新型高分辨率电子能量损失谱仪与表面元激发研究
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摘要
高分辨率电子能量损失谱仪利用单色平行电子束入射样品表面,与表面吸附基团的化学键振动、表面声子、电子及其集体激发模式等相互作用而被散射,通过分析散射电子的能量和动量,可以测量表面化学键、晶格动力学、电子态占据以及表面等离激元等的精确信息,是表面科学研究的有力工具.最近,能够对电子能量、动量做二维成像探测分析的半球形电子能量分析器被引入电子能量损失谱仪,实现了高能量、动量分辨率的高效率测量.在对FeSe/SrTiO_3界面超导增强物理机制的研究中,不同厚度的FeSe膜表面的电子能量损失谱表明衬底光学声子产生的偶极电场能够穿透到薄膜内部,诱导较强的电子-声子耦合作用,从而增强薄膜中电子的配对作用,进而使超导转变温度显著提高.三维拓扑绝缘体Bi_2Se_3表面大动量范围的电子能量损失谱还显示出一支奇异的电子集体激发模式,其色散特征不受晶格周期性的限制,而且其寿命和强度几乎不随动量的增加而衰减.这说明在拓扑绝缘体表面,不仅是狄拉克电子态本身,其集体激发也受到拓扑保护.充分发挥新型电子能量损失谱仪观测表面元激发分辨率高、动态范围大的优势,将有力地推动表面界面凝聚态物理问题研究的深入和发展.
High-resolution electron energy loss spectroscopy(HREELS) is a powerful technique to probe vibrational and electronic excitations at solid surfaces. A monochromatic electron beam incident on the crystal surface may interact with the vibrations of adsorbed molecules, surface phonons or electronic excitations before being back-scattered. By analyzing the energy and momentum of the scattered electrons, we can obtain the information about the chemical bonds, lattice dynamics, occupation of electronic states, and surface plasmons. However the application of traditional HREELS to dispersion analyses is restricted by its point-by-point measurement of the energy loss spectrum for each momentum. Recently, a new strategy for HREELS was realized by utilizing a specially designed lens system with a double-cylindrical monochromator combined with a commercial Scienta hemispherical electron energy analyzer, which can be used to simultaneously measure the energy and momentum of the scattered electrons. The new system possesses improved momentum resolution, high detecting efficiency and high sampling density with no loss in energy resolution.The new HREELS system was employed to study the mechanism of the superconductivity enhancement at FeSe/SrTiO_3 interface. By surface phonon measurements on samples with different film thickness, it is revealed that the electric field associated with phonon modes of SrTiO_3 substrate can penetrate into Fe Se film and interact with the electrons therein, playing the key role in the superconductivity enhancement. The surface collective modes of three-dimensional topological insulator was also studied by using this new HREELS system. A highly unusual acoustic plasmon mode is revealed on the surface of a typical three-dimensional topological insulator Bi_2Se_3. This mode exhibits an almost linear dispersion to the second Brouillion zone center without reflecting lattice periodicity, and it remains prominent over a large momentum range, with unusually weak damping unseen in any other system. This observation indicates that the topological protection exists not only in single-particle topological states but also in their collective excitations. The application of the new HREELS system with the ability to measure large momentum range with high-efficiency, will definitely promote the development of related researches on condensed matter physics.
High-resolution electron energy loss spectroscopy(HREELS) is a powerful technique to probe vibrational and electronic excitations at solid surfaces. A monochromatic electron beam incident on the crystal surface may interact with the vibrations of adsorbed molecules, surface phonons or electronic excitations before being back-scattered. By analyzing the energy and momentum of the scattered electrons, we can obtain the information about the chemical bonds, lattice dynamics, occupation of electronic states, and surface plasmons. However the application of traditional HREELS to dispersion analyses is restricted by its point-by-point measurement of the energy loss spectrum for each momentum. Recently, a new strategy for HREELS was realized by utilizing a specially designed lens system with a double-cylindrical monochromator combined with a commercial Scienta hemispherical electron energy analyzer, which can be used to simultaneously measure the energy and momentum of the scattered electrons. The new system possesses improved momentum resolution, high detecting efficiency and high sampling density with no loss in energy resolution.The new HREELS system was employed to study the mechanism of the superconductivity enhancement at FeSe/SrTiO_3 interface. By surface phonon measurements on samples with different film thickness, it is revealed that the electric field associated with phonon modes of SrTiO_3 substrate can penetrate into Fe Se film and interact with the electrons therein, playing the key role in the superconductivity enhancement. The surface collective modes of three-dimensional topological insulator was also studied by using this new HREELS system. A highly unusual acoustic plasmon mode is revealed on the surface of a typical three-dimensional topological insulator Bi_2Se_3. This mode exhibits an almost linear dispersion to the second Brouillion zone center without reflecting lattice periodicity, and it remains prominent over a large momentum range, with unusually weak damping unseen in any other system. This observation indicates that the topological protection exists not only in single-particle topological states but also in their collective excitations. The application of the new HREELS system with the ability to measure large momentum range with high-efficiency, will definitely promote the development of related researches on condensed matter physics.
