Magnetotransport for Dirac Semimetal Phase of Topological Insulator Sb₂Te₃

Antimony Telluride (Sb₂Te₃) makes up the second generation of Topological Insulator (TI) materials with other layered chalcogenides Bi₂Se₃ and Bi₂Te₃. The TI phase in these materials arises from a spin-orbit induced band crossing of opposite parity orbitals at the Γ point of the Brillouin Zone, resulting in a single topologically protected Dirac cone projected to all surfaces.¹ Another set of surface states have been identified in Sb₂Te₃: intrinsic Rashba spin-orbit split surface bands extending from 300 to 750 meV below the valence band edge exist within a partial valence band gap.^2–5 Also, a strong linear character to the bulk valence band dispersion has been established in Angle Resolved Photo-Emission Spectroscopy (ARPES) experiments,⁴ where accidental band crossing points^2,3,6,7 imply a Dirac energy spectrum and so Dirac semimetal phase.^8,9<br/>Sb₂Te₃ is usually heavily hole doped due to a combination of Te vacancies and Sb_Te anti-site defects,^10,11 with p ∼ 10²⁰ cm⁻³ the typical carrier density for nominally stoichiometric samples.^12,13 The intrinsic doping effects in this material class are typically difficult to overcome, however they should also place the chemical potential close to the Dirac-like spectrum of bulk bands,^2,3,12 meaning these could contribute to the transport without significant tuning of the carrier density.<br/>So far no studies of the electronic transport looking for indications of these states has been carried out. To better understand the material system and probe for these contributions, Sb₂Te₃ single crystals have been grown using a modified Bridgman method with excess Te in the melt, and the magnetotransport of (001) oriented single crystal Sb₂Te₃ with p-type carrier densities in the range 2.4 - 12 × 10¹⁹ cm⁻³ is studied up to 8 T. It is found that the semiclassical magnetotransport is described by a two-carrier band model, finding contributions from majority hole and minority electron bands, and clear Shubnikov de Haas Oscillations (SdHO) are resolved at 1.5 K across the carrier density range. The convolution of different frequency SdHO cause novel beating envelopes for samples with reduced carrier densities and non-trivial Berry phases are extracted for carrier densities in the range 4.1 - 7.9 × 10¹⁹ cm⁻³. Detailed consideration of the SdHO points away from either the Rashba or Dirac surface bands causing these, and instead the region of multiple pockets of linearly dispersive Dirac-like bulk band crossing points in the upper valence band is found responsible. This work therefore confirms a bulk Dirac semimetal phase in the well-known TI Sb₂Te₃.<br/><br/>References:<br/>1 H. Zhang et al., Nat. Phys. <b>5</b>, 438 (2009).<br/>2 L. Plucinski et al., J. Appl. Phys. <b>113</b>, 053706 (2013).<br/>3 C. Pauly et al., Phys. Rev. B <b>86</b>, 235106 (2012).<br/>4 C. Seibel et al., Phys. Rev. Lett. <b>114</b>, 066802 (2015).<br/>5 C. Seibel et al., J. Electron. Spectros. Relat. Phenomena <b>201</b>, 110 (2015).<br/>6 N. Shukla and G. A. Ahmed, Materials Today: Proceedings <b>45</b>, 4819 (2021).<br/>7 S. K. Verma et al., IEEE Transactions on Electron Devices <b>69</b>, 4342 (2022).<br/>8 N. Armitage, E. Mele, and A. Vishwanath, Rev. Mod. Phys. <b>90</b>, 015001 (2018).<br/>9 S. Li et al., Front. Phys. <b>15</b>, 43201 (2020).<br/>10 R. J. Cava et al., J. Mater. Chem. C <b>1</b>, 3176 (2013).<br/>11 C. Drasar, P. Lostak, and C. Uher, J. Electron. Mater. <b>39</b>, 2162 (2010).<br/>12 A. von Middendorff , K. Dietrich, and G. Landwehr, Solid State Commun. <b>13</b>, 443 (1973).<br/>13 V. Kulbachinskii et al., J. Phys.: Condens. Matter <b>11</b>, 5273 (1999).