Iron-based superconductivity extended to the novel silicide LaFeSiH

We report the synthesis and characterization of the novel silicide LaFeSiH displaying superconductivity with onset at 11 K. We find that this pnictogen-free compound is isostructural to LaFeAsO, with a similar low-temperature tetragonal to orthorhombic distortion. Using density functional theory we show that this system is also a multiband metal in which the orthorhombic distortion is likely related to single-stripe antiferromagnetic order. Electrical resistivity and magnetic susceptibility measurements reveal that these features occur side by side with superconductivity, which is suppressed by external pressure.

Figure 1

Left: Room-temperature x-ray powder diffraction pattern of LaFeSiH ($p1$). Ticks indicate the Bragg peaks of the $P4/nmm$ structure of the main LaFeSiH phase while stars, crosses, and circles indicate extra peaks due to the secondary phases ${\mathrm{La}}_2{\mathrm{O}}_3$, $\alpha$-Fe, and La(Fe,${\mathrm{Si})}_{13}{\mathrm{H}}_x$, respectively, that could not be completely eliminated by annealing. The $\left(hk0\right)$ plane of the LaFeSiH single-crystal diffraction pattern at room temperature is shown in the inset ($s1$). Right: Ball-and-stick model of the crystal structure of LaFeSiH.

Figure 2

(a) Band structure and total DOS and PDOS of the Fe-$3d$ states. (b) Three-dimensional view of the Fermi surface and (c) cross section in the $k_z=0$ plane.

Figure 3

Relative difference between the $a$ and $b$ lattice parameters of LaFeSiH at 15 K as a function of pressure. Lines are guides to the eye.

Figure 4

Calculated Fe magnetic moment in the single-stripe AFM state (top) and energy difference with respect to the nonmagnetic state (bottom) as a function of pressure. The results obtained with LDA and PBE functionals are represented by blue and green points, respectively. Lines are guides to the eye.

Figure 5

Low-temperature resisitivity as a function of temperature measured in single-crystal LaFeSiH ($s2$) for different values of the magnetic field applied in the $ab$ plane. The inset shows the upper critical field as a function of temperature obtained from this data.

Figure 6

Superconducting onset as a function of pressure obtained from the resistance of the powder $p1$.

Figure 7

(a) Magnetization as a function of the external field at 2 K in $p1$. The diamagnetic response $dM/dH=-0.18$ evidences superconductivity in LaFeSiH. Inset: magnetization as a function of temperature at $B=1$ mT in $p2$, revealing an $\sim 64\%$ superconductor volume fraction in this powder sample. (b) Superconducting hysteresis loop obtained from the magnetization loop at $2\mathrm{K}$ (below $T_c$) by subtracting by the loop at 10 K (above $>T_c$) ($p2$). The gray points correspond to the same subtraction for the nonhydrogenated original LaFeSi powder, which contains the same secondary ferromagnetic phases but is not a superconductor (and hence displays no hysteresis).