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Register a new userProximity-Induced Superconductivity with Subgap Anomaly in Type II Weyl Semi-Metal WTe2
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Due to the non-trivial topological band structure in type-II Weyl semimetal Tungsten ditelluride (WTe2), unconventional properties may emerge in its superconducting phase. While realizing intrinsic superconductivity has been challenging in the type-II Weyl semimetal WTe2, proximity effect may open an avenue for the realization of superconductivity. Here, we report the observation of proximity-induced superconductivity with a long coherence length along c axis in WTe2 thin flakes based on a WTe2/NbSe2 van der Waals heterostructure. Interestingly, we also observe anomalous oscillations of the differential resistance during the transition from superconducting to normal state. Theoretical calculations show excellent agreement with experimental results, revealing that such a sub-gap anomaly is the intrinsic property of WTe2 in superconducting state induced by the proximity effect. Our findings enrich the understanding of superconducting phase of type-II Weyl semimetals, and pave the way for their future applications in topological quantum computing.
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The search for unconventional superconductivity in Weyl semimetal materials is currently an exciting pursuit, since such superconducting phases could potentially be topologically nontrivial and host exotic Majorana modes. The layered material TaIrTe4 is a newly predicted time-reversal invariant type II Weyl semimetal with minimum number of Weyl points. Here, we report the discovery of surface superconductivity in Weyl semimetal TaIrTe4. Our scanning tunneling microscopy/spectroscopy (STM/S) visualizes Fermi arc surface states of TaIrTe4 that are consistent with the previous angle-resolved photoemission spectroscopy (ARPES) results. By a systematic study based on STS at ultralow temperature, we observe uniform superconducting gaps on the sample surface. The superconductivity is further confirmed by electrical transport measurements at ultralow temperature, with an onset transition temperature (Tc) up to 1.54 K being observed. The normalized upper critical field h*(T/Tc) behavior and the stability of the superconductivity against the ferromagnet indicate that the discovered superconductivity is unconventional with the p-wave pairing. The systematic STS, thickness and angular dependent transport measurements reveal that the detected superconductivity is quasi-one-dimensional (quasi-1D) and occurs in the surface states. The discovery of the surface superconductivity in TaIrTe4 provides a new novel platform to explore topological superconductivity and Majorana modes.
We determine the band structure and spin texture of WTe2 by spin- and angle-resolved photoemission spectroscopy (SARPES). With the support of first-principles calculations, we reveal the existence of spin polarization of both the Fermi arc surface states and bulk Fermi pockets. Our results support WTe2 to be a type-II Weyl semimetal candidate and provide important information to understand its extremely large and nonsaturating magnetoresistance.
Very recently, NiTe2 has been reported to be a type II Dirac semimetal with Dirac nodes near the Fermi surface. Furthermore, it is unveiled that NiTe2 presents the Hall Effect, which is ascribed to orbital magnetoresistance. The physical properties behavior of NiTe2 under high pressure attracts us. In this paper, we investigate the electrical properties of polycrystalline NiTe2 by application of pressure ranging from 3.4GPa to 54.45Gpa. Superconductivity emerges at critical pressure 12GPa with a transition temperature of 3.7K, and Tc reaches its maximum, 6.4 K, at the pressure of 52.8GPa. Comparing with the superconductivity in MoP, we purposed the possibility of topological superconductivity in NiTe2. Two superconductivity transitions are observed with pressure increasing in single crystal.
A monopole harmonic superconductor is a novel topological phase of matter with topologically protected gap nodes that result from the non-trivial Berry phase structure of Cooper pairs. In this work we propose to realize a monopole superconductor by the proximity effect between a time-reversal broken Weyl semi-metal and an $s$-wave superconductor. Furthermore, we study the zero-energy vortex bound states in this system by projection methods and by exact solutions. The zero modes exhibit a non-trivial phase winding in real space as a result of the non-trivial winding of the order parameter in momentum space. By mapping the Hamiltonian to the $(1+1)$d Dirac Hamiltonian, it is shown that the zero modes, analogous to the Jackiw-Rebbi mode, are protected by the index theorem. Finally, we propose possible experimental realizations.
Quantum topological materials, exemplified by topological insulators, three-dimensional Dirac semimetals and Weyl semimetals, have attracted much attention recently because of their unique electronic structure and physical properties. Very lately it is proposed that the three-dimensional Weyl semimetals can be further classified into two types. In the type I Weyl semimetals, a topologically protected linear crossing of two bands, i.e., a Weyl point, occurs at the Fermi level resulting in a point-like Fermi surface. In the type II Weyl semimetals, the Weyl point emerges from a contact of an electron and a hole pocket at the boundary resulting in a highly tilted Weyl cone. In type II Weyl semimetals, the Lorentz invariance is violated and a fundamentally new kind of Weyl Fermions is produced that leads to new physical properties. WTe2 is interesting because it exhibits anomalously large magnetoresistance. It has ignited a new excitement because it is proposed to be the first candidate of realizing type II Weyl Fermions. Here we report our angle-resolved photoemission (ARPES) evidence on identifying the type II Weyl Fermion state in WTe2. By utilizing our latest generation laser-based ARPES system with superior energy and momentum resolutions, we have revealed a full picture on the electronic structure of WTe2. Clear surface state has been identified and its connection with the bulk electronic states in the momentum and energy space shows a good agreement with the calculated band structures with the type II Weyl states. Our results provide spectroscopic evidence on the observation of type II Weyl states in WTe2. It has laid a foundation for further exploration of novel phenomena and physical properties in the type II Weyl semimetals.
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