*Topological Insulator: a new state of matter*

#### LECTURER

Prof. Gang Li

ShanghaiTech University

#### DATE: 30th** August 2019 **

TIME: 16:00 – 17:00 pm

LOCATION: Rigoni Stern Institute, Asiago

Condensed matter physics is a branch of physics that deals with the physical properties of condensed phase of matter. It seeks to understand the behavior of these phases by using physical laws, including the laws of quantum mechanics, electromagnetism and statistical mechanics. Conventionally, there are only three condensed phases, i.e. metal, semiconductor and insulator. Metals have free electrons and are highly conductive, while insulators have high resistivity. Semiconductor phase lies in between the metal and the insulator, i.e. it has large resistivity but can become conductive by thermal or optical excitations. In the past fifteen year, a new state of matter that is characteristically distinct to all the above three phases has been discovered, which is known as topological insulators. The interior part of the topological insulators is insulating, while at the surface/edge there exists conductive charge/spin currents.

The unique feature of the topological insulators manifests themselves a promising solution forthe Moore’s law which restricts the development of the integrated circuit in semiconductorindustry. The conductive surface/edge current is dissipationless, thus no energy lost or heat generated during the transportation of the current. As a result, the circuit density of integration can be dramatically increased. This lecture will cover the basic concept of topological insulators, the unique mechanism and the potential applications in spintronics and quantum computers.

Dr.** Gang Li**

Assistant professor in theoretical condensed matter physics School of Physical Science and Technology (SPST) ShanghaiTech University, Shanghai, China

I am interested in the theoretical study of strongly correlated electronic systems and topological materials with quantum many-body method and density functional theory.

WORK EXPERIENCE

Jan. 2017 – today:

Mar. 2015 – Jan. 2017: Jan. 2014 – Mar. 2015: Feb. 2009 – Jan. 2014:

EDUCATION

Oct. 2005 – Feb. 2009

Assistant professor (tenure track)

Project Assistant at Vienna Unversity of Technology, Vienna, Austria Principal Investigator of SFB-ToCoTronics, Würzburg University, Germany Postdoc at Würzburg University, Germany

Bonn University, Germany Doctor

Doctor of Science in Physics, Bonn University, Bonn, Germany

1.0/5.0 (the less the best in German grading system), “magna cum laude”

Thesis: Non-local correlations within dynamical mean-field theory, advised by Prof. H. Monien

Sep. 2002 – Jul. 2005 Beijing, China Master

Master of Science in Physics, Peking University, China GPA 3.7/4.0

Thesis: Some rigorous results of Hubbard model on the complete graph, advised by Prof. G.S. Tian

SKILLS

- Quantum Monte Carlo: Continuous-time quantum Monte Carlo including both interaction-expansion and hybridization-expansion flavors.
- Dynamical Mean-Field Theory: Single impurity Anderson model (SIAM), Dynamical Cluster Approach (DCA), Cellular-DMFT, Dual-Fermion approach, Non-Local Expansion, Dynamical Vertex Approximation(DΓA)
- Programming Language: Fortran 2003, C, C++
- Density Functional Theory: Quantum Espresso, Wien2k, Vasp, Elk, Wannier90AWARDS

Jun. 2006 – Feb. 2009

2005:

2002 – 2005:LANGUAGES

Chinese Native

Cologne-Bonn graduate school fellow

Bonn University scholarship

Bonn international graduate school fellow

Competitive awards for excellent graduate students Peking University Guanghua awards for distinct students Peking University

Bonn University Bonn University Bonn University

English Excellent German: Intermediate level (B1)

TECHING EXPERIENCES

2018 WS 2018 SS 2017 WS 2017 SS 2016 SS 2015 SS

LECTURE TUTOR

2013 WS 2013 SS 2012 SS 2008 SS 2006 SS 2004 SS 2003 SS

Quantum Field Theory

Computational Physics

Quantum Field Theory

Computational Physics

Quantum Field Theory (with A Toschi, K. Held) Hauptseminar: Superconductivity

Electrodynamics

Thermodynamics and Statistical Mechanics Quantum Field Theory for Condensed Matter Theoretical Physics I

Theoretical Physics IV

Thermodynamics

Quantum Statistic Mechanics

ShanghaiTech University, China ShanghaiTech University, China ShanghaiTech University, China ShanghaiTech University, ChinaTU Wien, Austria

Würzburg University, Germany

Würzburg University, Germany Würzburg University, Germany Würzburg University, Germany Bonn University, Germany Bonn University, Germany Peking University, China Peking University, China

