Angle-resolved photoemission spectroscopy is performed to study the bulk and surface electronic structures of non- superconducting IrTe2 and superconducting Pto.oblro.95 Te2. In addition to the bulk electronic bands p...Angle-resolved photoemission spectroscopy is performed to study the bulk and surface electronic structures of non- superconducting IrTe2 and superconducting Pto.oblro.95 Te2. In addition to the bulk electronic bands predicted by the local density approximation calculations, we observe two Dirac cone-like bands at the Brillouin zone center, which are non-dispersive along kz, suggesting that the extra bands are surface state bands. As the experimental results are well consistent with the ab initio calculations of surface states, the parity analysis proves that these surface state bands are topologically trivial and thus exclude (PtxIr1-x)Te2 as a possible topological superconductor candidate.展开更多
The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show ...The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c(~21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.展开更多
We report the growth process of FeTe1-xSex (0 〈 x 〈 1) monolayer films on SrTi03 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parame...We report the growth process of FeTe1-xSex (0 〈 x 〈 1) monolayer films on SrTi03 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parameters of substrate treatment, growth control and post growth annealing, we successfully obtain a series of FeTe1-xSex monolayer films. In the whole growth process, we find the significance of the temperature control through surface roughness monitored by the reflection high-energy electron diffraction and scanning tunneling microscopy. We obtain the best quality of FeSe monolayer films with the STO substrate treated at T = 900 950℃ before growth, the FeSe deposited at T = 310℃ during growth and annealed at T = 380℃ after growth. For FeTe1-xSex (x-1), both the growth temperature and annealing temperature decrease to T=260℃. According to the angle- resolved photoemission spectroscopy measurements, the superconductivity of the FeTe1-xSex film is robust and insensitive to Se concentration. All the above are instructive for further investigations of the superconductivity in FeTe1-xSex films.展开更多
We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca_(0.83)La_(0.17)Fe_(2)As_(2).A surface reconstruction associate...We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca_(0.83)La_(0.17)Fe_(2)As_(2).A surface reconstruction associated with the dimerization of As atoms is observed directly in the real space,as well as the consequent band folding in the momentum space.Besides this band folding effect,the Fermi surface topology of this material is similar to that reported previously for BaFe_(1.85)Co_(0.15)As_(2),with Γ-centered hole pockets quasi-nested to M-centered electron pockets by the antiferromagnetic wave vector.Although no superconducting gap is observed by ARPES possibly due to low superconducting volume fraction,a gap-like density of states depression of 7.7±2.9 meV is determined by scanning tunneling microscopy.展开更多
We report an angle-resolved photoemission investigation of optimally doped Ca0.33Na0.67Fe2As2. The Fermi surface topology of this compound is similar to that of the well-studied Ba0.6K0.4Fe2As2 material, except for la...We report an angle-resolved photoemission investigation of optimally doped Ca0.33Na0.67Fe2As2. The Fermi surface topology of this compound is similar to that of the well-studied Ba0.6K0.4Fe2As2 material, except for larger hole pockets resulting from a higher hole concentration per Fe atoms. We find that the quasi-nesting conditions are weakened in this compound compared to Ba0.6K0.4Fe2 As2. Similar to Ba0.6K0.4Fe2As2, we observe nearly isotropie superconducting gaps with Fermi surface-dependent magnitudes for Ca0.33Na0.67 Fe2As2. A small variation in the gap size along the momentum direction perpendicular to the surface is found for one of the Fermi surfaces. Our superconducting gap results on all Fermi surface sheets fit simultaneously very well to a global gap function derived from a strong coupling approach, which contains only 2 global parameters.展开更多
基金Supported by the National Basic Research Program of China under Grant No 2013CB921700the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB07000000the National Natural Science Foundation of China under Grant Nos 11204359 and 11121063
文摘Angle-resolved photoemission spectroscopy is performed to study the bulk and surface electronic structures of non- superconducting IrTe2 and superconducting Pto.oblro.95 Te2. In addition to the bulk electronic bands predicted by the local density approximation calculations, we observe two Dirac cone-like bands at the Brillouin zone center, which are non-dispersive along kz, suggesting that the extra bands are surface state bands. As the experimental results are well consistent with the ab initio calculations of surface states, the parity analysis proves that these surface state bands are topologically trivial and thus exclude (PtxIr1-x)Te2 as a possible topological superconductor candidate.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB921700,2015CB921300 and2015CB921301the National Natural Science Foundation of China under Grant Nos 11234014,11622435,11274362,11674371 and11474340+1 种基金the National Key Research and Development Program of China under Grant Nos 2016YFA0300300,2016YFA0300600,2016YFA0401000 and 2016YFA0400902the Open Large Infrastructure Research of Chinese Academy of Sciences,and the Pioneer Hundred Talents Program(Type C)of Chinese Academy of Sciences
文摘The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c(~21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.