引文
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[54]Zhu X,Santos L,Howard C,Sankar R,Chou F C,Chamon C,El-Batanouny M 2012 Phys.Rev.Lett.108185501
[2]Lagos M J,Trugler A,Hohenester U,Batson P E 2017Nature 543 529
[3]Ibach H,Mills D L 1982 Electron Energy Loss Spectroscopy and Surface Vibrations(New York:Academic Press)pp1-20
[4]Qin H J,Shi J R,Cao Y W,Wu K H,Zhang J D,Plummer E W,Wen J,Xu Z J,Gu G D,Guo J D 2010 Phys.Rev.Lett.105 256402
[5]Kogar A,Rak M S,Vig S,Husain A A,Flicker F,Joe Y I,Venema L,Macdougall G J,Chiang T C,Fradkin E 2017 Science 358 1314
[6]Zhu X,Cao Y,Zhang S,Jia X,Guo Q,Yang F,Zhu L,Zhang J,Plummer E W,Guo J 2015 Rev.Sci.Instrum.86 083902
[7]LK-Technologies http://www.lktech.com/products/els-5000.php[2018-4-12]
[8]SPECS http://www.specs.de/cms/front_content.php?idart=134[2018-4-12]
[9]Valla T,Fedorov A V,Johnson P D,Wells B O,Hulbert S L,Li Q,Gu G D,Koshizuka N 1999 Science 2852110
[10]Damascelli A,Hussain Z,Shen Z X 2003 Rev.Mod.Phys.75 473
[11]Fadley C S 2010 J.Electron Spectrosc.Relat.Phenom.178 2
[12]Ibach H 1991 Electron Energy Loss SpectrometersThe Technology of High Performance(Vol.63)(Berlin:Springer-Verlag)pp131-146
[13]Wang Q,Li Z,Zhang W,Zhang Z,Zhang J,Li W,Ding H,Ou Y,Deng P,Chang K,Wen J,Song C,He K,Jia J,Ji S,Wang Y,Wang L,Chen X,Ma X,Xue Q 2012Chin.Phys.Lett.29 037402
[14]Hsu F C,Luo J Y,Yeh K W,Chen T K,Huang T W,Wu P M,Lee Y C,Huang Y L,Chu Y Y,Yan D C 2008Proc.Natl.Acad.Sci.USA 105 14262
[15]Bozovic I,Ahn C 2014 Nat.Phys.10 892
[16]Wang L,Ma X,Xue Q 2016 Supercond Sci.Technol.29123001
[17]Wang Z,Liu C,Liu Y,Wang J 2017 J.Phys.:Condens.Matter 29 153001
[18]Huang D,Hoffman J E 2017 Annual Rev.Condens.Matter Phys.8 311
[19]Shiogai J,Ito Y,Mitsuhashi T,Nojima T,Tsukazaki A2016 Nat.Phys.12 42
[20]Lei B,Cui J H,Xiang Z J,Shang C,Wang N Z,Ye GJ,Luo X G,Wu T,Sun Z,Chen X H 2016 Phys.Rev.Lett.116 077002
[21]Hanzawa K,Sato H,Hiramatsu H,Kamiya T,Hosono H 2016 Proc.Natl.Acad.Sci.USA 113 3986
[22]Miyata Y,Nakayama K,Sugawara K,Sato T,Takahashi T 2015 Nat.Mater.14 775
[23]Wen C H P,Xu H C,Chen C,Huang Z C,Lou X,Pu Y J,Song Q,Xie B P,Abdel-Hafiez M,Chareev D A,Vasiliev A N,Peng R,Feng D L 2016 Nat.Commun.710840
[24]Lu X F,Wang N Z,Wu H,Wu Y P,Zhao D,Zeng XZ,Luo X G,Wu T,Bao W,Zhang G H,Huang F Q,Huang Q Z,Chen X H 2015 Nat.Mater.14 325
[25]Zhao L,Liang A,Yuan D,Hu Y,Liu D,Huang J,He S,Shen B,Xu Y,Liu X,Yu L,Liu G,Zhou H,Huang Y,Dong X,Zhou F,Liu K,Lu Z,Zhao Z,Chen C,Xu Z,Zhou X J 2016 Nat.Commun.7 10608
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[27]Zhang P,Peng X L,Qian T,Richard P,Shi X,Ma J Z,Fu B B,Guo Y L,Han Z Q,Wang S C,Wang L L,Xue Q K,Hu J P,Sun Y J,Ding H 2016 Phys.Rev.B 94104510