CONFERNCES AND TALKS (selected)

- July 1-7, 2018: (Invited)
- Oct. 21-22, 2016:
- Jun. 21-24, 2016:
- Apr. 11-12, 2016:
- Apr. 08-10, 2015:
- Oct. 24-29, 2014:
- May 16-22, 2014:
- May 16-22, 2014:
- Jun. 04-07, 2013:
- Mar. 06-10, 2013:
- Nov. 28-30, 2012:
- Feb. 10-12, 2012:
- Aug. 15-17, 2010:
- Aug. 01-08, 2010:

Summer School: Bandstructure meets Quantum Field Theory, Vienna, Austria

New Frontiers of Strongly Correlated Electron Materials, KITS, Beijing(Invited)

Asia Pacific Center for Theoretical Physics, Workshop “Computational Approaches to Magnetic Systems”, Pohang, South Korea (Invited talk)

- Aug. 6-24, 2018:
- Aug. 27-28, 2018:

Volga-River, Russia (invited talk)

ViCom meeting at Vienna, Vienna, Austria (contributed talk) EMN meeting at Prague, Prague, CZ (invited talk)

Jan Kunes’s group at Prague, CZ (invited talk)

SFB-Vicom, Spring Workshop, Austria (invited talk)

Second International conference of Young Researchers on Advanced conductors, Haikou, China (invited talk)

The next generation of strongly correlated electron systems, Nice, France (invited talk)

NGSCES – next generation of strongly correlated electron systems, Nice, France (invited talk)

CECAM – Green’s function methods, Toulouse, France (invited talk)

APS March Meeting, Baltimore, USA (contributed talk)

Institute talk invited by Prof. K. Held, Vienna, Austria (invited talk) Max-Planck Institute, invited by S. Kirshner, Dresden, Germany (invited talk) Institute of Physics, Chinese Academy of Science (CAS), Beijing (invited talk) Realistic Theories of Correlated electrons in Condensed Matter, Moscow and

PUBLICATIONS

5 most important papers

- F. Reis*, G. Li*, L. Dudy, M. Bauernfeind, S. Glass, W. Hanke, R. Thomale, J. Schaefer, R. Claessen,Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material, Science357, 8142 (2017)
- G. Li, P. Hoepfner, J. Schaefer, R. Claessen, W. Hanke, Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface. Nat. Commun. 4, 2617 (2013)
- L. Peng, Y. Yuan, G. Li#, X. Yang, J.J. Xian, C.J. Yi, Y.G. Shi, Y.S. Fu#, Observation of topological states residing at step edges of WTe2, Nat. Commun. 8, 41467 (2017)
- G. Li#, Hidden physics in the dual-fermion approach: A special case of a nonlocal expansion, Phys. Rev. B 91, 165134 (2015)
- L. Si, O. Janson, G. Li#, Z. Zhong, Z.L. Liao, G. Koster, K. Held#, Quantum anomalous Hall states in ferromagnetic SrRuO3(111) Bilayers, Phys. Rev. Lett. 119, 026402 (2017)Full list of publicationsPublication in 2019

- Petra Pudleiner, Anna Kauch, Karsten Held* and Gang Li*, Competition between antiferromagnetic and charge density wave fluctuations in the extended Hubbard model. Phys. Rev. B 100, 075108 (2019)
- Jiaxin Zhang, Xiaochan Cai, Wie Xia, Aiji Liang, Junwei Huang, Chengwei Wang, Lexian Yang, Hongtao Yuan, Yulin Chen, Shilei Zhang, Yanfeng Guo*, Zhongkai Liu* and Gang Li*, Unveiling Electronic Correlation and the Ferromagnetic Superexchange Mechanism in the van der Waals Crystal CrSiTe3, Phys. Rev. Lett. 123, 047203 (2019)
- G. Li*, A. Kauch, P. Pudleiner and K. Held, The victory project v1.0: An efficient parquet equations solver, Comp. Phys. Commun. 03.008 (2019), doi.org/10.1016/j.cpc.2019.03.008
- Jiajun Zhu, Yunyouyou Xia, Gang Li, Shengqiang Zhou, S. Wimmer, G. Spingholz, A. Pashkin, M. Helm and H. Schneider, Absorption edge, urbach tail, and electron-phonon interactions in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3. App. Phys. Lett. 114, 162105 (2019)
- M. Ye, T. Xu, G. Li, S. Qian, Y. Takeda, Y. Saitoh, X.-Y. Zhu, M. Nurmamat, K. Sumida, Y. Ishida, S. Shin, and A. Kimura, Negative Te spin polarization responsible for ferromagnetic order in the doped topological insulator V0.04(Sb1−xBix)1.96Te3, Phys. Rev. B 99, 144413 (2019)Publication in 2018

