Signature of type-II Weyl semimetal phase in MoTe2

Jiang, Juan; Liu, Z. K.; Sun, Yan; Yang, Haifeng; Rajamathi, Catherine R.; Qi, Yue; Yang, Lexian; Chen, C.; Han, Peng; Hwang, Choongyu; Sun, Song; Mo, S.-K.; Vobornik, I.; Fujii, Jun; Parkin, Stuart S. P.; Felser, Claudia; Chen, Y. L.

doi:10.1038/ncomms13973

Cited by 413 publications

(306 citation statements)

References 41 publications

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“…The origin of this large surface state is currently not understood theoretically-the fact that it is single degenerate is quite unusual, since its Rashba partner seems to be missing in the surface bands. 35 While the topological properties of the surface bands are quite different in the two calculations, the actual extent ) corresponding intensity maps (2nd derivative) measured through ARPES at various energies. The color map chosen for the calculated Fermi surface uses red for the most intense values, and blue for the rest of the band structure.…”

Section: Resultsmentioning

confidence: 99%

Temperature-driven topological transition in 1T'-MoTe2

et al. 2018

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The topology of Weyl semimetals requires the existence of unique surface states. Surface states have been visualized in spectroscopy measurements, but their connection to the topological character of the material remains largely unexplored. 1T'-MoTe 2 , presents a unique opportunity to study this connection. This material undergoes a phase transition at 240 K that changes the structure from orthorhombic (putative Weyl semimetal) to monoclinic (trivial metal), while largely maintaining its bulk electronic structure. Here, we show from temperature-dependent quasiparticle interference measurements that this structural transition also acts as a topological switch for surface states in 1T'-MoTe 2 . At low temperature, we observe strong quasiparticle scattering, consistent with theoretical predictions and photoemission measurements for the surface states in this material. In contrast, measurements performed at room temperature show the complete absence of the scattering wavevectors associated with the trivial surface states. These distinct quasiparticle scattering behaviors show that 1T'-MoTe 2 is ideal for separating topological and trivial electronic phenomena via temperature-dependent measurements.

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Section: Resultsmentioning

confidence: 99%

Temperature-driven topological transition in 1T'-MoTe2

et al. 2018

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“…While transition metal dichalcogenides materials, MoTe 2 and WTe 2 , were found to show superconductivity under high pressure and both of them were considered to be the type-II Weyl semimetal. 19,[23][24][25][26][27][28][29][30][31][32][33][34][35] In this paper, we report, for the first time, the discovery of bulk superconductivity accompanied by a structure phase transition in Weyl semimetal TaP by applying high pressure. More importantly, first-principles calculations confirm that the P-6m2 phase with superconductivity induced by high pressure has the Weyl semimetal feature, but is distinct from the ambient phase.…”

Section: Introductionmentioning

confidence: 99%

Concurrence of superconductivity and structure transition in Weyl semimetal TaP under pressure

Zhou

Guo

et al. 2017

npj Quant Mater

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Weyl semimetal defines a material with three-dimensional Dirac cones, which appear in pair due to the breaking of spatial inversion or time reversal symmetry. Superconductivity is the state of quantum condensation of paired electrons. Turning a Weyl semimetal into superconducting state is very important in having some unprecedented discoveries. In this work, by doing resistive measurements on a recently recognized Weyl semimetal TaP under pressures up to about 100 GPa, we show the concurrence of superconductivity and a structure transition at about 70 GPa. It is found that the superconductivity becomes more pronounced when decreasing pressure and retains when the pressure is completely released. High-pressure x-ray diffraction measurements also confirm the structure phase transition from I4 1 md to P-6m2 at about 70 GPa. More importantly, ab-initial calculations reveal that the P-6m2 phase is a new Weyl semimetal phase and has only one set of Weyl points at the same energy level. Our discovery of superconductivity in TaP by high pressure will stimulate investigations on superconductivity and Majorana fermions in Weyl semimetals.

