transfer effects similar to other doped phenanthrene superconductors.

Contribution

First demonstration of La- and Sm-doped phenanthrene superconductors with enhanced $T_c$ and analysis of their unconventional superconductivity characteristics.

Findings

Superconductivity at ~6 K in La- and Sm-doped phenanthrene.

Superconducting shielding fractions of 46.1% and 49.8%.

Charge transfer effects consistent with other doped phenanthrenes.

Abstract

We successfully synthesized La- and Sm-doped phenanthrene powder samples and discovered superconductivity at $T_{\rm c}$ around 6 K in them. The $T_{\rm c}$s are 6.1 K for LaPhenanthrene and 6.0 K for SmPhenanthrene, which are enhanced by about 1 K and 0.5 K compared to those in $A_3$Phenanthrene ($A$=K and Rb) and in $Ae_{1.5}$Phenanthrene ($Ae$ = Sr and Ba) superconductors respectively. The superconductive shielding fractions for LaPhenanthrene and SmPhenanthrene are 46.1%$ and 49.8$%$ at 2 K, respectively. The little effect of the doping of the magnetic ion Sm$^{3+}$ on $T_c$ and the positive pressure dependence coefficient on $T_{\rm c}$ strongly suggests unconventional superconductivity in the doped phenanthrene superconductors. The charge transfer to organic molecules from dopants of La and Sm induces a redshift of 7 cm$^{-1}$ per electron for the mode at 1441 cm$^{-1}$ in the Raman spectra, which is almost the same as those observed in $A_3$Phenanthrene ($A$=K and Rb) and $Ae_{1.5}$Phenanthrene ($Ae$ = Sr and Ba) superconductors.