[28]Zhou G,Zhang D,Liu C,Tang C,Wang X,Li Z,Song C,Ji S,He K,Wang L,Ma X,Xue Q 2016 Appl.Phys.Lett.108 202603
[29]Ding H,LüY,Zhao K,Wang W,Wang L,Song C,Chen X,Ma X,Xue Q 2016 Phys.Rev.Lett.117 067001
[30]Rebec S N,Jia T,Zhang C,Hashimoto M,Lu D H,Moore R G,Shen Z X 2017 Phys.Rev.Lett.118 067002
[31]Peng R,Xu H C,Tan S Y,Cao H Y,Xia M,Shen XP,Huang Z C,Wen C H P,Song Q,Zhang T,Xie B P,Gong X G,Feng D L 2014 Nat.Commun.5 5044
[32]Zhang S,Guan J,Wang Y,Berlijn T,Johnston S,Jia X,Liu B,Zhu Q,An Q,Xue S,Cao Y,Yang F,Wang W,Zhang J,Plummer E W,Zhu X,Guo J 2018 Phys.Rev.B 97 035408
[33]Gnezdilov V,Pashkevich Y G,Lemmens P,Wulferding D,Shevtsova T,Gusev A,Chareev D,Vasiliev A 2013Phys.Rev.B 87 144508
[34]Zhang S,Guan J,Jia X,Liu B,Wang W,Li F,Wang L,Ma X,Xue Q,Zhang J,Plummer E W,Zhu X,Guo J 2016 Phys.Rev.B 94 081116
[35]Zhang W H,Liu X,Wen C H P,Peng R,Tan S Y,Xie B P,Zhang T,Feng D L 2016 Nano Lett.16 1969
[36]Pines D,Bohm D 1952 Phys.Rev.85 338
[37]Ritchie R H 1957 Phys.Rev.106 874
[38]Landau L 1957 Soviet Physics Jetp-Ussr 3 920
[39]Pines D,Nozières P 1966 The Theory of Quantum Liquids:Normal Fermi Liquids(Vol.1)(New York:Benjamin Inc.)
[40]Ninham B W,Powell C J,Swanson N 1966 Phys.Rev.145 209
[41]Liu Y,Willis R F,Emtsev K V,Seyller T 2008 Phys.Rev.B 78 201403
[42]Roushan P,Seo J,Parker C V,Hor Y S,Hsieh D,Qian D,Richardella A,Hasan M Z,Cava R J,Yazdani A 2009Nature 460 1106
[43]Zhang T,Cheng P,Chen X,Jia J F,Ma X,He K,Wang L,Zhang H,Dai X,Fang Z,Xie X,Xue Q K 2009 Phys.Rev.Lett.103 266803
[44]Das Sarma S,Hwang E H 2009 Phys.Rev.Lett.102206412
[45]Raghu S,Chung S B,Qi X L,Zhang S C 2010 Phys.Rev.Lett.104 116401
[46]Kogar A,Vig S,Thaler A,Wong M H,Xiao Y,Reig IP D,Cho G Y,Valla T,Pan Z,Schneeloch J,Zhong R,Gu G D,Hughes T L,Mac Dougall G J,Chiang T C,Abbamonte P 2015 Phys.Rev.Lett.115 257402
[47]Di Pietro P,Ortolani M,Limaj O,Di Gaspare A,Giliberti V,Giorgianni F,Brahlek M,Bansal N,Koirala N,Oh S,Calvani P,Lupi S 2013 Nat.Nano 8 556
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[49]Politano A,Silkin V M,Nechaev I A,Vitiello M S,Viti L,Aliev Z S,Babanly M B,Chiarello G,Echenique PM,Chulkov E V 2015 Phys.Rev.Lett.115 216802
[50]Glinka Y D,Babakiray S,Johnson T A,Holcomb M B,Lederman D 2016 Nat.Commun.7 13054
[51]Zhang F,Zhou J,Xiao D,Yao Y 2017 Phys.Rev.Lett.119 266804
[52]Jia X,Zhang S Y,Sankar R,Chou F C,Wang W H,Kempa K,Plummer E W,Zhang J D,Zhu X T,Guo JD 2017 Phys.Rev.Lett.119 136805
[53]Zhu X,Santos L,Sankar R,Chikara S,Howard C,Chou F C,Chamon C,El-Batanouny M 2011 Phys.Rev.Lett.107 186102
[54]Zhu X,Santos L,Howard C,Sankar R,Chou F C,Chamon C,El-Batanouny M 2012 Phys.Rev.Lett.108185501