Role of chiral quantum Hall edge states in nuclear spin polarization

Kaifeng Yang,Yoshiro Hirayama,Katsumi Nagase,Tetsuya D Mishima,Michael B Santos,Hongwu Liu

doi:10.1038/ncomms15084

Kaifeng Yang, Yoshiro Hirayama + Show 4 more

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https://doi.org/10.1038/ncomms15084

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Abstract

Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques.

Highlights

Detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear
The RDNMR technique depends on the current-induced dynamic nuclear polarization (DNP) that is expected to occur by transferring spin polarization from electrons to nuclei via the electron–nuclear hyperfine interaction at a domain wall (DW) separating two energetically degenerate domains[12]
We present comparative RDNMR measurements of the simplest easy-axis QHF at n 1⁄4 2 of InSb 2DEGs29 patterned into Hall bar and Corbino disk configurations

Summary

Introduction

Detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques. The absence of edge states in the Corbino disk allows us to investigate DNP in bulk[16], which provides a basis for discussion of DNP via edge states of the Hall bar This side-by-side comparison experiment reveals a reciprocity principle of the NMR response in the n 1⁄4 2 QHF at temperatures where the bulk contribution to DNP vanishes but the intraedge-scattering-induced DNP still operates, highlighting the important role of chiral edge states on DNP. Our results clearly show that the chiral edge state has direct effects on the nuclear spin polarization besides its known effects on the electron transport in QH systems

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