7 results on '"Xu, Du"'
Search Results
2. Uncovering Topological Edge States in Twisted Bilayer Graphene
- Author
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Matthieu Fortin-Deschênes, Rui Pu, Yan-Feng Zhou, Chao Ma, Patrick Cheung, Kenji Watanabe, Takashi Taniguchi, Fan Zhang, Xu Du, and Fengnian Xia
- Subjects
Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Abstract
Twisted bilayer graphene (t-BLG) has recently been introduced as a rich physical platform displaying flat electronic bands, strongly correlated states, and unconventional superconductivity. Studies have hinted at an unusual
- Published
- 2022
3. Moiré Band Topology in Twisted Bilayer Graphene
- Author
-
Takashi Taniguchi, Chao Ma, Shaofan Yuan, Scott Mills, Cheng Li, Xiaolong Chen, Fan Zhang, Bingchen Deng, Fengnian Xia, Kenji Watanabe, Qiyue Wang, and Xu Du
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Superconductivity ,Mechanical Engineering ,Flatness (systems theory) ,Bioengineering ,02 engineering and technology ,General Chemistry ,Moiré pattern ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Topology ,Condensed Matter - Strongly Correlated Electrons ,General Materials Science ,0210 nano-technology ,Bilayer graphene ,Topology (chemistry) - Abstract
Recently twisted bilayer graphene (t-BLG) emerges as a new strongly correlated physical platform near a magic twist angle, which hosts many exciting phenomena such as the Mott-like insulating phases, unconventional superconducting behavior and emergent ferromagnetism. Besides the apparent significance of band flatness, band topology may be another critical element in determining strongly correlated twistronics yet receives much less attention. Here we report compelling evidence for nontrivial noninteracting band topology of t-BLG moir\'e Dirac bands through a systematic nonlocal transport study, in conjunction with an examination rooted in $K$-theory. The moir\'e band topology of t-BLG manifests itself as two pronounced nonlocal responses in the electron and hole superlattice gaps. We further show that the nonlocal responses are robust to the interlayer electric field, twist angle, and edge termination, exhibiting a universal scaling law. While an unusual symmetry of t-BLG trivializes Berry curvature, we elucidate that two $Z_2$ invariants characterize the topology of the moir\'e Dirac bands, validating the topological edge origin of the observed nonlocal responses. Our findings not only provide a new perspective for understanding the emerging strongly correlated phenomena in twisted van der Waals heterostructures, but also suggest a potential strategy to achieve topologically nontrivial metamaterials from topologically trivial quantum materials based on twist engineering., Comment: 26 pages, 4 figures, and 1 table
- Published
- 2020
4. Random Gauge Field Scattering in Monolayer Graphene
- Author
-
Xu Du and Fen Guan
- Subjects
Materials science ,Condensed matter physics ,Graphene ,Mechanical Engineering ,Bioengineering ,Charge (physics) ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Magnetic field ,Electrical resistivity and conductivity ,law ,0103 physical sciences ,Valleytronics ,General Materials Science ,Gauge theory ,010306 general physics ,0210 nano-technology ,Vector potential - Abstract
Strain-induced lattice deformation affects electron hopping between the atoms. This effectively gives rise to a gauge field which impacts on the charge transport. In graphene, such gauge field is associated with a vector potential which mimics that of a magnetic field. Understanding the impact of the gauge field on charge transport is of essential importance for emerging topics including straintronics and valleytronics in two-dimensional materials. While extensive theoretical works have been carried out over the past decade, experimental progress has been largely limited to local probe and optical studies. Experimental charge transport study has been baffled by the challenge in creating an effective and independent tuning knob of strain without compromising the quality of graphene. Here we studied high quality suspended graphene field effect transistors fabricated on flexible Polyimide substrates. Applying uniaxial strain by bending the substrate, we observed a strain-induced resistivity with power-law carrier density dependence. The power factor is found to be correlated with the surface fractal dimension of the rippled graphene, in good agreement with the random gauge field scattering theory. Both phase coherent transport and magnetotransport properties are found to be strain-dependent, which can be understood in terms of a strain-tunable disorder.
