Magnetic and structural properties of the iron silicide superconductor LaFeSiH

TL;DR

This study investigates the magnetic and structural properties of LaFeSiH, a superconductor with a Tc of about 10 K, revealing no magnetic order and characteristics similar to overdoped iron pnictides, suggesting potential for Tc enhancement.

Contribution

The paper provides comprehensive experimental evidence showing LaFeSiH is a homogeneous metal without magnetic or nematic instability, and compares its properties to overdoped iron pnictides, highlighting avenues for increasing Tc.

Findings

No long-range magnetic order detected.

LaFeSiH remains tetragonal down to 2 K.

Similar Fermi surface properties to overdoped iron pnictides.

Abstract

The magnetic and structural properties of the recently discovered pnictogen/chalcogen-free superconductor LaFeSiH ($T_c\simeq10$~K) have been investigated by $^{57}$Fe synchrotron M{\"o}ssbauer source (SMS) spectroscopy, x-ray and neutron powder diffraction and $^{29}$Si nuclear magnetic resonance spectroscopy (NMR). No sign of long range magnetic order or local moments has been detected in any of the measurements and LaFeSiH remains tetragonal down to 2 K. The activated temperature dependence of both the NMR Knight shift and the relaxation rate $1/T_1$ is analogous to that observed in strongly overdoped Fe-based superconductors. These results, together with the temperature-independent NMR linewidth, show that LaFeSiH is an homogeneous metal, far from any magnetic or nematic instability, and with similar Fermi surface properties as strongly overdoped iron pnictides. This raises the prospect of enhancing the $T_c$ of LaFeSiH by reducing its carrier concentration through appropriate chemical substitutions. Additional SMS spectroscopy measurements under hydrostatic pressure up to 18.8~GPa found no measurable hyperfine field.