Query: Chiral Majorana fermion modes in a quantum anomalous Hall insulator–superconductor structure

Candidate papers:

abstract: A propagating Majorana mode Although Majorana fermions remain elusive as elementary particles, their solid state analogs have been observed in hybrid semiconductor superconductor nanowires. In a nanowire setting, the Majorana states are localized at the ends of the wire. He et al. built a two dimensional heterostructure in which a one dimensional Majorana mode is predicted to run along the sample edge (see the Perspective by Pribiag) The heterostructure consisted of a quantum anomalous Hall insulator (QAHI) bar contacted by a superconductor. The authors used an external magnetic field as a "knob" to tune into a regime where a Majorana mode was propagating along the edge of the QAHI bar covered by the superconductor. A signature of this propagation half quantized conductance was then observed in transport experiments. Science, this issue p. 294; see also p. 252 Transport experiments showing half integer quantized conductance indicate a propagating Majorana edge mode. Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing.
author_names: Qing Lin He

Lei Pan

Alex Stern

Edward C Burks

Xiaoyu Che

Gen Yin

Jing Wang

Biao Lian

Quan Zhou

Eun Sang Choi

Koichi Murata

Xufeng Kou

Zhijie Chen

Tianxiao Nie

Qiming Shao

Yabin Fan

Shou-Cheng Zhang

Kai Liu

Jing Xia

Kang L Wang
title: Chiral Majorana fermion modes in a quantum anomalous Hall insulator superconductor structure
venue: Science
year: 2017

abstract: The conductance measurement of a half quantized plateau in a quantum anomalous Hall insulator superconductor structure is reported by a recent experiment [Q. L. He \textit{et al. Science 357, 294 299 (2017) which suggests the existence of the chiral Majorana fermion modes. However, such half quantized conductance plateau may also originates from a disorder induced metallic phase. To identify the exact mechanism, we study the transport properties of such a system in the presence of strong disorders. Our results show that the local current density distributions of these two mechanisms are different. In particular, the current noises measurement can be used to distinguish them without any further fabrication of current experimental setup.
author_names: Yu-Hang Li

Jie Liu

Haiwen Liu

Hua Jiang

Qing-feng Sun

X C Xie
title: Noise signatures for determining chiral Majorana fermion modes
year: 2018

abstract: The discovery of Chiral Majorana fermion modes in a quantum anomalous Hall insulator superconductor structure (arXiv:1606.05712) has been widely discussed since its publication in Science, including a commentary by Jason Alicea in the July issue of the Journal Club. As it should be, a breakthrough announcement such as this is being scrutinized for alternative interpretations. In the case of the 2012 report of a Majorana zero mode such critical examinations have helped a lot in strengthening the experimental claim, and I presume the same will happen here. It is in that constructive spirit that I wish to discuss the two preprints by Ji Wen and by Huang, Setiawan Sau, which address the question: How unique a signature of Majorana fermions is a conductance plateau at half the conductance quantum? To appreciate the issue, we recall that in this context a quasiparticle is called a Majorana fermion if it is a coherent equal weight superposition of a Dirac fermion and its antiparticle (electron e and hole h) The Majorana fermion is charge neutral, but so is an incoherent equal weight mixture of electrons and holes. Since the former has been dubbed the "angel particle" one might stay true to this theme and call the latter a "demon" As explained in Figure 1, a conductance measurement cannot distinguish between the current carried by the coherent superposition psangel 2 1/2(|e> |h> and the incoherent mixture rdemon 1 2 |e> <e| |h> <h| both give rise to a conductance of 1 2 e/h. For a Majorana fermion the equal weight property is fundamental: it is required by electron hole symmetry at the Fermi level. The incoherent electron hole mixture is not so constrained, and one might wonder how reasonable it is to assume a charge neutral mixture.
author_names: Xiao-Gang Wen

Jay Deep Sau
title: 2 h Th Conductance Plateau without 1 D Chiral Majorana Fermions
year: 2017

abstract: Significance With the recent involvement of large companies in the development of quantum computation, we are at a stage where this technology appears to be being realized. However, we also urgently need new materials to engineer qubits that are more immune to quantum decoherence processes and can easily be entangled. Majorana fermion in the form of condensed matter quasiparticles is considered the key to a topological qubit that would be much more robust against decoherence. One way to develop such a qubit is to introduce superconductivity into a quantum anomalous Hall insulator. We provide spectroscopic evidence of chiral Majorana modes in this material in qualitatively good agreement with the theoretical predictions. With the recent discovery of the quantum anomalous Hall insulator (QAHI) which exhibits the conductive quantum Hall edge states without external magnetic field, it becomes possible to create a topological superconductor (SC) by introducing superconductivity into these edge states. In this case, 2 distinct topological superconducting phases with 1 or 2 chiral Majorana edge modes were theoretically predicted, characterized by Chern numbers (N) of 1 and 2, respectively. We present spectroscopic evidence from Andreev reflection experiments for the presence of chiral Majorana modes in an Nb/(Cr0.12Bi0.26Sb0.62)2Te3 heterostructure with distinct signatures attributed to 2 different topological superconducting phases. The results are in qualitatively good agreement with the theoretical predictions.
author_names: Junying Shen

