Signatures of the order parameter of a superconducting adatom layer in quasiparticle interference patterns*

Superconductivity has been observed in a 2D triangular lattice of Sn adatoms deposited on a Si (111) surface. As with any novel superconductor, identifying the symmetry of the superconducting order parameter is of the utmost importance, in order to shed light on the underlying pairing mechanism. To that end, we calculate the quasiparticle interference (QPI) patterns which would result from several putative order parameters, for scattering from charge disorder (impurities) and order parameter disorder (vortices). These patterns can be obtained experimentally as the Fourier transform of the real-space local density of states, measured by scanning tunneling spectroscopy. By performing the experiment in a varying magnetic field, the relative contributions to the QPI pattern from charge scattering and vortex scattering can be tuned. We show that characteristic differences between the charge and vortex scattering signals, at particular momentum transfers, can be used to distinguish between order parameters with different angular momenta.