Anomalously Small Reorganization Energy of the Half Redox Reaction of Azurin.

Small values of the reorganization energy, 0.2-0.3 eV, were reported by electrochemical kinetic measurements for the half redox reaction of the redox-active protein azurin. This theoretical study explores possible mechanisms for the low activation barrier for electrochemical protein electron transfer: (1) electronic polarizability of the active site, (2) altering protonation states of far-away histidine residues not directly connected to the active site, and (3) a partial desolvation of the protein when attached to the electrode. The last mechanism provides the most robust explanation of the observations. Constraints imposed by the protein fold on its ability to sample the configuration space lead to the breakdown of the fluctuation-dissipation relation (FDR) and a strong separation of the Stokes-shift and variance reorganization energies. The resulting nonergodic kinetic reorganization energy observed experimentally is significantly lowered compared to predictions of standard models based on Gibbsian statistics and the FDR. The fast rate of protein electron transfer is directly related to the ability of the protein scaffold to maintain nonequilibrium statistics of electrostatic fluctuations projected on the electron-transfer reaction coordinate.

Giant Goos-Hänchen-like shifts at the merging point in strained graphene double barriers.

Tunneling and the Goos-Hänchen-like (GHL) shifts of quasiparticles through double rectangular potential barriers in mono-layer graphene under uniaxial strain were considered. Expressions for the transmission coefficient and the lateral shift of the transferred beam were obtained by considering the boundary conditions and the stationary phase method, respectively. Moreover, the numerical results of the transmission probability and the lateral shifts for three values of the merging parameter,δwere presented. It was observed, for two values ofδ, very large shifts could be obtained and we found the demeanor of the GHL shift is adjustable by changing parameters and is influenced strongly byδ. Finally, our calculations were examined by the limit condition in accordance with the results obtained for a single barrier in presence of the strong uniaxial strain.

Rod separation by sawtooth channel.

By applying entropic barriers, we present a rod separation mechanism that induces the movement of rods of different sizes in the opposite directions. This mechanism is based on the combination of the saw-tooth channel, a static force, and an oscillating driving force. The asymmetric shape of the channel and the elongated shape of the rod causesa complicated interaction effect between the rods and the channel walls which reduces the accessible configuration space for the rods and leads to entropic free-energy effects.

From Klein to anti-Klein tunneling in graphene tuning the Rashba spin-orbit interaction or the bilayer coupling.

We calculate the transmission coefficient for a particle crossing a potential barrier in monolayer graphene with Rashba spin-orbit coupling and in bilayer graphene. We show that in both cases one can go from Klein tunneling regime, characterized by perfect normal transmission, to anti-Klein tunneling regime, with perfect normal reflection, by tuning the Rashba spin-orbit coupling for a monolayer or the interplane coupling for a bilayer graphene. We show that the intermediate regime is characterized by a non-monotonic behavior with oscillations and resonances in the normal transmission amplitude as a function of the coupling and of the potential parameters.

Electronic transmission through p-n and n-p-n junctions of graphene.

In this paper, we first evaluate the electronic transmission of Dirac fermions into a p-n junction of gapped graphene and show that the final result depends on the sign of the refractive index, n. We also, by considering the appropriate wavefunctions in the region of the electrostatic potential, show that both transmission and the reflection probability turn out to be positive and less than unity instead of the negative transmission and higher than unity reflection coefficient commonly referred to as the Klein paradox. We then obtain the transmission probability corresponding to a special p-n junction for which there exists a region in which the low energy excitations of graphene acquire a finite mass and, interestingly, find that in this case the transmission is independent of the index of refraction, in contrast with the corresponding result for gapped graphene. We then discuss the validity of the solutions reported in some of the papers cited in this work which, considering the Büttiker formula, turn out to lead to the wrong results for conductivity.

Conductance of graphene-based double-barrier nanostructures.

The effect of a mass gap on the conductance of graphene double-barrier heterojunctions is studied. By obtaining the 2D expression for the electronic transport of the low energy excitations of pure graphene through double-barrier systems, it is found that the conductivity of these structures does not depend on the type of charge carriers in the zones of the electric field. However, a finite induced gap in the graphene spectrum makes conductivity dependent on the energy band index. We also discuss a few controversies concerning double-barrier systems stemming from an improper choice of the scattering angle. Then it is observed that, for some special values of the incident energy and potential's height, graphene junctions behave like left-handed materials, resulting in a maximum value for the conductivity.