Research Article
Transport property of topological crystalline insulator SnTe (100) and ferrimagnetic insulator heterostructures

https://doi.org/10.1016/j.jmst.2022.05.033Get rights and content

Highlights

  • High quality SnTe/RE3Fe5O12 (RE=Eu, Y) epitaxial heterostructures were prepared.

  • Domain disorder is induced by Fe atom diffusion in SnTe through magnetic interface.

  • Two different magnetoelectrical transport in two heterostructures are observed.

  • Linear magnetoresistance and nonlinear Hall appear in SnTe/Eu3Fe5O12.

Abstract

Topological crystalline insulator (TCI) SnTe is a potential material for quantum electronic devices because of its attractive inherent sensitivity of band topology and highly mobile characteristic of Dirac fermions. The proximity effect at the interface of SnTe film can affect the topological surface transport and may result in novel quantum magneto-electric effects. Here, we study the magnetoelectrical transport properties of SnTe thin films grown on ferrimagnetic insulators Eu3Fe5O12 (110) (EuIG (110)) and Y3Fe5O12 (111) (YIG (111)) single-crystal underlayers by molecular beam epitaxy. Linear magnetic resistance (LMR) is observed in SnTe/EuIG heterostructures in the low field range, which is different from the weak antilocalization (WAL) characteristic of SnTe/YIG heterostructures. Especially, the double carrier characteristic with the coexistence of holes and electrons in SnTe/EuIG heterostructure is quite different from the holes as main carriers in SnTe/YIG, although the SnTe layer remains the same crystal plane (100) in the two heterostructures. The LMR in SnTe/EuIG is attributed to the topological surface Dirac electrons and disordered domain distribution in the SnTe layer which is in sharp contrast to the WAL of SnTe/YIG with ordered domain distribution in the SnTe layer. The present studies of transport properties not only provide a fundamental understanding of the transport mechanism of TCI and magnetite insulator heterostructure but also display the promising application probability for tunable topological electronic devices.

Introduction

Topological crystalline insulator (TCI) is a new class of topological classification of quantum matter whose topological surface states (TSSs) are protected by the crystalline symmetry instead of the time-reversal symmetry (TRS), therefore their novel topological protection mechanisms make the surface states more easily operative than conventional topological insulator [1]. Some exotic properties, such as Lifshiz transition [2], Fermion mass generation [3], and thermoelectric properties [4], [5], [6], [7], [8], have been reported in TCI. SnTe is firstly anticipated to be a typical TCI material whose TSSs are theoretically expected in {111}, {001}, and {110} planes of a rock-salt crystal structure [9]. With great potential for tunable Dirac electronics [10,11], SnTe is an ideal material to study valley-degenerate topological systems in transport experiments for developing attractive magnetoelectrical transport properties as a potential quantum electronic device in the future [12,13]. Generally, the strategies to modulate the magnetoelectrical transport of SnTe are classified into lattice doping and interface engineering. Through element doping in the SnTe lattice, the numbers of Sn vacancies not only can be controlled to reduce the bulk hole density to enhance the surface state contribution to transport but also induce the crystalline symmetry breaking of SnTe to realize the quantum phase transition modulation [1,14]. Through doping Cr, Mn, and Pb in SnTe lattice, the macroscopic electrical transport or quantum transport properties, including metal-semiconductive transition, weak antilocalization (WAL), anomalous Hall effect (AHE), the surface transport channel, and coherent scattering length modulation were realized, supplying an experimental basement in designing novel quantum devices [15], [16], [17], [18], [19], [20], [21]. On the other hand, the interface engineering is also used to induce the proximity effect to modulate the surface quantum state of SnTe, especially induce the quantum anomalous Hall effect (QAHE) or linear magnetoresistance (LMR) to promote the sensitive magnetoelectrical signal conversion in new generation quantum devices [16,[19], [20], [21], [22], [23], [24]].

