Ning Lu

Date of Award

Spring 2019

Document Type

Open Access Dissertation


Physics and Astronomy

First Advisor

Scott Crittenden


An electron interferometer was designed and fabricated via a normal metal (supercon- ductor)/insulator/ferromagnet non-local lateral spin valve with a ring-shaped normal metal/insulator spacer, and spin current interference was observed. At 4.2 K, a very high spin signal of 200 mΩ was found in a device with 2 µm injector-detector dis- tance and magnetic field swept parallel to the plane. With a perpendicular magnetic field sweep, a Hanle effect measurement showed both spin precession and h/e oscil- lation. Because of the non-adiabatic nature of the precessing spins at low fields as they traverse the normal metal ring, this is an experimental observation of Aharonov- Anandan’s non-adiabatic geometric phase.

In addition, our observation of identical spin resistance for normal and supercon- ducting Aluminum is inconsistent with theoretical predictions based on the quasi- particle picture. In this designed sample, at the injector region, it is actually a superconductor/ferromagnet/superconductor lateral Josephson junction. Such a lateral Josephson junction convert spin singlet Cooper pairs from Aluminum to the long range triplet components in ferromagnet with projection of Sz = ±1. Such long range triplet components could diffuse a long distance in ferromagnet bar which is shorter than 3µm. The spin current results in superconducting Aluminum not only suggested the singlet-triplet conversion in ferromagnet, but may also suggest a new phenomenon, that is the long range triplet correlation in ferromagnet may also re- versely spread out into type I superconductor and exist for a short period of time in the superconductor and finally convert to singlet correlation due to exchange inter- action and spin-orbital coupling. Such an unstable triplet correlation in Aluminum could be detected in the non-local geometry. Although additional experimental work is needed to further confirm this supposition, our results might be the direct observa- tion of superconducting spin current which was under experimental pursuit recently. The experimental results may also suggest a new research area, that is triplet-singlet conversion in type I superconductor.

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