Feedback Control and Characterization of a Microcantilever Using Optical Radiation Pressure

We describe a method for feedback-regulation of a microcantilever's response using optical radiation pressure. One laser measures the position of the cantilever and another laser applies a force that is a phase-shifted function of that position. The force is due solely to the momentum of the photons in the laser. The feedback changes the microcantilever's effective quality factor Qeff and effective temperature Teff. Reduction of both Qeff and Teff by more than a factor of 15 is demonstrated. Additionally, we suggest a method for determination of a microcantilever's spring constant using the known force exerted on it by radiation pressure.Comment: 10 pages, 3 figures. Updated acknowledgements and used smaller file format for Figure

Hidden quasi one-dimensional superconductivity in Sr2_2RuO4_4

Using an asymptotically exact weak coupling analysis of a multi-orbital Hubbard model of the electronic structure of \SRO, we show that the interplay between spin and charge fluctuations leads unequivocally to triplet pairing which originates in the quasi-one dimensional bands. The resulting superconducting state spontaneously breaks time-reversal symmetry and is of the form $\Delta \sim p_x + i p_y \hat{z}$ with sharp gap minima and a d-vector that is only {\it weakly} pinned. The supercondutor is topologically {\it trivial} and hence lacks robust chiral Majorana fermion modes along the boundary. The absence of topologically protected edge modes could explain the surprising absence of experimentally detectable edge currents in this system.Comment: 5 pages, 3 figure

STM Studies of TbTe3: Evidence for a fully Incommensurate Charge Density Wave

We observe unidirectional charge density wave ordering on the cleaved surface of TbTe3 with a Scanning Tunneling Microscope at ~6 K. The modulation wave-vector q_{CDW} as determined by Fourier analysis is 0.71 +/- 0.02 * 2 pi/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of ~(1/3) * 2 pi/a ordering perpendicular to the CDW. Our analysis indicates that the CDW is incommensurate.Comment: 4 pages, 4 figure