Recently, Zou Liangjian, a researcher at the Institute of Solid State Physics, Institute of Solid State Physics, Chinese Academy of Sciences, and Professor Warren Pickett of the University of California, Davis, collaborated to make new progress in the research on the electronic properties of new hydrogen-based iron-based superconductors. The hydrogen doping causes an unconventional energy band dispersion in the system, resulting in a special van Hove singularity below the Fermi level, which may favor the formation of a high superconducting transition temperature in the system. Related results were published in Phys. Rev. B 93, 195148 (2016).
Currently, there are four major classes of iron-based superconducting materials. Although the basic structural units of these compounds are very similar, the difference in the superconducting transition temperature of different compounds is very large. At the same time, the comparative study of the electronic properties of different systems can be used for the clarification. The superconducting key mechanism of iron-based superconducting materials provides a very effective means. The newly discovered La-doped hydrogen-containing iron-based superconductors, calcium, iron, arsenic, hydrogen (CaFeAsH), have a superconducting transition temperature as high as 47 K, which has become an important research object for the electronic properties of new iron-based high-temperature superconductors, and may be unconventional for high-temperature superconductors. The research of superconductivity brings new inspiration.
In order to study the different effects of H and F equivalent ion doping, the researchers calculated the energy bands before and after H was replaced by F in CaFeAsH, as well as energy bands with different substitution amounts (Figure 1), density of states, Fermi surface, and charge density difference ( Fig. 2) The properties of isoelectronic structures, and it was found that the hydrogen doping causes the system to form an unconventional strong-dispersion band. As shown in Fig. 1, a special van Hofer singularity appears at the Fermi level, resulting in CaFeAsH. The three-dimensional feature Fermi surface is different from calcium iron arsenic fluoride (CaFeAsF). This unique electronic structural feature may have a very important effect on improving superconductivity. At the same time, the researchers further calculated the magnetic ground state of CaFeAsH and analyzed the Fermi surface nesting, as shown in Figure 3, to prove that the ground state is a striped antiferromagnetic phase; for experimental doping concentrations, studies have shown that La or Co doping It will obviously inhibit the Fermi surface nesting of CaFeAsH, destroy the magnetic order of the parent phase, and lead to superconductivity in the system.
The above research results have been funded by the National Natural Science Foundation of China and the National Science Foundation.
Paper Information: YN Huang, DY Liu, LJ Zou*, Warren E. Pickett*, Role of Hydrogen in the Electronic Properties of CaFeAsH-based Superconductors, Physical Review B 93, 195148 (2016).
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