Speaker
Junsaku Nitta
Description
We have investigated a geometric phase, also known as a
Berry phase, of electron spin in gate-fitted InGaAs ring
arrays subject to Rashba spin-orbit (SO) coupling. Studying
the spin geometric phase is important because it is
associated with various spin-dependent phenomena such as
persistent spin currents, and it may be utilized for robust
control of a spin phase. In this study, we electrically
observe the spin geometric phase by measuring the radius
dependence of the Aharonov-Casher (AC) spin-interference
effect. An InGaAs/InAlAs heterostructure was employed to
fabricate ring arrays which consist of a huge number of
rings. Five ring arrays with different radii were fabricated
by electron beam lithography and reactive-ion etching. A
gate electrode on top of the ring arrays was attached with a
200-nm-thick Al2O3 insulation layer in order to control the
Rashba SO strength. Magnetoresistances of the ring arrays
were measured as a function of the Rashba SO strength at 1.7
K. By applying a perpendicular magnetic field, clear
Al’tshuler-Aronov-Spivak (AAS) oscillations with h/2e period
were observed due to the ensemble averaging. Since the AAS
effect stems from the interference between time-reversal
symmetric paths, the orbital phase always makes constructive
interference at zero magnetic field. Therefore, the gate
voltage dependence of the AAS oscillations’ amplitude along
B = 0 corresponds to the time-reversal symmetric AC
oscillations. By increasing the radius of the ring, the AC
oscillations are shifted towards weaker Rashba SO regions
with their shortened period. The phase shift in the AC phase
can be attributed to the modulation of the spin geometric
phase. The spin geometric phase tends to increase with a
larger radius, which is in good agreement with the
theoretical prediction [1].
[1] F. Nagasawa, J. Takagi, Y. Kunihashi, M. Kohda, and J. Nitta, Phys. Rev. Lett. 108, 086801 (2012).
[1] F. Nagasawa, J. Takagi, Y. Kunihashi, M. Kohda, and J. Nitta, Phys. Rev. Lett. 108, 086801 (2012).
