Cooper pairs in non-centrosymmetric superconductors can acquire finite centre-of-mass momentum in the presence of an external magnetic field. Recent theory predicts that such finite-momentum pairing can lead to an asymmetric critical current, where a dissipationless supercurrent can flow along one direction but not in the opposite one. Here we report the discovery of a giant Josephson diode effect in Josephson junctions formed from a type-II Dirac semimetal, NiTe2. A distinguishing feature is that the asymmetry in the critical current depends sensitively on the magnitude and direction of an applied magnetic field and achieves its maximum value when the magnetic field is perpendicular to the current and is of the order of just 10 mT. Moreover, the asymmetry changes sign several times with an increasing field. These characteristic features are accounted for by a model based on finite-momentum Cooper pairing that largely originates from the Zeeman shift of spin-helical topological surface states. The finite pairing momentum is further established, and its value determined, from the evolution of the interference pattern under an in-plane magnetic field. The observed giant magnitude of the asymmetry in critical current and the clear exposition of its underlying mechanism paves the way to build novel superconducting computing devices using the Josephson diode effect.

No abstract

No abstract

Transition-metal dichalcogenides (WTe2 and MoTe2) have drawn much attention, recently, because of the nonsaturating extremely large magnetoresistance (XMR) observed in these compounds in addition to the predictions of likely type-II Weyl semimetals. Contrary to the topological insulators or Dirac semimetals where XMR is linearly dependent on the field, in WTe2 and MoTe2 the XMR is nonlinearly dependent on the field, suggesting an entirely different mechanism. Electron-hole compensation has been proposed as a mechanism of this nonsaturating XMR in WTe2, while it is yet to be clear in the case of MoTe2 which has an identical crystal structure of WTe2 at low temperatures. In this paper, we report low-energy electronic structure and Fermi surface topology of MoTe2 using angle-resolved photoemission spectrometry (ARPES) technique and first-principle calculations, and compare them with that of WTe2 to understand the mechanism of XMR. Our measurements demonstrate that MoTe2 is an uncompensated semimetal, contrary to WTe2 in which compensated electron-hole pockets have been identified, ruling out the applicability of charge compensation theory for the nonsaturating XMR in MoTe2. In this context, we also discuss the applicability of the existing other conjectures on the XMR of these compounds.Materials showing extremely large magnetoresistance (XMR) have potential applications in spintronics. Among them, the semimetals, WTe 2 and MoTe 2 , have attracted a great deal of research interests recently as they show nonsaturating extremely large MR 1,2 even at 60 T of applied field in addition to the prediction of Weylnodes 3,4 . While a negative MR is widely known in many magnetic materials 5-7 , positive MR has been noticed in some nonmagnetic materials [8][9][10][11] . Some of these nonmagnetic compounds such as Ag 2+δ Te/Se 9,11 , graphene 12 , Bi 2 Te 3 13,14 , and Cd 3 As 2 15,16 show linearly field dependent MR, while type-II Weyl semimetals (WTe 2 and MoTe 2 ) 1,2 , LaSb 17 and ZrSiS 18 show quadratic dependence of MR on the field. Charge compensation is explained as a mechanism of nonsaturating XMR in the compounds showing quadratic field dependent MR, while nontrivial band topology is thought to be responsible for the same in compounds showing linear field dependent MR. An ARPES report on WTe 2 demonstrated temperature dependent band structure that is consistent with the temperature dependent MR 19 , thus supporting the conjecture of the charge compensation 1 , while the other ARPES reports point to the importance of the spin orbit coupling and the impact of the thickness dependence of the charge compensation 20,21 . An ARPES report on LaSb showed temperature independent band structure, while MR is still temperature dependent 17 . Interestingly, a recent ARPES report on YSb has pointed that these two mechanisms could not explain the observed XMR in YSb which is neither a topological semimetal nor a Weyl semimetal 22 . All of these experimental observations are clearly demonstrating that there is no consensus yet on the...

Noncollinear antiferromagnets with a D019 (space group = 194, P63/mmc) hexagonal structure have garnered much attention for their potential applications in topological spintronics. Here, we report the deposition of continuous epitaxial thin films of such a material, Mn3Sn, and characterize their crystal structure using a combination of x-ray diffraction and transmission electron microscopy. Growth of Mn3Sn films with both (0001) c-axis orientation and (404 ̅ 3) texture is achieved. In the latter case, the thin films exhibit a small uncompensated Mn moment in the basal plane, quantified via magnetometry and x-ray magnetic circular dichroism experiments. This cannot account for the large anomalous Hall effect simultaneously observed in these films, even at room temperature, with magnitude σxy (µ0H = 0 T) = 21 Ω -1 cm -1 and coercive field µ0Hc = 1.3 T. We attribute the origin of this anomalous Hall effect to momentumspace Berry curvature arising from the symmetry-breaking inverse triangular spin structure of Mn3Sn. Upon cooling through the transition to a glassy ferromagnetic state at around 50 K, a peak in the Hall resistivity close to the coercive field indicates the onset of a topological Hall effect contribution, due to the emergence of a scalar spin chirality generating a real-space Berry phase. We demonstrate that the polarity of this topological Hall effect, and hence the chiral-nature of the noncoplanar magnetic structure driving it, can be controlled using different field cooling conditions.