Fig. 4: Chiral ground state and comparison with spectroscopic measurements.
From: Friedel oscillations and chiral superconductivity in monolayer NbSe2
a Square root of the average square amplitude of the first three gaps solving the self-consistent gap equation as a function of temperature. The thick curve is the solution with the lowest free energy; its colour encodes the ratio Rch of the contribution from a purely chiral mixture px + ipy of the two nematic solutions. The stars indicate the position at which the fits to the experimental curves in panel e were performed. b At T = 340 mK the gap equation predicts a fully gapped chiral phase of p + ip type. The phase of the order parameter winds clockwise around each contiguous Fermi surface. c Free energy per electronic state for the first three gap solutions, calculated in the range of energies ± 2 meV. The absence of nodes makes the chiral solution the favoured solution at low T. d Differential conductance spectra, with curves offset for clarity, recorded by STM at 340 mK, at different positions along a NbSe2 monolayer grown on a bilayer graphene/SiC(0001) substrate. A clear hard gap is observed, which can be fitted using the chiral gap in (a). e One of the experimental dI/dV curves in (d), fitted with the gaps Δkσ obtained from the nematic and chiral solutions of the self-consistent gap equation (see the marker in a). A very good agreement is found for the chiral solution on the Γ Fermi surface; the nematic ones display a clear V-shape gap that departs from the experimental data. f Experimental traces for different temperatures and corresponding theoretical fits with the leading Δch shown in (b, c).
