Nonreciprocal charge transport in noncentrosymmetric superconductors

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Science Advances  21 Apr 2017:
Vol. 3, no. 4, e1602390
DOI: 10.1126/sciadv.1602390
  • Fig. 1 Schematic illustration of nonreciprocal transport in noncentrosymmetric bulk crystals.

    (A) I-V curve in the normal state of a noncentrosymmetric crystal, whose nonreciprocal current is usually small. (The dashed line is the linear I-V relation.) Inset: Electron motion in the asymmetric potential, which represents the lack of inversion symmetry. (B) I-V curve in the resistive superconducting state, whose nonreciprocal current is much larger than that of the normal state below the critical current (Ic), whereas it remains unchanged at larger I. Inset: Enhanced nonreciprocity due to the coherence of Cooper pairs.

  • Fig. 2 Crystal and band structures of 2H-MoS2 and experimental setup.

    (A) Top and side views of a 2H-MoS2 2D crystal. In monolayers, spatial inversion symmetry is broken because the Mo and S sites are not equivalent, but the inversion symmetry is restored in 2H-type multilayers. (B) Schematic band structure of the conduction bottom of 2D MoS2. The magnetic field is applied perpendicular to the plane. Owing to the combination of the spin-orbit interaction and Zeeman effect, the band asymmetry appears between the K and K′ = −K points. Their spin splittings are 2(ΔSO + ΔZ) and 2(ΔSO − ΔZ), respectively. (C) Schematic image of a MoS2-EDLT. Vxx is a four-probe longitudinal voltage of the channel. Here, the channel direction was parallel to the zigzag edge (29).

  • Fig. 3 Magnetochiral anisotropy in ion-gated MoS2.

    (A) Temperature (T) dependence of sheet resistance Rsheet of a MoS2-EDLT at a gate voltage VG of 5.0 V. Inset: A close-up of the resistive transition. The Tc is 8.8 K as defined at the midpoint of the transition with sheet resistance Rsheet being 50% of the normal state. (B) Antisymmetrized sheet Embedded Image and Hall Embedded Image second harmonic magnetoresistance at 2 K. Compared to the signals of Embedded Image, the value of Embedded Image is much smaller. (C) Magnetoresistance at 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, and 15K at IDS of 17 μA. (D) Antisymmetrized second harmonic sheet magnetoresistance Embedded Image at 2 to 10 K. (E) Maximum of the Embedded Image as a function of temperature. (F) Temperature dependence of γ at the IDS of 17 μA. The γ suddenly increases up to ~1200 T−1 A−1 around the superconducting transition. Error bars are estimated by the uncertainty of the Rsheet because of the broad peak of the Embedded Image

  • Table 1 Character table for the point group C3v.
    A1+1+1+1zx2 + y2, z2z3, x(x2 − 3y2), z(x2 + y2)
    E+2−10(x, y), (Rx, Ry)(x2y2, xy), (xz, yz)(xz2, yz2), (xyz, z(x2y2)), (x(x2 + y2), y(x2 + y2))

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