Flux periodic magnetoconductance oscillations in GaAs/InAs core/shell nanowires

Ö. Gül, N. Demarina, C. Blömers, T. Rieger, H. Lüth, M. I. Lepsa, D. Grützmacher, and Th. Schäpers

Phys. Rev. B 89, 045417 – Published 21 January 2014

Abstract

Magnetotransport experiments on epitaxial GaAs/InAs core/shell nanowires are performed in which the InAs shell forms a tube-like conductive channel around the highly resistive GaAs core. The core/shell nanowires are grown by molecular beam epitaxy. It is found that the nanowire conductance oscillates with the magnetic field oriented parallel to its axis, with a period of the magnetic flux quantum $ϕ_{0} = h / e$ . Related to that, it is shown that the electronic transport is mediated by closed loop quantum states encircling the wire axis rather than by electron interference of partial waves. By means of a gate voltage the conductance at zero magnetic field can be changed between an oscillation minimum and maximum. The experimental findings are supported by numerical calculations.

Received 15 October 2013
Revised 18 December 2013

DOI:https://doi.org/10.1103/PhysRevB.89.045417

Authors & Affiliations

Ö. Gül¹, N. Demarina², C. Blömers¹, T. Rieger¹, H. Lüth¹, M. I. Lepsa¹, D. Grützmacher¹, and Th. Schäpers^1,*

¹Peter Grünberg Institute (PGI-9) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
²Peter Grünberg Institute (PGI-2) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

^*th.schaepers@fz-juelich.de

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Vol. 89, Iss. 4 — 15 January 2014

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Images

Figure 1
(a) Scanning electron micrograph of as-grown GaAs/InAs core/shell nanowires. The different colors in the nanowire at the left illustrate the top of the GaAs core and the InAs shell. (b) Scanning electron micrograph of the contacted GaAs/InAs core/shell nanowire. (c) Schematic of the nanowire contacting the Au electrodes. The magnetic field B is oriented parallel to the nanowire axis.
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Figure 2
$ϕ_{0}$ -periodic conductance oscillations: magnetoconductance in units of $e^{2} / h$ at back-gate voltages of 6 and 8 V, respectively, for (a) the 100-nm-long and (b) the 370-nm-long nanowire segment. The peak-to-peak amplitudes of the oscillations are about 5% of the total conductance. The slowly varying background fluctuations in the magnetoconductance are attributed to universal conductance fluctuations. (c, d) The corresponding Fourier transforms. Background fluctuations in the magnetoconductance are subtracted prior to the Fourier analysis.
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Figure 3
(a–c) Color plot of the magnetoconductance normalized to $e^{2} / h$ as a function of the magnetic field $B$ and gate voltage $V_{g}$ for the 70-, 100-, and 370-nm-long nanowire segments, respectively, where the background conductance is subtracted. (d–f) Color plot of the amplitude of the corresponding Fourier transforms along $B$ as a function of $V_{g}$ and frequency $B^{- 1}$ .
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Figure 4
(a) Calculated conduction band profile $E_{c}$ and probability density $| ξ_{n, l} {(r) |}^{2}$ for $n = 1$ and 2 at various angular momentum quantum numbers $l$ of a GaAs/InAs core/shell nanowire with circular symmetry at $B = 0$ . $E_{F}$ denotes the Fermi energy. The intersection of $| ξ_{n, l} {(r) |}^{2}$ with the energy axis $E$ at radial distance $r = 0$ reflects the energy of the eigenstates. (b) Dependence of the energy $E$ of the states shown in (a) on the magnetic field $B$ . (c) Electron density $n_{2 D}$ in the shell as a function of magnetic field $B$ .
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Figure 5
(a, b) Energy $E$ of the angular momentum states and electron concentration $n_{2 D}$ , respectively, as functions of the magnetic field $B$ for a gate voltage of 6.7 V, corresponding to $E_{F} - E_{c} = 115$ meV. (c, d) Respective energy of the angular momentum states and electron concentration for a gate voltage of 8.2 V, corresponding to $E_{F} - E_{c} = 124$ meV.
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Figure 6
Conductance $G$ of a nanowire with a 370-nm-long contact separation averaged over a gate voltage range from 0 to 20 V is plotted against the magnetic field $B$ . The background conductance is subtracted. Inset: The corresponding Fourier transform. Clear peaks corresponding to $ϕ_{0}$ - and $ϕ_{0} / 2$ -periodic oscillations are resolved.
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