Measurements of the normal state persistent current in gold mesoscopic rings

​Flux biased normal metal mesoscopic rings can sustain persistent current (PC) if their size is smaller than the electron dephasing length. The contribution to PC stemming from electron-electron interactions is proportional to the interaction coupling constant. Previous experiments on the PC in gold, silver and copper rings have suggested an attractive interaction, which would lead to a superconducting transition in these metals, in contrast to what has been observed to date. Some attempts to explain this discrepancy have considered the role of magnetic impurities and spurious rf radiation from the SQUID magnetometers used in previous experiments. We employ cantilever torque magnetometry to detect PC with high sensitivity, efficient background rejection, and in an electromagnetically clean environment. We have fabricated arrays of 100,000 rings on ultrasensitive silicon cantilevers. At high magnetic fields, we find that the PC agrees with single-particle theory. I will present current progress in the low-field regime where the interaction contribution is expected to dominate. I will also describe ongoing torque magnetometry studies of superconducting rings, and the prospects for using this technique to study topological effects in graphene.​​