Publications
Highlights
Tunable Excitons in Bilayer Graphene
Bilayer graphene has a unique bandstructure where a electrically tunable bandgap exists at corners of the first Brillouin Zone. By opening the gap with external gates, excitons--as the fundamental optical excitation of semiconductors--are expected to host pseudospin-related properties that are distinct from other semiconductors.
For the first time, we observed such excitons in bilayer graphene that have unusual selections rules, significant oscillator strength, extremely narrow linewidth and they can be tuned from mid-infrared to Terahertz range. More interestingly, these excitons exhibit a large valley g-factor of 20 in magnetic fields as determined by the outstanding Berry curvature effects.
Topological Valley Transport at Graphene Domain Walls
Electron valley, a degree of freedom that is analogous to spin, can lead to novel topological phases in bilayer graphene. Gapped bilayer graphene is predicted to be a topological insulating phase protected by no-valley mixing symmetry, featuring quantum valley Hall effects and chiral edge states. Theoretical work has shown that domain walls between AB- and BA-stacked bilayer graphene can support protected chiral edge states of quantum valley Hall insulators.
We employ near-field infrared nanoscopy to image in situ bilayer graphene layer-stacking domain walls on device substrates, and we fabricate dual-gated field effect transistors based on the domain walls. These devices feature one-dimensional valley-polarized conducting channels with a ballistic length of about 400 nanometres at 4 kelvin.
See also, L. Ju et al., Topological Valley Transport at Bilayer Graphene Domain Walls, Nature 520, 650(2015)
Complete List
T. Han*, Z. Lu*, Y. Yao*, J. Yang, J. Seo, C. Yoon, K. Watanabe, T. Taniguchi, L. Fu, F. Zhang, L. Ju, "Large Quantum Anomalous Hall Effect in Spin-Orbit Proximitized Rhombohedral Graphene", Science in press (2024), (arXiv)
Z. Lu*, T. Han*, Y. Yao*, A. Reddy, J. Yang, J. Seo, K. Watanabe, T. Taniguchi, L. Fu, L. Ju, "Fractional Quantum Anomalous Hall Effect in Multilayer Graphene", Nature (2024), (arXiv, Nature News, CMP Journal Club, CMP Journal Club 2, MIT news, Nature research briefing)
T. Han*, Z. Lu*, G. Scuri, J. Sung, J. Wang, T. Han, K. Watanabe, T. Taniguchi, L. Fu, H. Park, L. Ju, "Orbital Multiferroicity in Pentalayer Rhombohedral Graphene", Nature (2023), (arXiv, MIT news)
T. Han*, Z. Lu*, G. Scuri, J. Sung, J. Wang, T. Han, K. Watanabe, T. Taniguchi, H. Park, L. Ju, "Correlated Insulator and Chern Insulators in Pentalayer Rhombohedral Stacked Graphene", Nature Nanotechnology (2023), (arXiv, Nature News and Views, MIT news, cover story)
J. Yang*, G. Chen*, T. Han*, Q. Zhang, Y-H. Zhang, L. Jiang, B. Lyu, H. Li, K. Watanabe, T. Taniguchi, Z. Shi, T. Senthil, Y. Zhang, F. Wang, L. Ju, "Spectroscopy Signatures of Electron Correlations in a Trilayer Graphene/hBN Moiré Superlattice", Science (2022) (https://arxiv.org/abs/2202.12330)
Z. Lu, P. Hollister, M. Ozerov, S. Moon, E. D. Bauer, F. Ronning, D. Smirnov, L. Ju, B. J. Ramshaw, "Weyl fermion magneto-electrodynamics and ultralow field quantum limit in TaAs", Science Advances. (2022)
T. Han, J. Yang, Q. Zhang, L. Wang, K. Watanabe, T. Taniguchi, P. L. McEuen, L. Ju "Accurate measurement of the gap of graphene/hBN moiré superlattice through photocurrent spectroscopy", Physical Review Letters. (2021)
L. Ju*, L. Wang*, X. Li, S. Moon, M. Ozerov, Z. Lu, T. Taniguchi, K. Watanabe, E. Mueller, F. Zhang, D. Smirnov, F. Rana & P. L. McEuen, "Unconventional valley-dependent optical selection rules and landau level mixing in bilayer graphene", Nature Communications. (2020)
