Scientists discover near-quantized conductance platform in Mayorana's zero-energy mode

[ Instrument Network Instrument R & D ] Mayorana Fermion is a basic particle predicted by physicist Ettore Majorana. It has electric neutrality and the antiparticle is itself. In the material system of condensed matter physics, Mayorana quasi-particles bound by topological defects, whose annihilation operator satisfies the self-conjugation relationship, usually presents a zero-energy conductance signal, which is called Mayorana zero-energy mold. The theory proves that Mayorana's zero-energy module satisfies the statistical laws of non-Abelian arbitrary subordinates, and it is one of the main paths to achieve fault-tolerant topological quantum computing.
In the past few years, the Gao Hongjun team of the Institute of Physics of the Chinese Academy of Sciences / University of Chinese Academy of Sciences and the Ding Hong team have used their own design and assembly of the world's top level ultra-low temperature strong magnetic field scanning tunneling microscope / spectroscopy (STM / S) joint system to accurately The superconducting vortices of FeTe0.55Se0.45 single crystal samples were measured, and experimental evidence of Mayorana zero-energy modes in iron-based superconductors was obtained (D. Wang et al., Science 362, 333 (2018)) . Subsequently, they investigated that the Mayorana zero energy mode exists only in part of the magnetic flux vortex, and further studied the Mayorana zero energy mode in the iron-based superconductor, and found that FeTe0.55Se0.45 single crystal sample There are two different types of magnetic flux vortexes on the surface at the same time. According to the presence or absence of Mayorana's zero energy mode, there is a half-integer shift in the quantized energy level sequence of the magnetic flux vortex bound states. They gave the micro-physical mechanism of the existence of Mayorana zero energy mode on the surface of FeTe0.55Se0.45 samples, and clarified the topological nature of Mayorana zero energy mode (Nature Physics 15, 1181 (2019)).
Existing experiments provide a lot of experimental evidence for the existence of Mayorana's zero-energy mode, and also explain the micro-physical mechanism of the existence of Mayorana's zero-energy mode. However, in condensed matter materials rich in novel physical phenomena, more needs to be done. Strong experimental evidence proves that zero-mode signals originate from Mayorana quasi-particles, for example, experimental observations of quantized conductance platforms. In solid material systems, the excited Mayorana quasi-particles have intrinsic particle-antiparticle symmetry, and their electrons and holes have the same composition. In the measurement of superconducting materials, an incident electron will inevitably bring a reflected hole. The appearance of the Mayorana zero-energy mode on the surface of the superconductor makes the tunneling probability of electrons and holes equal and Andreev resonance reflection occurs, resulting in a unique quantized conductivity platform feature. This feature is the key experimental evidence for the existence of Mayorana's zero-energy mode.
Recently, Gao Hongjun's team and Ding Hong's team further cooperated to carry out related research using its extremely low temperature and strong magnetic field STM / S joint system. By continuously and controllably changing the tunneling coupling strength between the tip and the FeTe0.55Se0.45 single crystal sample, they observed the near-quantized conductance platform characteristics of Mayorana's zero-energy mode. A large number of experimental observations show that the characteristic of this conductance platform is unique to Mayorana's zero energy mode protected by Mayorana's intrinsic electron / hole symmetry, and other topologically mediocre magnetic flux vortex bound states do not exist. This conductivity platform features. The rigorous experimental measurement excludes the influence of the electronic state of the superconductor itself, and also excludes the possibility of quantized ballistic transport in the measurement. Through statistical analysis of magnetic flux and vorticity, the distribution law of platform conductance value near quantization was found, and the influencing factors that may cause the platform conductance value to be smaller than the quantized conductance 2e2 / h, system energy broadening and quasiparticle poisoning effects were further analyzed. The entire measurement process ensures that the state of the sample and the needle tip will not change, and the measurement process can be repeated. The results of this series of experiments prove that platform conductance characteristics are prevalent in Mayorana's zero-energy mode.
This work uses STM / S technology to observe the characteristics of the near-quantized conductance platform of the Mayorana zero-energy mode in the magnetic flux vortex. Experimental evidence has played an important role in studying Mayorana's zero-energy mode and promoting future topological quantum computing. Related research results were published online in the journal Science on December 12. Zhu Shiyu, Kong Lingyuan, Cao Lu, and Dr. Chen Hui, PhD students of the Institute of Physics, Chinese Academy of Sciences, are co-first authors, and Zhang Yuyang (National University of Science and Technology), Ding Hong, and Gao Hongjun are co-corresponding authors. Gu Genda, a researcher at Brookhaven National Laboratory in the United States, provided high-quality single crystal samples, and Fu Liang, a professor at the Massachusetts Institute of Technology, provided theoretical support. This work was supported by the Ministry of Science and Technology (2015CB921000, 2015CB921300, 2016YFA0202300), the National Natural Science Foundation of China (11234014, 61888102), and the Chinese Academy of Sciences (XDB28000000, XDB07000000, 112111KYSB20160061).

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