Strong coupling between a permalloy ferromagnetic contact and helical edge channel in a narrow HgTe quantum well
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LECTRONIC PROPERTIES OF SOLID
Strong Coupling between a Permalloy Ferromagnetic Contact and Helical Edge Channel in a Narrow HgTe Quantum Well1 A. Kononova, S. V. Egorova, Z. D. Kvonb,c, N. N. Mikhailovb, S. A. Dvoretskyb, and E. V. Deviatova,* a
Institute of Solid State Physics, Russian Academy Sciences, Chernogolovka, Moscow oblast, 142432 Russia b Institute of Semiconductor Physics, Novosibirsk, 630090 Russia c Novosibirsk State University, Novosibirsk, 630090 Russia * e-mail: [email protected] Received June 14, 2016
Abstract—We experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band inversion, realized in a narrow, 8 nm wide, HgTe quantum well. In zero magnetic field, we observe strong asymmetry of the edge potential distribution with respect to the ferromagnetic ground lead. This result indicates that the helical edge channel, specific for the structures with band inversion even at the conductive bulk, is strongly coupled to the ferromagnetic side contact, possibly due to the effects of proximity magnetization. This allows selective and spin-sensitive contacting of helical edge states. DOI: 10.1134/S1063776116130045
1. INTRODUCTION Recently, there is a strong interest in two-dimensional semiconductor systems with an inverted band structure, like narrow HgTe quantum wells. This interest is mostly connected with the quantum spin Hall (QSH) effect regime [1, 2]. Similarly to the conventional quantum Hall (QH) effect in high magnetic fields [3], QSH regime is characterized [4, 5] by presence of two spin-resolved, current-carrying helical edge states [6–9] even in a zero magnetic field. The helical QSH edge states are regarded to be suitable for different applications like quantum computing and cryptography. Experimental investigations of helical QSH edge states are mostly based on charge transport along the edge, which has been detected in local and nonlocal resistance measurements [1, 2, 4, 5] and by a direct visualization technique [10]. In the last case, the edge current has even been demonstrated to coexist with the conductive bulk [10], which is also possible from theoretical considerations [6, 11]. Despite the initial idea of a topological protection [1, 7–9], backscattering appears at macroscopic distances [2, 5], possibly due to the allowed two-particle process [12] or the electron puddles [13]. It is clear that for possible applications, it is necessary to develop a technique of selective contacting of these edge states. A possible variant is to use spin effects: QSH edge transport is supposed to be essen1 The article is published in the original.
tially spin-dependent [6–9] even in a zero magnetic field. Strong coupling between the spin-resolved helical edge states and a ferromagnet can also be anticipated from theoretical considerations [14, 15]. Here, we experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band in
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