Zeitschriftenaufsätze

We report on the excitation of surface plasmon polaritons (SPP's) on a periodic arrangement of metallic ribbons with tunable periodicity. The ability to vary its lattice constant results in an additional degree of freedom, permitting excitation of SPP's for any combination of wavelength and angle of incidence within the tuning range of the system. Moreover, the designed smart material allows fundamental questions to be answered regarding SPP propagation and localization. Finally, the concept opens vistas in the development of other methodologies in spectroscopy including plasmonic sensors and chips.

Systems of strongly correlated fermions on certain geometrically frustrated lattices at particular filling factors support excitations with fractional charges ±e/2. We calculate quantum mechanical ground states, lowlying excitations and spectral functions of finite lattices by means of numerical diagonalization. The ground state of the most thorough-fully studied case, the criss-crossed checkerboard lattice, is degenerate and shows longrange order. Static fractional charges are confined by a weak linear force, most probably leading to bound states of large spatial extent. Consequently, the quasi-particle weight is reduced, which reflects the internal dynamics of the fractionally charged excitations. By using an additional parameter, we finetune the system to a special point at which fractional charges are manifestly deconfinedthe socalled RokhsarKivelson point. For a deeper understanding of the lowenergy physics of these models and fornumerical advantages, several conserved quantum numbers are identified.