Fig. 3: Two dimensional superconductivity of IrTe2 nanoflakes.
From: Superconductivity emerging from a stripe charge order in IrTe2 nanoflakes
a, Magnetic field dependence of ρ(H) of a 56-nm-thick IrTe2 nanoflake, measured with different field orientations θ at T = 0.35 K. b, Upper critical field Bc2 as a function of field angle θ for IrTe2 nanoflakes with different thickness (d) at T = 0.35 K, together with the fit (solid line) to the 2D Tinkham model. Inset: the anisotropy factor \({{\Gamma }}={B}_{c2}^{ab}\)/\({B}_{c2}^{c}\) as a function of d, following 1/d dependence (grey line). Schematic illustration shows the field orientation θ. c, Angle dependence of Bc2(θ) of IrTe2 nanoflakes with d = 56 and 140 nm at T = 0.35 K. Good agreement with the 2D Tinkham model (red), rather than the 3D Ginzburg-Landau model (black), confirms the 2D superconductivity. d, Normalised Bc2/Bc2(0) as a function of T/Tc for IrTe2 nanoflakes with different d. All data collapse into dashed lines described by 1 − T/Tc and \({(1-T/{T}_{c})}^{1/2}\) for B∥c (open circles) and B∥ab (solid circles), respectively. e, Ginzburg-Landau coherence length ξab (square) and the effective superconducting thickness dSC (circle) as a function of d. ξab is nearly independent of d, whereas dSC grows linearly with d (dSC ~ 0.8d) and exceeds ξc of doped bulk IrTe2. f, Schematic illustration of the size effect of vdW superconductors. In normal vdW superconductors with a large anisotropy ξc ≪ ξab, 2D superconductivity appears only for a-few-layer-thick crystals. In IrTe2 with a stripe order and the resulting cross-layer quasi-2D state, the increased ξc ~ ξab induces 2D superconductivity in relatively thick nanoflakes.