6. P. Pudleiner, P. Thunstrom, A. Valli, A. Kauch, G. Li and K. Held, Parquet approximation for molecules: Spectrum

and optical conductivity of the Pariser-Parr-Pople model, Phys. Rev. B 99, 125111 (2019)

7. G. Li*, W. Hanke, E.M. Hankiewicz, F. Reis, J. Schaefer, R. Claessen, C. Wu and R. Thomale, Theoretical paradigm |

for the quantum spin Hall effect at high temperatures, Phys. Rev. B 98, 165146 (2018) - F. Dominguez, B. Scharf, G. Li, J. Schaefer, R. Claessen, W. Hanke, R. Thomale and E.M. Hankiewicz, Testing topological protection of edge stats in hexagonal quantum spin Hall candidate materials, Phys. Rev. B 98, 161407(2018)
- X. Su, Z. Xue, G. Li* and P. Yu*, Edge State Engineering of Graphene Nanoribbons, Nano Lett. 18, 5744 (2018)
- C. Chen, M. Wang, J. Wu, H. Fu, H. Yang, Z. Tian, T. Tu, H. Peng, Y. Sun, X. Xu, J. Jiang, N. B. M. Schröter, Y. Li, D. Pei, S. Liu, S. A. Ekahana, H. Yuan, J. Xue, G. Li, J. Jia, Z. Liu, B. Yan, H. Peng, and Y. Chen, Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, Bi2O2Se, Science
Advances 4:eaat8355 (2018) |

11. Y. Shang, G. Li, W. Liu and Z. Ning, Quasi-2D Inorganic CsPbBr3 perovskite for efficient and stable light- emitting diodes, Advanced Functional Materials, 28, 22 (2018)

12. C. Turner, D. Koumoulis, G. Li, Z. Zujovic, R.E. Taylor, R.B. Kaner, Synthesis and characterization of aluminum diboride products using Al-27, B-11 NMR and n.04-07, ab-initio studies, Journal of Materials Science 53, 3309 (2018)

Publication in 2017

13. F. Reis*, G. Li*, L. Dudy, M. Bauernfeind, S. Glass, W. Hanke, R. Thomale, J. Schaefer, R. Claessen,Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material, Science 357, 8142 (2017)

14. L. Peng, Y. Yuan, G. Li#, X. Yang, J.J. Xian, C.J. Yi, Y.G. Shi, Y.S. Fu#, Observation of topological states residing at step edges of WTe2, Nat. Commun. 8, 41467 (2017)

15. L. Si, O. Janson, G. Li#, Z. Zhong, Z.L. Liao, G. Koster, K. Held#, Quantum anomalous Hall states in ferromagnetic SrRuO3(111) Bilayers, Phys. Rev. Lett. 119, 026402 (2017)

16. C. Platt, G. Li, M. Fink, R. Thomale, Evolution of superconducting gap anisotropy in hole-doped 122 iron pnictides, Physica status solidi B-basic solid state physics 254 (2017)

17. C.W. Wang, Y.Y.Y. Xia, Z. Tian, J. Jiang, B.H. Li, S.T. Cui, H.F. Yang, A.J. Liang, X.Y. Zhan, G.H. Hong, S. Liu, C. Chen, M.X. Wang, L.X. Yang, Z. Liu, Q.X. Mi, G. Li, J.M. Xue, Z.K. Liu, Y.L. Chen, Photoemission study of the electronic structure of valence band convergent SnSe, Phys. Rev. B 96, 165118 (2017)

18. G. Li*#, B.H. Yan, Z.J. Wang, K. Held, Topological Dirac semimetal phase in Pd and Pt oxides, Phys. Rev. B 95, 035102 (2017)

19. Y.W. Li, Y.Y.Y. Xia, S.A. Ekahana, N. Kumar, J. Jiang, L.X. Yang, C. Chen, C.X. Liu, B.H. Yan, C. Felser, G. Li, Z.K. Liu, Y.L. Chen, Topological origin of the type-II Dirac fermions in PtSe2, Phys. Rev. Mat. 7, 074202 (2017)

20. Y.Y.Y. Xia, G. Li#, Triply degenerate nodal points and topological phase transitions in NaCu3Te2, Phys. Rev. B 96, 241204 (2017)

