Lateral imaging of the superconducting vortex lattice using Doppler-modulated scanning tunneling microscopy

By spatially mapping the Doppler effect of an in-plane magnetic field on the quasiparticle tunneling spectrum, we have laterally imaged the vortex lattice in superconducting 2H-NbSe2. Cryomagnetic scanning tunneling spectroscopy was performed at 300 mK on the ab-surface oriented parallel to the field H. Conductance images at zero bias show stripe patterns running along H, with the stripe separation varying as H^-0.5. Regions of higher zero-bias conductance show lower gap-edge conductance, consistent with spectral redistribution by spatially-modulated superfluid momentum. Our results are interpreted in terms of the interaction between vortical and screening currents, and demonstrate a general method for probing subsurface vortices.