Two-Dimensional Quadrupole Topological Insulator in γ-Graphyne.

Two-dimensional quadrupole topological insulator (2D QTI), as a new class of second-order topological phases, has been experimentally confirmed in various artificial systems recently. However, its realization in electronic materials has seldom been reported. In this Letter, we predict that the experimentally synthesized γ-graphyne is a large-gap (~0.2 eV) 2D QTI. Three characterized features for 2D QTI are simultaneously observed in γ-graphyne: quantized finite bulk quadrupole moment, gapped topological edge states and in-gap topological corner states. Intriguingly, we found that gapped topological edge states exist on armchair edge with C≡C (but not C-C) termination, and in-gap topological corner states exist at corner with 120˚ (but not 60˚) termination, which can be explained by different edge hopping textures and corner chiral charges. Moreover, the robustness of in-gap topological corner states is further identified by varying edge-disorder and system-size calculations. Our results demonstrate a realistic electronic material for large-gap 2D QTI, which are expected to draw immediate experimental attention.

[1]  Jun Kang,et al.  Graphyne and Its Family: Recent Theoretical Advances. , 2019, ACS applied materials & interfaces.

[2]  Andrea Alù,et al.  Observation of higher-order topological acoustic states protected by generalized chiral symmetry , 2018, Nature Materials.

[3]  Chaofan Yang,et al.  Synthesis of γ-graphyne by mechanochemistry and its electronic structure , 2018, Carbon.

[4]  Y. Chong,et al.  Acoustic higher-order topological insulator on a kagome lattice , 2018, Nature Materials.

[5]  Jinlong Yang,et al.  Surface alloy engineering in 2D trigonal lattice: giant Rashba spin splitting and two large topological gaps , 2018 .

[6]  M. Vergniory,et al.  Higher-Order Topology in Bismuth , 2018, Nature Physics.

[7]  Gaurav Bahl,et al.  A quantized microwave quadrupole insulator with topologically protected corner states , 2017, Nature.

[8]  Luis Guillermo Villanueva,et al.  Observation of a phononic quadrupole topological insulator , 2017, Nature.

[9]  M. Vergniory,et al.  Higher-order topological insulators , 2017, Science Advances.

[10]  Florian Bayer,et al.  Topolectrical-circuit realization of topological corner modes , 2017, Nature Physics.

[11]  Kevin P. Chen,et al.  Topological protection of photonic mid-gap defect modes , 2016, Nature Photonics.

[12]  Wladimir A. Benalcazar,et al.  Quantized electric multipole insulators , 2016, Science.

[13]  Feng Liu,et al.  Quantum spin Hall phase in 2D trigonal lattice , 2016, Nature Communications.

[14]  Qian Niu,et al.  Topological phases in two-dimensional materials: a review , 2015, Reports on progress in physics. Physical Society.

[15]  X. Hu,et al.  Topological Properties of Electrons in Honeycomb Lattice with Detuned Hopping Energy , 2015, Scientific Reports.

[16]  Jinyang Xi,et al.  Electron-phonon couplings and carrier mobility in graphynes sheet calculated using the Wannier-interpolation approach. , 2014, The Journal of chemical physics.

[17]  Huibiao Liu,et al.  Graphdiyne and graphyne: from theoretical predictions to practical construction. , 2014, Chemical Society reviews.

[18]  Wanlin Guo,et al.  Intrinsic electronic and transport properties of graphyne sheets and nanoribbons. , 2013, Nanoscale.

[19]  Yisong Zheng,et al.  Electronic properties of four typical zigzag-edged graphyne nanoribbons , 2013, Journal of physics. Condensed matter : an Institute of Physics journal.

[20]  W. Duan,et al.  The existence/absence of Dirac cones in graphynes , 2013 .

[21]  Fengmin Wu,et al.  Elastic, Electronic, and Optical Properties of Two-Dimensional Graphyne Sheet , 2011 .

[22]  Shou-Cheng Zhang,et al.  Quantum Spin Hall Effect and Topological Phase Transition in HgTe Quantum Wells , 2006, Science.

[23]  Ray H. Baughman,et al.  Structure‐property predictions for new planar forms of carbon: Layered phases containing sp2 and sp atoms , 1987 .