Faraday effect in rippled graphene: Magneto-optics and random gauge fields

A beam of linearly polarized light transmitted through magnetically biased graphene can have its axis of polarization rotated by several degrees after passing the graphene sheet. This large Faraday effect is due to the action of the magnetic field on graphene's charge carriers. As deformations of the graphene membrane result in pseudomagnetic fields acting on the charge carriers, the effect of random mesoscopic corrugations (ripples) can be described as the exposure of graphene to a random pseudomagnetic field. We aim to clarify the interplay of these typically sample inherent fields with the external magnetic bias field and the resulting effect on the Faraday rotation. In principle, random gauge disorder can be identified from a combination of Faraday angle and optical spectroscopy measurements.Comment: 7 pages, 4 figure

Many-body effects in doped graphene on a piezoelectric substrate

We investigate the many-body properties of graphene on top of a piezoelectric substrate, focusing on the interaction between the graphene electrons and the piezoelectric acoustic phonons. We calculate the electron and phonon self-energies as well as the electron mobility limited by the substrate phonons. We emphasize the importance of the proper screening of the electron-phonon vertex and discuss the various limiting behaviors as a function of electron energy, temperature, and doping level. The effect on the graphene electrons of the piezoelectric acoustic phonons is compared with that of the intrinsic deformation acoustic phonons of graphene. Substrate phonons tend to dominate over intrinsic ones for low doping levels at high and low temperatures.Comment: 13 pages, 8 figure

The quality of experiencing and the process of learning

In der Arbeit wird argumentiert, daß das Erleben von "Flow" im Prozeß des Lernens für das Entstehen von intrinsischer Lernmotivation und für die kognitive Entwicklung der Schüler von entscheidender Bedeutung ist. Die Flow-Theorie von M. Csikszentmihalyi wird ausführlich dargestellt und ihre Relevanz für den Lernprozeß erläutert. Es wird über zwei empirische Studien berichtet, die die Auswirkungen des Flow-Erlebens auf schulisches Lernen belegen. Schließlich wird der Versuch gemacht, Folgerungen für die pädagogische Praxis abzuleiten. (DIPF/Text übernommen)This article argues that the experience of "flow" while learning is of crucial importance for students\u27 intrinsic motivation to learn and cognitive development. A presentation of M. Csikszentmihalyis flow theory is given and its relevance for the process of learning is discussed. Two studies are reported that support the significance of flow for learning in school. Finally, suggestions for educational practice are made. (DIPF/Orig.