In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3A...In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.展开更多
The electronic structure characters are calculated for the Zn1-∞MxO alloys with some Zn atoms in ZnO substituted by 3d transition-metal atoms （M）, in order to find out which of these alloys could provide an interme...The electronic structure characters are calculated for the Zn1-∞MxO alloys with some Zn atoms in ZnO substituted by 3d transition-metal atoms （M）, in order to find out which of these alloys could provide an intermediate band material used for fabricating high efficiency solar cell. Especially, among of these alloys, the electronic structure character and optical performance of Zn1-xCr∞ 0 alloys clearly show an intermediate band filled partially and isolated from the VB and the CB in energy band structure of ZnO host, and the intermediate band characters can be preserved with increasing Cr concentrations no more than 8.33% in Zn1-xCrxO alloys, at the same time, the ratio 0.52 of Eg^FC to EVE in Zn1-xCrxO, （x = 4.16%） alloy is closest to the optimal ratio of 0,57. Besides, compared to the ZnO, the optical absorption does indicate a great improved absorption below the calculated band gap of the ZnO and an enhancement of the optical absorption in the whole solar spectral energy range.展开更多
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.
基金Supported by the State Key Program for Basic Research of China under Grant No.2006CB921803Project of High Technology Research&Development of China(Project No.2007AA03Z404)+1 种基金National Natural Science Foundation of China under Grant Nos.61274058,60990312,and 61025020Natural Science Foundation of Anhui Province under Grant No.1208085QF116
文摘The electronic structure characters are calculated for the Zn1-∞MxO alloys with some Zn atoms in ZnO substituted by 3d transition-metal atoms （M）, in order to find out which of these alloys could provide an intermediate band material used for fabricating high efficiency solar cell. Especially, among of these alloys, the electronic structure character and optical performance of Zn1-xCr∞ 0 alloys clearly show an intermediate band filled partially and isolated from the VB and the CB in energy band structure of ZnO host, and the intermediate band characters can be preserved with increasing Cr concentrations no more than 8.33% in Zn1-xCrxO alloys, at the same time, the ratio 0.52 of Eg^FC to EVE in Zn1-xCrxO, （x = 4.16%） alloy is closest to the optimal ratio of 0,57. Besides, compared to the ZnO, the optical absorption does indicate a great improved absorption below the calculated band gap of the ZnO and an enhancement of the optical absorption in the whole solar spectral energy range.
