摘要
自旋翻转和自旋转移是实现基于内嵌富勒体系自旋逻辑功能器件设计的先决条件.本文以双磁性中心内嵌富勒烯Y_2C_2@C8_2-C_2(1)体系为例,采用第一性原理计算方法,结合Λ进程理论模型和自编的遗传算法程序,在该内嵌富勒烯体系中分别实现了亚皮秒时间尺度内的自旋翻转和自旋转移过程.计算结果表明,优化后的内嵌Y_2C_2团簇结构和实验得到的各项数据基本吻合,并且会对外部的C8_2-C_2(1)笼结构产生一定的排斥力,但由于富勒烯笼状结构具有很强的稳定性,所以整个体系仍然保持碳笼结构的完整性.通过对自旋密度分布与激光脉冲作用下自旋期望值演化的具体分析,经由Λ进程的自旋翻转是基于两个Y元素的整体自旋翻转;自旋转移则源自两个磁性中心以及碳笼之间在激光脉冲作用下的自旋密度重新分布.本文结果揭示了Y_2C_2@C8_2-C_2(1)体系中的超快自旋动力学机理,可望为基于实际内嵌富勒烯分子的自旋逻辑功能器件设计提供理论依据.
Spin switching and spin transfer are essential prerequisites for designing the spin-logic devices based on endohedral fullerenes. In this paper by combining the theoreticalΛ-process model with a self-designed genetic algorithm, we are able to theoretically observe spin-switching and spin-transfer scenarios on the subpicosecond time scale in the endohedral fullerene Y_2 C_2@C_(82)-C_2(1) from first principles. The results show that the geometry of the optimized enclosed Y_2 C_2 cluster is consistent with the experimental data. There exists a certain repulsive force between the external C_(82)-C_2(1) cage and the encaged cluster. However, the whole system still maintains its integral cage structure due to the excellent stability of the fullerene. In the Y_2 C_2@C82-C_2(1) system, it is found that the spin density is highly localized on the two Y atoms and only minimally distributed on the carbon cage.By analyzing the spin-density distribution and the evolution of the spin expectation values as influenced by the laser pulses, it is found that global spin switching can be achieved on the two Y atoms, while spin transfer between the two Y atoms actually results from the redistribution of the spin density among the two magnetic centers and the carbon cage under the action of the optimized laser pulses. The achieved spin-switching scenario completes within about 1000 fs and its fidelity reaches 97.8%, while the obtained spin-transfer process completes within 200 fs and its fidelity reaches 95.1%. The electron absorption spectra of the system verify that optical transitions are possible between the main intermediate states and the initial and final states involved in the spin-switching and spin-transfer scenarios. Therefore, by analyzing the electron absorption spectra corresponding to the initial and final states, the energy of the laser pulses adopted for the studied spin-dynamics process can be predicted, and the spin transferability can be evaluated. In addition, it is found that the smaller the detuning between the required energy difference and the applied laser pulse energy is, the greater the probability for spin switching/transfer scenarios becomes. The present results reveal the mechanisms of the laser-induced ultrafast spin dynamics in Y_2 C_2@C82-C_2(1) and can provide a theoretical basis for designing the spin-logic devices on realistic endohedral fullerenes.