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“…WTe 2 [7] and MoTe 2 [8][9][10] have been proposed as possible type-II WSMs. While the topological phase of WTe 2 is still under debate, the existence of the WSM phase in the low temperature non-centrosymmetric structure of MoTe 2 is supported by the observation of surface Fermi arcs [11][12][13][14][15]. The Weyl points, however, are located above the Fermi level E F and this hinders a direct observation by conventional angle-resolved photoelectron spectroscopy (ARPES).…”

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confidence: 95%

Enhanced ultrafast relaxation rate in the Weyl semimetal phase of MoTe2 measured by time- and angle-resolved photoelectron spectroscopy

et al. 2017

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MoTe2 has recently been shown to realize in its low-temperature phase the type-II Weyl semimetal (WSM). We investigated by time-and angle-resolved photoelectron spectroscopy (tr-ARPES) the possible influence of the Weyl points in the electron dynamics above the Fermi level EF, by comparing the ultrafast response of MoTe2 in the trivial and topological phases. In the low-temperature WSM phase, we report an enhanced relaxation rate of electrons optically excited to the conduction band, which we interpret as a fingerprint of the local gap closure when Weyl points form. By contrast, we find that the electron dynamics of the related compound WTe2 is slower and temperature-independent, consistent with a topologically trivial nature of this material. Our results shows that tr-ARPES is sensitive to the small modifications of the unoccupied band structure accompanying the structural and topological phase transition of MoTe2.The recent discovery of Weyl fermions as low-energy quasiparticles in TaAs [1][2][3] and other related compounds [4,5] has boosted the interest in topological semimetals (TSMs) [6]. Type-II Weyl semimetals (WSMs) are a novel class of materials that host fermions violating Lorentz invariance [7]. These quasiparticles are realized in the strongly tilted cones that form in momentum space around special Weyl points (WPs) where the valence and conduction bands touch. WTe 2 [7] and MoTe 2 [8-10] have been proposed as possible type-II WSMs. While the topological phase of WTe 2 is still under debate, the existence of the WSM phase in the low temperature non-centrosymmetric structure of MoTe 2 is supported by the observation of surface Fermi arcs [11][12][13][14][15]. The Weyl points, however, are located above the Fermi level E F and this hinders a direct observation by conventional angle-resolved photoelectron spectroscopy (ARPES). To circumvent this difficulty, one would need a probe that is sensitive to the presence/absence of small energy band gaps in the unoccupied density of states.In this Letter we show that time-and angle-resolved photoelectron spectroscopy (tr-ARPES) can provide such information. We report a shortening of the relaxation time in the gapless type-II Weyl phase of MoTe 2 , which reflects the enhanced interband scattering from the conduction band (CB) to the valence band (VB) mediated by electron -electron scattering along the Weyl cone. These scattering processes are active only when the band gap is locally closed. This conclusion is supported by the observation of a slower, temperatureindependent dynamics in WTe 2 , indicative of a local direct band gap, which acts as an effective bottleneck for the electron relaxation.MoTe 2 is a layered material. It can be cleaved to expose large flat (001) terraces, ideal for ARPES studies. Figure 1 illustrates the WSM phase, which is only realized in the lowtemperature orthorhombic (space group Pmn2 1 ) structurehereafter referred to as the 1T' phase [17] -where inversion symmetry is broken. The crystal structure is sketched in Fig. 1 (a), along wi...

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Signature of type-II Weyl semimetal phase in MoTe2

Cited by 413 publications

References 41 publications

Temperature-driven topological transition in 1T'-MoTe2

Temperature-driven topological transition in 1T'-MoTe2

Concurrence of superconductivity and structure transition in Weyl semimetal TaP under pressure

Enhanced ultrafast relaxation rate in the Weyl semimetal phase of MoTe2 measured by time- and angle-resolved photoelectron spectroscopy

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