14 research outputs found
Youth and new media: the appeal and educational ramifications of digital game play for children and adolescents.
The prevalence of digital media use among children and adolescents is indisputable. One medium to which children and adolescents dedicate a sizeable portion of their time is that of the digital game. Accordingly, digital game play continues to grow as a context for cognitive development. We showcase new research and practice addressing the impact of this very popular activity on children’s and adolescents’ learning. Our goal is to stimulate new research and interest in examining the positive ramifications of digital play for development among today’s youth
Microscopic theory of weak pseudogap behavior in the underdoped cuprate superconductors I: General theory and quasiparticle properties
We derive in detail a novel solution of the spin fermion model which is valid
in the quasi-static limit pi T<<omega_sf, found in the intermediate
(pseudoscaling) regime of the magnetic phase diagram of cuprate
superconductors, and use it to obtain results for the temperature and doping
dependence of the single particle spectral density, the electron-spin
fluctuation vertex function, and the low frequency dynamical spin
susceptibility. The resulting strong anisotropy of the spectral density and the
vertex function lead to the qualitatively different behavior of_hot_ (around
k=(pi,0)) and_cold_ (around k=(pi/2,pi/2)) quasiparticles seen in ARPES
experiments. We find that the broad high energy features found in ARPES
measurements of the spectral density of the underdoped cuprate superconductors
are determined by strong antiferromagnetic (AF) correlations and incoherent
precursor effects of an SDW state, with reduced renormalized effective coupling
constant. The electron spin-fluctuation vertex function, i.e. the effective
interaction of low energy quasiparticles and spin degrees of freedom, is found
to be strongly anisotropic and enhanced for hot quasiparticles; the
corresponding charge-fluctuation vertex is considerably diminished. We thus
demonstrate that, once established, strong AF correlations act to reduce
substantially the effective electron-phonon coupling constant in cuprate
superconductors.Comment: REVTEX with EPS figures, uses multicol.sty, epsfig,sty, psfig.st
Hidden Order in the Cuprates
We propose that the enigmatic pseudogap phase of cuprate superconductors is
characterized by a hidden broken symmetry of d(x^2-y^2)-type. The transition to
this state is rounded by disorder, but in the limit that the disorder is made
sufficiently small, the pseudogap crossover should reveal itself to be such a
transition. The ordered state breaks time-reversal, translational, and
rotational symmetries, but it is invariant under the combination of any two. We
discuss these ideas in the context of ten specific experimental properties of
the cuprates, and make several predictions, including the existence of an
as-yet undetected metal-metal transition under the superconducting dome.Comment: 12 pages of RevTeX, 9 eps figure
Carrier relaxation, pseudogap, and superconducting gap in high-Tc cuprates: A Raman scattering study
We describe results of electronic Raman-scattering experiments in differently
doped single crystals of Y-123 and Bi-2212. The comparison of AF insulating and
metallic samples suggests that at least the low-energy part of the spectra
originates predominantly from excitations of free carriers. We therefore
propose an analysis of the data in terms of a memory function approach.
Dynamical scattering rates and mass-enhancement factors for the carriers are
obtained. In B2g symmetry the Raman data compare well to the results obtained
from ordinary and optical transport. For underdoped materials the dc scattering
rates in B1g symmetry become temperature independent and considerably larger
than in B2g symmetry. This increasing anisotropy is accompanied by a loss of
spectral weight in B2g symmetry in the range between the superconducting
transition at Tc and a characteristic temperature T* of order room temperature
which compares well with the pseudogap temperature found in other experiments.
The energy range affected by the pseudogap is doping and temperature
independent. The integrated spectral loss is approximately 25% in underdoped
samples and becomes much weaker towards higher carrier concentration. In
underdoped samples, superconductivity related features in the spectra can be
observed only in B2g symmetry. The peak frequencies scale with Tc. We do not
find a direct relation between the pseudogap and the superconducting gap.Comment: RevTeX, 21 pages, 24 gif figures. For PostScript with embedded eps
figures, see http://www.wmi.badw-muenchen.de/~opel/k2.htm