Quantum Oscillations at Integer and Fractional Landau Level Indices in Single-Crystalline ZrTe5

Abstract

A three-dimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but with linear energy dispersion in all (three) momentum directions. 3D DSs have been a fertile playground in discovering novel quantum particles, for example Weyl fermions, in solid state systems. Many 3D DSs were theoretically predicted and experimentally confirmed. We report here the results in exfoliated ZrTe5 thin flakes from the studies of aberration-corrected scanning transmission electron microscopy and low temperature magneto-transport measurements. Several unique results were observed. First, a π Berry phase was obtained from the Landau fan diagram of the Shubnikov-de Haas oscillations in the longitudinal conductivity σxx. Second, the longitudinal resistivity ρxx shows a linear magnetic field dependence in the quantum limit regime. Most surprisingly, quantum oscillations were also observed at fractional Landau level indices N = 5/3 and 7/5, demonstrating strong electron-electron interaction effects in ZrTe5.

Observation of Optical and Electrical In-Plane Anisotropy in High-Mobility Few-Layer ZrTe5

“…The extracted effective mass is 0.032me which is very close to the results in other works 10, 16,17,19 .…”

“…Therefore we can measure the lattice constants from TEM image: a = 0.40 nm and c =1.41 nm, which are very close to the results in the literature 19,30 .…”

“…On the other hand, its monolayer form is also claimed to be a candidate of quantum spin Hall insulator 12,13 , which is very rare among the natural compounds 14 . Shubnikov-de Haas oscillations 10,15,16 , Zeeman Splitting 17,18 , and fractional quantum Hall effect 19 were also observed in bulk ZrTe5.…”

Coexistence of topological Dirac fermions on the surface and three-dimensional Dirac cone state in the bulk of ZrTe5 single crystal

“…Subsequently, the concept of polaronic conduction10, semimetal-semiconductor phase transition11 and so on, have emerged until a recent theoretical work suggests that the monolayer of ZrTe 5 and Hf Te 5 is the most promising candidate for the quantum spin Hall due to the large bulk gap12. Suddenly, a material known for its large thermoelectric power6, resistivity anomaly1 and large positive magnetoresistance13, has been brought to our attention to study the topological properties of relativistic Dirac fermion in condensed matter physics451415161718192021.…”

Evidence for a Strong Topological Insulator Phase in ZrTe5

“…The close vicinity to the topological phase transition suggests the possibility of engineering the topological phase by a small variation of the interlayer distance, entering in the WTI phase. This can be achieved by changing the concentration of defects, that may vary depending on the growth conditions, thus also accounting for the experimental observation of different T* in different studies [11,15,28,29] . The topological phase transition may also be achieved in a controlled way either via alkali metal intercalation, as exploited for decoupling MoS 2 single layer [30], or via chemical substitution.…”