Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

Abstract

3d-element dopants. Hence, the broken time-reversal symmetry may enable the detection of the quantum anomalous Hall effect (QAHE) due to the presence of dissipationless edge states. [10][11][12] The combination of such devices with conventional superconductors were predicted to host Majorana fermions, which are suitable for braiding devices for use in topological quantum computers. [13,14] As the band structure of real materials is complex, it is challenging to realize the QAHE or Majorana fermions at a higher temperature. Highly precise band structure engineering is required to suppress the contribution of the bulk bands effectively. To date, this has posed one of the main limiting barriers to the development of practical devices based on the QAHE. Therefore, a deeper understanding of how the band structure of TI can be artificially designed is inevitable.Shubnikov-de Hass (SdH) oscillations are a quantum coherence phenomenon commonly observed in clean metals, where the charge carriers can complete at least one full cyclotron motion without impurity scattering under magnetic field. [15] Wealth parameters such as the Fermi surface topology and mean-free path can be extracted from the oscillation period and the temperature-dependent amplitude variation. [16] Quantum oscillations have been extensively used as a tool to study high temperature superconductors and topological materials. [17][18][19][20] The recent observation of the three-dimensional (3D) quantum Hall effect (QHE) in ZrTe 5 has attracted further enthusiasm to study of quantum oscillations in TI materials. [21] Quantum oscillations have been observed in binary compounds, Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 bulk crystals and thin flakes. [22][23][24][25] In these systems, the oscillations originate from either the surface states or the bulk bands, depending on the position of the chemical potential. [26] Recently, quantum oscillations were discovered in 3d elements doped TI single crystals, such as Fe-doped Sb 2 Te 3 and V doped (Bi, Sn, Sb) 2 (Te, S) 3 . [24,27] However, no long-range FM order was observed. The results motivated the preparation of thin films of similar materials with the potential for FM order coexisting with high mobility topological surface states.So far, to our knowledge, there are only a few reports on the observation of quantum oscillations in magnetically doped TIs, such as V-doped (Bi, Sb) 2 Te 3 , Sm-doped Bi 2 Se 3 . [28,29] However,effective way of manipulating 2D surface states in magnetic topological insulators may open a new route for quantum technologies based on the quantum anomalous Hall effect. The doping-dependent evolution of the electronic band structure in the topological insulator Sb 2−x V x Te 3 (0 ≤ x ≤ 0.102) thin films is studied by means of electrical transport. Sb 2−x V x Te 3 thin films were prepared by molecular beam epitaxy, and Shubnikov-de Hass (SdH) oscillations are observed in both the longitudinal and transverse transport channels. Doping with the 3d element, vanadium, induces long-range ferromagne...

Two‐Dimensional Van Der Waals Topological Materials: Preparation, Properties, and Device Applications

“…These robust, novel electronic states in 2D TMs can affect the motion of electrons in a material and be usually revealed by the transport properties of nanodevices. [ 41 ] Recently, many attempts have been made to control the Fermi level and carrier density of 2D vdW TMs, including doping, [ 65,198–200 ] and field‐effect gating. [ 4,55,80,167 ] In particular, 2D vdW TMs often exhibit exotic transport properties such as giant magnetoresistances, [ 45,80,81,109,224 ] quantum oscillation, [ 46,72,82,83,199 ] QHE, [ 47,57 ] superconductivity, [ 110,193,225 ] weak localization (WL) and weak antilocalization (WAL).…”

“…[ 46 ] In general, quantum oscillations are mainly concerned with longitudinal resistance of 2D vdW TMs, while Felser et al. [ 199 ] reported the oscillation in both longitudinal resistance and Hall resistance in 2D Sb 2‐ x V x Te 3 thin film, a vdW ferromagnetic TIs ( Figure a). Its stronger Hall resistance oscillation provides a platform for QHE if the bulk band contributions are nearly eliminated.…”

“…Reproduced with permission. [ 199 ] Copyright 2021, Wiley‐VCH. c) MR curves in 2D T d ‐MoTe 2 nanosheet under varying temperatures.…”

“…For magnetic materials with time‐reversal symmetry broken, possessing long‐range magnetic order in nonmagnetic 2D vdW TMs is a challenge. Up to now, during unremitting efforts, some breakthroughs have been made in intrinsic magnetic 2D vdW TMs and their heterostructures, such as Cr‐doped (Bi x Sb 1‐ x ) 2 Te 3 , [ 7 ] V‐doped (Bi x Sb 1‐ x ) 2 Te 3 , [ 65 ] Sb 2‐ x V x Te 3 , [ 199 ] MnBi 2 Te 4 , [ 8,18,186 ] (Bi x Sb 1‐ x ) 2 Te 3 /Tm 3 Fe 5 O 12 , [ 197 ] WTe 2 /CrI 3 , [ 22 ] and ZnCrTe/(Bi,Sb) 2 Te 3 /ZnCrTe. [ 23 ] These representative magnetic 2D vdW TMs and heterostructures will be discussed below, and the summary of magnetism in 2D vdW TMs is listed in Table 5 .…”

“…Although this type of material was first proposed in time‐reversal invariant systems, the introduction of long‐range ferromagnetic order will break the time‐reversal symmetry and result in an exchange gap opening around the Dirac points. [ 288 ] Many attempts have been established for magnetic‐doped 2D vdW TIs, such as Sb 2‐ x V x Te 3 , [ 199 ] Cr x Sb 2‐ x Te 3 , [ 278 ] Cr 0.22 Bi 1.78 (Se x Te 1‐ x ) 3 , [ 207 ] and Mn x Bi 2‐ x Te 3‐ y Se y , [ 280 ] all above 2D vdW TIs with tunable dopant concentrations and high T C up to 176 K. However, many of them only implement the AHE rather than QAHE even under electric‐field gating, implying the harsh conditions for QAHE.…”