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[Results] BNU He Lin Group Published Papers in the “Physical Review Letters”

Published: 2016-10-12

 
Recently, the high energy quantum physics research center Professor He Lin’s research group using strong magnetic field scanning tunnel microscope observed the direct evidence for the first time ever a single atomic vacancy in graphene produced localized magnetic moments. Physics Department of Tsinghua University professor Duan Wenhui’s group provides a theoretical support in the completion of the work. The Related research recently published in the top Journal of physics "Physical Review Letters". Professor He Lin’s undergraduate student Zhang Yu (He has now been recommended directly to become Professor Lin’s doctoral student) and doctoral student Li Siyu tied for first authors. Professor He Lin is the corresponding author.
 
It is generally believed that the magnetic moment in the material comes from the magnetic atom, while the magnetic moment of the magnetic atom is generally originated from the 3D or 4f shell which is not completely occupied. But scientists have always believed that the nonmagnetic materials can produce local magnetic moment and even the macroscopic magnetic order under certain conditions. One of the widely studied nonmagnetic materials is graphene. Graphene consists entirely of carbon atoms, so the ideal graphene is nonmagnetic (actual graphene is a good anti magnetic material). Theoretical calculations show that the number of A and B atoms in graphene can be varied with the introduction of single atom vacancy defects. That may cause graphene produce local magnetic moment. The first principle calculation results indicate that a single atomic vacancy makes π electrons in graphene produced two spin splitting state density peak. This feature is considered the direct evidence of defects induced local magnetic moment of π electrons in graphene. However, in the past ten years of experiments, different research groups have never detected single atomic vacancy defects induced by two spin splitting state, which has become one of the important scientific problems and also the difficult pending scientific problem in the field of graphene.
 
Professor He Lin analysis the past experiments in different experimental groups and pointed out that these experimental work is through the high-energy particle bombardment of graphene to produce a single atomic vacancy. It is extremely likely that vacancy defects are not generated in the energy ground state. In fact, while a single atomic vacancy is in metastable state (energy higher than the ground state about 50-100 meV), the π electron localized magnetic moments will disappear. So the development of a unique method to make the single atom vacancy defect in graphene stay in energy ground state is the key to study this scientific problem. Over the past few years, Professor He Lin’s research group deeply studied the growth and properties of graphene on metal rhodium. Nearly ten high quality research result papers have been published in the relevant fields. Recently their team found that by using normal atmospheric pressure chemical vapor deposition (CVD) the growth of graphene on the metal can spontaneously produce large number of single atom vacancy defects in energy ground state; In addition, under the support of Beijing Normal University 985 fund, professor He Lin in Physics Department began to build extremely low temperature super high vacuum high-intensity magnetic field scanning tunnel microscope since 2014. The maturity of these two conditions laid a good foundation for successfully studying the scientific problems of localized magnetic moment caused by a single atomic vacancy defects in graphene. In recent experiments, professor He Lin guided Zhang Yu and Li Siyu et al by high resolution scanning tunnel microscopy successfully detected the single atomic vacancy defects of graphene on metal rhodium. And using scanning tunnel spectroscopy for the first time ever detected the defect of splitting phenomenon. It provided strong evidence for single atom vacancy defects induced local π electron magnetic moment. This work indicate that the magnetic moment of graphene can be controlled by the vacancy defects in graphene. On the one hand, it has important scientific significance in understanding the local magnetic moment and magnetic of nonmagnetic materials. On the other hand, it has opened a new way of using graphene in future application of spin electronic device.
 
(Physics Department)


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