Topologically nontrivial interband plasmons in type-II Weyl semimetal MoTe₂

In many realistic topological materials, more than one kind of fermions contribute to the electronic bands crossing the Fermi level, leading to various novel phenomena. Here, using momentum-resolved inelastic electron scattering, we investigate the plasmons and their evolution across the phase transition in a type-II Weyl semimetal MoTe2, in which both Weyl fermions and trivial electrons contribute to the Fermi surface in the T d phase. One plasmon mode in the 1T′ phase at high temperature and two plasmon modes in the topological T d phase at low temperature are observed. Combining with first-principles calculations, we show that all the plasmon modes are dominated by the interband correlations between the inverted bands of MoTe2. Especially in the T d phase, since the electronic bands split due to inversion symmetry breaking and spin-orbit coupling, the plasmon modes manifest the interband correlation between the topological Weyl fermions and the trivial electrons. Our work emphasizes the significance of the interplay between different kinds of carriers in plasmons of topological materials.