Chiral tunneling in a twisted graphene bilayer.

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.

Differential proteomics analysis of proteins from human diabetic and age-related cataractous lenses.

BACKGROUND: To investigate the differential lens proteomics between diabetic cataract, age-related cataract, and natural subjects. MATERIALS AND METHODS: Two-dimensional electrophoresis (2-DE), mass spectrometry (MS), and enzyme-linked immunosorbent assay (ELISA) were employed. Total soluble proteins in lenses of type I diabetic cataract, age-related cataract (nondiabetic) patients, and normal control were extracted and subjected to 2-DE. The differential protein spots were recovered, digested with trypsin, and further applied to MALDI-TOF-MS. ELISA analysis was used to determine the levels of differential proteins in lenses of three groups. RESULTS: 2-DE analysis reflected that lens proteins of normal control, diabetic, and age-related cataract subjects were in the section of pH 5-9 and the relative molecular weights were 14-97 kDa, while relative molecular weight of more abundant crystallines was localized at 20-31 kDa. five differential protein spots were detected and identified using MALDI-TOF-MS, including beta-crystallin A3, alpha-crystallin B chain, chain A of crystal structure of truncated human beta-B1-crystallin, beta-crystallin B1, and an interesting unnamed protein product highly similar to alpha-crystallin B chain, respectively. ELISA analysis revealed that lenses of diabetic cataract patients should contain significantly more concentrations of beta-crystallin A3, alpha-crystallin B chain, and beta-crystallin B1 than those of age-related cataract patients and normal control. CONCLUSION: This study clearly reflected the differential proteins of diabetic cataract, age-related cataract lenses compared with natural subjects, and it is helpful for the further research on the principles and mechanisms of different types of cataract.

Angle-dependent van Hove singularities in a slightly twisted graphene bilayer.

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 ΔE(vhs)∼ℏν(F)ΔK between 1.0° and 3.0° [here ν(F)∼1.1 × 10(6) 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 ΔE(vhs)∼0.11 eV is much smaller than the expected value ℏν(F)ΔK∼0.28 eV at 1.3°. The origin of the reduction of ΔE(vhs) at 1.3° is discussed.

Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer.

It is well established that strain and geometry could affect the band structure of graphene monolayer dramatically. Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature, which are found to strongly affect the local band structures of the twisted graphene bilayer. The energy difference of the two low-energy van Hove singularities decreases with increasing lattice deformation and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive chiral fermions in a magnetic field of about 100 T, along a graphene wrinkle. The joint effect of strain and out-of-plane distortion in the graphene wrinkle also results in a valley polarization with a significant gap. These results suggest that strained graphene bilayer could be an ideal platform to realize the high-temperature zero-field quantum valley Hall effect.