Gate-controlled spin precession in narrow diffusive 2DEG channels*

The spin field effect transistor (sFET) concept envisioned by Datta and Das [1] is already three decades old, but its realization has been so far impeded by various constraints imposed in the original proposal. One of them is the requirement of ballistic transport in the sFET channel, imposed as the prerequisite for voltage-controlled, coherent precession of the traveling spins around the unidirectional spin-orbit field B_so, which constitutes the basic functionality of the sFET. The requirement of ballistic transport means, that the length of the sFET’s channel has to be shorter than the electrons’ mean free path, which typically corresponds to lengths around one micrometer. To be able to reverse the orientation of spins on such a small distance via coherent spin precession, systems with large spin-orbit coupling (SOC) must be used [2], which severely limits the selection of suitable materials.

In this presentation, I will discuss the results of our recent investigations on precession of spins in long and narrow diffusive channels formed in a two-dimensional electron gas (2DEG), defined in an (In,Ga)As quantum well with a low In content.  Lateral confinement of motion of electrons in a narrow 2DEG channel reduces the possible number of transversal k-vectors, which leads to a unidirectional orientation of B_so. To demonstrate coherent precession of spins, we electrically inject spins into an array of such channels using a highly efficient (Ga,Mn)/GaAs spin Esaki diode as a spin injector [3]. Utilizing the gate placed on top of the array, we tune B_so, and observe clear oscillations of a nonlocal signal as a function of the gate voltage. Particularly, we show that we can rotate the spin ensemble by an angle of π, thus reversing their orientation about the magnetization of injecting and detecting contacts, on a distance one order of magnitude larger than the mean free path of the system. Therefore, our experiment demonstrates, that the requirement of the ballistic channel and the large SOC is not crucial for the realization of the Datta-Das sFET.

[1] S. Datta, & B. Das, Appl. Phys. Lett. 56, 665 (1990)

[2] H. C.  Koo et al., Science 325, 1515 (2009)

[3] F. Eberle et al., Phys. Rev. Appl. 16, 014010 (2021)