Different from conventional topological insulators with a layer lattice structure, the surface states of TCI are more easily tuned by the interface epitaxial effect, because the cubic lattice structure more easily changes its lattice symmetry through interface stress induction or supplying element diffusion channel into SnTe lattice by the epitaxial interface. The design and construction of SnTe epitaxial heterostructure, therefore, become an attractive strategy to obtain novel magnetoelectrical transport properties. The magnetic proximity effect (MPE) was proposed [25], [26], [27] and it was predicted that surface states on {100} of TCI, such as SnTe, can remain gapless or gapped depending on the direction of magnetic fields at the interface which prospectively leads to the QAHE [28]. Therefore, the single crystalline TCI thin film becomes a suitable platform for studying MPE and the transport properties of the TCI's surface states due to its controllable-growth advantage in the planes of different orientations with a higher surface to volume ratio. In previous work on MPE of TCI, proximity induced hysteretic negative magnetoresistance and an AHE were observed in SnTe-EuS-SnTe trilayer grown on Si (100), indicating that the magnetism was induced at the interface between the nonmagnetic TCI and the ferromagnetic insulator [29]. The advantage of the proximity method is that since it does not rely on doping the bulk with magnetic transition metal ions [30], [31], [32], avoiding the reduction of carrier mobility by the doping method. It is of great significance to explore the corresponding mechanism of its novel transport-related phenomena on the special topological surface. Subsequently, the interface diffusion engineering was developed in PbTe/SnTe heterostructure and the Pb atom was controlled to diffuse into the SnTe layer to realize the mutual conversion between the LMR and WAL [16,19,21]. Based on the above two strategies, a new heterostructure route combining the interface magnetism and element diffusion was expected to induce topological modulation in TCI. It is urgently required to explore the new type of magnetic TCI heterostructure.

Unlike ferromagnetic insulator EuS with Curie temperature (TC) 16 K [29,33], a number of ferrimagnetic insulators (FI) RE3Fe5O12 (RE representing Y and rare earth elements) with TC exceeding 550 K, including europium iron garnet (EuIG) and yttrium iron garnet (YIG) [26,[34], [35], [36], [37], [38], [39]], have a potential to become the magnetic underlayers for epitaxially growing the TCI heterostructures. The intrinsic magnetic anisotropy including in-plane or out-plane magnetic moment orientation of EuIG and YIG films also supplies tunable factors in the heterostructure interface to realize the interface coupling [26,[37], [38], [39]]. Furthermore, the interfacial coupling between TCI and FI may form a magnetic order or a magnetic element diffusion to reorganize the structure of TCI to result in different magnetoelectrical transport behaviors. In this way, it is beneficial to better understand the transport behavior in TCI SnTe and the role of magnetic interfaces in realizing novel phenomena such as topological magnetoelectrical effect [40], LMR, or QAHE [[22], [23], [24],40]. However, the influences of the magnetic interface on the structure, surface states, and transport behaviors of TCI are still lacking relevant research and it is necessary to supply an essential step to achieve systematical studies on the transport properties for promoting the development of topological crystalline electronic devices as well as TCI-based hybrid structures.

In this work, the magnetoelectrical transport behaviors of SnTe (100) thin films epitaxially grown on ferrimagnetic oxide insulator EuIG and YIG underlayers are comparatively studied. By changing interface magnetic orientation to promote the element diffusion, the LMR is observed in the low field range in SnTe/EuIG heterostructure which is distinct from the SnTe/YIG heterostructure presenting a conventional WAL characteristic. Especially, the non-linear Hall curves of SnTe/EuIG heterostructure meaning two types of carriers, that are electrons and holes, simultaneously exist in SnTe (100) film indicating the presence of different transport essence when compared with the SnTe/YIG heterostructure only with holes as the carriers. The structural influence was detected and the LMR is considered to be related to the topological surface electrons and disordered domain distribution induced by the element diffusion under the magnetic interface effect. The present research on topological transport properties of TCI/FI SnTe (100) heterostructures is a necessary prerequisite for the future pursuit of exotic quantum phenomena arising from proximity-magnetized topological crystalline surface states.

