Andreev reflection spectroscopy on SnAs single crystals

Abstract

Binary compounds of SnT family(T= As, Sb, Te, S, Se, P) exhibit novel properties like superconductivity, topologically protected states etc. Some of these compounds crystallize in NaCl type structure or in layered structure, both of which are considered potentially important for hightemperature/unconventional superconductivity. It was previously shown that K-doped BaBiO 3 with NaCl type structure exhibits superconducting state below ∼ 30 K. SnAs has crystallographic configuration that is exactly similar to K-doped BaBiO 3 and this warrants for the investigation of superconductivity in this material. Previously it was reported that SnAs exhibits weakly coupled type I superconductivity with an energy gap of 0.7 meV. Recently, the electronic bandstructure calculations has hinted to the existence of possible topologically protected states in SnAs. This has motivated us to investigate the superconducting nature of SnAs using point contact Andreev reflection spectroscopy. Our investigation revealed that superconductivity in SnAs can be well explained within the BCS framework in the weak coupling limit.

Detailed magneto heat capacity analysis of SnAs topological superconductor

“…The obtained value of α from the fitted plot is 3.36, which is also lower than the BCS limit for weakly coupled superconductors. The obtained value of α, corresponds to the superconducting energy gap Δ(0) of 0.54 eV, which is comparable to that is obtained from STS measurements on the same sample [22] and as in reference [18]. As mentioned before, the only two reports available on heat capacity measurements of SnAs do contradict each other [18,21].…”

“…Magneto transport and AC susceptibility measurements show the presence of superconductivity around 4 K. The parameters obtained from magneto heat capacity measurements suggest SnAs to be a conventional BCS superconductor with isotropic superconducting gap. The obtained value of superconducting gap at absolute zero Δ(0) in our report is in good agreement with that obtained from STS measurements in references [18,22]. Also the superconductivity is observed above 180 Oe in both magneto transport and magneto heat capacity measurements as seen earlier in reference [18].…”

“…In reference [21], SnAs is reported to be within BCS weak coupling limit, on the other hand the same is shown to be well above the BCS weak coupling limit in reference [18]. Also, the scanning tunnelling spectroscopic (STS) measurements suggested SnAs to be a conventional superconductor with isotropic gap [18,22]. The order parameter obtained from STS measurements in both available reports [18,22], indicated that the superconductivity of SnAs is well defined under BCS weak coupling limit.…”

“…Also, the scanning tunnelling spectroscopic (STS) measurements suggested SnAs to be a conventional superconductor with isotropic gap [18,22]. The order parameter obtained from STS measurements in both available reports [18,22], indicated that the superconductivity of SnAs is well defined under BCS weak coupling limit. The contradiction between the two available reports on heat capacity measurements [18,21], motivates us to study more about the nature of bulk superconductivity of SnAs, through detailed analysis of magneto heat capacity measurements.…”

“…The superconducting properties of SnAs are though known from a long time [20], but its type of superconductivity is yet inconclusive [18][19][20][21][22][23]. Though SnAs is reported to be type-I superconductor in reference [21], yet there are clear indications towards weak type-II superconductivity in magnetization measurements in references [18,19].…”