Giant planar Hall effect in the Dirac semimetal ZrTe5−δ

Abstract

Recently, giant planar Hall effect originating from chiral anomaly has been predicted in nonmagnetic Dirac/Weyl semimetals. ZrTe 5 is considered to be an intriguing Dirac semimetal at the boundary of weak topological insulators and strong topological insulators, though this claim still remains controversial. Here, we report the observation in ZrTe 5-δ of the giant planar Hall resistivity that shows two different magnetic-field dependences as predicted by theory and a maximum at the Lifshitz transition temperature. We found that the giant planar Hall resistivity fades out with decreasing the thickness of ZrTe 5-δ nanoplates, which may be ascribed to the vanishing of the 3D nature of the samples. In addition, we have observed a nontrivial Berry phase, chiral-anomaly-induced negative longitudinal magnetoresistance, and a giant in-plane anisotropic magnetoresistance in these ZrTe 5-δ nanoplates. All the experimental observations demonstrated coherently that ZrTe 5-δ is a Dirac semimetal.

Nonunique connection between bulk topological invariants and surface physics

“…This means in particular that one could observe a gap-closing transition with thickness for systems sufficiently close to a 3D topological phase transition. Such a thickness-tuned transition is reminiscent of recent works on ZrTe 5 [24,25], especially since it was calculated to be close to the transition between a weak and a strong topological insulating phases [22,23].…”

“…A thickness-driven transition between a topological semimetallic state and a conventional metal was conjectured from resistivity measurements [24]. Moreover, the strong in-plane Hall resistivity in this material, considered to be a signature of a semimetal, vanishes in very thin films [25]. Thickness appears to be a key parameter in the study of topological states.…”

“…The evolution of the 2D topological invariant ν with thickness in a slab geometry was shown to feature three different regions as a function of the Dirac mass [18,19]: an ordinary insulating (OI) region where ν = 0 at any thickness, a 'stripe' region where ν = 1 and ν = 0 for odd and even number of layers respectively, and between these two a 'mosaic' region where ν oscillates with thick-arXiv:1909.11782v1 [cond-mat.mes-hall] 25 Sep 2019 ness. The two latter where related to the two regimes of exponential decay of the surface gap: without and with oscillations.…”

Anisotropic planar Hall effect in the type-II topological Weyl semimetal WTe2

“…Chiral-anomalyinduced PHE for the case of E //tilting direction of Weyl cone (b axis) will also result in a sinϕ term [14]. Although the magnetic field is rotating in plane during the measurement of PHE, the slight out-of-plane components of the external magnetic fields will inadvertently introduce Hall signals in the measurements, resulting in a sinϕ behavior [17,19]. The phase shifts ϕ 1 and ϕ 2 in Eq.…”

“…The planar Hall resistivity in type-I and type-II Weyl semimetals are quadratically and linearly dependent on the magnetic field, respectively [14]. Since the prediction of theoretical work, the giant PHE has been observed in several Dirac/type-I Weyl semimetals, such as ZrTe 5 , and GdPtBi [17][18][19][20]. Although several studies report observing a chiral-anomaly-induced PHE in type-II Dirac/Weyl semimetals, e.g., VAl 3 and WTe 2 [21,22], the strong orbital magnetoresistance (OMR) in type-II Weyl makes it challenging to know, with certainty, the real physical origin of the observed PHE [23].…”