The electronic structure and superconducting gap structure are prerequisites to establish microscopic theories in understanding the superconductivity mechanism of iron-based superconductors.However,even for the most e...The electronic structure and superconducting gap structure are prerequisites to establish microscopic theories in understanding the superconductivity mechanism of iron-based superconductors.However,even for the most extensively studied optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2),there remain outstanding controversies on its electronic structure and superconducting gap structure.Here we resolve these issues by carrying out high-resolution angle-resolved photoemission spectroscopy(ARPES)measurements on the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2)superconductor using both Helium lamp and laser light sources.Our results indicate the‘‘flat band"feature observed around the Brillouin zone center in the superconducting state originates from the combined effect of the superconductivity-induced band back-bending and the folding of a band from the zone corner to the center.We found direct evidence of the band folding between the zone corner and the center in both the normal and superconducting state.Our resolution of the origin of the flat band makes it possible to assign the three hole-like bands around the zone center and determine their superconducting gap correctly.Around the zone corner,we observe a tiny electronlike band and an M-shaped band simultaneously in both the normal and superconducting states.The obtained gap size for the bands around the zone corner(~5.5 meV)is significantly smaller than all the previous ARPES measurements.Our results establish a new superconducting gap structure around the zone corner and resolve a number of prominent controversies concerning the electronic structure and superconducting gap structure in the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2).They provide new insights in examining and establishing theories in understanding superconductivity mechanism in iron-based superconductors.展开更多
基金financial support from the National Key Research and Development Program of China(2016YFA0300300,2017YFA0302900,2018YFA0704200 and 2019YFA0308000)the National Natural Science Foundation of China(11888101,11922414,11874405,and 62022089)+2 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB25000000 and XDB33000000)the Youth Innovation Promotion Association of CAS(2017013 and 2019007)the Research Program of Beijing Academy of Quantum Information Sciences(Y18G06)。
文摘The electronic structure and superconducting gap structure are prerequisites to establish microscopic theories in understanding the superconductivity mechanism of iron-based superconductors.However,even for the most extensively studied optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2),there remain outstanding controversies on its electronic structure and superconducting gap structure.Here we resolve these issues by carrying out high-resolution angle-resolved photoemission spectroscopy(ARPES)measurements on the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2)superconductor using both Helium lamp and laser light sources.Our results indicate the‘‘flat band"feature observed around the Brillouin zone center in the superconducting state originates from the combined effect of the superconductivity-induced band back-bending and the folding of a band from the zone corner to the center.We found direct evidence of the band folding between the zone corner and the center in both the normal and superconducting state.Our resolution of the origin of the flat band makes it possible to assign the three hole-like bands around the zone center and determine their superconducting gap correctly.Around the zone corner,we observe a tiny electronlike band and an M-shaped band simultaneously in both the normal and superconducting states.The obtained gap size for the bands around the zone corner(~5.5 meV)is significantly smaller than all the previous ARPES measurements.Our results establish a new superconducting gap structure around the zone corner and resolve a number of prominent controversies concerning the electronic structure and superconducting gap structure in the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2).They provide new insights in examining and establishing theories in understanding superconductivity mechanism in iron-based superconductors.
