Hole-spin dynamics and hole $g$-factor anisotropy in coupled quantum well systems

Hole-spin dynamics and hole $g$ -factor anisotropy in coupled quantum well systems

C. Gradl, M. Kempf, D. Schuh, D. Bougeard, R. Winkler, C. Schüller, and T. Korn

Phys. Rev. B 90, 165439 – Published 30 October 2014

Abstract

Due to its $p$ -like character, the valence band in GaAs-based heterostructures offers rich and complex spin-dependent phenomena. One manifestation is the large anisotropy of Zeeman spin splitting. Using undoped, coupled quantum wells (QWs), we examine this anisotropy by comparing the hole-spin dynamics for high- and low-symmetry crystallographic orientations of the QWs. We directly measure the hole $g$ factor via time-resolved Kerr rotation, and for the low-symmetry crystallographic orientations (110) and ( $113 a$ ), we observe a large in-plane anisotropy of the hole $g$ factor, in good agreement with our theoretical calculations. Using resonant spin amplification, we also observe an anisotropy of the hole-spin dephasing in the (110)-grown structure, indicating that crystal symmetry may be used to control hole-spin dynamics.

Received 12 August 2014
Revised 13 October 2014

DOI:https://doi.org/10.1103/PhysRevB.90.165439

Authors & Affiliations

C. Gradl¹, M. Kempf¹, D. Schuh¹, D. Bougeard¹, R. Winkler², C. Schüller¹, and T. Korn^1,*

¹Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany
²Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA

^*tobias.korn@physik.uni-regensburg.de

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Vol. 90, Iss. 16 — 15 October 2014

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Images

Figure 1
(a) Sample structure. Spin-polarized electron-hole pairs can be created by resonant optical excitation in the narrow or the wide QW. The states in the X valley of the AlAs barrier layers are energetically close to the electron states in the narrow QW. (b) After resonant excitation in the narrow QW, electrons can rapidly tunnel into the AlAs barrier if the QW is tilted by the gate bias, so that only holes remain in the QW. (c), (d) Depending on the bias, after resonant excitation in the wide QW, either electrons tunnel out of the QW, or additional electrons tunnel into the QW from the top contact.
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Figure 2
(a) TRKR traces measured on the wide QW in sample A at a fixed in-plane magnetic field of 2 T for different gate biases. (b) Electron and hole $g$ factors and spin dephasing times as a function of gate bias. The vertical line indicates the crossover from a hole- to an electron-dominated regime. (c), (d) RSA measurements on the narrow QW in sample A as a function of (c) gate bias and (d) excitation wavelength.
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Figure 3
(a) Electron and hole $g$ factors as a function of gate bias in sample C. The vertical line indicates the crossover from a hole- to an electron-dominated regime. (b) TRKR traces measured on sample B for a fixed magnitude of the in-plane magnetic field applied at various angles $α$ relative to the $[00 \bar{1}]$ axis. (c) Hole SDTs as a function of in-plane magnetic field for samples B and C. The data are averaged over all in-plane orientations of the samples. The solid line indicates a fit to the data using Eq. (1). (d) RSA measurements on sample B using different gate voltages. The field is applied parallel to the $[\bar{1} 10]$ axis.
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Figure 4
(a) Schematic of the coordinate system used in the paper. (b) Numerical calculation of the hole $g$ factor for two different in-plane magnetic-field directions as a function of the angle between the growth axis and [001] assuming a QW width of 12 nm. (c), (d) Hole $g$ factor of (c) sample B and (d) sample C as a function of in-plane magnetic-field angle $α$ relative to the $[n n \bar{(2 m)}]$ ( $x$ ) axis. The solid lines in (c) and (d) indicate fits to the data using Eq. (2), and dashed lines indicate values calculated with Eq. (2) using the data depicted in (b).
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Figure 5
(a) Low- and high-field regions of the RSA trace measured on the narrow QW in sample A for a 16 V gate bias compared to a simulated RSA trace. (b) RSA traces measured on sample B (top trace, dots) and sample A (bottom trace, open circles) compared to simulated RSA traces (solid lines).
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Figure 6
(a) TRKR traces measured on the wide QW in sample C at a fixed magnetic field $B = 1$ T for two different in-plane orientations of the field. The vertical lines serve as a guide to the eye. (b) Electron $g$ factors as a function of in-plane magnetic-field angle for samples B and C.
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