L. Ju*, L. Wang*, T. Cao, K. Watanabe, T. Taniguchi, S. G. Louie, F. Rana, J. Park, J. Hone, F. Wang & P. L. McEuen, “Tunable Excitons in Bilayer Graphene”, Science. (2017)
J. Velasco Jr*, L. Ju*, D. Wong, S. Kahn, J. Lee, H. Tsai, C. Germany, S. Wickenburg, J. Lu, T. Taniguchi, K. Watanabe, A. Zettl, F. Wang, M. F. Crommie, “Nanoscale Control of Rewriteable Doping Patterns in Pristine Graphene/Boron Nitride Heterostructures”, Nano Letters. (2016)
D. Wong*, J. Velasco Jr*, L. Ju*, J. Lee, S. Kahn, H. Tsai, C. Germany, T. Taniguchi, K. Watanabe, A. Zettl, F. Wang & M. F. Crommie, “Characterization and Manipulation of Defects in Hexagonal Boron Nitride Using Scanning Tunneling Microscopy”, Nature Nanotechnology. (2015)
L. Ju*, Z. Shi*, N. Nair, Y. Lv, C. Jin, J. Velasco Jr., C. Ojeda-Aristizabal, H. A. Bechtel, M. C. Martin, A. Zettl, J. Analytis & F. Wang, “Topological Valley Transport at Bilayer Graphene Domain Walls”, Nature. (2015)
L. Ju*, J. Velasco Jr*, E. Huang, S. Kahn, C. Nosiglia, H. Tsai, W. Yang, T. Taniguchi, K. Watanabe, Y. Zhang, G. Zhang, M. Crommie, A. Zettl & F. Wang, “Photoinduced Doping in Heterostructures of Graphene and Boron Nitride”, Nature Nanotechnology. (2014)
L. Ju, B. Geng, J. Horng, C. Girit, M. Martin, Z. Hao, H. A. Bechtel, X. Liang, A. Zettl, Y. R. Shen & F. Wang, “Graphene Plasmonics for Tunable Terahertz Metamaterials”, Nature Nanotechnology. (2011)
L. Jiang, Z. Shi, B. Zeng, S. Wang, J. Kang, T. Joshi, C. Jin, L. Ju, J. Kim, T. Lyu, Y. Shen, M. Crommie, H. Gao & F. Wang, “Soliton-dependent Plasmon Reflection at Bilayer Graphene Domain Walls”, Nature Materials. (2016)
Y. Bie, J. Horng, Z. Shi, L. Ju, Q. Zhou, A. Zettl, D. Yu, and F. Wang, “Vibrational Spectroscopy at Electrolyte/Electrode Interfaces with Graphene Gratings”, Nature Communications. (2015)
Z. Shi*, C. Jin*, W. Yang, L. Ju, J. Horng, X. Lu, H. A. Bechtel, M. C. Martin, D. Fu, J. Wu, K. Watanabe, T. Taniguchi, Y. Zhang, X. Bai, E. Wang, G. Zhang & F. Wang, “Gate-dependent Pseudospin Mixing in Graphene/Boron Nitride Moiré Superlattices”, Nature Physics. (2014)
J. Lee, W. Bao, L. Ju, P. J. Schuck, F. Wang, & A. W. Bargioni, “Switching Individual Quantum Dot Emission through Electrically Controlling Resonant Energy Transfer to Graphene”, Nano Letters. (2014)
Z. Yan, Y. Liu, L. Ju, Z. Peng, J. Lin, G. Wang, H. Zhou, C. Xiang, E. L. G. Samuel, C. Kittrell, V. I. Artyukhov, F. Wang, B. I. Yakobson & J. M. Tour, “Large Hexagonal Bi- and Trilayer Graphene Single Crystals with Varied Interlayer Rotation”, Angewandte Chemie. (2014)
S. F. Shi, T.-T. Tang, B. Zeng, L. Ju, Q. Zhou, A. Zettl, & F. Wang, Controlling Graphene “Ultrafast Hot Carrier Response from Metal-like to Semiconductor-like by Electrostatic Gating”, Nano Letters. (2014)
B. Chapler, S. Mack, L. Ju, T. W. Elson, B. W. Boudouris, E. Namdas, J. D. Yuen, A. J. Heeger, N. Samarth, M. Di Ventra, R. A. Segalman, D. D. Awschalom, F. Wang & D. N. Basov, “Infrared Conductivity of Hole Accumulation and Depletion Layers in (Ga, Mn) As-and (Ga, Be) As-based Electric Field-Effect Devices”, Phys. Rev. B. (2012)
K. F. Mak, L. Ju, F. Wang & T. F. Heinz, “Optical Spectroscopy of Graphene: From the Far Infrared to the Ultraviolet”, Solid State Communications. (2012)
M. Liu *, X. Yin *, E. Ulin-Avila, B. Geng, T. Zentgraf, L. Ju, F. Wang & X. Zhang, “A Graphene-based Broadband Optical Modulator”, Nature. (2011)
X. Xie*, L. Ju*, X. Feng, Y. Sun, R. Zhou, K. Liu, S. Fan, Q.Li & K. Jiang, “Controlled Fabrication of High-Quality Carbon Nanoscrolls from Monolayer Graphene”, Nano Letters. (2009)