arXiv subjects

J. -B. Vaney

Publications and source records attributed to J. -B. Vaney.

4 recordsLinked to original sources

arXiv2026

Stabilization of a non-superconducting, orthorhombic phase by over-hydrogenating LaFeSiH

Chemical composition provides a powerful route to tune the electronic ground state of iron-based superconductors and other quantum materials, yet access to highly doped phases remains limited. Here we demonstrate that high-pressure thermal decomposition of hydrogen-rich precursors enables over-hydrogenation of LaFeSi. Using anthracene, we synthesize tetragonal superconducting LaFeSiH, including a single hydrogen site, while ammonia borane yields a structurally distorted over-hydrogenated phase, LaFeSiH1+x, with an orthorhombic structure. Chemical analysis reveal excess hydrogen (x ~ 0.6), implying a second H site in LaFeSiH1.6 whose localization and occupancy are determined by neutron diffraction. In contrast to metallic LaFeSi and superconducting LaFeSiH, orthorhombic LaFeSiH1.6 exhibits semiconductor-like behavior. Upon hydrogen release near 100 °C, it transforms into tetragonal superconducting LaFeSiH1+δ (δ << 0.6). These results establish the chemical flexibility of the layered LaFeSiX (X = H, O, F) family and provide access to a high hydrogen-doping regime, creating new opportunities to investigate superconductivity in Fe-based silicides.

cond-mat.supr-con↗

arXiv2023

Magnetic and structural properties of the iron silicide superconductor LaFeSiH

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{ö}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.

cond-mat.supr-con↗

arXiv2022

Superconductivity in the crystallogenide LaFeSiO$_{1-δ}$ with squeezed FeSi layers

Pnictogens and chalcogens are both viable anions for promoting Fe-based superconductivity and intense research activity in the related families has established systematic correlation between the Fe-anion height and the superconducting critical temperature $T_c$, with an optimum Fe-anion height of $\sim$ 1.38 Å. Here, we report the discovery of superconductivity in a novel compound LaFeSiO$_{1-δ}$ that incorporates a crystallogen element, Si, and challenges the above picture: considering the strongly squeezed Fe-Si height of 0.94 Å, the superconducting transition at $T_{c}$ = 10 K is unusually high. In the normal state, the resistivity displays non-Fermi-liquid behavior while NMR experiments evidence weak antiferromagnetic fluctuations. According to first-principles calculations, the Fermi surface of this material is dominated by hole pockets without nesting properties, which explains the strongly suppressed tendency towards magnetic order and suggests that the emergence of superconductivity materializes in a distinct set-up, as compared to the standard $s_\pm$- and $d$-wave electron-pocket-based situations. These properties and its simple-to-implement synthesis make LaFeSiO$_{1-δ}$ a particularly promising platform to study the interplay between structure, electron correlations and superconductivity.

cond-mat.supr-con↗

arXiv2020

Evidence of nodal superconductivity in LaFeSiH

Unconventional superconductivity has recently been discovered in the first iron-based superconducting silicide LaFeSiH. By using the complementary techniques of muon spin rotation, tunneling diode oscillator and density functional theory, we investigate the magnetic penetration depth and thereby the superconducting gap of this novel high-temperature superconductor. We find that the magnetic penetration depth displays a sub-$T^2$ behavior in the low-temperature regime below $T_c/3$, which evidences a nodal structure of the gap (or a gap with very deep minima). Even if the topology of the computed Fermi surface is compatible with the $s_\pm$-wave case with accidental nodes, its nesting and orbital-content features may eventually result in a $d$-wave state, more unusual for high-temperature superconductors of this class.

cond-mat.supr-con↗