- Published
- 2017
5. Bulk Separative Enrichment in Metallic or Semiconducting Single-Walled Carbon Nanotubes
- Author
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C. Daniel Rancken, Andrew G. Rinzler, Xu Du, Hai-Ping Cheng, Mao-Hua Du, and Zhihong Chen
- Subjects
Nanotube ,Materials science ,Bromine ,Absorption spectroscopy ,Mechanical Engineering ,Selective chemistry of single-walled nanotubes ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,General Chemistry ,Carbon nanotube ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Catalysis ,law.invention ,Metal ,Condensed Matter::Materials Science ,chemistry ,Chemical engineering ,law ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,Gravity separation - Abstract
A postsynthesis method of separating metallic from semiconducting single-walled carbon nanotubes and a method based on absorption spectroscopy for assay of the separation efficiency are described. The separation method relies on chemical discrimination in the charge-transfer complex formation between bromine and the metallic versus semiconducting nanotubes and takes advantage of the resulting density difference to effect a centrifugation-based separation. Calculations support the proposed separation mechanism.
- Published
- 2003
6. Extrinsic and intrinsic charge trapping at the graphene/ferroelectric interface
- Author
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Xu Du, Matthew Dawber, M. Humed Yusuf, and Bent Nielsen
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Graphene ,Mechanical Engineering ,Superlattice ,Transition temperature ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Bioengineering ,Charge (physics) ,General Chemistry ,Trapping ,Condensed Matter Physics ,Ferroelectricity ,law.invention ,Hysteresis ,Condensed Matter::Materials Science ,law ,Volume fraction ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science - Abstract
The interface between graphene and the ferroelectric superlattice $\mathrm{PbTiO_3/SrTiO_3}$ (PTO/STO) is studied. Tuning the transition temperature through the PTO/STO volume fraction minimizes the adsorbates at the graphene-ferroelectric interface, allowing robust ferroelectric hysteresis to be demonstrated. Intrinsic charge traps from the ferroelectric surface defects can adversely affect the graphene channel hysteresis, and can be controlled by careful sample processing, enabling systematic study of the charge trapping mechanism., Comment: 25 pages, 5 figures. Published online in Nano letters, Article ASAP, August 18, 2014, http://pubs.acs.org/doi/abs/10.1021/nl502669v
- Published
- 2014
7. Random Gauge Field Scattering in Monolayer Graphene.
- Author
-
Fen Guan and Xu Du
- Subjects
- *
MONOMOLECULAR films , *GAUGE field theory , *GRAPHENE , *MAGNETIC fields , *SUBSTRATES (Materials science) , *TWO-dimensional materials (Nanotechnology) - Abstract
Strain-induced lattice deformation affects electron hopping between the atoms. This effectively gives rise to a gauge field which impacts on the charge transport. In graphene, such gauge field is associated with a vector potential which mimics that of a magnetic field. Understanding the impact of the gauge field on charge transport is of essential importance for emerging topics including straintronics and valleytronics in two-dimensional materials. While extensive theoretical works have been carried out over the past decade, experimental progress has been largely limited to local probe and optical studies. Experimental charge transport study has been baffled by the challenge in creating an effective and independent tuning knob of strain without compromising the quality of graphene. Here we studied high quality suspended graphene field effect transistors fabricated on flexible Polyimide substrates. Applying uniaxial strain by bending the substrate, we observed a strain-induced resistivity with power-law carrier density dependence. The power factor is found to be correlated with the surface fractal dimension of the rippled graphene, in good agreement with the random gauge field scattering theory. Both phase coherent transport and magnetotransport properties are found to be strain-dependent, which can be understood in terms of a strain-tunable disorder. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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