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Transport properties of topological insulator heterostructures and ultrathin films

Transport properties of topological insulator heterostructures and ultrathin films. Jian Wang ( 王健 ). 2013 Sanya. International Center for Quantum Materials, School of Physics, Peking University. Demonstration of surface transport in a hybrid Bi 2 Se 3 /Bi 2 Te 3 heterostructure

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Transport properties of topological insulator heterostructures and ultrathin films

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  1. Transport properties of topological insulator heterostructures and ultrathin films Jian Wang (王健) 2013Sanya International Center for Quantum Materials, School of Physics, Peking University

  2. Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction

  3. 1. Demonstration of Surface Transport in a Hybrid Bi2Se3/Bi2Te3 Heterostructure arXiv: 1308.5311 Prof. Qi-Kun Xue, Prof. Xucun Ma, Prof. Ke He, Dr. Cuizu Chang Prof. Yong Wang Yanfei Zhao

  4. Motivation: heterostructure is important Topological insulator-superconductor: Majorana fermions Topological insulator-ferromagnet: QAHE, magnetic monopole etc Topological insulator-trival insulator: topological surface state Topological insulator-topological insulator: nothing happened?

  5. Experiment: MBE+ARPES • ARPES: • He-Iα (21.21 eV) • MBE: • Bi, Se, Te co-evaporation • Substrate: • Graphene-terminated SiC (0001) • (for ARPES) • Sapphire (0001) • (for transport measurements) From Xue’s group

  6. Experiment: TEM TEM Images of 1 QL Bi2Se3 / 19 QL Bi2Te3 film The work was done at department of Materials Science and Engineering, Zhejiang university

  7. Experiment: Transport Physical Property Measurement System (PPMS) Temperature: 1.9K~400K (Dilution: 50mK) Magnetic Field: 16 Tesla PhD Student: Yanfei Zhao

  8. Topological Insulator Bi2Se3 thin film Y. Zhang, Nature Physics (2009) Bi2Te3 thin film Y. L. Chen, Science (2009)

  9. Growing only 1 QL Bi2Se3 film on Bi2Te3 thick films ------ Heterostructure What will happen？ Question 1: Is it a 3D topological insulator? Question 2: If it is a topological insulator, it behaves like Bi2Se3 or Bi2Te3?

  10. ARPES for Bi2Se3, Bi2Te3 and Heterostructure

  11. Question 1: Is it a 3D topological insulator? Yes, it is ! Question 2: If it is a topological insulator, the surface state behaves more like Bi2Se3 or Bi2Te3? Bi2Se3

  12. Resistance -Temperature Behavior • With decreasing temperature (T), Rsq displays metallic behavior at high T region and becomes weakly insulating at low T regime • Resistance upturn is due to the coexistence of weak antilocalization and electron-electron interaction PHYSICAL REVIEW B 83, 245438 (2011)

  13. Magneto-resistance Behavior Linear and non-saturating MR Nonlinear MR Linear and non-saturated MR The behaviors were confirmed by many samples grown by MBE 1 QL Bi2Se3 on the top of heterostructure plays a significant role in the transport property

  14. Weak Antilocalization Effect Weak antilocalization effect in the 1 QL Bi2Se3 / 19 QLs Bi2Te3 film is similar to 20 QL Bi2Se3 Good fit using the HLN formula

  15. 2D Weak Antilocalization Effect After subtracting bulk weak anti-localization effect in the 1 QL Bi2Se3 / 19 QLs Bi2Te3 film, it also behaves similar to 20 QL Bi2Se3

  16. Transport Measurement: Question 2: If it is a 3D topological insulator, it behaves more like Bi2Se3 or Bi2Te3? Answer: Bi2Se3 (Linear MR & WAL) Moreover, 1 QL Bi2Se3 on the top of heterostructure plays a significant role in the transport property

  17. The fitting combined weak antilocalization with e-e interaction theory of 1 QL Bi2Se3 / 19 QLs Bi2Te3 film in low field at T=4K PHYSICAL REVIEW B 83, 245438 (2011) Solid lines are the results of a combined WAL and EEI theory. Considering the g-factor of 1 QL Bi2Se3 / 19 QLs Bi2Te3 film is not so sure, we fixed g-factor to be 30 and 20. The fitting curves are plotted by blue and orange respectively.