Section snippets

Experimental

The EuIG and YIG targets were prepared by mixing oxides Eu2O3 (99.99 wt.%), Y2O3 (99.99 wt.%), and Fe2O3 (99.99 wt.%) together into targets and annealing them at 1100 °C for 24 h in the air. The single-crystal EuIG (110) and YIG (111) thin films with a thickness of 25–150 nm were deposited at 700 °C with 1 Pa O2 pressure on Ga3Fe5O12 (GGG) (110) and GGG (111) substrates respectively by pulsed laser deposition (PLD) (laser wavelength 248 nm) with a frequency of 5 Hz and energy of 400 mJ. Then

Results and discussion

In Fig. 1(a, b), the XRD patterns of prepared films show the epitaxial growth correlation of the FI and TCI films. The single-phase EuIG layer without other impurity phases is detected to grow along [110] crystallographic orientation indicating its epitaxial growth on GGG (110) substrate (Fig. 1(a)). A similar situation is observed in YIG (111) film (Fig. 1(b)). When SnTe layers are grown on EuIG (110) and YIG (111) films, however, only [100] crystallographic orientation of SnTe is detected on

Conclusion

In summary, the high-quality SnTe (100)/EuIG (110) and SnTe (100)/YIG (111) single crystalline heterostructures were prepared by MBE combined PLD technique on GGG (110) and GGG (111) substrates respectively. The two types of heterostructures show different magnetoelectrical transport behaviors, in which the SnTe (100)/EuIG (110) exhibits LMR but the SnTe (100)/YIG (111) presents a WAL effect at 5 K in the low field range. The LMR effect is considered to originate from the topological surface

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos. 52071324, 51871219, and 52031014) and the National Key R&D Program of China (No. 2017YFA0206301).

References (52)

  • Z.Y. Chen et al.

    Mater. Today Phys.

    (2021)
  • J.Y. Deng et al.

    J. Magn. Magn. Mater.

    (2018)
  • C.H. Yan et al.

    J. Mater. Sci. Technol.

    (2020)
  • K. Kobayashi

    Surf. Sci.

    (2015)
  • L.A. Fu

    Phys. Rev. Lett.

    (2011)
  • I. Pletikosić et al.

    Phys. Rev. Lett.

    (2014)
  • I. Zeljkovic et al.

    Nat. Mater.

    (2015)
  • J. Tang et al.

    Adv. Funct. Mater.

    (2018)
  • H.M. Pang et al.

    J. Am. Chem. Soc.

    (2021)
  • Z.Y. Chen et al.

    J. Mater. Chem. A

    (2020)
  • Z.Y. Chen et al.

    J. Mater. Sci. Technol.

    (2020)
  • T.H. Hsieh et al.

    Nat. Commun.

    (2013)
  • L. Zhao et al.

    Phys. Rev. B

    (2015)
  • L. Zhao et al.

    Phys. Rev. B

    (2015)
  • S.V. Eremeev et al.

    Phys. Rev. B

    (2014)
  • B.A. Assaf et al.

    Appl. Phys. Lett.

    (2014)
  • Y. Tanaka et al.

    Nat. Phys.

    (2012)
  • Y.H. Choi et al.

    Appl. Phys. Lett.

    (2012)
  • F. Wei et al.

    J. Phys. D

    (2019)
  • C.W. Liu et al.

    Nano Lett.

    (2018)
  • A.Q. Zhang et al.

    Nanotechnology

    (2019)
  • F. Wei et al.

    Phys. Status Solidi B

    (2019)
  • F. Wang et al.

    Phys. Rev. B

    (2018)
  • F. Wei et al.

    Phys. Rev. B

    (2018)
  • R. Yu et al.

    Science

    (2010)
  • C.Z. Chang et al.

    Science

    (2013)
  • Cited by (0)

    View full text