Superconductivity induced at a point contact on the topological semimetal tungsten carbide

Abstract

We report the observation of local superconductivity induced at the point contact formed between a normal metal tip and WC -a triple point topological semimetal with super hardness. Remarkably, the maximum critical temperature is up to near 12 K but insensitive to the tip's magnetism. The lateral dimensions of the superconducting puddles were evaluated and the temperature dependencies of superconducting gap and upper critical field were also obtained. These results put constraints on the explanation of the induced superconductivity and pave a pathway for exploring topological superconductivity.Unconventional superconductors and topological materials have attracted tremendous attentions due to their novel physical properties and potential applications. Integration of superconductivity and topological nature may lead to new emergent phenomena such as exotic topological superconductivity, for the interesting interplay between electron pairing and the spin-orbit coupling [1][2][3][4]. Recently, superconductivity was induced at a point contact between a normal metal tip and the 3D Dirac semimetal Cd 3 As 2 [5, 6]. Soon after, similar phenomenon was reproduced in the Weyl semimetal TaAs [7,8]. In particular, the induced superconductivity could coexist with preserved topological properties in the line-nodal semimetal ZrSiS [9]. Such tip-induced superconductivity (TISC) is very exciting since it is extremely rare in common metals and provides a unique way of searching topological superconductivity [10]. Although the most likely origins of the TISC were speculated to be tip pressureinduced band reconstruction, confinement effect, charge carrier doping [7], or remarkable enhancement of density of states under the tip [9], the dominant mechanism remains elusive. Meanwhile, unconventional superconductivity has been proposed for Cd 3 As 2 , yet based on two distinct experimental observations, i.e., a pseudogap behavior above the critical temperature [5] or an abnormal spectral shape at low temperatures [6]. For TaAs, such unconventionality is still in debate [7,8]. Therefore, more evidences are desired to clarify this issue.Most recently, a new type of topological quasiparticles was proposed for the metals hosting symmetry-protected three-band crossings (three-fold degeneracy) near the Fermi level [11][12][13]. These triple point fermions were first observed in MoP [14] and the non-trivial topology of the new semimetal state was identified in WC subsequently [15]. As a triple point topological semimetal, WC can be regarded as an intermediate state between Dirac and Weyl semimetals with four-and two-fold degenerate points, respectively. Furthermore, the super hardness of WC ensures its topological band structure to be robust against tip pressure, providing an ideal platform to inspect the universality and mechanism of TISC in topological semimetals.In this work, we performed point contact experiments on WC using both non-magnetic and ferromagnetic normal metal tips. Local superconductivity with various lateral sizes could be i...

Formation of tungsten carbide by focused ion beam process: A route to high magnetic field resilient patterned superconducting nanostructures

“…A recent band structure calculation supported by ARPES data also identified non-trivial topological aspects of surface states of WC [53]. The interface of single-crystal WC and metal have shown superconductivity till considerably high magnetic fields [7,10]. The large interfacial area of the nanocrystals with the Ga-C composite may be fulfilling similar conditions in these samples.…”

“…There has been a number of efforts to find exotic superconductors (e.g FFLO, spin-triplet, topological ) in recent past which might compatible with relatively high magnetic field. Several methods including metal intercalation between layers of a material [5,6], applying high pressure, hard and soft tip contact [7][8][9] and interface between two materials [10,11] has been tried for achieving this. In this paper, we point out an emerging class of materials, composed of Ga and a heavy metal carbide, fabricated using FIB which are undoubtedly granular and highly disordered, but with H c2 significantly above the Pauli limit.…”

Applications of point-contact spectroscopy in the study of topological materials

“…从图 [4] . 另外, 少数点接触的H c2 (0)超过了泡利顺磁极限, 图 13 (网络版彩图) (a)-(c) WC上得到的三种典型的点接触电导谱(见正文) [122] ; (d) 在WC上使用不同材质针尖得到的T c 统计 图 [122] ; (e) 在TaAs 2 和NbAs 2 的(001)或(111)表面上使用不同材质针尖得到的T c 统计图 [128] Figure 13 (Color online) (a)-(c) Typical point-contact spectra obtained on WC (see in main text) [122]; (d) statistics of T c values achieved on WC with various metal tips [122]; (e) T c statistics for the (001) plane of TaAs 2 and the (001) and ( 111) planes of NbAs 2 [128].…”

Superconductivity and topological states in hexagonal TaC and NbC

“…Compared to the NaCl-type TMCs, there is another structure of TMCs with the same crystal structure as θ -TaN, 39,40 which exhibits a hexagonal space group. The study of θ -TaN type TMCs mainly focuses on the topological properties, such as the triply degenerate nodal topological semimetal of WC, 41,42 the spin–orbit coupling (SOC) induced nodal chain to the Weyl semimetal in HfC, 43 etc. By point contact, the superconductivity in hexagonal WC has also been observed, providing a path for exploring the topological superconductivity in hexagonal binary TMCs.…”

“…By point contact, the superconductivity in hexagonal WC has also been observed, providing a path for exploring the topological superconductivity in hexagonal binary TMCs. 42…”