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There are two possible electronic structures in a single layer of FeSe, one with a mediocre topological topology and one with a non-trivial topology.
Iron-based superconductors and topological insulators are hot topics in condensed matter physics in recent years. Iron-based superconductors are unconventional superconductors. Unlike traditional BCS superconductors with electro-acoustic coupling, the interpretation of the superconducting pairing mechanism is still a difficult point in condensed matter physics theory. At the same time, unlike single-band copper-based unconventional superconductors, iron The multi-band nature of the base superconductor gives it a more abundant electronic structure.
The discovery of topological insulators has broken through people's understanding of the insulating phase. This type of material has an insulating state, but there is a conductive metallic state on the surface or interface. Similarly, topological insulators have complex electronic structures, and the appearance of their topological phase is usually accompanied by the reversal of energy bands. However, in the past few years, people have not found that these two characteristics may be symbiotic.
Recently, single-layer FeSe heterojunctions grown on substrates such as SrTiO3Nb:SrTiO3/KTaO3, Nb:BaTiO3/KTaO3 have been experimentally fabricated, which has greatly expanded the understanding of the complex electronic structures of iron-based superconductors. Compared with the bulk material with lower superconducting transition temperature, in addition to the superconducting phase with a transition temperature of up to 65K observed in a single-layer FeSe heterojunction, another significant feature is that the electronic structure of the single-layer FeSe is very large. The change is as follows: the hole-type Fermi surface near the Brillouin area will be annihilated below the Fermi level, and a new band gap will appear near the M point, and the size of the band gap will vary. The substrate can be adjusted.
In order to understand the changes in the electronic structure of FeSe, recently, Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics (CPC) Hu Jiangping, a researcher and postdoctoral fellow Hao Ningning of the condensed matter theory and materials calculation laboratory through crystal symmetry analysis and dp-based The microscopic analysis of the orbital hybridization gave an electronic structure evolution image of body FeSe to a single layer of FeSe. The renormalized image of the electronic structure of this substrate conforms to the results obtained in recent experiments on different substrate systems. .
They further found that when the new band gap that can be modulated by the substrate near M point has the same order of magnitude as the spin-orbit coupling of germanium in the d orbit, the energy band at point M can be inverted, and the system will have a topological phase change. The results of this study present for the first time the possible manifestation of topological properties in iron-based superconducting materials. In addition, this work provides insights into why people have such a high transition temperature in a single-layer FeSe, and suggests a new possible system to implement the iron-based material version of Majorana fermions. This result was published in the recently published Phys. Rev. X 4, 031053 (2014).
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