Factorizing twists and R-matrices for representations of the quantum affine algebra U_q(\hat sl_2)

We calculate factorizing twists in evaluation representations of the quantum affine algebra U_q(\hat sl_2). From the factorizing twists we derive a representation independent expression of the R-matrices of U_q(\hat sl_2). Comparing with the corresponding quantities for the Yangian Y(sl_2), it is shown that the U_q(\hat sl_2) results can be obtained by `replacing numbers by q-numbers'. Conversely, the limit q -> 1 exists in representations of U_q(\hat sl_2) and both the factorizing twists and the R-matrices of the Yangian Y(sl_2) are recovered in this limit.Comment: 19 pages, LaTe

Fine Structure of the Radial Breathing Mode in Double-Wall Carbon Nanotubes

The analysis of the Raman scattering cross section of the radial breathing modes of double-wall carbon nanotubes allowed to determine the optical transitions of the inner tubes. The Raman lines are found to cluster into species with similar resonance behavior. The lowest components of the clusters correspond well to SDS wrapped HiPco tubes. Each cluster represents one particular inner tube inside different outer tubes and each member of the clusters represents one well defined pair of inner and outer tubes. The number of components in one cluster increases with decreasing of the inner tube diameter and can be as high as 14.Comment: 5 pages, 3 figure

Resonant Phonon Scattering in Quantum Hall Systems Driven by dc Electric Fields

Using dc excitation to spatially tilt Landau levels, we study resonant acoustic phonon scattering in two-dimensional electron systems. We observe that dc electric field strongly modifies phonon resonances, transforming resistance maxima into minima and back into maxima. Further, phonon resonances are enhanced dramatically in the non-linear dc response and can be detected even at low temperatures. Most of our observations can be explained in terms of dc-induced (de)tuning of the resonant acoustic phonon scattering and its interplay with intra-Landau level impurity scattering. Finally, we observe a dc-induced zero-differential resistance state and a resistance maximum which occurs when the electron drift velocity approaches the speed of sound.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Giant microwave photoresistivity in a high-mobility quantum Hall system

We report the observation of a remarkably strong microwave photoresistivity effect in a high-mobility two-dimensional electron system subject to a weak magnetic field and low temperature. The effect manifests itself as a giant microwave-induced resistivity peak which, in contrast to microwave-induced resistance oscillations, appears only near the second harmonic of the cyclotron resonance and only at sufficiently high microwave frequencies. Appearing in the regime linear in microwave intensity, the peak can be more than an order of magnitude stronger than the microwave-induced resistance oscillations and cannot be explained by existing theories.Comment: 4 pages, 4 figure

Magnetoresistance Oscillations in Two-dimensional Electron Systems Induced by AC and DC Fields

We report on magnetotransport measurements in a high-mobility two-dimentional electron system subject simultaneously to AC (microwave) and DC (Hall) fields. We find that DC excitation affects microwave photoresistance in a nontrivial way. Photoresistance maxima (minima) evolve into minima (maxima) and back, reflecting strong coupling and interplay of AC- and DC-induced effects. Most of our observations can be explained in terms of indirect electron transitions using a new, ``combined'' resonant condition. Observed quenching of microwave-induced zero resistance by a DC field cannot be unambiguously linked to a domain model, at least until a systematic theory treating both excitation types within a single framework is developed

Temperature Dependence of Microwave Photoresistance in 2D Electron Systems

We report on the temperature dependence of microwave-induced resistance oscillations in high-mobility two-dimensional electron systems. We find that the oscillation amplitude decays exponentially with increasing temperature, as $\exp(-\alpha T^2)$, where $\alpha$ scales with the inverse magnetic field. This observation indicates that the temperature dependence originates primarily from the modification of the single particle lifetime, which we attribute to electron-electron interaction effects.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let