17 research outputs found
Quasiparticles dynamics in high-temperature superconductors far from equilibrium: an indication of pairing amplitude without phase coherence
We perform time resolved photoelectron spectroscopy measurements of optimally
doped \tn{Bi}_2\tn{Sr}_2\tn{CaCu}_2\tn{O}_{8+\delta} (Bi-2212) and
\tn{Bi}_2\tn{Sr}_{2-x}\tn{La}_{x}\tn{Cu}\tn{O}_{6+\delta} (Bi-2201). The
electrons dynamics show that inelastic scattering by nodal quasiparticles
decreases when the temperature is lowered below the critical value of the
superconducting phase transition. This drop of electronic dissipation is
astonishingly robust and survives to photoexcitation densities much larger than
the value sustained by long-range superconductivity. The unconventional
behaviour of quasiparticle scattering is ascribed to superconducting
correlations extending on a length scale comparable to the inelastic path. Our
measurements indicate that strongly driven superconductors enter in a regime
without phase coherence but finite pairing amplitude. The latter vanishes near
to the critical temperature and has no evident link with the pseudogap observed
by Angle Resolved Photoelectron Spectroscopy (ARPES).Comment: 7 pages, 5 Figure
Transfer of spectral weight across the gap of Sr2IrO4 induced by La doping
We study with Angle Resolved PhotoElectron Spectroscopy (ARPES) the evolution
of the electronic structure of Sr2IrO4, when holes or electrons are introduced,
through Rh or La substitutions. At low dopings, the added carriers occupy the
first available states, at bottom or top of the gap, revealing an anisotropic
gap of 0.7eV in good agreement with STM measurements. At further doping, we
observe a reduction of the gap and a transfer of spectral weight across the
gap, although the quasiparticle weight remains very small. We discuss the
origin of the in-gap spectral weight as a local distribution of gap values
Ultrafast dynamics of fluctuations in high-temperature superconductors far from equilibrium
Despite extensive work on high-temperature superconductors, the critical
behavior of an incipient condensate has so far been studied exclusively under
equilibrium conditions. Here, we excite Bi2Sr2CaCu2O8+d with a femtosecond
laser pulse and monitor the subsequent nonequilibrium dynamics of the
mid-infrared conductivity. Our data allow us to discriminate temperature
regimes where superconductivity is either coherent, fluctuating or vanishingly
small. Above the transition temperature Tc, we make the striking observation
that the relaxation to equilibrium exhibits power-law dynamics and scaling
behavior, both for optimally and underdoped superconductors. Our findings can
in part be modeled using time-dependent Ginzburg-Landau theory and provide
strong indication of universality in systems far from equilibrium.Comment: 5 pages, 4 figure
Bias-controlled ultrafast demagnetization in magnetic tunnel junctions
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Photoinduced filling of near-nodal gap in Bi 2 Sr 2 CaCu 2 O 8 + δ
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