二维应变作用下超导薄膜LiFeAs的磁性和电子性质
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摘要
基于密度泛函理论的第一性原理计算,研究了二维应变作用下LiFeAs超导薄膜的磁性结构、电子能带和态密度变化,分析了应变对其超导电性的作用.结果显示,对体系施加1%—6%的二维平面张、压应变均不改变其基态条形反铁磁性结构,费米面附近的电子态密度主要来自于Fe-3d轨道电子以及少量的As-4p电子.研究发现,与无应变情形相比,当施加压应变时,体系中Fe离子的反平行的电子自旋局域磁矩减小,薄膜反铁磁性受到抑制,费米面上电子态密度增加,超导电性来自于以反铁磁超交换耦合作用为媒介的空穴型费米面和电子型费米面间嵌套的Cooper电子对.而在张应变作用时,局域反铁磁性增强,费米面上电子态密度减小,金属性减弱,特别是张应变时费米面上空穴型能带消失, Cooper电子对出现概率显著降低,将抑制超导相变.
The magnetism, band properties and electronic density of states of LiFeAs superconducting thin film with two-dimensional strain are investigated by using the first principles calculations based on density functional theory, and the influences of different strains on the characteristics of superconducting films are analyzed in detail. The results show that the magnetic ground configuration is the striped antiferromagnetic state of nostrained LiFeAs thin film, and the ground structure of this system is unchanged in the range of applied1%-6% compressive and tensile strain. The density of states near the Fermi level is mainly from the contribution of Fe-3d orbital and a few As-4p electrons. The electron spin exchange coupling between Fe ions is realized by As ions. Furthermore, unlike the case of the nostrain and the tensile strain, with increasing the compressive strain, the localized antiparallel electron spin magnetic moments of Fe ion decrease, the density of states at the Fermi surface improves, and the itinerant electron magnetism of Fe ions increases, which all greatly suppress the antiferromagnetic properties of thin film and enhance the superconducting phase transition temperature. The superconductivity of LiFeAs thin film originates from the Cooper pairs of electrons between the hole-type and electronic-type bands near the Fermi surface through the antiferromagnetic superexchange coupling effect. Instead, the LiFeAs thin film with the tensile strain presents completely opposite properties,that is to say, the decrease of the electronic density of states in the Fermi level brings about the weakening of the metal properties and the increasing of the antiferromagnetic exchange coupling. Particularly, the band structure of hole-type near the Fermi surface disappears, and the occurrence of Cooper pairs of electrons becomes significantly reduced, resulting in the suppressed superconducting phase transition when the LiFeAs thin film is subjected to tensile strain. In addition, the change of antiferromagnetic exchange coupling and magnetic moments of Fe ions are also explained according to the variation of electronic density of states of the Fe-3d energy levels during the distortion of FeAs tetrahedrons due to compressive strain. In brief, our researches provide an effective way to improve the superconducting properties of LiFeAs thin film and may promote the relevant practical applications of iron-based superconductors in the future.
The magnetism, band properties and electronic density of states of LiFeAs superconducting thin film with two-dimensional strain are investigated by using the first principles calculations based on density functional theory, and the influences of different strains on the characteristics of superconducting films are analyzed in detail. The results show that the magnetic ground configuration is the striped antiferromagnetic state of nostrained LiFeAs thin film, and the ground structure of this system is unchanged in the range of applied1%-6% compressive and tensile strain. The density of states near the Fermi level is mainly from the contribution of Fe-3d orbital and a few As-4p electrons. The electron spin exchange coupling between Fe ions is realized by As ions. Furthermore, unlike the case of the nostrain and the tensile strain, with increasing the compressive strain, the localized antiparallel electron spin magnetic moments of Fe ion decrease, the density of states at the Fermi surface improves, and the itinerant electron magnetism of Fe ions increases, which all greatly suppress the antiferromagnetic properties of thin film and enhance the superconducting phase transition temperature. The superconductivity of LiFeAs thin film originates from the Cooper pairs of electrons between the hole-type and electronic-type bands near the Fermi surface through the antiferromagnetic superexchange coupling effect. Instead, the LiFeAs thin film with the tensile strain presents completely opposite properties,that is to say, the decrease of the electronic density of states in the Fermi level brings about the weakening of the metal properties and the increasing of the antiferromagnetic exchange coupling. Particularly, the band structure of hole-type near the Fermi surface disappears, and the occurrence of Cooper pairs of electrons becomes significantly reduced, resulting in the suppressed superconducting phase transition when the LiFeAs thin film is subjected to tensile strain. In addition, the change of antiferromagnetic exchange coupling and magnetic moments of Fe ions are also explained according to the variation of electronic density of states of the Fe-3d energy levels during the distortion of FeAs tetrahedrons due to compressive strain. In brief, our researches provide an effective way to improve the superconducting properties of LiFeAs thin film and may promote the relevant practical applications of iron-based superconductors in the future.
