Electron Spin Resonance on a Two-Dimensional Electron Gas in a Single AlAs Quantum Well

Abstract

Direct electron spin resonance (ESR) on a high mobility two dimensional electron gas in a single AlAs quantum well reveals an electronic g-factor of 1.991 at 9.35 GHz and 1.989 at 34 GHz with a minimum linewidth of 7 Gauss. The ESR amplitude and its temperature dependence suggest that the signal originates from the effective magnetic field caused by the spin orbit-interaction and a modulation of the electron wavevector caused by the microwave electric field. This contrasts markedly to conventional ESR that detects through the microwave magnetic field. [5,6], without the need for Ohmic contacts to the samples. Moreover, from the dependence of the g-factor anisotropy on Fermi wavevector and from the dependence of the g-factor on angle between microwave field and static magnetic field, recently the (tiny) Bychkov-Rashba spin-orbit interaction of 2D electrons in Si/SiGe samples could be determined [7,8]. In this paper we show that in high mobility 2D samples, this spin-orbit interaction allows to resonantly manipulate the electron spin by means of GHz electric fields.Direct ESR on a two dimensional electron gas (2DEG) has proved difficult because of the typically small number of spins in the 2DEG. So far it has been restricted to Si (either in Si/SiC or in Si/SiGe samples) because of its favourable physical properties. As the sensitivity of ESR is proportional to the inverse of the linewidth squared, narrow linewidths are a prerequisite. In Si linewidths down to 3 µT are observed [8], as little T 1 -broadening occurs. This is because Si has a rather small spin-orbit (SO) interaction. Also it has only one isotope with nuclear spin ( 29 Si) which additionally has only a small natural abundance (4.7 %). This contrasts markedly to the III-V semiconductors where there are many isotopes with nuclear spin ( 69 Ga, 71 Ga, 27 Al, 75 As, 115 In, 31 P etc.) with large natural abundance, many of which have a strong SO coupling. This leads to considerable line broadening and at low temperatures, where ESR usually has the best sensitivity, to large hyperfine fields that vary slowly with time. Consequently direct ESR has never been demonstrated on 2D electrons in III-V semiconductors.Here, we present the first direct ESR on a 2DEG in a III-V semiconductor. We study ESR of high mobility 2D electrons in a single AlAs quantum well. At 9.35 GHz and at 34 GHz g-factors of 1.991 and 1.989 were determined respectively. By rotating the sample in the cavity we demonstrate that our ESR originates from the microwave electric field (E 1 -field) and not from the microwave magnetic field (B 1 -field). For small power (P ) of the E 1 -field, the ESR follows a P 0.5 -law, but for larger powers, the exponent increases to ∼1. The temperature dependence of the ESR is much stronger than the 2D magnetisation expected for such a system [2]. Our observations can be explained by assuming that the spin transitions occur through the effective magnetic field caused by SO interaction and the modulation of the electron wavevector around k F induced by the mi...

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Theory of electric dipole spin resonance in a parabolic quantum well

“…Nevertheless, the intensity of EDSR exceeded the intensity of electron paramagnetic resonance ͑EPR͒ ͑excited by the magnetic component of microwave field͒ by four orders of magnitude. As Schulte et al emphasize in their paper, 62 the very fact of the observation of a spin-flip line represented a puzzle because in their sample the EPR intensity was two orders of magnitude smaller than the noise level.…”

“…29 It was only very recently that EDSR driven by the orbital mechanism has been reported for a A 3 B 5 quantum well. 62 And ironically again, this observation has been made with an AlAs quantum well where the weakness of SO coupling manifested itself in a small g shift, g Ϸ 1.99. Nevertheless, the intensity of EDSR exceeded the intensity of electron paramagnetic resonance ͑EPR͒ ͑excited by the magnetic component of microwave field͒ by four orders of magnitude.…”

“…In Ref. 62 are as follows. The signal of spin resonance originates from the effective magnetic field caused by the SO interaction.…”

g-factor modification in a bulk InGaAs epilayer by an in-plane electric field

“…Electron spin resonance (ESR) was shown to induce spin flips in a quantum dot when the frequency of an oscillating magnetic field matched the resonance frequency of the spin in a perpendicular static magnetic field, gµ B B stat = hf osc 1 . As this technique requires high magnitude, high frequency magnetic fields, alternative methods were developed that instead used an alternating electric field to produce the resonance, either by creating a oscillating spin-orbit (SO) field 2 or by electrically modulating the g-tensor, called gtensor modulation resonance (g-TMR) 3 . The use of an electric field also allows for more local manipulation than that possible with magnetic fields 4 .…”