22 results on '"Lin He"'
Search Results
2. Realizing One-Dimensional Electronic States in Graphene via Coupled Zeroth Pseudo-Landau Levels
- Author
-
Yi-Wen Liu, Zhen Zhan, Zewen Wu, Chao Yan, Shengjun Yuan, and Lin He
- Subjects
General Physics and Astronomy - Abstract
Strain-induced pseudomagnetic fields can mimic real magnetic fields to generate a zero-magnetic-field analog of the Landau levels (LLs), i.e., the pseudo-Landau levels (PLLs), in graphene. The distinct nature of the PLLs enables one to realize novel electronic states beyond what is feasible with real LLs. Here, we show that it is possible to realize exotic electronic states through the coupling of zeroth PLLs in strained graphene. In our experiment, nanoscale strained structures embedded with PLLs are generated along a one-dimensional (1D) channel of suspended graphene monolayer. Our results demonstrate that the zeroth PLLs of the strained structures are coupled together, exhibiting a serpentine pattern that snakes back and forth along the 1D suspended graphene monolayer. These results are verified theoretically by large-scale tight-binding calculations of the strained samples. Our result provides a new approach to realizing novel quantum states and to engineering the electronic properties of graphene by using localized PLLs as building blocks.
- Published
- 2022
3. Characterization and Manipulation of Intervalley Scattering Induced by an Individual Monovacancy in Graphene
- Author
-
Fei Gao, Mads Brandbyge, Yu Zhang, Lin He, and Shiwu Gao
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences ,General Physics and Astronomy - Abstract
Intervalley scattering involves microscopic processes that electrons are scattered by atomic-scale defects on nanometer length scales. Although central to our understanding of electronic properties of materials, direct characterization and manipulation of range and strength of the intervalley scattering induced by an individual atomic defect have so far been elusive. Using scanning tunneling microscope, we visualized and controlled intervalley scattering from an individual monovacancy in graphene. By directly imaging the affected range of intervalley scattering of the monovacancy, we demonstrated that it is inversely proportional to the energy, i.e., it is proportional to the wavelength of massless Dirac Fermions. A giant electron-hole asymmetry of the intervalley scattering is observed because that the monovacancy is charged. By further charging the monovacancy, the bended electronic potential around the monovacancy softened the scattering potential, which, consequently, suppressed the intervalley scattering of the monovacancy., 18 pages, 4 figures
- Published
- 2022
4. Oscillations of the Spacing between van Hove Singularities Induced by sub-Ångstrom Fluctuations of Interlayer Spacing in Graphene Superlattices
- Author
-
Ya-Xin Zhao, Xiao-Feng Zhou, Yu Zhang, and Lin He
- Subjects
General Physics and Astronomy - Abstract
Physical properties of two-dimensional van der Waals (vdWs) structures depend sensitively on both stacking orders and interlayer interactions. Yet, in most cases studied to date, the interlayer interaction is considered to be a "static" property of the vdWs structures. Here we demonstrate that applying a scanning tunneling microscopy (STM) tip pulse on twisted bilayer graphene (TBG) can induce sub-Ångstrom fluctuations of the interlayer separation in the TBG, which are equivalent to dynamic vertical external pressure of about 10 GPa on the TBG. The sub-Ångstrom fluctuations of the interlayer separation result in large oscillations of the energy separations between two van Hove singularities (VHSs) in the TBG. The period of the oscillations of the VHSs spacing is extremely long, about 500-1000 sec, attributing to tip-induced local stress in the atomic-thick TBG. Our result provides an efficient method to tune and measure the physical properties of the vdWs structures dynamically.
- Published
- 2021
5. Realizing Valley-Polarized Energy Spectra in Bilayer Graphene Quantum Dots via Continuously Tunable Berry Phases
- Author
-
Ya-Ning Ren, Qiang Cheng, Qing-Feng Sun, and Lin He
- Subjects
General Physics and Astronomy - Abstract
The Berry phase plays an important role in determining many physical properties of quantum systems. However, tuning the energy spectrum of a quantum system via Berry phase is comparatively rare because the Berry phase is usually a fixed constant. Here, we report the realization of an unusual valley-polarized energy spectra via continuously tunable Berry phases in Bernal-stacked bilayer graphene quantum dots. In our experiment, the Berry phase of electron orbital states is continuously tuned from about π to 2π by perpendicular magnetic fields. When the Berry phase equals π or 2π, the electron states in the two inequivalent valleys are energetically degenerate. By altering the Berry phase to noninteger multiples of π, large and continuously tunable valley-polarized energy spectra are realized. Our result reveals the Berry phase's essential role in valleytronics and the observed valley splitting, on the order of 10 meV at a magnetic field of 1 T, is about 100 times larger than Zeeman splitting for spin, shedding light on graphene-based valleytronics.