  18. Summary • ARPES experiments provide the direct evidence that the surface state of 1 QL Bi2Se3 / 19 QL Bi2Te3 heterostructure exhibits similar surface state of 20 QL Bi2Se3 • Both linear MR and WAL effect have unambiguously shown that the hetero-structure behaves more like Bi2Se3 even though there is only 1 QL Bi2Se3 film grown on 19 QL Bi2Te3 film in the heterostructure • Studying on this TI-TI heterostructure may provide a platform to artificially modulate the bulk and surface electronic structures of TIs respectively and pave a way to design new TI devices arXiv: 1308.5311

  19. 2. Crossover between Weak Antilocalization and Weak Localization of Bulk States in Ultrathin Bi2Se3 Films Jian Wang Collaborators: X. C. Xie, H. C. Wang, H. W. Liu, Y. F. Zhao, Y. Sun Q. K. Xue, K. He, X. C. Ma, C. Z. Chang, Z. C. Xia, H. K. Zuo, Huichao Wang

  20. Motivation • Bulk states cannot be neglected in present 3D topological insulators • The study of magnetoresistance in parallel field of topological insulator films is not much • Pulsed magnetic field (up to 100 T) is an effective way to study topological insulators Nature Physics 6, 960 (2010): 60 T

  21. Outline • Research Status of Transport Properties of Topological Insulator(TI) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Linear magneto-resistance (MR) in perpendicular field • Negative MR phenomena of TI films in parallel magnetic field • Theoretical explanation • Summary

  22. New quantum materials---Topological Insulator • Topological insulators are a type of materials protected by time-reversal symmetry with special surface states crossing the bulk gap. • The surface states has a linear energy dispersion, revealing a spin-polarized Dirac cone. • The spin-momentum locked surface states always show weak antilocalization (WAL) effect. ARPES is a direct way to detect surface state. X. L. Qi and S. C. Zhang, Phys. Today 63(1), 33 (2010). M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).

  23. Transport properties of topological insulators Universal conductance fluctuation (UCF), weak antilocalization (WAL), A-B effect, SdH oscillations, e-e interaction… PRL 103, 246601 (2009) Nat. Mater. 2609, 225 (2010) PRB 83, 245438 (2011) Science 329, 821 (2010) PRB 83, 165440 (2011)

  24. Bulk states of the existing 3D topological insulators The existing three-dimensional TIs are not ideally insulating even at low temperatures. By selective cleaving from Bi2Te3 crystals Science 329, 821 (2010) (molecular beam epitaxy)MBE-grown 45 QLs (quintuple layers) Bi2Se3 films PHYSICAL REVIEW B 83, 245438 (2011)

  25. TI bulk states with strong spin-orbit coupling(SOC) cannot be neglected

  26. Outline • Research Status of Transport Properties of Topological Insulator(TI) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Linear magneto-resistance (MR) in perpendicular field • Negative MR phenomena of TI films in parallel magnetic field • Theoretical explanation • Summary

  27. Samples----grown by MBE for 5QLs Bi2Se3 ultrathin film An ultra-high vacuum MBE-ARPES-STM combined system Prof. Qi-Kun Xue, Prof. Xucun Ma, Prof. Ke He, Dr. Cuizu Chang

  28. Transport Measurements • Physical Property Measurement System (PPMS) • Scan field mode: linear, driven; • Stable magnetic field V- I- I+ V+ Se capping layer 5QL Bi2Se3 Sapphire Au wires/ In balls as leads • Pulsed High Magnetic Field (PHMF) • 15ms rise time and 135 ms descend time. • magnetic and current directions are reversed.

  29. R-T Characteristic of Sample 1 (5QLs Bi2Se3 ultrathin film) PHYSICAL REVIEW B 83, 245438 (2011)

  30. Hall Resistance of Sample 1 (5QL Bi2Se3 thin film) • 4.2 K • The sheet carrier density • ns~1.89×1013 cm-2 • Mobility • μ~316.6 cm2/Vs

  31. Linear MR In Perpendicular Magnetic Field Linear MR WAL

  32. Linear MR is likely due to linear energy dispersion of the gapless topological surface states of quantum origin (Abrikosov’s quantum linear MR model). Bi2Se3 nanoribbons by V-L-S mechanism “it is likely that this linear MR is intrinsically tied to the 2D Dirac electrons occupying the surface state.” Xuan P. A. Gao Group ACS NANO 5(9),7510-7516 (2011)

  33. Outline • Research Status of Transport Properties of Topological Insulator(TI) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Linear magneto-resistance (MR) in perpendicular field • Negative MR phenomena of TI films in parallel magnetic field • Theoretical explanation • Summary

