Conductance spectra of (Nb, Pb, In)/NbP superconductor/Weyl semimetal junctions

Abstract

The possibility of inducing superconductivity in Weyl semimetal through coupling its surface to a superconductor was investigated. A single crystal of NbP, grown by chemical vapor transport method, was carefully characterized by XRD, EDX, SEM, ARPES techniques and by electron transport measurements. The mobility spectrum of the carriers was determined and it was found that there are four separate sharp peaks visible, which indicates that the carriers participating in the conductance have four different (almost discrete) mobilities. For the studies of interface transmission, the (001) surface of the crystal was covered by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC current-voltage characteristics and AC differential conductance through the interfaces were investigated. The measurements were carried out as a function of temperature and the results were interpreted in terms of the modified Blonder-Tinkham-Klapwijk model. Upon cooling of the devices during which the metals become superconducting, qualitatively different behavior of each type of junctions was observed. The junctions with Nb and Pb show high interface transmission pointing out the Andreev reflection as a prevalent contribution to the subgap conductance. This also indicates that both Pb and Nb superconductors are promising candidates for further studies of the proximity-induced superconducting Weyl semimetals. However, in the case of In, an alloyed interface region is formed, which presumably excludes this metal from such studies.

From narrow-gap and semimagnetic semiconductors to spintronics and topological matter: a life with spins

“…In our lab, we found superconductivity in Kiev's bulk PbTe [205] and in IFPAN's bulk Pb 0.63 Sn 0.37 Se [22], presenting in both cases strong arguments that metallic Pb and Sn precipitates, respectively were a source of Cooper pairs. Somewhat related and also surprising were Andreev reflection results for In/PbTe [206] and In/NbP heterostructures [21], taken by Grzegorz Grabecki et al at IFPAN. The former pointed to T c magnitudes higher than that of metallic In.…”

“…In the simplest interpretation, In diffusion into PbTe resulted in superconducting Pb precipitates [206]. In contrast, the In/NbP data suggest the presence of a low-gap superconductivity, presumably appearing in the Weyl semimetal NbP, proximitized by the superconducting In [21].…”

“…Among others, Matthias Bode's STM group in Würzburg discovered, on surfaces of Szczerbakow's Pb 1−x Sn x Se, 1D topological Dirac cones adja-cent to odd surface step edges [20], presumably, the first observation of higher-order topological states. Present studies of topological surface bands, making used of wonderfully working Kraków's SOLARIS ARPES facilities, include Weyl semimetals [21] and ferromagnetic TCIs [22], also examined from a theoretical perspective [23,24].…”

Equilibrium current in a Weyl-semimetal - superconductor heterostructure

“…One prominent type of such heterostructures is the Josephson junction (SNS-heterostructure), which has been extensively studied theoretically exploring the influence of various types of superconducting pairing mechanisms [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], and has also been realized experimentally [19,[36][37][38][39][40]. Other examples of similar heterostructures are NS-type [17,20,[41][42][43][44][45][46][47][48][49][50][51], and NSN-type [52][53][54][55][56] heterostructures.…”

Connection between the semiconductor--superconductor transition and the spin-polarized superconducting phase in the honeycomb lattice

“…Relevant examples of such systems are superconductors containing the honeycomb sublattices (e.g., FePSe 3 [34], CrPS 4 [35], CrSiTe 3 [36], SnPS 3 [37], or Cu 2 I 2 Se 6 [38]) as well as certain transition metal dichalcogenides [39]. However, also interfaces between Dirac semimetals and superconductors can reveal similar properties [40][41][42][43][44]. Moreover, recent progress in the experimental realization of artificial lattices, e.g., the artificial honeycomb lattice created within optical lattices [45][46][47] or by atomic nanostructures [48], leads also to great opportunities of studying the described unique phenomena.…”