Manipulation of mobile spin coherence using magnetic-field-free electron spin resonance

Abstract

. In general, ESR requires two external magnetic fields: a static field (B 0 ) to split the spin states in energy and an oscillating field (B 1 ) with the frequency resonant to the splitting energy. However, spin manipulation methods relying on real magnetic fields-much broader than the size of individual electrons-are energetically inefficient and unsuitable for future device applications. Here we demonstrate an alternative approach where the spin-orbit interaction 7 of trajectory-controlled electrons induces effective B 0 and B 1 fields. These fields are created when electron spins surf on sound waves [8][9][10] along winding semiconductor channels. The resultant spin dynamics-mobile spin resonance-is equivalent to the usual ESR but requires neither static nor time-dependent real magnetic fields to manipulate electron spin coherence.In the electron systems in inhomogeneous magnetic fields or systems with spin-orbit coupling, the motion of electrons is converted to time-dependent effective magnetic fields. The latest studies have reported that ESR can be driven by effective B 1 fields, which are produced by the reciprocating motion of electrons with spatially dependent spin splitting [11][12][13] or with spin-orbit coupled systems [14][15][16] , but these techniques still need external B 0 fields. A promising approach for incorporating effective B 0 fields is the use of long-distance spin transport, which induces spin precessions around the static spin-orbit magnetic fields 9,17 . In addition, spin-qubit operations using moving quantum dots have been theoretically proposed 18 . Thus, we expect all of the magnetic fields needed for ESR to be replaced with spin-orbit effective magnetic fields (B SO ) by using trajectorycontrolled travelling electrons.Mobile spin resonance is based on the dependence of B SO on the electron momentum vector k. For simplicity, we assume a two-dimensional electron system in a (001) III-V quantum well with only k-linear terms in the Dresselhaus spin-orbit interaction 19 (SOI). The effective Dresselhaus field is described bywhere we used a coordinate system with base vectorsx Now we consider electrons travelling along the sinusoidal channel shown in Fig. 1b. At each position of the channel, the deflection angle of the path determines the direction of the k-vector. As a result, the moving electrons experience an effective magnetic field that swings with the frequency f = v y /λ, where v y is the time-averaged y-component of the electron velocity and λ is the period of the winding channel. In the reference frame moving with the electrons, the time-dependent effective magnetic field can be expressed as the sum of a static field (B To control the trajectory of travelling electrons, we adopted acoustically induced moving dots 21,22 produced in an undoped 20-nm-thick GaAs/AlGaAs (001) quantum well, where the SOI acting on the two-dimensionally confined electrons is dominated by the Dresselhaus term 10 . The piezoelectric field induced by a surface acoustic wave (SAW) beam propagating alongŷ (...

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