Aharonov-Bohm Oscillations in the Presence of Strong Spin-Orbit Interactions

Abstract

We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring structure defined by local anodic oxidation on a p-type GaAs heterostructure with strong spin-orbit interactions. Clear beating patterns observed in the raw data can be interpreted in terms of a spin geometric phase. Besides h/e oscillations, we resolve the contributions from the second harmonic of AB oscillations and also find a beating in these h/2e oscillations. A resistance minimum at B = 0 T, present in all gate configurations, is the signature of destructive interference of the spins propagating along time-reversed paths.Interference phenomena with particles have challenged physicists since the foundation of quantum mechanics. A charged particle traversing a ring-like mesoscopic structure in the presence of an external magnetic flux Φ acquires a quantum mechanical phase. The interference phenomenon based on this phase is known as the Aharonov-Bohm (AB) effect [1], and manifests itself in oscillations of the resistance of the mesoscopic ring with a period of Φ 0 = h/e, where Φ 0 is the flux quantum. The Aharonov-Bohm phase was later recognized as a special case of the geometric phase [2,3] acquired by the orbital wave function of a charged particle encircling a magnetic flux line.The particle's spin can acquire an additional geometric phase in systems with spin-orbit interactions (SOI) [4,5,6]. The investigation of this spin-orbit (SO) induced phase in a solid-state environment is currently the subject of intensive experimental work [7,8,9,10,11,12]. The common point of these experiments is the investigation of electronic transport in ring-like structures defined on two-dimensional (2D) semiconducting systems with strong SOI. Electrons in InAs were investigated in a ring sample with time dependent fluctuations [7], as well as in a ring side coupled to a wire [9]. An experiment on holes in GaAs [8] showed B-periodic oscillations with a relative amplitude ∆R/R < 10 −3 . These observations [7,8] were analyzed with Fourier transforms and interpreted as a manifestation of Berry's phase. Further studies on electrons in a HgTe ring [10] and in an InGaAs ring network [11] were discussed in the framework of the AharonovCasher effect.In systems with strong SOI, an inhomogeneous, momentum dependent intrinsic magnetic field B int , perpendicular to the particle's momentum, is present in the reference frame of the moving carrier [13]. The total magnetic field seen by the carrier is therefore B tot = B ext + B int , where B ext is the external magnetic field perpendicular to the 2D system and B int is the intrinsic magnetic field in the plane of the 2D system present in the moving reference frame (right inset Fig. 1(a)). The particle's spin precesses around B tot and accumulates an additional geometric phase upon cyclic evolution.Effects of the geometric phases are most prominently expressed in the adiabatic limit, when the precession frequency of the spin around the local field B tot is much faster than the orbital frequency of the charged particl...

Evidence for localization and 0.7 anomaly in hole quantum point contacts

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