Development of tailored scanning probes to study condensed matter systems at the nanoscale: From high mobility two-dimensional electron systems to the nitrogen-vacancy center in diamond

High mobility electron systems have traditionally been difficult to spatially probe on a local scale because they are typically found at buried semiconductor interfaces instead of surfaces. I will begin by introducing a new technique that allows for local tunneling into a high mobility two-dimensional electron system (2DES), virtual scanning tunneling microscopy (VSTM). In VSTM, a specially designed bilayer GaAs/AlGaAs heterostructure is utilized where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating. Scanning gate microscopy measurements on these samples will be presented, which show that the local tunneling can be controlled on a length scale approaching the Fermi wavelength. An overview of the system built to carry out these measurements in a cryogen-free dilution refrigerator will also be described, which is able to achieve electron temperatures down to 45 mK.

In the second part of the talk, I will transition to a complimentary system that also is amenable to integration with scanning probes, the nitrogen-vacancy (NV) center in diamond. The NV center is an atomic scale defect in the diamond lattice that has recently been shown to have electronic and optical properties that render it very useful as a magnetic sensor. One sensing scheme, relaxometry, relies on measuring the spin relaxation of the NV as it interacts with a paramagnetic sample. One element well suited for relaxometry studies is gadolinium, which is commonly utilized in MRI contrast agents due to its large unpaired electron spin (S=7/2). I will describe our initial efforts to perform scanning relaxometry with Gd, where the Gd-NV separation can be controlled with a scanning probe tip. This opens the door to scanning relaxometry with single Gd spin sensitivity, with future applications in single molecule sensing.