Resistively Detected NMR in GaAs/AlGaAs

Abstract

Since its development in the late 1940s, nuclear magnetic resonance (NMR) has emerged as a powerful technique for probing the local field distribution in liquid and solid matter as well as providing important information on spin and vortex dynamics. While significant progress has been achieved in NMR spectroscopy, conventional inductively detected NMR remains essentially a bulk technique that proves to be extremely difficult to scale down to systems of very small sizes. For the most part, NMR remains limited to systems with a total number of nuclear spins present in the sample exceeding ∼10¹⁶, hence prohibiting the NMR detection in a wide variety of systems. Recent advances in the engineering, design and fabrication of meso- and nanoscaled materials have resulted in an experimental measurement gap where conventional NMR techniques cannot be utilized because of the “too few spins” problem. For example, a GaAs/AlGaAs semiconductor heterostructure interface ∼30 nm wide has less than 10¹⁵ nuclear spins, a quantum dot ∼10⁶–10¹⁰ spins and a single carbon nanotube 10³ spins. The very few nuclei available in these systems makes traditional NMR measurements extremely difficult, if not totally impossible, unless the NMR detection scheme could be redefined in an entirely new way.

One appealing alternative to the conventional inductive NMR exists and makes it possible to obtain the nucleus’ point-of-view in GaAs-based semiconductors through a resistive detection. This approach seems promising to tackle a broader class of problems in systems of small sizes such as mesoscopic quantum dots and other nanostructures. We shall review here the state-of-the-art in the field of resistively detected NMR, and discuss recent advances such as the relaxation-time experiments and the development of pulsed techniques. Finally, we discuss how resistively detected NMR might be pushed towards the bottom so as to obtain a complete nucleus’ point-of-view of the nanoscale with “very little spins”.