Lifshitz Transitions Induced by Temperature and Surface Doping in Type‐II Weyl Semimetal Candidate T_d‐WTe₂

Abstract

Using high resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of T d -WTe 2 , which has attracted substantial research attention due to its diverse and fascinating properties, especially the predicted type-II topological Weyl semimetal (TWS) phase. The observed significant lattice contraction and the fact that our ARPES measurements are well reproduced by our ab initio calculations under reduced lattice constants support the theoretical prediction of a type-II TWS phase in T d -WTe 2 at temperatures below 10 K. We also investigate the evolution of the electronic structure of T d -WTe 2 and realize two-stage Lifshitz transitions induced by temperature regulation and surface modification, respectively. Our results not only shed light on the understanding of the electronic structure of T d -WTe 2 , but also provide a promising method to manipulate the electronic structures and physical properties of the type-II TWS T d -XTe 2 .Topological Weyl semimetals (TWSs) are characterized by the existence of bulk Weyl fermions and topological surface Fermiarcs connecting each pair of Weyl points (WPs) of opposite chirality. [1] Upon their discovery, TWSs have evoked enormous research interests due to their intriguing physical properties and broad application potential. [1][2][3][4][5][6][7][8][9] Soon after the establishment of the TWS phase in the transition metal mono-pnictide (TMMP) family, [10][11][12][13][14][15][16][17] the type-II TWS phase was theoretically proposed in T d -XTe 2 (X ¼ W, Mo) that violates the Lorentz symmetry, [18] thus the strongly tilted bulk Weyl cones introduce non-vanishing bulk (both electron and hole) Fermi pockets on the Fermi surface (FS). [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Compared to the complicated distribution of 24 Weyl fermions in the TMMPs and their three-dimensional (3D) crystal structures, [10][11][12][13][14][15] T d -XTe 2 not only has much more concise distribution of Weyl fermions, but also crystallizes into layered structure, thus providing a more promising material basis to design, process, and fabricate TWS-based electronic and spintronic devices.Besides being recognized as type-II TWSs, T d -XTe 2 materials are well known to possess other rich and intriguing physical properties, such as quantum spin Hall effect, [36][37][38] nonsaturating magnetoresistance, [39,40] strong spin-orbit

125Te spin-lattice relaxation in a candidate to Weyl semimetals WTe2

“…The quadratic temperature dependence of tellurium spin relaxation in WTe 2 might result from changes of the band structure induced by temperature [34,52,53].…”

“…For semimetals the temperature dependence of the Knight shift can be pronounced even below room temperature because of the low Fermi energy (and associated fast variation of the chemical potential)[42] and transformation of the electron and hole pockets. For the particular case of WTe 2 the Knight shift should be additionally affected by pronounced changes in the electron and hole bands upon increasing temperature, which led to the Lifshitz transition[34,52,53]. It was shown in[34] that the band transformation is associated with the complete disappearance of the hole pockets above 160 K. On the contrary, the chemical shift varies feebly with temperature except for the ranges of the structural phase transitions.…”

Angle‐Resolved Photoemission of Topological Matter: Examples from Magnetism, Electron Correlation, and Phase Transitions

“…This enabled the observation of a Lifshitz transition by temperature [ 115 ] and by surface doping with potassium. [ 116 ] Despite enormous experimental progress, there are several outstanding issues such as the direct observation of the Weyl points, the clarification of the number of Fermi pockets, [ 112,116 ] and a determination of the length of the Fermi arcs. The spin texture is apparently rather complex but spin polarization in agreement with time‐reversal symmetry has been measured for the range of the Fermi arc [ 117 ] and the hole pocket.…”

Mode-resolved reciprocal space mapping of electron-phonon interaction in the Weyl semimetal candidate Td-WTe$_2$

“…1(b)] [8]. Even though ARPES studies did not succeed in observing Weyl points in this material so far [11][12][13][14][15][16][17], the observation of Weyl orbit related quantum oscillations and an anisotropic magnetoresistance [18], the detection of Weyl points via scanning tunneling spectroscopy [19], and the observation of an anisotropic Adler-Bell-Jackiw anomaly [20] give strong experimental evidence that Td -WTe 2 is indeed a type-II WSM.…”