Chiral anomaly and ultrahigh mobility in crystallineHfTe5

Abstract

HfTe 5 is predicted to be a promising platform for studying topological phases. Here through an electrical transport study, we present the first observation of chiral anomaly and ultrahigh mobility in HfTe 5 crystals. Negative magneto-resistivity in HfTe 5 is observed when the external magnetic and electrical fields are parallel (B//E) and quickly disappears once B deviates from the direction of E. Quantitative fitting further confirms the chiral anomaly as the underlying physics. Moreover, by analyzing the conductivity tensors of longitudinal and Hall traces, ultrahigh mobility and ultralow carrier density are revealed in HfTe 5 , which paves the way for potential electronic applications. Chiral anomaly is a quantum anomaly phenomenon that breaks the chiral symmetry and leads to the non-conservation of chiral current [1,2]. This anomaly was proposed to be observed in lattice system in 1983 [3]. Recently, the study of Weyl fermions pushes forward the realization of chiral anomaly in crystals [4][5][6]. In Dirac/Weyl semimetals, the axial current is non-conserved due to the chiral anomaly, and further leads to charge pumping effect between the Weyl nodes with opposite chirality. This anomaly effect is suggested to give rise to negative magneto-resistivity when the magnetic and electrical fields are parallel (B//E) [4]. Related experimental evidences have been intensively pursued in various condensed matter systems Here we present the first electrical transport evidence for the chiral anomaly and the ultrahigh mobility in HfTe 5 crystals.

Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

“…As will be shown below, the resistivity peak and the thermopower sign reversal at T p can be reproduced by our parameter-free transport calculations when taking into account the intrinsic band structure anisotropies at the valence band maximum and conduction band minimum. Our results also provide a simple physical explanation for the contradictory reports in the literature regarding the electronic structure of ZrTe 5 , i.e., semiconductor versus Dirac semimetal [12][13][14][15][16][17][18].…”

“…The ZrTe 5 single crystals used in the present study were grown by chemical vapor transport for the CVT samples [16] and by the Te-flux method for the Flux samples [18]. We employed iodine (I 2 ) as the transport agent during the CVT crystal growth.…”

“…1(b). On the other hand, we used a Canfield crucible set (CCS) [19] to grow ZrTe 5 crystals out of the Te flux [18]. A Zr slug (99.95%, Hf nominal 3%) and Te shots (5N) in an atomic ratio of 1∶49 were loaded into the CCS and then sealed in a silica ampoule under vacuum.…”

“…More recently, these compounds have become of interest as topological materials whose low-energy electronic structure is controlled by spin-orbit interactions [11]. Nevertheless, it is currently under hot debate whether they are insulators or Dirac semimetals [6,[12][13][14][15][16][17][18].…”

Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

“…6,7 Another physical mechanism for large MR effects are magnetic field induced metal-insulator transitions in special transition metal oxides and ferromagnetic semiconductors. 8,9 In such materials the negative MR, which is called "colossal", can exceed 100,000 % at 77 K and fields of 6 T. 10 In manganese-substituted zinc oxide the magnetically induced transition from hopping to band conduction leads to a giant negative MR of more than 200 % at 1.4 K and 12 T. 11 Recently, it has been supposed that under hopping conditions even quantum interferences can cause a giant negative MR. 12 Topological semimetals 13,14 and insulators 15 with complex band structure and high mobility carriers demonstrate anomalous, large positive and negative MR, too. Extremely large positive MRs up to 750,000 % have been obtained in semiconductor structures with extrinsic 16 or intrinsic inhomogeneities.…”