Abstract
WTe2, as a type-II Weyl semimetal, has 2D Fermi arcs on the (001) surface in the bulk and 1D helical edge states in its monolayer. These features have recently attracted wide attention in condensed matter physics. However, in the intermediate regime between the bulk and monolayer, the edge states have not been resolved owing to its closed band gap which makes the bulk states dominant. Here, we report the signatures of the edge superconductivity by superconducting quantum interference measurements in multilayer WTe2 Josephson junctions and we directly map the localized supercurrent. In thick WTe2 (n}{}sim 60{rm{ nm}}), the supercurrent is uniformly distributed by bulk states with symmetric Josephson effect (n}{}| {I_c^ + ( B )} | {=} | {I_c^ - ( B )} | ). In thin WTe2 (10 nm), however, the supercurrent becomes confined to the edge and its width reaches up to n}{}1.4{rm{ mu m }}and exhibits non-symmetric behavior n}{}| {I_c^ + ( B )} | ne | {I_c^ - ( B )} |. The ability to tune the edge domination by changing thickness and the edge superconductivity establishes WTe2 as a promising topological system with exotic quantum phases and a rich physics.
Highlights
Layered WTe2 was suggested as the first material candidate to be a type-II Weyl semimetal, where eight separated Weyl points exist in the bulk and topological Fermi arcs occur on the (001) crystal surfaces owing to the reflection symmetry [1]
When the thickness is reduced to the monolayer, WTe2 turns to be a quantum spin Hall insulator with edge states [3], which have been demonstrated in numerous experiments involving low-temperature transport [4,5], angle-resolved photoelectron spectroscopy [6], scanning tunneling microscopy [7,8], and microwave impedance microscopy [9]
By studying the Fraunhofer interference, our measurements provide the supercurrent distribution in type-II Weyl semimetal WTe2
Summary
Layered WTe2 was suggested as the first material candidate to be a type-II Weyl semimetal, where eight separated Weyl points exist in the bulk and topological Fermi arcs occur on the (001) crystal surfaces owing to the reflection symmetry [1]. When the thickness is reduced to the monolayer, WTe2 turns to be a quantum spin Hall insulator with edge states [3], which have been demonstrated in numerous experiments involving low-temperature transport [4,5], angle-resolved photoelectron spectroscopy [6], scanning tunneling microscopy [7,8], and microwave impedance microscopy [9]. While the boundary modes of WTe2 have been well studied in both the 3D and 2D limits [11,12], in multilayers these modes become rather complicated due to the intervening bulk and edge states and they remain largely unexplored. In Nb/Bi2Te3/Nb Josephson junctions the surface states enable the ballistic Josephson current rather than the diffusive bulk transport [14]. The supercurrent distribution in real space can be quantitatively extracted from the superconducting quantum interference (SQI)
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