  34. MR In Parallel Magnetic Field of Sample 1 (5QL Bi2Se3 thin film): crossover [-110] [-110] Interestingly, MR of the films are closely related to the relative orientation of the parallel magnetic field and the excitation current. [001] [001] [110] [110] I+ I+ I- I- B B V- V- V+ V+ The results by ac measurement and dc measurement in pulsed magnetic field are identical. 0.8% decrease from ~25T to 50T at 4.2K; 0.6% decrease from ~11T to 50T at 77K

  35. Sample 2 shows similar properties as sample 1

  36. Control experiments with sample 1 — different crystal orientation • Weaker negative MR effect. • Similar angular dependence on the angle between the parallel field and current.

  37. Angular dependence of MR in parallel field The MR behavior is closely related to the angle between the in-plane magnetic field and the current.

  38. Control experiments with sample 1 Negative MR is independentof the current intensity and the current direction.

  39. Outline • Research Status of Transport Properties of Topological Insulator(TI) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Linear magneto-resistance (MR) in perpendicular field • Negative MR phenomena of TI films in parallel magnetic field • Theoretical explanation • Summary

  40. Quantum interferences in system with strong SOC Two main parameters dominant for the quantum interference: the phase coherence time tjand the spin-orbit scattering time tSO 3. SmallertSOthan 2. WAL(—WL?) 2. SmallertSO than 1. WAL—WL 1. tj < tSO WL G. Bergmann, Phys. Rep. 107, 1 (1984).

  41. Crossover from WAL to WL in TI bulk states at 4.2 K at 4.2 K at 77 K at 77 K [1] B. L. Altshuler, A. G. Aronov, D. E. Khmelnitskii, and A. I. Larkin, Quantum Theory of Solids, edited by I. M. Lifshitz (Mir, Moscow, 1982), P. 130. [2] V. K. Dugaev and D. E. Khmelnitskii, Sov. Phys. JETP59, 1038 (1984).

  42. Explanation for the MR anisotropy • In SOC mechanism, the moving electron experiences an effective magnetic field Be. • The WAL effect can be suppressed more largely by the perpendicular field than by the parallel field (relative to the motion path). I Be B// Be I • Compared with the B////I case, the aforementioned differences lead to weaker effective SOC effect and larger effective tso in the case of B//┴I . I----the excitation current in the film plane; B//----the external magnetic field in the plane; Be----theeffective magnetic field of electrons due to the carrying momentum; main trend of the motion paths in the configuration;

  43. Outline • Research Status of Transport Properties of Topological Insulator(TI) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • Linear magneto-resistance (MR) in perpendicular field • Negative MR phenomena of TI films in parallel magnetic field • Theoretical explanation • Summary

  44. Summary • The crossover from WAL to WL in TI bulk states is demonstrated directly by the parallel field MR behaviors of the 5 QLs Bi2Se3 films, which is quite significant for a better understanding of the existing 3D TI materials. • Besides, we find novel MR anisotropy under different relative orientations of the parallel magnetic field and current, which can be explained qualitatively in the SOC mechanism. More detailed analysis needs further theoretical investigations.

  45. 3. Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction Dr. Zhaoquan Zeng University of Arkansas AIP Advances 3, 072112 (2013); doi: 10.1063/1.4815972

  46. AIP Advances 3, 072112 (2013); doi: 10.1063/1.4815972 • Encourage experts in applications: • Topological insulator (TI) PN junction • devices on GaAs or TI-GaAs PN junctions • 2D excitons? • Optical electrics • Thermoelectrics

  47. Eurek Alert “中美科学家在光滑基座上种出拓扑绝缘体”（新华网、人民网、科技日报、中国科学院等）

  48. Conclusions • Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure • Jian Wang Group, SCIENTIFIC REPORTS 3, 3060 (2013); DOI: 10.1038/srep03060 1 (arXiv: 1308.5311 ) • Crossover between weak antilocalization and weak localization of bulk states in ultrathin Bi2Se3 films • arXiv:1310.5194 (2013) • Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction • Jian Wang Group, AIP Advances 3, 072112 (2013); doi: 10.1063/1.4815972 (arXiv:1301.0362)

  49. International Center for Quantum Materials, School of Physics, Peking University My postdoc and PhD candidates: Yangwei Zhang Yi Liu Huichao Wang Yanfei Zhao Ying Xing Dr. Yi Sun Welcome to Jian Wang’s Group: http://www.phy.pku.edu.cn/icqmjianwanggroup/index.html Thanks !

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