When graphene is deformed in a dynamical manner, a time-dependent potential is induced for the electrons. The potential is antisymmetric with respect to valleys, and some straightforward applications are found for Raman spectroscopy. We show that a v
alley-antisymmetric potential broadens Raman $D$ band but does not affect $2D$ band, which is already observed by recent experiments. The space derivative of the valley antisymmetric potential gives a force field that accelerates intervalley phonons, while it corresponds to the longitudinal component of the previously discussed pseudoelectric field acting on the electrons. Effects of a pseudoelectric field on the electron is quite difficult to observe due to the valley-antisymmetric coupling constant, on the other hand, such obstacle is absent for intervalley phonons with $A_{1g}$ symmetry that constitute the $D$ and $2D$ bands.
In Raman spectroscopy of graphite and graphene, the $D$ band at $sim 1355$cm$^{-1}$ is used as the indication of the dirtiness of a sample. However, our analysis suggests that the physics behind the $D$ band is closely related to a very clear idea fo
r describing a molecule, namely bonding and antibonding orbitals in graphene. In this paper, we review our recent work on the mechanism for activating the $D$ band at a graphene edge.
Spin-1/2 electrons are scattered through one or two diamond-like loops, made of quantum dots connected by one-dimensional wires, and subject to both an Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With some symmetry betwee
n the two branches of each diamond, and with appropriate tuning of the electric and magnetic fields (or of the diamond shapes) this device completely blocks electrons with one polarization, and allows only electrons with the opposite polarization to be transmitted. The directions of these polarizations are tunable by these fields, and do not depend on the energy of the scattered electrons. For each range of fields one can tune the site and bond energies of the device so that the transmission of the fully polarized electrons is close to unity. Thus, these devices perform as ideal spin filters, and these electrons can be viewed as mobile qubits; the device writes definite quantum information on the spinors of the outgoing electrons. The device can also read the information written on incoming polarized electrons: the charge transmission through the device contains full information on this polarization. The double-diamond device can also act as a realization of the Datta-Das spin field-effect transistor.
