Comparison of physical properties in BaAlSi and CaAlSi

Abstract

CaAlSi, with the AlB 2 -type structure, is a superconductor with relatively high T c of 7.7 K and the related compounds, SrAlSi and BaAlSi have the same crystal structure. Despite the fact that the density of states in SrAlSi and BaAlSi is higher than that of CaAlSi, T c of SrAlSi is 4.2 K and BaAlSi does not show superconductivity down to 2 K. We synthesize polycrystalline and single crystalline BaAlSi and compare their physical properties with those in CaAlSi. The transport and the specific heat measurements show the higher density of states in BaAlSi, consistent with the band structure calculations. We interpret that the absence of superconductivity in BaAlSi is due to the much weaker electron-phonon coupling constant compared with that in CaAlSi, because of the absence of the soft-phonon mode. In the course of the study, we find a superconductor with a composition close to Ba 2 Al 4 Si 3 .

Crystal structure, electronic structure, and vibrational properties ofMAlSiH(M=Ca,Sr,Ba)<

“…Our lattice parameters ͑Table I͒ are in good agreement with previous reports. [3][4][5][6][7][8] As mentioned earlier, the actual distribution of Al and Si on the hexagon layer is most difficult to establish experimentally. Although Al and Si may have a tendency to order, it is reasonable to assume that our specimens obtained from hightemperature arc-melting are to a large extent Al/Si disordered.…”

“…2 In this respect the ternary silicides MAlSi ͑M =Ca,Sr,Ba͒ have shown interesting behavior. [3][4][5][6][7][8] Here Al and Si atoms are commonly distributed over the site of the boron atoms forming hexagon layers and M atoms occupy the "intercalating" position. For CaAlSi and SrAlSi the superconducting temperatures T c are 7.8 and 5.1 K, respectively, while, remarkably, stoichiometric BaAlSi is not a superconductor above 2 K, but slightly silicon-rich, BaAl 0.95 Si 1.05 ͑T c = 2.8 K͒.…”

Two-gap to Single-gap Superconducting Transition on a Honeycomb Lattice in Ca$_{1-x}$Sr$_{x}$AlSi

“…Most recently, SrPtAs with a critical temperature of T c ≈ 2.4 K has been of great interest, since it was predicted to be the first chiral, and therefore first intrinsic topological superconductor with a d + id gap on a layered hexagonal lattice [19][20][21]. Among the ternary honeycomb-based superconductors has the MAlSi (M= Ca, Sr, Ba) family been most prominently discussed, with their critical temperature of up to T c = 7.8 K [22][23][24][25][26][27][28][29][30]. SrAlSi and BaAlSi crystallize in the AlB 2 -type structure with Al/Si honeycomb layers, which are intercalated by the earth-alkaline metal [25,26,30].…”

“…Among the ternary honeycomb-based superconductors has the MAlSi (M= Ca, Sr, Ba) family been most prominently discussed, with their critical temperature of up to T c = 7.8 K [22][23][24][25][26][27][28][29][30]. SrAlSi and BaAlSi crystallize in the AlB 2 -type structure with Al/Si honeycomb layers, which are intercalated by the earth-alkaline metal [25,26,30]. The structure of CaAlSi is related to the AlB 2 structure, but more complex.…”