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拓扑半金属磷化钼(MoP)同时具有三重和二重简并费米子. 为了研究其费米面以上的激发态超快动力学特性, 对其进行了时间分辨超快泵浦-探测实验. 获得了MoP的准粒子动力学, 包含来源于电子-声子散射的快分量, 寿命为0.3 ps, 以及来源于声子-声子散射的慢分量, 寿命为150 ps. 温度依赖的研究表明, 快分量和慢分量的弛豫寿命均随着温度的增加产生微小增大. 同时还激发并探测到一支相干态声学支声子, 其由热应力引起, 频率为0.033 THz且不随温度而改变. 对于MoP激发态准粒子超快动力学以及相干态声子的研究为理解该体系总体的激发态超快动力学特性以及电子-声子相互作用对温度的依赖提供了有益的实验依据.We employ the time resolved pump probe experiment to investigate the ultrafast dynamics in a topological semimetal molybdenum phosphide (MoP), which exhibits triple degenerate points in the momentum space. Two relaxation processes with the lifetime of 0.3 and 150 ps have been observed. We attribute the fast component to the electron-phonon scattering and the slow component to the phonon-phonon scattering, respectively. Temperature dependence investigation shows that both the lifetimes of the fast and slow components enhance slightly with increasing temperature. We also successfully generate and detect a thermal-stress-induced coherent acoustic phonon mode with a frequency of 0.033 THz, which does not vary with temperature. Our ultrafast spectroscopy investigation of the quasiparticle dynamics and the coherent phonon in MoP provides useful experimental facts and information about the overall excited state dynamics and the temperature dependence of electron-phonon coupling.
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Keywords:
- ultrafast spectroscopy /
- triple degenerate fermions /
- electron-phonon coupling /
- topological semimetal
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图 1 MoP的时间分辨超快动力学过程 (a) 温度从7 K到290 K变化的∆R/R0曲线; (b)进行泵浦探测实验所用MoP样品的SEM图片; (c)和(d)分别为MoP样品在不同角度下的晶格结构. 蓝色和红色小球分别代表Mo原子和P原子
Fig. 1. Time-resolved pump-probe spectroscopy showing the ultrafast dynamics of MoP: (a) The ∆R/R0 of MoP at several typical temperatures from 7 to 290 K; (b) SEM image of our sample; (c) and (d) Schematic lattice structures of MoP. Blue and red balls: Mo and P atoms, respectively.
图 3 温度为7 K的∆R/R0的拟合结果, 其中空心圆圈代表原始实验数据, 蓝色实线代表拟合曲线. 插图为激发的相干态声学支声子的频率对温度的依赖, 在整个温区均为0.033 THz
Fig. 3. Fitting of the ∆R/R0 at 7 K, where the black circles represent the raw data and the blue curve represents the fitting result, respectively. The inset illustrates the temperature dependence of the frequency of the coherent acoustic phonon, which stays 0.033 THz for the whole temperature range.
图 4 光激发载流子的弛豫过程对温度的依赖 (a)Afast, (b)τfast, (c)Afast和(d)τslow分别表示快分量和慢分量的幅值和寿命随温度的变化.红色和蓝色分别代表快分量和慢分量
Fig. 4. Temperature dependence of the amplitudes and lifetimes: (a)Afast, (b)τfast, (c)Afast和(d)τslow. The red and blue linesdenote the fast and slow components, respectively.
