Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

GAAS-ALGAS superlattice band structure under hydrostatic pressure: An analysis based on the envelope function approximation

We propose new interface connection rules to determine the electronic properties of superlattices. Although similar to the so-called two-band model, these new rules are more general. Our approach is used to study the electronic structure of superlattices under high hydrostatic pressure. In our model, the influence of the pressure is taken into account by considering the modification of the energy gap and layer width of each material separately. It is demonstrated that the low value observed in the experimental determination of the pressure coefficient θ^SL of the GaAs layers is a consequence of the increasing rigidity of the energy band for energies away from the edges. Moreover the apparent homogeneity of θ^SL (GaAs) is the result of two opposing effects—the variation of the band rigidity and the narrowing of the layer thickness—which compensate each other.     

Mid-infrared intersubband emission from optically pumped asymmetric coupled quantum wells

Mid-infrared optical emission due to intersubband transitions between excited conduction subbands of a coupled quantum well structure is studied. The emission process is based on optical pumping of free carriers from the ground subband into the third subband followed by a radiative transition from the third subband into the second subband and a fast phonon assisted relaxation into the ground subband. We have observed spontaneous emission at 14 μm that persists up to room temperature. Our results indicate that population inversion between conduction subbands and large stimulated gain can be achieved.     

Controllable tuning of the electronic transport in pre-designed graphene nanoribbon

We make use of ab initio density functional theory calculation to explore the electronic and transport properties of zigzag-edged graphene nanoribbon (ZGNR) with peculiar designed electronic transport channels by tailoring the atomic configuration of the nanostructure. Tailoring the atomic structure has significant influences on the electronic transport of the defective nanostructure, and eventually the metal-semiconducting transition are identified with the increasing number of missing atoms. Our results demonstrate that pre-designed graphene nanoribbon by selective tailoring with high precision is expected to be served as the basic component for nanoelectronic device.