- Published
- 2021
6. Tunable Lattice Reconstruction, Triangular Network of Chiral One-Dimensional States, and Bandwidth of Flat Bands in Magic Angle Twisted Bilayer Graphene
- Author
-
Sheng Han, Chao Yan, Lin He, Yu Zhang, Si-Yu Li, Ying Su, Qian Yang, Yi-Wen Liu, Long-Jing Yin, Ya-Ning Ren, Zhong-Qiu Fu, Wei Yan, and Xiao-Feng Zhou
- Subjects
Physics ,Magic angle ,Condensed matter physics ,Bandwidth (signal processing) ,Lattice distortion ,General Physics and Astronomy ,01 natural sciences ,law.invention ,Electronic states ,symbols.namesake ,law ,Lattice (order) ,0103 physical sciences ,symbols ,Scanning tunneling microscope ,van der Waals force ,010306 general physics ,Bilayer graphene - Abstract
The interplay between interlayer van der Waals interaction and intralayer lattice distortion can lead to structural reconstruction in slightly twisted bilayer graphene (TBG) with the twist angle being smaller than a characteristic angle θ_{c}. Experimentally, the θ_{c} is demonstrated to be very close to the magic angle (θ≈1.08°). Here we address the transition between reconstructed and unreconstructed structures of the TBG across the magic angle by using scanning tunneling microscopy (STM). Our experiment demonstrates that both structures are stable in the TBG around the magic angle. By using a STM tip, we show that the two structures can be changed to each other and a triangular network of chiral one-dimensional states hosted by domain boundaries can be switched on and off. Consequently, the bandwidth of the flat band, which plays a vital role in the emergent strongly correlated states in the magic angle TBG, is tuned. This provides an extra control knob to manipulate the exotic electronic states of the TBG near the magic angle.
- Published
- 2020
7. Local Berry Phase Signatures of Bilayer Graphene in Intervalley Quantum Interference
- Author
-
Lin He, Ying Su, and Yu Zhang
- Subjects
Physics ,Condensed matter physics ,Condensed Matter::Other ,Graphene ,Oscillation ,Texture (cosmology) ,Scattering ,General Physics and Astronomy ,Fermi surface ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,law.invention ,Geometric phase ,law ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,Bilayer graphene - Abstract
Chiral quasiparticles in Bernal-stacked bilayer graphene have valley-contrasting Berry phases of $\ifmmode\pm\else\textpm\fi{}2\ensuremath{\pi}$. This nontrivial topological structure, associated with the pseudospin winding along a closed Fermi surface, is responsible for various novel electronic properties. Here we show that the quantum interference due to intervalley scattering induced by single-atom vacancies or impurities provides insights into the topological nature of the bilayer graphene. The scattered chiral quasiparticles between distinct valleys with opposite chirality undergo a rotation of pseudospin that results in the Friedel oscillation with wavefront dislocations. The number of dislocations reflects the information about pseudospin texture and hence can be used to measure the Berry phase. As demonstrated both experimentally and theoretically, the Friedel oscillation, depending on the single-atom vacancy or impurity at different sublattices, can exhibit $N=4$, 2, or 0 additional wavefronts, characterizing the $2\ensuremath{\pi}$ Berry phase of the bilayer graphene. Our results provide a comprehensive study of the intervalley quantum interference in bilayer graphene and can be extended to multilayer graphene, shedding light on the pseudospin physics.
