Doping-Induced Superconductivity in the Topological Semimetal Mo₅Si₃

Abstract

Chemical doping of topological materials may provide a possible route for realizing topological superconductivity. However, all such cases known so far are based on chalcogenides. Here we report the discovery of superconductivity induced by Re doping in the topological semimetal Mo 5 Si 3 with a tetragonal structure. Partial substitution of Re for Mo in Mo 5−x Re x Si 3 results in an anisotropic shrinkage of the unit cell up to the solubility limit of approximately x = 2. Over a wide doping range (0.5 ≤ x ≤ 2), these silicides are found to be weakly coupled superconductors with a fully isotropic gap. T c increases monotonically with x from 1.67 to 5.78 K, the latter of which is the highest among superconductors of the same structural type. This trend in T c correlates well with the variation of the number of valence electrons and is mainly ascribed to the enhancement of electron−phonon coupling. In addition, band structure calculations reveal that superconducting Mo 5−x Re x Si 3 exhibits nontrivial band topology characterized by Z 2 invariants (1;000) or (1;111) depending on the Re doping level. Our results suggest that transition metal silicides are a fertile ground for the exploration of candidate topological superconductors.

Strong-coupling superconductivity with Tc ∼ 10.8 K induced by P doping in the topological semimetal Mo5Si3

“…Z 2 indexes for these two gaps are (0;111) and (0;000), respectively. Our results are consistent with previous studies [24,39], sug-gesting that bulk Mo 5 Si 3 (with SOC) falls into the weak topological insulator state. Unfortunately, this means that the TSSs in Mo 5 Si 3 are fragile, and are unlikely to survive with P doping, which inevitably introduces defects.…”

“…For the undoped sample Mo 5 Si 3 , ρ reads ~0.22 mΩ cm at 300 K and decreases monotonously with the decrease of temperature. ρ(T) for Mo 5 Si 3 shows no superconducting transitions down to 1.8 K. These results are in good agreement with those in the literature [24,29], where no superconductivity was observed above 0.15 K. P doping into Mo 5 Si 3 introduces superconductivity, as revealed by abrupt drops of ρ(T) curves for the doped samples. The region of the superconducting transitions is emphasized in Fig.…”

“…1c, the a-axis shrinks while the c-axis expands monotonously, indicating a successful P doping into Mo 5 Si 3 . This doping behavior is different from that in Mo 5−x Re x Si 3 , where only the a-axis was changed [24]. We note that the shrinkage of a-axis of Mo 5 SiP 2 compared with Mo 5 Si 3 is around 1.6%, while the changes of the lattice parameters of Mo 3 P impurity are less than 0.1%.…”

“…Recently, superconductivity was observed in Re-doped Mo 5 Si 3 , with a maximal T c of 5.8 K in Mo 3 Re 2 Si 3 [24]. Not only did Ref.…”

“…Not only did Ref. [24] set a record-high T c in W 5 Si 3 -type superconductors, it also emphasized the nontrivial band topology, making Mo 3 Re 2 Si 3 a candidate for topological superconductors. We noticed that, just like the cases of Cu/Sr/Nb-doped Bi 2 Se 3 [14][15][16][17]19], superconductivity was successfully induced by carrier doping in topological material Mo 5 Si 3 .…”