Strong mobility degradation in ideal graphene nanoribbons due to phonon scattering

We investigate the low-field phonon-limited mobility in armchair graphene nanoribbons (GNRs) using full-band electron and phonon dispersion relations. We show that lateral confinement suppresses the intrinsic mobility of GNRs to values typical of common bulk semiconductors, and very far from the impressive experiments on 2D graphene. Suspended GNRs with a width of 1 nm exhibit a mobility close to 500 cm^2/Vs at room temperature, whereas if the same GNRs are deposited on HfO2 mobility is further reduced to about 60 cm^2/Vs due to surface phonons. We also show the occurrence of polaron formation, leading to band gap renormalization of ~118 meV for 1 nm-wide armchair GNRs.Comment: 11 pages, 4 figure

The effect of dark strings on semilocal strings

Dark strings have recently been suggested to exist in new models of dark matter that explain the excessive electronic production in the galaxy. We study the interaction of these dark strings with semilocal strings which are solutions of the bosonic sector of the Standard Model in the limit $\sin^2\theta_{\rm w}=1$, where $\theta_{\rm w}$ is the Weinberg angle. While embedded Abelian-Higgs strings exist for generic values of the coupling constants, we show that semilocal solutions with non-vanishing condensate inside the string core exist only above a critical value of the Higgs to gauge boson mass ratio when interacting with dark strings. Above this critical value, which is greater than unity, the energy per unit length of the semilocal-dark string solutions is always smaller than that of the embedded Abelian-Higgs-dark string solutions and we show that Abelian-Higgs-dark strings become unstable above this critical value. Different from the non-interacting case, we would thus expect semilocal strings to be stable for values of the Higgs to gauge boson mass ratio larger than unity. Moreover, the one-parameter family of solutions present in the non-interacting case ceases to exist when semilocal strings interact with dark strings.Comment: 16 pages including 6 figures; stability analysis adde

Quasi Exactly Solvable NxN-Matrix Schroedinger Operators

New examples of matrix quasi exactly solvable Schroedinger operators are constructed. One of them constitutes a matrix generalization of the quasi exactly solvable anharmonic oscillator, the corresponding invariant vector space is constructed explicitely. Also investigated are matrix generalizations of the Lame equation.Comment: 16 latex pages, new results adde

The Strange Case of Savonarola and the Painted Fish. On the Bolzanization of Polish Thought

When Twardowski came to Lvov in 1895, his aim was to establish a philosophical trend heavily inspired by Brentanism, although peppered with Bolzanian ideas. As shows from a comparison between the lectures in logic he gave in Vienna in 1894/5 and in Lvov in 1895/6, Twardowski's teaching activity in Poland was even more Brentanian than in Vienna, I There is little doubt that the reason for this is that Brentano's thought was unknown in late 19th Century Poland.' It is well-known that Twardowski's own thought was also significantly influenced by Bolzano, and that he played also a major role in disseminating some of Bolzano's ideas in Poland, the most important being perhaps the notion oftime-independent truth. 1 have previously discussed in several papers specific Bolzanian elements present in the Polish tradition. This paper will not, for the most part, add anything in particular to that. The new - and rather blunt hypothesis to be put forward here is that, despite appearances, Twardowski also contributed de facto to slowing down the reception of Bolzano's most modem logical discoveries. For in Poland Bolzano was to remain one logician among many for rather long. It was chiefly thanks to two factors that Bolzano's star could, slowly, begin to rise in Poland, or, at least, that the fundamental achievements of his logic could be known. One factor is antipsychologistic (more precisely Platonistic) influence coming from Husserl and from Twardowski's student Lukasiewicz. The other factor is the change in the conception of logic which took Polish logic from, say, Sigwart, to Tarski through Lesniewski and Lukasiewicz, What I am going to say is meant to have impact on the standard picture of the all-Brentanian background of the Lvov-Warsaw school, though my account will be limited to two pupils of Twardowski's of the first generation, Lukasiewicz and Lesniewski, I hope this paper will contribute both to the debate on the scope of Polish Brentanism, and to prompting further investigation into the reception ofBolzano's thought in Poland