- Published
- 2020
8. Valley Polarization and Inversion in Strained Graphene via Pseudo-Landau Levels, Valley Splitting of Real Landau Levels, and Confined States
- Author
-
Ying Su, Lin He, Si-Yu Li, and Ya-Ning Ren
- Subjects
Physics ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Spin polarization ,Graphene ,Scanning tunneling spectroscopy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,Landau quantization ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Polarization (waves) ,01 natural sciences ,law.invention ,Magnetic field ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Valleytronics ,010306 general physics ,Spin (physics) - Abstract
It is quite easy to control spin polarization and spin direction of a system via magnetic fields. However, there is no such a direct and efficient way to manipulate valley pseudospin degree of freedom. Here, we demonstrate experimentally that it is possible to realize valley polarization and valley inversion in graphene by using both strain-induced pseudomagnetic fields and real magnetic fields. The pseudomagnetic fields, which are quite different from real magnetic fields, pointing in opposite directions at the two distinct valleys of graphene. Therefore, coexistence of the pseudomagnetic fields and the real magnetic fields leads to imbalanced effective magnetic fields at two distinct valleys of graphene. This allows us to control the valley in graphene as convenient as the electron spin. In this work, we report consistent observation of valley polarization and inversion in strained graphene via pseudo-Landau levels, splitting of real Landau levels and valley splitting of confined states using scanning tunneling spectroscopy. Our results highlight a pathway to valleytronics in strained graphene-based platforms., 4 figures in main text, accepted by Phys. Rev. Lett
- Published
- 2019
9. High-Magnetic-Field Tunneling Spectra of ABC-Stacked Trilayer Graphene on Graphite
- Author
-
Li-Juan Shi, Long-Jing Yin, Zi-Han Guo, Yu Zhang, Lin He, and Si-Yu Li
- Subjects
Materials science ,Condensed matter physics ,law ,Graphene ,Quasiparticle ,General Physics and Astronomy ,Electron ,Landau quantization ,Scanning tunneling microscope ,Scaling ,Quantum tunnelling ,law.invention ,Magnetic field - Abstract
ABC-stacked trilayer graphene (TLG) was predicted to exhibit novel many-body phenomena due to the existence of almost dispersionless flat bands near the charge neutrality point. Here, using high-magnetic-field scanning tunneling microscopy, we present Landau Level (LL) spectroscopy measurements of high-quality ABC-stacked TLG on graphite. We observe an approximately linear magnetic-field scaling of valley splitting and spin splitting in the ABC-stacked TLG. Our experiment indicates that the spin splitting decreases dramatically with increasing the LL index. When the lowest LL is partially filled, we find an obvious enhancement of the spin splitting, attributing to strong many-body effects. Moreover, we observe linear energy scaling of the inverse lifetime of quasiparticles, providing an additional evidence for the strong electron-electron interactions in the ABC-stacked TLG. These results imply that interesting broken-symmetry states and novel electron correlated effects could emerge in the ABC-stacked TLG in the presence of high magnetic fields.
- Published
- 2018
10. Scanning Tunneling Microscopy of theπMagnetism of a Single Carbon Vacancy in Graphene
- Author
-
Si-Yu Li, Wen-Tian Li, Huaqing Huang, Lin He, Wenhui Duan, Jia-Bin Qiao, Yu Zhang, Ke-Ke Bai, Wen-Xiao Wang, and Long-Jing Yin
- Subjects
Materials science ,Condensed matter physics ,Magnetism ,Graphene ,General Physics and Astronomy ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Resonance (particle physics) ,law.invention ,Paramagnetism ,law ,Vacancy defect ,0103 physical sciences ,Diamagnetism ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology - Abstract
Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the $\ensuremath{\pi}$ magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this $\ensuremath{\pi}$ magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the $\ensuremath{\pi}$ magnetism experimentally elusive. Here, we report direct experimental evidence of $\ensuremath{\pi}$ magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective $g$ factor around the atomic defect is measured to be about 40, which is about 20 times larger than the $g$ factor for electron spins.
- Published
- 2016
11. Comment on 'Coexistence of Coulomb Blockade and Zero Bias Anomaly in a Strongly Coupled Nanodot'
- Author
-
Hui Yan, Lin He, and Rui Xu
- Subjects
Physics ,Strongly coupled ,Single electron tunneling ,Condensed matter physics ,Quantum dot ,Quantum mechanics ,General Physics and Astronomy ,Coulomb blockade ,Nanodot ,Anomaly (physics) ,Zero bias ,Quantum tunnelling - Published
- 2011
12. Comment on 'Evidence for Quantization of Mechanical Rotation of Magnetic Nanoparticles'
- Author
-
Lin He
- Subjects
Physics ,Quantization (physics) ,Condensed matter physics ,Quantum mechanics ,General Physics and Astronomy ,Magnetic nanoparticles - Published