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[1] Armitage N P, Mele E J, Vishwanath A 2018 Rev. Mod. Phys. 90 015001
Google Scholar
[2] Wang Z J, Weng H M, Wu Q S, Dai X, Fang Z 2013 Phys. Rev. B 88 125427
Google Scholar
[3] Liu Z K, Jiang J, Zhou B, Wang Z J, Zhang Y, Weng H M, Prabhakaran D, Mo S K, Peng H, Dudin P, Kim T, Hoesch M, Fang Z, Dai X, Shen Z X, Feng D L, Hussain Z, Chen Y L 2014 Nat. Mater. 13 677
Google Scholar
[4] Wan X G, Turner A M, Vishwanath A, Savrasov S Y 2011 Phys. Rev. B 83 205101
Google Scholar
[5] Huang X C, Zhao L X, Long Y J, Wang P P, Chen D, Yang Z H, Liang H, Xue M Q, Weng H M, Fang Z, Dai X, Chen G F 2015 Phys. Rev. X 5 031023
[6] Bradlyn B, Cano J, Wang Z J, Vergniory M G, Felser C, Cava R J, Bernevig B A 2016 Science 353 6299
Google Scholar
[7] Lv B Q, Feng Z L, Xu Q N, Gao X, Ma J Z, Kong L Y, Richard P, Huang Y B, Strocov V N, Fang C, Weng H M, Shi Y G, Qian T, Ding H 2017 Nature 546 627
Google Scholar
[8] Chi Z H, Chen X L, An C, Yang L X, Zhao J G, Feng Zili, Zhou Y H, Zhou Y, Gu C C, Zhang B W, Yuan Y F, Curtis K B, Yang W G, Wu G, Wan X G, Shi Y G, Yang X P, Yang Z R 2018 npj. Quantum. Materials 3 28
Google Scholar
[9] Zhu Z M, Winkler G W, Wu Q S, Li J, Soluyanov A A 2016 Phys. Rev. X 6 031003
[10] Tian Y C, Zhang W H, Li F S, Wu Y L, Wu Q, Sun F, Zhou G Y, Wang L L, Ma X C, Xue Q K, Zhao J M 2016 Phys. Rev. Lett. 116 107001
Google Scholar
[11] Wu Q, Zhou H X, Wu Y L, Hu L L, Ni S L, Tian Y C, Sun F, Zhou F, Dong X L, Zhao Z X, Zhao J M 2019 arXiv 1910 09859
[12] Toda Y, Kawanokami F, Kurosawa T, Oda M, Madan I, Mertelj T, Kabanov V V, Mihailovic D 2014 Phys. Rev. B 90 094513
Google Scholar
[13] 曹宁, 龙拥兵, 张治国, 高丽娟, 袁洁, 赵伯儒, 赵士平, 杨乾生, 赵继民, 傅盘铭 2008 57 2543
Google Scholar
Cao N, Long Y B, Zang Z G, Gao L J, Yuan J, Zhao B R, Zhao S P, Yang Q S, Zhao J M, Fu P M 2008 Acta Phys. Sin. 57 2543
Google Scholar
[14] Cao N, Wei Y F, Zhao J M, Zhao S P, Yang Q S, Zhang Z G, Fu P M 2008 Chin. Phys. Lett. 25 2257
Google Scholar
[15] Sun F, Yang M, Yang M W, Wu Q, Zhao H, Ye X, Shi Y G, Zhao J M 2018 Chin. Phys. Lett. 35 116301
Google Scholar
[16] Sun F, Wu Q, Wu Y L, Zhao H, Yi C J, Tian Y C, Liu H W, Shi Y G, Ding H, Dai X, Richard P, Zhao J M 2017 Phys. Rev. B 95 235108
Google Scholar
[17] Wang M C, Qiao S, Jiang Z, Luo S N, Qi J 2016 Phys. Rev. Lett. 116 036601
Google Scholar
[18] Hu L L, Yang M, Wu Y L, Wu Q, Zhao H, Sun F, Wang W, He R, He S L, Zhang H, Huang R J, Li L F, Shi Y G, Zhao J M 2019 Phys. Rev. B 99 094307
Google Scholar
[19] Hsieh D, Mahmood F, Torchinsky D H, Cao G, Gedik N 2012 Phys. Rev. B 86 035128
Google Scholar
[20] SieE J, MclverJ, Lee Y H, Fu L, Kong J, Gedik N 2015 Nat. Mater. 14 290
Google Scholar
[21] Ge S F, Liu X F, Qiao X A, Wang Q S, Xu Z, Qiu J, Tan P H, Zhao J M, Sun D 2015 Sci. Rep. 4 5722
[22] Wang R, Wang T, Zhou Y, Wu Y L, Zhang X X, He X Y, Peng H L, Zhao J M, Qiu X H 2019 2D Mater. 6 035034
[23] Wang Y J, Chen H L, Sun M T, Yao Z G, Quan B G, Liu Z, Weng Y X, Zhao J M, Gu C Z, Li J J 2017 Carbon 122 98
Google Scholar
[24] Zhao J M, Bragas A V, Lockwood D J, Merlin R 2004 Phys. Rev. Lett. 93 107203
Google Scholar
[25] Zhao J M, Bragas A V, Merlin R, Lockwood D J 2006 Phys. Rev. B 73 184434
Google Scholar
[26] Aku-Leh C, Zhao J M, Merlin R, Menéndez J, Cardona M 2005 Phys. Rev. B 71 205211
Google Scholar
[27] Bragas A V, Aku-Leh C, Costantino S, Ingale A, Zhao J M, Merlin R 2004 Phys. Rev. B 69 205306
Google Scholar
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