Optical self-energy in graphene due to correlations

In highly correlated systems one can define an optical self-energy in analogy to its quasiparticle (QP) self-energy counterpart. This quantity provides useful information on the nature of the excitations involved in inelastic scattering processes. Here we calculate the self-energy of the intraband optical transitions in graphene originating in the electron-electron interaction (EEI) as well as electron-phonon interaction (EPI). Although optics involves an average over all momenta (k) of the charge carriers, the structure in the optical self-energy is nevertheless found to mirror mainly that of the corresponding quasiparticles for k equal to or near the Fermi momentum k(F). Consequently, plasmaronic structures which are associated with momenta near the Dirac point at k = 0 are not important in the intraband optical response. While the structure of the electron-phonon interaction (EPI) reflects the sharp peaks of the phonon density of states, the excitation spectrum associated with the electron-electron interaction is in comparison structureless and flat and extends over an energy range which scales linearly with the value of the chemical potential. We introduce a method whereby detailed quantitative information on such excitation spectra can be extracted from optical data. Modulations seen on the edge of the interband optical conductivity as it rises towards its universal background value are traced to structure in the quasiparticle self-energies around k(F) of the lower Dirac cone associated with the occupied states.     

A HYBRID TECHNIQUE FOR COMPRESSION TESTING AT INTERMEDIATE STRAIN RATES

It is difficult to obtain accurate load information at strain rates on the order of 10² s^-1 using a quartz load cell. We have developed a hybrid apparatus which combines the loading capability of a hydraulic test machine with the load-measurement technique of the Hopkinson bar. Tests comparing the output of the Hopkinson bar to the quartz cell clearly demonstrate the increase in resolution obtained with the hybrid technique.     

Preparation of 5-Alkylthio and 5-Arylthiotetrazoles from Thiocyanates Using Phase Transfer Catalysis

A very efficient method of preparation for 5-alkyl and 5-arylthiotetrazoles from the corresponding alkyl or aryl halides is described. The halides are first transformed into thiocyanates which further react with azide, yielding the corresponding tetrazoles with [2+3] polar cycloaddition. All synthetic transformations are performed under phase transfer catalytic conditions. The yields vary from good to excellent except for the preparation of 5-benzylthiotetrazole, where the reaction between benzyl thiocyanate and azide [2+3] cycloaddition is in competition with nucleophilic substitution, with benzyl azide as product.     

A CALORIMETRIC DETERMINATION OF THE QUANTUM YIELD FOR THE JONIZATION OF MALACHITE GREEN CYANIDE BY ULTRAVIOLET RADIATION

Abstract The quantum yield for the conversion of malachite green cyanide (MGL) to the oxidized form MG⁺ has been measured over the wavelength range from 225 to 289 nm using a total absorption aluminium calorimeter to measure the flux of photons. The number of molecules of MGL converted was determined from the increase in absorbance of the solution at 622 nm. MG⁺ was found to have a maximum extinction coefficient of 10.63 × 10⁴ at 622 nm. The quantum yield for the conversion of MGL to MG⁺ is constant over the wavelength range with a value of 0.91 ± 0.01. The use of MGL as an actinometer for photochemical studies is described.