Temperature-driven topological transition in 1T'-MoTe2

Ayelet Notis Berger,Nader Zaki,Maria C Asensio,Jaewook Kim,Chaoyu Chen,Alexander Kerelsky,Bogdan A Bernevig,Erick Andrade,Drew Edelberg,Jian Li,Lunyong Zhang,Jose Avila,Zhijun Wang,Abhay N Pasupathy,Sang-Wook Cheong

doi:10.1038/s41535-017-0075-y

Ayelet Notis Berger, Nader Zaki + Show 13 more

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https://doi.org/10.1038/s41535-017-0075-y

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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'-MoTe2, 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'-MoTe2. 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'-MoTe2 is ideal for separating topological and trivial electronic phenomena via temperature-dependent measurements.

Highlights

The Weyl fermion[1] is a massless chiral solution of the Dirac equation
Our scanning tunneling microscopy (STM) and ARPES measurements are performed on crystals grown by the flux method and quenched from high temperature to preserve the metastable 1T' phase at room temperature
The complete absence of the feature at high temperature rather than a suppression of the intensity could arise from a loss of topological protection of the surface state

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Several solid-state materials whose crystal structures break time reversal or inversion symmetry have been predicted[2,3,4,5,6,7,8,9,10,11] and observed[12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40] to host quasiparticle excitations that mimic free Weyl fermions In these Weyl semimetals, Weyl points exist as a touching between a hole and an electron pocket. Many unique transport characteristics have been predicted for the Weyl band structures in general and the Fermi arc states in particular.[44,45,46,47,48,49,50,51]

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