Resistance measurements of a “111” type superconductor ${\text{Li}}_x\text{FeAs}$ $\left(x=0.8,1.0,1.1\right)$ were performed at high pressure. The superconductivity transition temperature $\left(T_c\right)$ is found to decrease almost linearly with increasing pressure and the pressure derivative, $d{T}_c/dP$, becomes smaller with increasing Li content. Electron spin resonance experiment at ambient pressure on a stoichometric sample shows gradual decrease in the spin moment and the loss of coherence of spin coupling as the temperature is lowered. A very weak Fe local moment is observed when the temperature is lowered to $T_c$. In situ synchrotron radiation powder x-ray diffraction at high pressure shows changes in the resistivity are not related to a structural transition.

• Received 12 March 2009

DOI:https://doi.org/10.1103/PhysRevB.80.014506