Scanning Hall probe microscopy of vortex matter

Scanning Hall probe microscopy (SHPM) is a novel scanned probe magnetic imaging technique whereby the stray fields at the surface of a sample are mapped with a sub-micron semiconductor heterostructure Hall probe. In addition an integrated scanning tunnelling microscope (STM) or atomic force microscope (AFM) tip allows the simultaneous measurement of the sample topography, which can then be correlated with magnetic images. SHPM has several advantages over alternative methods; it is almost completely non-invasive, can be used over a very wide range of temperatures (0.3–300 K) and magnetic fields (0–7 T) and yields quantitative maps of the z-component of magnetic induction. The approach is particularly well suited to low temperature imaging of vortices in type II superconductors with very high signal:noise ratios and relatively high spatial resolution (>100 nm). This paper will introduce the design principles of SHPM including the choice of semiconductor heterostructure for different measurement conditions as well as surface tracking and scanning mechanisms. The full potential of the technique will be illustrated with results of vortex imaging studies of three distinct superconducting systems: (i) vortex chains in the “crossing lattices” regime of highly anisotropic cuprate superconductors, (ii) vortex–antivortex pairs spontaneously nucleated in ferromagnetic-superconductor hybrid structures, and (iii) vortices in the exotic p-wave superconductor Sr₂RuO₄ at milliKelvin temperatures.