An ARPES view on the high-Tc problem: phonons vs spin-fluctuations

We review the search for a mediator of high-Tc superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially strong electron-phonon coupling that suggests important role of phonons for high-Tc superconductivity in pnictides.Comment: A summary of the ARPES part of the Research Unit FOR538, http://for538.wmi.badw.d

The Photoactive Excited State of the B12-Based Photoreceptor CarH

7 pags., 5 figs.We have used transient absorption spectroscopy in the UV-visible and X-ray regions to characterize the excited state of CarH, a protein photoreceptor that uses a form of B12, adenosylcobalamin (AdoCbl), to sense light. With visible excitation, a nanosecond-lifetime photoactive excited state is formed with unit quantum yield. The time-resolved X-ray absorption near edge structure difference spectrum of this state demonstrates that the excited state of AdoCbl in CarH undergoes only modest structural expansion around the central cobalt, a behavior similar to that observed for methylcobalamin rather than for AdoCbl free in solution. We propose a new mechanism for CarH photoreactivity involving formation of a triplet excited state. This allows the sensor to operate with high quantum efficiency and without formation of potentially dangerous side products. By stabilizing the excited electronic state, CarH controls reactivity of AdoCbl and enables slow reactions that yield nonreactive products and bypass bond homolysis and reactive radical species formation.This work was supported by grants from the National Science Foundation NSF-CHE 1464584 and NSFCHE 1836435 to R.J.S., NSF-CHE 1565795 to K.J.K., NSFCHE 1608553 and NSF-CHE-1904759 to E.N.G.M., and NSF-CHE 1945174 to M.K.; from the Agencia Estatal de Investigación (AEI)-Spain and the European Regional Development Fund (FEDER) grants PGC2018-094635-BC21 (to M.E.-A.) and PGC2018-094635-B-C22 (to S.P.); and from the Fundacion Seneca (Murcia)-Spain grant 20992/PI/ ́ 18 (to M.E.-A.). Portions of this work were carried out in the Laboratory for Ultrafast Multidimensional Optical Spectroscopy (LUMOS) supported by NSF-CHE 1428479. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract no. DE-AC02-76SF00515

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems with electron-electron interactions

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems is studied by taking account of electron-electron interactions under the D’yakonov-Perel’ mechanism. The diffusion equations for charge and spin densities are obtained through decoupling of the interactions using the auxiliary Bose field. We show that the electron-electron interaction has no effect on the infinite spin lifetime when the Rashba and Dresselhaus coupling constants satisfy the condition α=±β. If the general condition α≠±β is satisfied, the spin lifetime is finite and enhanced by the electron-electron interaction with the increment of the temperature in the ballistic regime. The increasing amplitude of the spin lifetime depends on the ratio of the temperature to the Fermi temperature. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010

Spin precession and electron spin polarization wave in [001]-grown quantum wells

72.25.Dc Spin polarized transport in semiconductors, 71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect, 85.75.Hh Spin polarized field effect transistors,