Publication before 2017

21. S. Glass, F. Reis, M. Bauernfeind, J. Aulbach, M.R. Scholz, F. Adler, L. Dudy, G. Li, R. Claessen, J. Schaefer,Atomic-scale mapping of layer-by-layer hydrogen etching and passivation of SiC(0001) substrates, J. Phys. Chem. C 120, 10361 (2016)

22. G. Li*#, N. Wentzell, P. Pudleiner, K. Held, Efficient implementation of the parquet equations: Role of the reducible vertex function and its kernel approximation, Phys. Rev. B 93, 165103 (2016)

23. P. Pudleiner, T. Schafer, D. Rost, G. Li, K. Held, N. Blumer, Momentum structure of the self-energy and its parameterization for the two-dimensional Hubbard model, Phys. Rev. B 93, 195134 (2016)

24. G. Li#, W. Hanke, G. Sangiovanni, B. Tauzettel, Interacting weak topological insulators and their transition to Dirac semimetal phases, Phys. Rev. B 92, 235149 (2016)

25. G. Li#, Hidden physics in the dual-fermion approach: A special case of a nonlocal expansion, Phys. Rev. B 91, 165134 (2015)

26. X. Zhang, W. Wu, G. Li, Q. Sun, A.C. Ji, Phase diagram of interacting Fermi gas in spin-orbit coupled squared lattice, New J. Phys. 17, 073036 (2015)

27. M. Laubach, R. Thomale, C. Platt, W. Hanke, G. Li#, Phase diagram of the Hubbard model on the anisotropic triangular lattice, Phys. Rev. B 91, 245125 (2015)

28. G. Li*#, B.H. Yan, R. Thomale, W. Hanke, Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductor, Sci. Rep. 5,10435 (2015)

29. S. Glass, G. Li, F. Adler, J. Aulbach, A. Fleszar, R. Thomale, W. Hanke, R. Claessen, J. Schaefer#, Triangular spin-orbit-coupled lattice with strong coulomb correlations: Sn atoms on a SiC(0001) substrate, Phys. Rev. Lett. 115, 247602 (2015)

30. G. Li*#, A. Antipov, A. Rubtsov, S. Kirchner, W. Hanke, Competing phases of the Hubbard model on a triangular lattice: Insights from the entropy, Phys. Rev. B 89, 161118(2014)

31. A. Barfuss, L. Dudy, M.R. Scholtz, M.R. Scholz, H. Roth, P. Hoepfner, C. Blumenstein, G. Landolt, J.H. Dil, N.C. Plumb, M. Radovic, A. Bostwick, E. Rotenberg, A. Fleszar, G. Bihlmayer, D. Wortmann, G. Li, W. Hanke, R. Claessen, J. Schaefer, Elemental topological insulator with tunable Fermi level: strained alpha-Sn on InSb(001), Phys. Rev. Lett. 111, 157205 (2013)

32. G. Li, P. Hoepfner, J. Schaefer, R. Claessen, W. Hanke, Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface. Nat. Commun. 4, 2617 (2013)

33. G. Li, W. Hanke, Efficient treatment of the high-frequency tail of the self-energy function and its relevance for multiorbital models, Phys. Rev. B 85, 115103 (2012)

34. J.C. Budich, R. Thomale, G. Li, M. Laubach, S.C. Zhang, Fluctuation-induced topological quantum phase transitions in quantum spin-Hall and anomalous-Hall insulators, Phys. Rev. B 86, 201407 (2012)

35. G. Li*#, M. Laubach, A. Fleszar, W. Hanke, Geometrical frustration and the competing phases of the Sn/Si(111) root 3 x root 3 R30 degress surface systems. Phys. Rev. B 83, 041104 (2011)

36. G. Li#, W. Hanke, A.N. Rubtsov, S. Baese, M. Potthoff, Accessing thermodynamics from dynamical cluster-embedding approaches. Phys. Rev. B 80, 195118 (2009)

37. H. Hafermann, G. Li, A.N. Rubtsov, M.I. Katsnelson, A.I. Lichtenstein, H. Monien, Efficient perturbation theory for quantum lattice model. Phys. Rev. Lett. 102, 206401 (2008)

38. G. Li, H. Lee, H. Monien, Determination of the lattice susceptibility within the dual fermion method,Phys. Rev. B. 78, 195105 (2008)

39. H. Lee, G. Li, H. Monien, Hubbard model on the triangular lattice using dynamical cluster approximation and dual fermion methods. Phys. Rev. B 78, 205117 (2008)

40. G. Li, G.S. Tian, Ferromagnetism in an itinerant electron cluster, Commun. Theore. Phys. 44, 188 (2005)

Will be provided during the lecture