Nearly isotropic superconductivity in the layered Weyl semimetal WTe2 at 98.5 kbar

Abstract

Layered transition metal dichalcogenide WTe2 has recently attracted significant attention due to the discovery of an extremely large magnetoresistance, a predicted type-II Weyl semimetallic state, and the pressure-induced superconducting state. By a careful measurement of the superconducting upper critical fields as a function of the magnetic field angle at a pressure as high as 98.5 kbar, we provide the first detailed examination of the dimensionality of the superconducting condensate in WTe2. Despite the layered crystal structure, the upper critical field exhibits a negligible field anisotropy. The angular dependence of the upper critical field can be satisfactorily described by the anisotropic mass model from 2.2 K (T /Tc ∼ 0.67) to 0.03 K (T /Tc ∼ 0.01), with a practically identical anisotropy factor γ ∼ 1.7. The temperature dependence of the upper critical field, determined for both H ⊥ ab and H // ab, can be understood by a conventional orbital depairing mechanism. Comparison of the upper critical fields along the two orthogonal field directions results in the same value of γ ∼ 1.7, leading to a temperature independent anisotropy factor from near Tc to < 0.01Tc. Our findings thus identify WTe2 as a nearly isotropic superconductor, with an anisotropy factor among one of the lowest known in superconducting transition metal dichalcogenides.The discovery of an extremely large and non-saturating magnetoresistance in semimetallic WTe 2 [1] has generated considerable research efforts [2][3][4][5][6][7][8][9][10][11]. The interest is further intensified with the prediction that WTe 2 can be a type-II Weyl semimetal, in which Weyl fermions emerge at the border between electron and hole pockets [12]. The crystal structure of WTe 2 consists of weaklybonded block-layers of W-Te atoms along the c direction. The layered nature of WTe 2 has facilitated the fabrication of devices based on thin layers of WTe 2 , enabling the application of gate voltage, and hence further exploration of fundamental physical properties in a controllable manner [8,[13][14][15][16].Another powerful tool to tune the properties of WTe 2 is pressure. With the application of pressure, superconductivity has been successfully induced in the bulk WTe 2 [17,18]. Although the temperature-pressure phase diagrams reported by two groups [17,18] are quite different, some qualitative similarities can still be observed. First, the superconducting transition temperature (T c ) takes a dome-shaped pressure dependence, with a maximum onset T c between 6.5 K and 7 K. Second, the magnetoresistance is significantly suppressed when the superconducting state sets in. In the work of Pan et al.[17], superconductivity can be induced with a pressure as low as ∼25 kbar, which is close to the pressure range where a subtle structural transformation from T d phase to 1T phase was detected via powder X-ray diffraction and Raman spectroscopy [19,20]. However, these results contradict the study of Kang et al. [18], which claims that the structure * skgoh@phy.cuhk.edu.hk of WTe...

Superconductivity in doped Weyl semimetal Mo$_{0.9}$Ir$_{0.1}$Te$_{2}$ with broken inversion symmetry

“…The nature of H C2 (θ) is in sharp contrast to pressure-induced two-dimensional superconductivity though the γ value is comparable [40]. Similar type of feature in H C2 (θ) has observed in 3D-anisotropic superconductor 2H-NbSe 2 [37][38][39], WTe 2 [41], and gated MoS 2 [42]. Furthermore, the in-plane, ξ GL and out-of-plane coherence lengths ξ ⊥ GL at T = 1.8 K can be extracted from the H C2 data, giving 247 and 166 Å.…”

A Review of the Characteristics, Synthesis, and Thermodynamics of Type-II Weyl Semimetal WTe2

“…Actually, the rebuilding of the Fermi surface depends on the anisotropy of lattice, and the a-axis, b-axis, and c-axis are compressed by 0.6%, 3.3% and 6.5% respectively. An interesting thing is that the anisotropy of superconductivity becomes very weak at 98.5 kpa by changing the magnetic field angle [ 39 ]. The critical temperature of superconductivity can also be enhanced by in-plane magnetic fields, although it may suppress the superconductivity because of the competition between thermodynamic and magnetic energies [ 40 ].…”

Transverse conductance in a three-dimensional Weyl semimetal and Weyl superconductor hybrid under a strong magnetic field

“…The integration and the sum in Eqs. (20) and (21) are taken over all the allowed channels specified by the energies E N (X k y , k z ). The reflection probabilities of electronlike and holelike quasiparticle states at the left and the right interfaces of WSM/SWSMs are given by R (e) N,X ky ,k z ,AL = T (he) N,X ky ,k z ,LD , R (e) N,X ky ,k z ,AR = T (he) N,X ky ,k z ,RU , R (h) N,X ky ,k z ,AL = T (eh) N,X ky ,k z ,LD , and R (h) N,X ky ,k z ,AR = T (eh) N,X ky ,k z ,RU , respectively, where T (ab) N,X ky ,k z ,ij is the transmission probability of the mode (N, X k y , k z ) from the type b quasiparticles in terminal j to the type a quasiparticles in terminal i, a and b represent the electronlike (e) and the holelike (h) quasiparticles, and i, j (= L, R, U, D) note the left, right, up, and down terminals, respectively.…”

“…Besides UPt 3 , the unconventional superconductivity is also discovered by hard point contact on the WSM TaAs crystals [16,17]. Experimentally, the superconducting states in the WSM have also been studied in other SWSMs, such as MoTe 2 , WTe 2 , TaP, and TaIrTe 4 [18][19][20][21][22][23].…”