引文
[1] Li J L, Yang G W 2009 Appl. Phys. Lett. 95 085411
[2] Li J L, Yang G W 2009 J. Phys. Chem. C 113 18292
[3] Wang J, Ma L, Liang Y, Gao M, Wang G 2014 J. Theor.Comput. Chem. 13 162
[4] Cox B J, Thamwattana N, Hill J M 2007 Proc. Math. Phys.Eng. Sci. 463 461
[5] Li C, Liu J, Zhang S, Lefkidis G, Hiibner W 2015 Carbon 87153
[6] Jin P, Hou Q, Tang C, Chen Z 2015 Theor. Chem. Acc. 134 1
[7] Xiao Y, Zhu S E, Liu D J, Suzuki M, Lu X, Wang G W 2014Angew. Chem. Int. Edit. 126 3050
[8] Zhang N, Zhang Y, Yang M Q, Tang Z R, Xu Y J 2013 J.Catal. 299 210
[9] Ren J M, Subbiah J, Zhang B, Ishitake K, Sat oh K,Kamigaito M, Qiao G G, Wong E H, Wong W W 2016 Chem.Commun. 52 3356
[10] Johnston H J, Hutchison G R, Christensen F M, Aschberger K, Stone V 2010 Toxicol. Sci. 114 162
[11] Shu C, Corwin F D, Zhang J, Chen Z, Reid J E, Sun M, Xu W, Sim J H, Wang C, Fatouros P P 2009 Bioconjugate.Chem. 20 1186
[12] Chai Y, Guo T, Jin C, Haufler R E, Chibante L P F, Fure J,Wang L, Alford J M, Smalley R E 1991 J. Phys. Chem. 95557
[13] Wang C R, Kai T, Dr T T, Yoshida T, Dr Y K, Dr E N, Dr M T, Sakata M, Dr H S 2001 Angew. Chem. Int. Ed. Engl. 40397
[14] Chen N, Chaur M N, Moore C, Pinzon J R, Valencia R,Rodriguezfortea A, Poblet J M, Echegoyen L 2010 Chem.Commun. 46 4818
[15] Li F F, Chen N, Muletgas M, Triana V, Murillo J,Rodriguezfortea A, Poblet J M, Echegoyen L 2013 Chem. Sci.4 3404
[16] Jin P, Tang C, Chen Z 2014 Coordin. Chem. Rev. 270-271 89
[17] Dunsch L, Yang S, Zhang L, Svitova A, Oswald S, Popov A A 2010 J. Am. Chem. Soc. 132 5413
[18] Harneit W 2002 Phys. Rev. A 65 184
[19] Benjamin S C, Ardavan A, Briggs G A D, Britz D A,Gunlycke D, Jefferson J, Jones M A G, Leigh D F, Lovett B W, Khlobystov A N 2005 J. Phys-Condens. Matt. 18 1599
[20] Ju C, Suter D, Du J 2011 Phys. Lett. A 375 1441
[21] Beaurepaire E, Merle J, Daunois A, Bigot J 1996 Phys. Rev.Lett. 76 4250
[22] Koopmans B, Ruigrok J J, Longa F D, de Jonge W J 2005Phys. Rev. Lett. 95 267207
[23] Bigot J Y, Vomir M, Beaurepaire E 2009 Nat. Phys. 5 515
[24] Battiato M, Carva K, Oppeneer P M 2010 Phys. Rev. Lett.105 027203
[25] Stohr J, Siegmann H C 2006 Magnetism-From Fundamentals to Nanoscale Dynamics(Berlin Heidelberg:Springer-Verlag)p753
[26] Li C, Liu J, Zhang S, Lefkidis G, Hubner W 2015 IEEE. T.Magn. 51 11
[27] Li C, Liu J, Lefkidis G, Hubner W 2017 Phys. Chem. Chem.Phys. 19 673
[28] Jin F, Tamm N B, Troyanov S I, Yang S 2018 J. Am. Chem.Soc. 140 3496
[29] Li C, Yang F, Lefkidis G, Hubner W 2011 Acta Phys. Sin. 60017802(in Chinese)[李春,杨帆,Georgios Lefkidis,Wolfgang Hiibner 2011物理学报60 017802]
[30] Li C, Jin W, Xiang H, Lefkidis G, Hiibner W 2011 Phys. Rev.B 84 2250
[31] Li C, Zhang S B, Jin W, Lefkidis G, Hubner W 2012 ActaPhys.Sin. 61 177502(in Chinese)[李春,张少斌,金蔚,Georgios Lefkidis, Wolfgang Hubner 2012物理学报61177502]
[32] Zhang N, Du H, Chang J, Jin W, Li C, Lefkidis G, Hubner W2018 Phys. Rev. B 98 104431
[33] Frisch M J, Trucks G W, Schlegel H B, Scuseria G E, Robb M A, Cheeseman J R 2009 Gaussian 09, Revision A.1.(Wallingford:Gaussian Inc.)
[34] Nakatsuji H 1979 Chem. Phys. Lett. 67 329
[35] Hay P J 1985 J. Chem. Phys. 82 299
