Strain-tuned topological phase transition and unconventional Zeeman effect in ZrTe5 microcrystals

Abstract

The geometric phase of an electronic wave function, also known as Berry phase, is the fundamental basis of the topological properties in solids. This phase can be tuned by modulating the band structure of a material, providing a way to drive a topological phase transition. However, despite significant efforts in designing and understanding topological materials, it remains still challenging to tune a given material across different topological phases while tracing the impact of the Berry phase on its quantum transport properties. Here, we report these two effects in a magnetotransport study of ZrTe5. By tuning the band structure with uniaxial strain, we use quantum oscillations to directly map a weak-to-strong topological insulator phase transition through a gapless Dirac semimetal phase. Moreover, we demonstrate the impact of the strain-tunable spin-dependent Berry phase on the Zeeman effect through the amplitude of the quantum oscillations. We show that such a spin-dependent Berry phase, largely neglected in solid-state systems, is critical in modeling quantum oscillations in Dirac bands of topological materials.

The Anomalous Photo‐Nernst Effect of Massive Dirac Fermions In HfTe5

“…We hypothesize that these differences between bulk and thin may be partially related to strain for the following reasons. For the case of ZrTe 5 , experiment [20,27,60,61] and theory [19,35] suggest that the electronic structure depends sensitively on the lattice parameters. Furthermore, angle resolved photoemission spectroscopy of HfTe 5 revealed direct evidence for strain tuning between a (gapped) Dirac phase, under tensile strain, and a strong topological insulator phase, under com-pressive strain.…”

“…[12] Yet, the exact bulk electronic structure remains under debate due to fact that small changes of the lattice parameters, e.g., due to strain, strongly modify the fundamental gap or induce secondary carrier pockets. [19,20] Experimentally, a (weakly gapped) 3D Dirac dispersion centered at the Γ-point has been established as an accepted, low-energy effective model. [21][22][23] High quality crystals achieve low charge carrier densities ≈1 × 10 16 cm −3 with high low-temperature mobilities ≈1 × 10 6 cm 2 V −1 s −1 [24,25] making it possible to reach the quantum limit at fields as low as 0.3 T. [25] Experimentally, indications of anomalous electric and thermoelectric responses [26][27][28][29][30][31][32] have been reported, which are, however, contrasted by multiple studies reporting quasi-quantized, 3D Hall transport under nominally similar conditions.…”

Controllable strain-driven topological phase transition and dominant surface-state transport in HfTe5

“…Recently, indications of a strain-tuned TPT from a WTI to an STI phase in ZrTe 5 were revealed from the transport properties of the bulk charge carriers, i.e., the manifestation of the chiral anomaly by negative longitudinal magnetoresistance (NLMR) 40 and the mass gap size extracted from the quantum oscillations 41 . In addition, also in ZrTe 5 , the WTI state was observed by angle-resolved photoemission spectroscopy (ARPES) with the bulk gap tunable with external strain 33 .…”

Engineering a pure Dirac regime in ZrTe$_5$

“…Recent work showed that strain [22,58,59], and even phonons [60], can drive ZrTe 5 from an STI to a WTI phase (coherent infrared phonons can also induce a Weyl semimetal phase [61]). However, as we discuss below, in the case of the recently studied uniaxial strain along the a-direction [22,58,59], this transition can be masked by additional, trivial, pockets that lower their energy as strain is applied, yielding an overall semimetallic phase at large strain.…”

“…Recent work showed that strain [22,58,59], and even phonons [60], can drive ZrTe 5 from an STI to a WTI phase (coherent infrared phonons can also induce a Weyl semimetal phase [61]). However, as we discuss below, in the case of the recently studied uniaxial strain along the a-direction [22,58,59], this transition can be masked by additional, trivial, pockets that lower their energy as strain is applied, yielding an overall semimetallic phase at large strain. Our calculations indicate that whether this scenario or the more conventional insulatorto-insulator transition takes place is determined by a crystal structure parameter largely unaffected by strain: the Van der Waals gap of the crystal along the c-direction.…”