引文
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[27] Yi W, Wu Q, Sun L L 2017 Acta Phys. Sin. 66 037402(in Chinese)[衣玮,吴奇,孙力玲2017物理学报66 037402]
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[29] Li B, Xing Z W, Liu M 2011 Acta Phys. Sin. 60 077402(in Chinese)[李斌,邢钟文,刘楣2011物理学报60 077402]
[2] Dai P C 2015 Rev. Mod. Phys. 87 855
[3] Du Z Y, Fang D L, Wang Z Y, Du G, Yang X, Yang H, Gu G D, Wen H H 2015 Acta Phys. Sin. 64 097401(in Chinese)[杜增义,方德龙,王震宇,杜冠,杨雄,杨欢,顾根大,闻海虎2015物理学报64 097401]
[4] Dubroka A, Kim K W, Rossle M, Malik V K, Drew A J, Liu R H, Wu G, Chen X H, Bernhard C 2008 Phys. Rev. Lett.101 097011
[5] Ma L, Zhang J, Chen G F, Yu W Q 2010 Phys. Rev. B 82180501
[6] Qureshi N, Steffens P, Drees Y, Komarek A C, Lamago D,Sidis Y, Harnagea L, Grafe H J, Wurmehl S, Buchner B,Braden M 2012 Phys. Rev. Lett. 108 117001
[7] Wang M, Wang M Y, Miao H, Carr S V, Abernathy D L,Stone M B, Wang X C, Xing L Y, Jin C Q, Zhang X T, Hu J P, Xiang T, Ding H, Dai P C 2012 Phys. Rev. B 86 144511
[8] Umezawa K, Li Y, Miao H, Nakayama K, Liu Z H, Richard P, Sato T, He J B, Wang D M, Chen G F, Ding H,Takahashi T, Wang S C 2012 Phys. Rev. Lett. 108 037002
[9] Qureshi N, Steffens P, Lamago D, Sidis Y, Sobolev O, Ewings R A, Harnagea L, Wurmehl S, Buchner B, Braden M 2014Phys. Rev. B 90 144503
[10] Zhang S J, Wang X C, Sammynaiken R, Tse J S,Yang L X,Li Z, Liu Q Q, Desgreniers S, Yao Y, Liu H Z, Jin C Q 2009Phys. Rev. B 80 014506
[11] Zeng B, Watanabe D, Zhang Q R, Li G, Besara T, Siegrist T,Xing L Y, Wang X C, Jin C Q, Goswami P, Johannes M D,Balicas L 2013 Phys. Rev. B 88 144518
[12] Jin C Q, Liu Q Q, Deng Z, Zhang S J, Xing L Y, Zhu J L,Kong P P, Wang X C 2013 Chinese Journal of High Pressure Physics 27 473(in Chinese)[靳常青,刘青清,邓正,张思佳,邢令义,朱金龙,孔盼盼,望贤成2013高压物理学报27 473]
[13] Li Y, Yin Z P, Wang X C, Tam D W, Abernathy D L,Podlesnyak A, Zhang C L, Wang M, Xing L Y, Jin C Q,Haule K, Kotliar G, Maier T A, Dai P C 2016 Phys. Rev.Lett. 116 247001
[14] Miao H, Qian T, Shi X, Richard P, Kim T K, Hoesch M,Xing L Y, Wang X C, Jin C Q, Hu J P, Ding H 2015 Nat.Commun. 6 6056
[15] Pitcher M J, Parker D R, Adamson P, Herkelrath S J C,Boothroyd A T, Ibberson R M, Brunell M, Clarke S J 2008Chem. Commun. 45 5918
[16] Li S C, Gan Y, Wang J H, Ran K J, Wen J S 2015 Acta Phys.Sin. 64 097503(in Chinese)[李世超,甘远,王靖辉,冉柯静,温锦生2015物理学报64 097503]
[17] Tapp J H, Tang Z J, Lv B, Sasmal K, Lorenz B, Chu P C W,Guloy A M 2008 Phys. Rev. B 78 060505
[18] Kawasaki S, Mabuchi T, Maeda S, Adachi T, Mizukami T,Kudo K, Nohara M, Zheng G Q 2015 Phys. Rev. B 92 180508
[19] Wang H D, Dong C H, Li Z J, Mao Q H, Zhu S S, Feng C M,Yuan H Q, Fang M H 2011 Europhys. Lett. 93 47004
[20] Tafti F F, Ouellet A, Juneau-Fecteau A, Faucher S,Lapointe-Major M, Doiron-Leyraud N, Wang A F, Luo X G,Chen X H, Taillefer L 2015 Phys. Rev. B 91 054511
[21] Kriiger E, Strunk H P 2014 J. Supercond. Nov. Magn. 27 601
[22] Mollah S 2004 J. Phys.:Condeus. Matter 16 R1237
[23] Zhang J H, Ma R, Liu S, Liu M 2006 Acta Phys. Sin. 55 4816(in Chinese)[张加宏,马荣,刘甦,刘楣2006物理学报554816]
[24] Yu R 2015 Acta Phys. Sin. 64 217102(in Chinese)[俞榕2015物理学报64 217102]
[25] Chen Z J, Xu G B, Yan J G, Kuang Z, Chen T H, Li D H2016 J. Appl. Phys. 120 235103
[26] Yu R, Zhu J X, Si Q M 2011 Phys. Rev. Lett. 106 186401
[27] Yi W, Wu Q, Sun L L 2017 Acta Phys. Sin. 66 037402(in Chinese)[衣玮,吴奇,孙力玲2017物理学报66 037402]
[28] Lankau A, Koepernik K, Borisenko S, Zabolotnyy V, Buchner B, Brink J V D, Eschrig H 2010 Phys. Rev. B 82 184518
[29] Li B, Xing Z W, Liu M 2011 Acta Phys. Sin. 60 077402(in Chinese)[李斌,邢钟文,刘楣2011物理学报60 077402]