Thermodynamic signature of Dirac electrons across a possible topological transition in ZrTe5

Abstract

We combine transport, magnetization, and torque magnetometry measurements to investigate the electronic structure of ZrTe5 and its evolution with temperature. At fields beyond the quantum limit, we observe a magnetization reversal from paramagnetic to diamagnetic response, which is characteristic of a Dirac semi-metal. We also observe a strong non-linearity in the magnetization that suggests the presence of additional low-lying carriers from other low-energy bands. Finally, we observe a striking sensitivity of the magnetic reversal to temperature that is not readily explained by simple band-structure models, but may be connected to a temperature dependent Lifshitz transition proposed to exist in this material.Thermodynamic signatures of the topological nature of a material have become increasingly important as numerous new topological insulator, Weyl, and Dirac materials are predicted [1][2][3]. In this study we focus on ZrTe 5 , a material whose topological nature is hotly debated; it has been predicted and verified as a Dirac semimetal [4][5][6][7][8], a topological insulator [9][10][11][12] and a trivial semiconductor [13,14]. In addition to its potential topological nature, there is also an unusual anomaly in the temperature dependence of the resistivity that has been conjectured to originate from a Lifshitz transition [15,16]. This anomaly is strongly sample dependent, ranging in its position from ∼ 10K to 150K. Recently, it has been suggested that the topological nature of the band structure and associated transport properties of ZrTe 5 depend strongly on the growth technique [17]. Nevertheless, the complicated history of this material highlights the need for robust low-energy signatures of Dirac-like band structures.We study the magnetic behavior of ZrTe 5 as it approaches and surpasses its quantum limit -the magnetic field at which all electrons are collapsed into the lowest, ν = 0 Landau level. In the most general case, all materials show some small degree of orbital diamagnetism arising from the local orbital moment of the ions. Trivial metals show an additional Landau diamagnetism arising from the orbital motion of their itinerant electrons. In a previous study of NbAs [18], we showed that topological metals exhibit a low-field paramagnetic response originating from their unique Landau quantization, which for a Dirac fermion in a magnetic field B along z is given bywhere ν is the Landau index, v F the Fermi velocity and γ is the quantum correction term which is 1/2 for trivial metals, but in Dirac systems γ = 0 due to the non-trivial Berry's phase. The Berry's phase associated with this quantization is often used as evidence for the existence of non-trivial topology, which can in principle be extracted from a plot of the Landau indices versus inverse magnetic field [19]. However, the influence of Zeeman splitting, the complicating effects of conductivity contributions from other bands and the presence of a Dirac mass can make this extraction unreliable, particularly in three dimensions [20,21]. Instea...

Unraveling the topology of ZrTe5 by changing temperature

“…We also note that increasing temperature leads to the closure of the band gap of the material, with the formation of a hole pocket at the Γ point and an associated electron pocket elsewhere in the BZ. This temperature-dependent shift of the electronic bands is consistent with experimental reports 63 and has been connected to the resistivity anomaly in ZrTe 5 5,16,17,64,65 .…”

Optical conductivity and resistivity in a four-band model for ZrTe5 from ab initio calculations

“…The temperature of the resistivity maximum varied with sample thickness and doping [25][26][27]. Recently, this resistivity peak was also related to the potential topological properties of ZrTe 5 and interpreted as a signature for a transition upon cooling [28] from a WTI to an STI state [29] or the reverse [30], as well as a signature of Dirac polarons [31].…”

Giant orbital diamagnetism of three-dimensional Dirac electrons in Sr3PbO antiperovskite

“…1A) with Sb x>xc=0.07. Recently discovered three-dimensional (3D) Dirac semimetals also show a large diamagnetism of similar magnitude in the bulk magnetic susceptibility (15)(16)(17)(18), when their EF is located near the Dirac points.…”