- 2010
13. Topological Transitions Induced by Antiferromagnetism in a Thin-Film Topological Insulator.
- Author
-
Qing Lin He, Gen Yin, Luyan Yu, Grutter, Alexander J., Lei Pan, Chui-Zhen Chen, Xiaoyu Che, Guoqiang Yu, Bin Zhang, Qiming Shao, Stern, Alexander L., Casas, Brian, Jing Xia, Xiaodong Han, Kirby, Brian J., Lake, Roger K., Law, K. T., and Wang, Kang L.
- Subjects
- *
ANTIFERROMAGNETISM , *MAGNETIC properties of thin films , *TOPOLOGICAL insulators - Abstract
Magnetism in topological insulators (TIs) opens a topologically nontrivial exchange band gap, providing an exciting platform for manipulating the topological order through an external magnetic field. Here, we show that the surface of an antiferromagnetic thin film can magnetize the top and the bottom TI surface states through interfacial couplings. During the magnetization reversal, intermediate spin configurations are ascribed from unsynchronized magnetic switchings. This unsynchronized switching develops antisymmetric magnetoresistance spikes during magnetization reversals, which might originate from a series of topological transitions. With the high Néel ordering temperature provided by the antiferromagnetic layers, the signature of the induced topological transition persists up to ~90 K. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
14. Chiral Tunneling in a Twisted Graphene Bilayer.
- Author
-
Wen-Yu He, Zhao-Dong Chu, and Lin He
- Subjects
- *
GRAPHENE , *ELECTRONS , *KLEIN paradox , *QUASIPARTICLES , *FERMIONS , *CHIRALITY - Abstract
The perfect transmission in a graphene monolayer and the perfect reflection in a Bernal graphene bilayer for electrons incident in the normal direction of a potential barrier are viewed as two incarnations of the Klein paradox. Here we show a new and unique incarnation of the Klein paradox. Owing to the different chiralities of the quasiparticles involved, the chiral fermions in a twisted graphene bilayer show an adjustable probability of chiral tunneling for normal incidence: they can be changed from perfect tunneling to partial or perfect reflection, or vice versa, by controlling either the height of the barrier or the incident energy. As well as addressing basic physics about how the chiral fermions with different chiralities tunnel through a barrier, our results provide a facile route to tune the electronic properties of the twisted graphene bilayer. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
15. Local Berry Phase Signatures of Bilayer Graphene in Intervalley Quantum Interference.
- Author
-
Yu Zhang, Ying Su, and Lin He
- Subjects
- *
GEOMETRIC quantum phases , *GRAPHENE , *QUANTUM interference , *FERMI surfaces , *QUASIPARTICLES , *PHYSICS , *CHIRALITY - Abstract
Chiral quasiparticles in Bernal-stacked bilayer graphene have valley-contrasting Berry phases of ±2π. This nontrivial topological structure, associated with the pseudospin winding along a closed Fermi surface, is responsible for various novel electronic properties. Here we show that the quantum interference due to intervalley scattering induced by single-atom vacancies or impurities provides insights into the topological nature of the bilayer graphene. The scattered chiral quasiparticles between distinct valleys with opposite chirality undergo a rotation of pseudospin that results in the Friedel oscillation with wavefront dislocations. The number of dislocations reflects the information about pseudospin texture and hence can be used to measure the Berry phase. As demonstrated both experimentally and theoretically, the Friedel oscillation, depending on the single-atom vacancy or impurity at different sublattices, can exhibit N=4, 2, or 0 additional wavefronts, characterizing the 2π Berry phase of the bilayer graphene. Our results provide a comprehensive study of the intervalley quantum interference in bilayer graphene and can be extended to multilayer graphene, shedding light on the pseudospin physics. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
