Li-Gang Wang

Electronic band gaps and transport properties in graphene superlattices with one-dimensional periodic potentials of square barriers

The electronic transport properties and band structures for the graphene-based one-dimensional (1D) superlattices with periodic potentials of square barriers are investigated. It is found that a new Dirac point is formed, which is exactly located at the energy which corresponds to the zero (volume) averaged wave number inside the 1D periodic potentials. The location of such a new Dirac point is robust against variations in the lattice constant, and it is only dependent on the ratio of widths of the potential barriers. The zero-averaged wave-number gap associated with the new Dirac point is insensitive to both the lattice constant and the structural disorder and the defect mode in the zero-averaged wave-number gap is weakly dependent on the incident angles of carriers.

Large negative Goos-Hänchen shift from a weakly absorbing dielectric slab.

It is theoretically shown that the negative Goos-Hänchen shifts near resonance, Re[k(z)d] = m pi, can be an order of magnitude larger than the wavelength for both TE- and TM-polarized beams reflected from a weakly absorbing dielectric slab if the absorption of the slab is sufficiently weak, which is different from the case for a lossless dielectric slab [Phys. Rev. Lett. 91, 133903 (2003)].

Autophagy activation is associated with neuroprotection against apoptosis via a mitochondrial pathway in a rat model of subarachnoid hemorrhage.

Autophagy, the bulk intracellular degradation of cytoplasmic constituents, can be a pro-survival or a pro-death mechanism depending on the context. A recent study showed that autophagy was activated in the phase of early brain injury following subarachnoid hemorrhage (SAH). However, whether autophagy activation after SAH is protective or harmful is still elusive. This study was undertaken to determine the potential role of autophagy pathway activation in early brain injury following SAH. The rats were pretreated with intracerebral ventricular infusion of either the autophagy inducer rapamycin (RAP) or inhibitor 3-methyladenine (3-MA) before SAH onset. The results from electron microscopic examinations showed that RAP administration caused the formation of autophagosomal vacuoles, and 3-MA induced neuronal apoptosis. RAP treatment significantly increased the expression of autophagic proteins Atg5 and Beclin 1, the ratio of microtubule-associated protein 1 light chain 3 (LC3)-II to LC3-I and reduced caspase-3 activity, the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL)-positive cells, brain edema and neurological deficits after SAH. Conversely, 3-MA treatment exacerbated early brain injury. RAP treatment significantly increased the expression of the autophagic proteins Atg5 and Beclin 1, the ratio of LC3-II to LC3-I and reduced caspase-3 activity, the number of TUNEL-positive cells, brain edema and neurological deficits after SAH. Conversely, 3-MA treatment reversed these changes and exacerbated early brain injury. To further clarify the mechanism of autophagy protection, we investigated the expression levels of key apoptosis-related molecules. The results showed that RAP administration decreased Bax translocation to the mitochondria and downstream cytochrome c release from the mitochondria to the cytosol. Taken together, our study indicates that activation of autophagic pathways reduces early brain injury after SAH. This neuroprotective effect is likely exerted by anti-apoptotic mechanisms.

Control of the Goos-Hänchen shift of a light beam via a coherent driving field

We present a proposal to manipulate the Goos-Haenchen shift of a light beam via a coherent control field, which is injected into a cavity configuration containing the two-level atomic medium. It is found that the lateral shifts of the reflected and transmitted probe beams can be easily controlled by adjusting the intensity and detuning of the control field. Using this scheme, the lateral shift at the fixed incident angle can be enhanced (positive or negative) under the suitable conditions on the control field, without changing the structure of the cavity.

Giant lateral shift of a light beam at the defect mode in one-dimensional photonic crystals

It is found that when a light beam is incident on a one-dimensional photonic crystal (1DPC) containing a defect layer, the lateral shifts of both the reflected and the transmitted beams are greatly enhanced near the defect mode of the 1DPC, whose location depends on the angles at a fixed frequency. The effect was studied by use of a Gaussian beam. The giant lateral displacement is due to the localization of the electromagnetic wave.

Electronic band gaps and transport in aperiodic graphene superlattices of Thue-Morse sequence

We have studied the electronic properties in aperiodic graphene superlattices of Thue-Morse sequence. Although the structure is aperiodic, an unusual Dirac point (DP) does exist and its location is exactly at the energy corresponding to the zero-averaged wave number (zero-k¯). Furthermore, the zero-k¯ gap associated with the DP is robust against the lattice constants and the incident angles, and multi-DPs may appear under the suitable conditions. A resultant controllability of electronic transport in Thue-Morse sequence is predicted, which may facilitate the development of many graphene-based electronics.

Partially coherent light pulse and its propagation

The concept of partially coherent Gaussian Schell-Model pulse (GSMP) is introduced in time domain, which can be used to characterize light pulses whose amplitude and phase are partially correlated. An analytical propagation formula of GSMP through dispersive media is derived rigorously by using tensor method. An application example showing the influences of coherence property on the propagation of pulses are illustrated.

Robust zero-averaged wave-number gap inside gapped graphene superlattices

In this paper, the electronic band structures and its transport properties in gapped graphene superlattices, with one-dimensional periodic potentials of square barriers, are systematically investigated. It is found that a zero-averaged wave-number (zero-k¯) gap is formed inside gapped graphene-based superlattices, and the condition for obtaining such a zero-k¯ gap is analytically presented. The properties of this zero-k¯ gap including its transmission, conductance and Fano factor are studied in detail. Finally, it is revealed that the properties of the electronic transmission, conductance, and Fano factor near the zero-k¯ gap are very insensitive to structural disorder for finite graphene-based periodic-barrier systems.

Large negative lateral shifts from the Kretschmann–Raether configuration with left-handed materials

A large negative lateral shift of a light beam reflected from the so-called Kretschmann–Raether configuration containing left-handed material is predicted due to the formation of the unusual standing wave. An analytical resonant condition is given when there is a large negative lateral shift.

Effect of spatial coherence on radiation forces acting on a Rayleigh dielectric sphere

We show that the radiation forces (RFs) on a Rayleigh dielectric sphere induced by a partially coherent light beam are greatly affected by the spatial coherence. We find that the magnitude of the RFs greatly decreases as the spatial coherence decreases and derive an inequality for the required correlation width sigma(0) (i.e., the spatial coherence of the beam) to stably trap the particles.