Dynamic nuclear polarization at high Landau levels in a quantum point contact

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Dynamic nuclear polarization at high Landau levels in a quantum point contact

M. H. Fauzi, A. Noorhidayati, M. F. Sahdan, K. Sato, K. Nagase, and Y. Hirayama

Phys. Rev. B 97, 201412(R) – Published 29 May 2018

Abstract

We demonstrate a way to polarize and detect nuclear spin in a gate-defined quantum point contact operating at high Landau levels. Resistively detected nuclear magnetic resonance (RDNMR) can be achieved up to the fifth Landau level and at a magnetic field lower than 1 T. We are able to retain the RDNMR signals in a condition where the spin degeneracy of the first one-dimensional (1D) subband is still preserved. Furthermore, the effects of orbital motion on the first 1D subband can be made smaller than those due to electrostatic confinement. This developed RDNMR technique is a promising means to study electronic states in a quantum point contact near zero magnetic field.

Received 8 April 2018
Revised 15 May 2018

DOI:https://doi.org/10.1103/PhysRevB.97.201412

Physics Subject Headings (PhySH)

Edge states Quantum Hall effect Quantum transport

Quantum wires

Nuclear magnetic resonance Transport techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. H. Fauzi^1,*, A. Noorhidayati², M. F. Sahdan^2,†, K. Sato², K. Nagase², and Y. Hirayama^1,2

¹Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
²Department of Physics, Tohoku University, Sendai 980-8578, Japan

^*fauzi@m.tohoku.ac.jp
^†Present address: Department of Physics, National University of Singapore, Singapore 117551, Singapore.

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Issue

Vol. 97, Iss. 20 — 15 May 2018

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Images

Figure 1
(a) Device schematic and measurement setup. (b) Hall conductance $G_{Hall}$ as a function of a perpendicular magnetic field in which several bulk even filling factors $ν_{b}$ are indicated. The sheet 2DEG electron density is $n = 2.36 \times 10^{15} m^{- 2}$ . The constriction is open during the conductance recording. (c) Zero magnetic field $G_{diag}$ conductance profile as a function of split gate bias. 2D-1D transition is indicated by the arrow at approximately $V_{SG} \approx - 0.5$ V. (d) Diagonal conductance $G_{diag}$ as a function of split gate bias voltage measured at several perpendicular magnetic fields. The open circles indicate the operating split gate bias at which RDNMR presented in the subsequent figure is measured. The corresponding subband indices $n$ are also indicated in the panel. The inset shows a blowup of the first conductance profile for zero and 0.98 T fields.
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Figure 2
(a) A typical time trace of conductance during current-induced dynamic nuclear polarization. (b) A schematic of an edge channel setup to create local nuclear spin polarization in a quantum point contact. The red and blue lines represent up and down electron spin channels. For the sake of clarity, we only picture a pair of up and down spin channels that can belong to any Landau level. The black arrows represent the likely hyperfine-mediated spin-flip scattering process. The scattering event creates positive nuclear polarization (parallel to the external field) in and around the quantum point contact. (c) The corresponding potential barrier for up and down electron spin along the black dashed line in (b) without (solid line) and with (dashed line) positive nuclear polarization buildup.
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Figure 3
(a)–(d) ${}^{75}{As}$ RDNMR spectra taken at perpendicular fields of 2.5 T $(ν_{b} = 4, ν_{qpc} < 3)$ , 1.65 T $(ν_{b} = 6, ν_{qpc} < 5)$ , 1.24 T $(ν_{b} = 8, ν_{qpc} < 7)$ , and 0.98 T $(ν_{b} = 10, ν_{qpc} < 9)$ . The rf is swept with increasing frequency at a scan rate of 0.1 kHz/s and rf power of $- 30$ dBm delivered to the top of the cryostat. $G_{Hall}$ and $G_{diag}$ are simultaneously recorded with five subsequent traces averaged to increase the signal-to-noise ratio. The appearance of threefold splitting noted in the $G_{diag}$ is due to the electric quadrupole interaction. The solid line is a Gaussian fit to the data.
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Figure 4
Center transition As resonance frequency detected at different fields. The dashed line is the linear fit to the data extrapolated to zero field. The measured slope is about 7.27 MHz/T.
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Figure 5
${}^{69}{Ga}$ and ${}^{71}{Ga}$ RDNMR spectra detected at the same condition as Fig. 3. The solid line is the Gaussian fit to the data with corresponding linewidths of 38 and 22 kHz, respectively.
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