Thickness‐Dependent Superconductivity in a Layered Electride on Silicon

Abstract

Layered materials exhibit a plethora of fascinating properties. The challenge is to make the materials into epitaxial films, preferably integrated with mature technological platforms to facilitate their potential applications. Progress in this direction can establish the film thickness as a valuable parameter to control various phenomena, superconductivity in particular. Here, a synthetic route to epitaxial films of SrAlSi, a layered superconducting electride, on silicon is designed. A set of films ranging in thickness is synthesized employing a silicene‐based template. Their structure and superconductivity are explored by a combination of techniques. Two regimes of TC dependence on the film thickness are identified, the coherence length being the crossover parameter. The results can be extended to syntheses of other honeycomb‐lattice ternary compounds on Si or Ge exhibiting superconducting, magnetic, and other properties.

Engineering of a Layered Ferromagnet via Graphitization: An Overlooked Polymorph of GdAlSi

“…To avoid this problem, we employ silicon as a substrate to synthesize GdAlSi. In this case, the substrate serves also as a reactant; the right amount of Si, controlled by the fluxes of Gd and Al, is supplied to the surface via the efficient vacancy mechanism. ,, Third, the substrate should stabilize the intended polymorph structure, i.e., have the same symmetry and matching lattice parameters. Therefore, we employ the (111) face of silicon: its surface represents a covalently bound silicene of the honeycomb structure compatible with the graphene-like AlSi layer.…”

“…To synthesize the layered (trigonal) polymorph of GdAlSi, we remove the natural oxide from the Si(111) surface to produce the characteristic 7 × 7 reconstruction and then deposit stoichiometric amounts of Gd and Al at the heated substrate (see the Materials and Methods section). It should be noted that the synthesis does not require any template layers; this is in contrast to the MBE synthesis of SrAlSi on Si(111) involving a self-sacrificial template of SrSi 2 for epitaxy. The procedure results in the layer-by-layer growth of the monocrystalline trigonal polymorph.…”

“…However, we can exploit the idea of isoelectronicity, useful in materials science: , replacement of half of Si atoms with Al to compensate the extra electrons from Gd suggests a material of the GdAlSi stoichiometry (see Figure a,b) isoelectronic to EuSi 2 (in both compounds, the valence electron count is equal to 10). The graphene-like structure of the AlSi anionic layer is well known in CaAlSi and SrAlSi, studied extensively for their superconducting properties. It should also be noted that rare-earth materials with different graphene-like anionic layers are established as candidates for realizing magnetically tuned topological properties .…”