Acta Physica Sinica, Volume. 68, Issue 22, 227102-1(2019)
Fig. 1. (a) Illustration of a photoemission experiment; (b) curve of electric IMFP vs energy; (c) energetics of the photoemission process; (d) illustration different FSs measured by ARPES under different photon energies due to the
Fig. 2. A picture of the synchrotron-based nano-ARPES workstation in SSRF BL03U.上海光源中同步辐射束线BL03U搭载的空间分辨角分辨光电子能谱实验工作站图
Fig. 3. (a) Illustration of a 3D Dirac Fermion in 4D energy-momentum space and its projection onto different 3D subspace; (b) the crystal structure of Na3Bi; (c) 1st Brillouin zone of Na3Bi; (d) measured Fermi surface map across the whole 3D BZ (top panel) and its projection on the surface BZ (bottom panel) on pristine surfaces. 3D intensity plot of the photoemission spectra (e) along the kDy–kDx direction and (f) along the
Fig. 4. (a) Schematic of Fermi surface in Na3Bi cleaved along (100) direction; (b) Fermi surface measured by ARPES experiment; (c) spectrum cut along α from (b); (d) theoretical calculated spin texture of Fermi arcs; (e) band structure along
; (f) calculated
projected bands corresponding to (c) when
Fig. 5. 3D visualization of type-II Dirac cone: (a) Schematic of type-II Dirac cone projected on kx-ky-E space; (b) 3D ARPES map (hν = 24 eV) which slices through the type-II BDP (pointed out by magenta arrow); (c) zoomed-in ARPES constant energy contours (CECs) of Fig.(b); (d) schematic of type-II Dirac cone projected on
Fig. 6. (a) Crystal structure (with its top view) and (b) 1st Brillouin zone (with surface BZ marked in blue) of PtTe2; (c) (d) evolution of crystal-field-derived levels with the out-of-plane kz momentum when hybridization is (c)neglected or (d)included, showing a protected crossing of the A1 and E-derived levels; (e) ARPES spectrum along
Fig. 7. (a) Crystal structure of TaAs; (b) schematic of a WSM electronic structure with spin-polarized Fermi arcs connecting projections of two bulk Weyl nodes (The red and blue colors represent opposite chirality. For clarity, only surface states on the top and bottom surfaces are indicated); (c) (i) calculated position of Weyl Fermions and Fermi arcs in 1st BZ with its (ii) top view; (iii) shows the photoemission intensity plot at
Fig. 8. Observation of bulk Weyl cones and Weyl nodes in TaAs using SX-ARPES: (a) Measured and first principles calculated
Fig. 9. (a) Illustration of the separation of Weyl points (with opposite chirality, marked as WP+ and WP–) in different materials of TaAs family with increasing spin-orbital coupling effect; (b)–(d) high-resolution ARPES measurements on the (i) spoon-like FS and (ii, iii) associated band dispersions indicated by the red dotted lines for NbP, TaP and TaAs, respectively (Δ
Fig. 10. Magnetic Weyl semimetal Co3Sn2S2: (a) Exotic neighboring states of the magnetic WSM can be achieved by tuning parameters such as magnetism, thickness, and electron correlation; (b) illustration of DP splitting (into one pair or two Weyl points) caused by time reversal symmetry broken in simplest magnetic WSMs. Magenta and green color of the Weyl points represent positive (+) and negative (–) chirality, respectively; the arrows illustrate the Berry curvature.
Fig. 11. (a) Schematic illustration of type-II Weyl Fermions in the momentum space; (b) crystal structure and (c) 1st Brillouin zone of Td-MoTe2; (d) calculated W1 and W2 Weyl Fermions and Fermi arcs on CECs; (e) (i) photon-energy dependent ARPES data (
Fig. 12. Crystal structure and band structure of MoP along the
Fig. 13. Electronic structure near TP1. (a)-(c) (i) ARPES, (ii) curvature intensity plots and (iii)calculated band structure along (a) C1, (b) C2 and (c) C3; (C1, C2, C3 are blue and green lines indicated in (d)) (e) 3D plot of the band dispersions along C1 near TP1. Spectrum along C1 is recorded on the (100) cleavage surface; those along C2 and C3 are obtained on the (001) cleavage surface.拓扑简并点TP1附近的电子结构 (a)—(c)沿C1, C2, C3方向((i)—(iii))的ARPES及其能带曲率谱图与理论计算能带色散; (d) C1, C2, C3方向在体布里渊区中的位置示意图; (e)沿C1演化的TP1点附近能带分布三维色散图. C1能谱由(100)解理面采得而C2, C3由(001)解理面采得
Fig. 14. (a)Schematics of the band structures of a Weyl Fermion, a Dirac Fermion, a spin-1 Fermion and a charge-2 Fermion; (b) schematics of the Fermi arcs connecting the projections of Fermions with opposite chiralities for Weyl semimetals(up) and CoSi (down); (c) crystal structure and (d) 1st Brillouin zone of CoSi; (e) diagram of chiral edge states and Fermi arcs in 3D momentum space; (f), (g) theoretical and experimental results of Fermi surface in CoSi; (h) in-plane (along k//) spectra cut along Loop1 and Loop2 in Fig. (g). (a)四种费米子的能带示意图; (b)外尔半金属(上)与CoSi(下)中连接手性相反费米子投影的费米弧图示; (c) CoSi的晶体结构及(d)第一布里渊区示意图; (e)三维动量空间中手性边界态与费米弧示意图; (f), (g)理论计算和实验得出的CoSi费米面结果; (h)沿图(g)中Loop1和Loop2所示切出的k//面内能谱
Fig. 15. (a) Schematic illustration of Dirac node and Dirac nodal line in the momentum space; (b) crystal structure and (c) 1st Brillouin zone (together with surface BZ) of
Fig. 16. (a) Zoomed-in Brillouin zone of ZrSiS; (b) Schematic plot of the band splitting of nodal line in an arbitrary
Fig. 17. (a) Schematics of four topological configurations formed by nodal lines; (b) calculated bulk FSs in the 3D BZ and the (c) projected calculation on the
Fig. 18. Topological Lifshitz transition induced by in-situ potassium decoration: (a) and (b) are band structures of the pristine and in-situ potassium-decorated NbAs (001) surface, respectively. (i) - (iv): Measured Fermi surface, calculated and measured Fermi surface patch around point, schematic illustration of the Fermi arc connectivity to projections of pairs of Weyl points. Trivial SS is short for trivial surface states, SFAs is short for surface Fermi arcs, and WP is short for Weyl point. 原位表面钾原子修饰诱发的拓扑Lifshitz转变 (a)和(b)分别是解离的NbAs的(001)面和钾原子修饰的电子能带结构. (i)到(iv)分别是实验测得的费米面、 点附近费米面的能带计算和实验测量、费米弧连接成对外尔点的示意图. Trivial SS指平庸的表面态, SFAs指费米弧表面态, WP指外尔点.
Fig. 19. (a) Band dispersion of WTe2 crystals along
direction, showing multiple band crossings at
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Tao Deng, Hai-Feng Yang, Jing Zhang, Yi-Wei Li, Le-Xian Yang, Zhong-Kai Liu, Yu-Lin Chen.
Received: Oct. 10, 2019
Accepted: --
Published Online: Sep. 17, 2020
The Author Email: Chen Yu-Lin (yulin.chen@physics.ox.ac.uk)