Spin dephasing in pseudomagnetic fields: susceptibility and geometry

We present a theory of spin dynamics caused by spin-orbit coupling for two-dimensional gases of cold atoms and other quasiparticles with pseudospin 1/2 moving in orbital gauge fields. Our approach is based on the gauge transformation in the form of a SU(2) rotation gauging out the spin-orbit coupling. As a result, the analysis of the spin dynamics is reduced to calculation of the density-related susceptibility of the system without spin-orbit coupling at the wavevector determined by the spin-rotation length. This approach allows one to treat the spin dynamics in terms of the linear response theory for bosonic and fermionic ensembles. We study different regimes of irreversible spin relaxation and coherent spin dynamics in these systems. For bosonic gases the effects of low temperature are crucial due to accumulation of particles in the small-momentum subspace even if the Bose–Einstein condensation does not occur due to the system low dimensionality

Ultrafast extrinsic spin-Hall currents

We consider the possibility of ultrafast extrinsic spin-Hall currents, generated by skew scattering following the optical injection of charge or pure spin currents. We propose a phenomenological model for this effect in quantum well structures. An injected charge current leads to a spin-Hall-induced pure spin current, and an injected pure spin current leads to a spin-Hall-induced charge current. The resulting spin or charge accumulation can be measured optically.Comment: 18 pages, 3 figure

Hole concentration and phonon renormalization in Ca-doped YBa_2Cu_3O_y (6.76 < y < 7.00)

In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta \omega) and linewidth (\Delta 2\gamma) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in \Delta \omega with p imply that the superconducting gap (\Delta_{max}) decreases monotonically with increasing hole concentration in the overdoped regime, and \Delta \omega falls to zero in the underdoped regime. The linewidth renormalization \Delta 2\gamma is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.Comment: 18 pages; 5 figures; submitted to Phys. Rev. B Oct. 24, 2002 (BX8292

Charge kinks as Raman scatterers in quarter-filled ladders

Charge kinks are considered as fundamental excitations in quarter-filled charge-ordered ladders. The strength of the coupling of the kinks to the three-dimensional lattice depends on their energy. The integrated intensity of Raman scattering by kink-antikink pairs is proportional to $\phi ^{5}$ or $\phi ^{4},$ where $\phi$ is the order parameter. The exponent is determined by the system parameters and by the strength of the electron-phonon coupling.Comment: To be published in Phys. Rev.B (june 2001

Anomalous Self-Energy Effects of the B_1g Phonon in Y_{1-x}(Pr,Ca)_xBa_2Cu_3O_7 Films

In Raman spectra of cuprate superconductors the gap shows up both directly, via a redistribution of the electronic background, the so-called "2Delta peaks", and indirectly, e.g. via the renormalization of phononic excitations. We use a model that allows us to study the redistribution and the related phonon self-energy effects simultaneously. We apply this model to the B_1g phonon of Y_{1-x}(Pr,Ca)_xBa_2Cu_3O_7 films, where Pr or Ca substitution enables us to investigate under- and overdoped samples. While various self-energy effects can be explained by the strength and energy of the 2\Delta peaks, anomalies remain. We discuss possible origins of these anomalies.Comment: 6 pages including 4 figure

Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs

Spin-dependent electron transport in a periodically stubbed quantum wire in the presence of Rashba spin-orbit interaction (SOI) is studied via the nonequilibrium Green's function method combined with the Landauer-Buttiker formalism. The coexistence of spin filtering, charge and spin switching are found in the considered system. The mechanism of these transport properties is revealed by analyzing the total charge density and spin-polarized density distributions in the stubbed quantum wire. Furthermore, periodic spin-density islands with high polarization are also found inside the stubs, owing to the interaction between the charge density islands and the Rashba SOI-induced effective magnetic field. The proposed nanostructure may be utilized to devise an all-electrical multifunctional spintronic device.Comment: 4 pages, 4 figure

Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature T_c=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at T_c and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure

Field- and pressure-induced magnetic quantum phase transitions in TlCuCl_3

Thallium copper chloride is a quantum spin liquid of S = 1/2 Cu^2+ dimers. Interdimer superexchange interactions give a three-dimensional magnon dispersion and a spin gap significantly smaller than the dimer coupling. This gap is closed by an applied hydrostatic pressure of approximately 2kbar or by a magnetic field of 5.6T, offering a unique opportunity to explore the both types of quantum phase transition and their associated critical phenomena. We use a bond-operator formulation to obtain a continuous description of all disordered and ordered phases, and thus of the transitions separating these. Both pressure- and field-induced transitions may be considered as the Bose-Einstein condensation of triplet magnon excitations, and the respective phases of staggered magnetic order as linear combinations of dimer singlet and triplet modes. We focus on the evolution with applied pressure and field of the magnetic excitations in each phase, and in particular on the gapless (Goldstone) modes in the ordered regimes which correspond to phase fluctuations of the ordered moment. The bond-operator description yields a good account of the magnetization curves and of magnon dispersion relations observed by inelastic neutron scattering under applied fields, and a variety of experimental predictions for pressure-dependent measurements.Comment: 20 pages, 17 figure

Interplay of structural and electronic phase separation in single crystalline La(2)CuO(4.05) studied by neutron and Raman scattering

We report a neutron and Raman scattering study of a single-crystal of La(2)CuO(4.05) prepared by high temperature electrochemical oxidation. Elastic neutron scattering measurements show the presence of two phases, corresponding to the two edges of the first miscibility gap, all the way up to 300 K. An additional oxygen redistribution, driven by electronic energies, is identified at 250 K in Raman scattering (RS) experiments by the simultaneous onset of two-phonon and two-magnon scattering, which are fingerprints of the insulating phase. Elastic neutron scattering measurements show directly an antiferromagnetic ordering below a N\'eel temperature of T_N =210K. The opening of the superconducting gap manifests itself as a redistribution of electronic Raman scattering below the superconducting transition temperature, T_c = 24K. A pronounced temperature-dependent suppression of the intensity of the (100) magnetic Bragg peak has been detected below T_c. We ascribe this phenomenon to a change of relative volume fraction of superconducting and antiferromagnetic phases with decreasing temperature caused by a form of a superconducting proximity effect.Comment: 9 pages, including 9 eps figures, submitted to PR