16. Creating One-Dimensional Nanoscale Periodic Ripples in a Continuous Mosaic Graphene Monolayer.
- Author
-
Ke-Ke Bai, Yu Zhou, Hong Zheng, Lan Meng, Hailin Peng, Zhongfan Liu, Jia-Cai Nie, and Lin He
- Subjects
- *
GRAPHENE , *CARBON , *POLYCYCLIC aromatic hydrocarbons , *HYDROCARBONS , *POLYCYCLIC aromatic compounds - Abstract
In previous studies, it has proved difficult to realize periodic graphene ripples with wavelengths of a few nanometers. Here we show that one-dimensional (ID) periodic graphene ripples with wavelengths from 2 nm to tens of nanometers can be implemented in the intrinsic areas of a continuous mosaic (locally N-doped) graphene monolayer by simultaneously using both the thermal strain engineering and the anisotropic surface stress of the Cu substrate. Our result indicates that the constraint imposed at the boundaries between the intrinsic and the N-doped regions play a vital role in creating these ID ripples. We also demonstrate that the observed rippling modes are beyond the descriptions of continuum mechanics due to the decoupling of graphene's bending and tensional deformations. Scanning tunneling spectroscopy measurements indicate that the nanorippling generates a periodic electronic superlattice and opens a zeroenergy gap of about 130 meV in graphene. This result may pave a facile way for tailoring the structures and electronic properties of graphene. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
17. Angle-Dependent van Hove Singularities in a Slightly Twisted Graphene Bilayer.
- Author
-
Wei Yan, Mengxi Liu, Rui-Fen Dou, Lan Meng, Lei Feng, Zhao-Dong Chu, Yanfeng Zhang, Zhongfan Liu, Jia-Cai Nie, and Lin He
- Subjects
- *
GRAPHENE , *MATHEMATICAL singularities , *SCANNING tunneling microscopy , *MONOMOLECULAR films , *DIRAC equation , *FERMI surfaces , *ELECTRONIC band structure - Abstract
Recent studies show that two low-energy van Hove singularities (VHSs) seen as two pronounced peaks in the density of states could be induced in a twisted graphene bilayer. Here, we report angle-dependent VHSs of a slightly twisted graphene bilayer studied by scanning tunneling microscopy and spectroscopy. We show that energy difference of the two VHSs follows ΔEvhs ~ hvFΔK between 1.0° and 3.0° [here vF ~1.l X 106 m/s is the Fermi velocity of monolayer graphene, and ΔK = 2Ksin(θ/2) is the shift between the corresponding Dirac points of the twisted graphene bilayer]. This result indicates that the rotation angle between graphene sheets does not result in a significant reduction of the Fermi velocity, which quite differs from that predicted by band structure calculations. However, around a twisted angle θ ~ 1.3°, the observed ΔEvhs ~ 0.11 eV is much smaller than the expected value hvFΔK ~ 0.28 eV at 1.3°. The origin of the reduction of ΔEvhs at 1.3° is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
18. Tunable Lattice Reconstruction, Triangular Network of Chiral One-Dimensional States, and Bandwidth of Flat Bands in Magic Angle Twisted Bilayer Graphene.
- Author
-
Wen Liu, Ying Su, Xiao-Feng Zhou, Long-Jing Yin, Chao Yan, Si-Yu Li, Wei Yan, Sheng Han, Zhong-Qiu Fu, Yu Zhang, Qian Yang, Ya-Ning Ren, and Lin He
- Subjects
- *
SCANNING tunneling microscopy , *MAGIC , *MAGIC angle spinning , *BANDWIDTHS - Abstract
The interplay between interlayer van der Waals interaction and intralayer lattice distortion can lead to structural reconstruction in slightly twisted bilayer graphene (TBG) with the twist angle being smaller than a characteristic angle θc. Experimentally, the θc is demonstrated to be very close to the magic angle (θ≈1.08°). Here we address the transition between reconstructed and unreconstructed structures of the TBG across the magic angle by using scanning tunneling microscopy (STM). Our experiment demonstrates that both structures are stable in the TBG around the magic angle. By using a STM tip, we show that the two structures can be changed to each other and a triangular network of chiral one-dimensional states hosted by domain boundaries can be switched on and off. Consequently, the bandwidth of the flat band, which plays a vital role in the emergent strongly correlated states in the magic angle TBG, is tuned. This provides an extra control knob to manipulate the exotic electronic states of the TBG near the magic angle. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