Jian Lyu

Jason Z Gao

Yingming Xie

Chui-zhen Chen

Chang-Woo Cho

Omargeldi Atanov

Zhijie Chen

Kai Liu

Y J Hu

King Yau Yip

Swee K Goh

Qing Lin He

Lei Pan

Kang L Wang

Kam Tuen Law

Rolf Lortz
title: Spectroscopic fingerprint of chiral Majorana modes at the edge of a quantum anomalous Hall insulator/superconductor heterostructure
venue: Proceedings of the National Academy of Sciences
year: 2019

abstract: Topological superconductors are in the focus of research because of their high potential for future applications of quantum computation. With the recent discovery of the quantum anomalous Hall insulator (QAHI) which exhibits the conductive quantum Hall edge states without external magnetic field, it becomes possible to create a novel topological superconductor by introducing superconductivity into these edge states. In this case, two distinct topological superconducting phases with one or two chiral Majorana edge modes formed, characterized by Chern numbers (N of 1 and 2, respectively. Recent experiments on a QAHI superconductor (SC) heterostructure revealed the presence of integer and half integer quantized plateaus in the conductance over a deposited SC strip and presented the quantization evidence of these states. However, these results also provoked a few controversies and thus additional direct evidence of a superconducting origin is urgently needed. We provided spectroscopic evidence for a superconducting QAHI state using nano point contacts at the edge of a QAHI SC heterostructure and obtained unique signatures of these two different topological superconducting phases. The phase with N 1 with a 2e^2/h conduction signature occurs in a narrow field regime during the QAHI magnetization reversal just before the QAHI enters the trivial insulating state. These results are consistent with theoretical analysis and further reaffirm the previous result of 1/2 quantization due to Majorana fermion.
author_names: J Shen

Jian Lyu

J Z Gao

Y M Xie

C -Z Chen

Chang-Woo Cho

Omargeldi Atanov

Zeshun Chen

K Liu

Y J Hu

King Yau Yip

Swee K Goh

Qing Lin He

Lei Pan

K L Wang

Kam Tuen Law

Rolf Lortz
title: Spectroscopic evidence of chiral Majorana modes in a quantum anomalous Hall insulator superconductor heterostructure
year: 2018

abstract: Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. Department of Physics, Southern University of Science and Technology, 1088 Xueyuan Road, Nanshan District, Shenzhen, Guangdong Province, China Physics Department, University of California, Davis, CA 95616, USA. Physics Department, Georgetown University, Washington, DC 20057, USA. Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong. Department of Electrical and Computer Engineering, Department of Physics, and Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, USA. International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China.
author_names: J Shen

Jian Lyu

J Z Gao

C -Z Chen

Chang-Woo Cho

Omargeldi Atanov

Z Chen

K Liu

Y J Hu

Y K

Swee K Goh

Qing Lin He

Lei Pan

K L Wang

Kam Tuen Law

Rolf Lortz
title: Fingerprint of chiral Majorana modes in resonant Andreev reflection at the edge of a quantum anomalous Hall insulator superconductor heterostructure
year: 2019

abstract: Chiral Majorana edge modes are theoretically proposed to perform braiding operations for the potential quantum computation. Here, we suggest a scheme to regulate trajectories of the chiral Majorana fermion based on a quantum anomalous Hall insulator (QAHI) topological superconductor heterostructure. An applied external gate voltage to the QAHI region introduces a dynamical phase so that the outgoing Majorana fermions can be prominently tuned to different leads. The trajectory is mechanically analyzed and the electrical manipulation is represented by the oscillating transmission coefficients versus the gate voltage. Through the optimization of devices, the conductance is likewise detectable to be periodically oscillating, which means an experimental control of chiral Majorana edge modes. Besides, this oscillating period which is robust against disorder also provides an attainable method of observing the energy dispersion relation of the edge mode of the QAHI. Furthermore, the oscillating behavior of conductance serves as smoking gun evidence of the existence of the chiral Majorana fermion, which could be experimentally confirmed.
author_names: Qing Yan

Yan-Feng Zhou

Qing-feng Sun
title: Electrically tunable chiral Majorana edge modes in quantum anomalous Hall insulator topological superconductor systems
year: 2019

abstract: With the recent discovery of the quantum anomalous Hall insulator (QAHI) which exhibits the conductive quantum Hall edge states without external magnetic field, it becomes possible to create a novel topological superconductor by introducing superconductivity into these edge states. In this case, two distinct topological superconducting phases with one or two chiral Majorana edge modes were theoretically predicted, characterized by Chern numbers (N of 1 and 2, respectively. We present spectroscopic evidence from Andreev reflection experiments for the presence of chiral Majorana modes in a Nb (Cr0.12Bi0.26Sb0.62)2Te3 heterostructure with unique signatures attributed to two different topological superconducting phases. The results are consistent with the theoretical predictions.
author_names: J Shen

Jian Lyu

J Z Gao

C -Z Chen

Chang-Woo Cho

Omargeldi Atanov

Zigao Chen

K Liu

Y J Hu

King Yau Yip

Swee K Goh

Qing Lin He

Lei Pan

K L Wang

Kam Tuen Law

Rolf Lortz
title: Fingerprint of Chiral Majorana Modes in Andreev Reflection at the Edge of a Quantum Anomalous Hall Insulator Superconductor Heterostructure
year: 2018

author_names: Qing Lin He

Lei Pan

Gen Yin

Xufeng Kou

Kang L Wang
title: Chiral Majorana edge state in a quantum anomalous Hall insulator superconductor structure
year: 2017

abstract: This is a short note presenting a repeated experiment of the half quantized transport signature given by Majorana chiral modes living in a heterostructure formed by an s wave superconductor and a quantum anomalous Hall insulator.
author_names: Peng Zhang

Lei Pan

Gen Yin

Qing-Lin He

Kang L Wang
title: A Note on Half quantized Conductance Plateau of Chiral Majorana in Quantum Anomalous Hall Insulator and Superconductor Structures
year: 2019