基金Supported by the Ministry of Science and Technology of China under Grant Nos 2015CB921000,2016YFA0401000,2015CB921301 and 2016YFA0300300the National Natural Science Foundation of China under Grant Nos 11274381,11574371,11274362,1190020,11334012 and 11674371
文摘We report the growth process of FeTe1-xSex (0 〈 x 〈 1) monolayer films on SrTi03 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parameters of substrate treatment, growth control and post growth annealing, we successfully obtain a series of FeTe1-xSex monolayer films. In the whole growth process, we find the significance of the temperature control through surface roughness monitored by the reflection high-energy electron diffraction and scanning tunneling microscopy. We obtain the best quality of FeSe monolayer films with the STO substrate treated at T = 900 950℃ before growth, the FeSe deposited at T = 310℃ during growth and annealed at T = 380℃ after growth. For FeTe1-xSex (x-1), both the growth temperature and annealing temperature decrease to T=260℃. According to the angle- resolved photoemission spectroscopy measurements, the superconductivity of the FeTe1-xSex film is robust and insensitive to Se concentration. All the above are instructive for further investigations of the superconductivity in FeTe1-xSex films.
基金Supported by Chinese Academy of Sciences(2010Y1JB6)the National Basic Research Program of China(2010CB923000 and 2011CBA001000)+3 种基金the National Natural Science Foundation of China(11004232 and 11050110422)the Sino-Swiss Science and Technology Cooperation(No IZLCZ2138954)The work in Houston is supported in part by US Air Force Office of Scientific Research under Contract No FA9550-09-1-0656Department of Energy Subcontract No 4000086706 through ORNL,AFRL Subcontract No R15901(CONTACT)through Rice University,the T.L.L.Temple Foundation and the John J.and Rebecca Moores Endowment,and the State of Texas through TCSUH.
文摘We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca_(0.83)La_(0.17)Fe_(2)As_(2).A surface reconstruction associated with the dimerization of As atoms is observed directly in the real space,as well as the consequent band folding in the momentum space.Besides this band folding effect,the Fermi surface topology of this material is similar to that reported previously for BaFe_(1.85)Co_(0.15)As_(2),with Γ-centered hole pockets quasi-nested to M-centered electron pockets by the antiferromagnetic wave vector.Although no superconducting gap is observed by ARPES possibly due to low superconducting volume fraction,a gap-like density of states depression of 7.7±2.9 meV is determined by scanning tunneling microscopy.
基金Supported by Chinese Academy of Sciences under Grant No 2010YIJB6, the National Basic Research Program of China under Grant Nos 2010CB923000, 2011CBA001000 and 2013CB921703, and the National Natural Science Foundation of China under Grant Nos 11004232, 11050110422, 11234014 and 11274362, and the Sino-Swiss Science and Technology Cooperation under Grant No IZLCZ2 138954. We thank J P Hu for useful discussions. This work was partly performed at the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland, and at BESSY, Helmholtz Zentrum, Berlin, Germany.
文摘We report an angle-resolved photoemission investigation of optimally doped Ca0.33Na0.67Fe2As2. The Fermi surface topology of this compound is similar to that of the well-studied Ba0.6K0.4Fe2As2 material, except for larger hole pockets resulting from a higher hole concentration per Fe atoms. We find that the quasi-nesting conditions are weakened in this compound compared to Ba0.6K0.4Fe2 As2. Similar to Ba0.6K0.4Fe2As2, we observe nearly isotropie superconducting gaps with Fermi surface-dependent magnitudes for Ca0.33Na0.67 Fe2As2. A small variation in the gap size along the momentum direction perpendicular to the surface is found for one of the Fermi surfaces. Our superconducting gap results on all Fermi surface sheets fit simultaneously very well to a global gap function derived from a strong coupling approach, which contains only 2 global parameters.