19. Movable Valley Switch Driven by Berry Phase in Bilayer-Graphene Resonators.
- Author
-
Yi-Wen Liu, Zhe Hou, Si-Yu Li, Qing-Feng Sun, and Lin He
- Subjects
- *
GEOMETRIC quantum phases , *SCANNING tunneling microscopy , *RESONATORS , *DEGREES of freedom , *BOUND states , *VALLEYS - Abstract
Berry phase, the geometric phase accumulated over a closed loop in parameter space during an adiabatic cyclic evolution, has been demonstrated to play an important role in many quantum systems since its discovery. In gapped Bernal bilayer graphene, the Berry phase can be continuously tuned from zero to 2π, which offers a unique opportunity to explore the tunable Berry phase on physical phenomena. Here, we report experimental observation of Berry-phase-induced valley splitting and crossing in movable bilayer-graphene p-n junction resonators. In our experiment, the resonators are generated by combining the electric field of a scanning tunneling microscope tip with the gap of bilayer graphene. A perpendicular magnetic field changes the Berry phase of the confined bound states in the resonators from zero to 2π continuously and leads to the Berry phase difference for the two inequivalent valleys in the bilayer graphene. As a consequence, we observe giant valley splitting and unusual valley crossing of the lowest bound states. Our results indicate that the bilayer-graphene resonators can be used to manipulate the valley degree of freedom in valleytronics. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
20. Valley Polarization and Inversion in Strained Graphene via Pseudo-Landau Levels, Valley Splitting of Real Landau Levels, and Confined States.
- Author
-
Si-Yu Li, Ying Su, Ya-Ning Ren, and Lin He
- Subjects
- *
GRAPHENE , *TUNNELING spectroscopy , *ELECTRON spin , *VALLEYS , *SPIN polarization , *LANDAU levels , *QUANTUM Hall effect - Abstract
It is quite easy to control spin polarization and the spin direction of a system via magnetic fields. However, there is no such direct and efficient way to manipulate the valley pseudospin degree of freedom. Here, we demonstrate experimentally that it is possible to realize valley polarization and valley inversion in graphene by using both strain-induced pseudomagnetic fields and real magnetic fields. Pseudomagnetic fields, which are quite different from real magnetic fields, point in opposite directions at the two distinct valleys of graphene. Therefore, the coexistence of pseudomagnetic fields and real magnetic fields leads to imbalanced effective magnetic fields at two distinct valleys of graphene. This allows us to control the valley in graphene as conveniently as the electron spin. In this work, we report a consistent observation of valley polarization and inversion in strained graphene via pseudo-Landau levels, splitting of real Landau levels, and valley splitting of confined states using scanning tunneling spectroscopy. Our results highlight a pathway to valleytronics in strained graphene-based platforms. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
21. High-Magnetic-Field Tunneling Spectra of ABC-Stacked Trilayer Graphene on Graphite.
- Author
-
Long-Jing Yin, Li-Juan Shi, Si-Yu Li, Yu Zhang, Zi-Han Guo, and Lin He
- Subjects
- *
SCANNING tunneling microscopy , *ELECTRON-electron interactions , *GRAPHENE , *LANDAU levels , *TUNNEL design & construction , *GRAPHITE - Abstract
ABC-stacked trilayer graphene (TLG) was predicted to exhibit novel many-body phenomena due to the existence of almost dispersionless flat bands near the charge neutrality point. Here, using high-magnetic-field scanning tunneling microscopy, we present Landau Level (LL) spectroscopy measurements of high-quality ABC-stacked TLG on graphite. We observe an approximately linear magnetic-field scaling of valley splitting and spin splitting in the ABC-stacked TLG. Our experiment indicates that the spin splitting decreases dramatically with increasing the LL index. When the lowest LL is partially filled, we find an obvious enhancement of the spin splitting, attributing to strong many-body effects. Moreover, we observe linear energy scaling of the inverse lifetime of quasiparticles, providing an additional evidence for the strong electron-electron interactions in the ABC-stacked TLG. These results imply that interesting broken-symmetry states and novel electron correlated effects could emerge in the ABC-stacked TLG in the presence of high magnetic fields. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
22. Scanning Tunneling Microscopy of the π Magnetism of a Single Carbon Vacancy in Graphene.
- Author
-
Yu Zhang, Si-Yu Li, Huaqing Huang, Wen-Tian Li, Jia-Bin Qiao, Wen-Xiao Wang, Long-Jing Yin, Ke-Ke Bai, Wenhui Duan, and Lin He
- Subjects
- *
MAGNETISM , *SCANNING tunneling microscopy , *GRAPHENE - Abstract
Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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