Optical Spectroscopy as a Probe of Gaps and Kinetic Electronic Energy in p- and n-type cuprates

The real part of the optical in-plane conductivity of p-- and n--type cuprates thin films at various doping levels was deduced from highly accurate reflectivity measurements. We present here a comprehensive set of optical spectral weight data as a function of the temperature $T (> T_c$), for underdoped and overdoped samples. The temperature dependence of the spectral weight is not universal. Using various cut-off frequencies for the spectral weight, we show that n--type Pr$_{2-x}$Ce$_x$CuO$_4$ and p--type Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ exhibit both similarities and striking differences. The Fermi surface is closed in overdoped metallic samples. In underdoped Pr$_{2-x}$Ce$_x$CuO$_4$ samples, it clearly breaks into arcs, giving rise to a "pseudogap" signature. It is argued that such a signature is subtle in underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$.Comment: Proceedings M2SHTSCVIII, to appear in Physica

Kinetic energy change with doping upon superfluid condensation in high temperature superconductors

In conventional BCS superconductors, the electronic kinetic energy increases upon superfluid condensation (the change DEkin is positive). Here we show that in the high critical temperature superconductor Bi-2212, DEkin crosses over from a fully compatible conventional BCS behavior (DEkin>0) to an unconventional behavior (DEkin<0) as the free carrier density decreases. If a single mechanism is responsible for superconductivity across the whole phase diagram of high critical temperature superconductors, this mechanism should allow for a smooth transition between such two regimes around optimal doping.Comment: 3 pages, 2 figure

Two-Fermi-surface superconducting state and a nodal d-wave gap in the electron-doped Sm(1.85)Ce(0.15)CuO(4-d) cuprate superconductor

We report on laser-excited angle-resolved photoemission spectroscopy (ARPES) in the electron-doped cuprate Sm(1.85)Ce(0.15)CuO(4-d). The data show the existence of a nodal hole-pocket Fermi-surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferromagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole-pocket is compatible with a d-wave symmetry.Comment: 4 pages, 3 figures, accepted to Phys. Rev. Let

Etude par spectroscopie infrarouge de l'électrodynamique du supraconducteur Pr2-xCexCuO4 et de la manganite La2/3Ca1/3MnO3

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Électrodynamique dans l'état normal et supraconducteur de Bi2Sr2CaCu2O8+ð (étude par spectroscopie infrarouge-visible)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Vortex-lattice melting, phase slips, and decoupling studied by microwave dissipation in Bi2Sr2CaCu2O8+δ

We have measured the microwave dissipation at 10 GHz in a Bi2Sr2CaCu2O8+delta single crystal, between 75 and 50 K, as a function of the static magnetic field applied parallel to the c axis. We observe a clear-cut onset in the dissipation precisely at the melting field. In the liquid phase, for fields ~1-2 kG, the in-plane and the c axis resistivities deduced from microwave absorption display a different temperature behavior, in contrast with dc measurements. Our c-axis high-frequency data and the dc results can be reconciled by including phase slips due to the motion of pancake vortices, as suggested by Koshelev. The microscopic origin of the c-axis dissipation is thus identified through its frequency dependence.info:eu-repo/semantics/publishe

Respuesta radiación infrarroja y visible de pelìculas delgadas de Bi2Sr2CaC2O8+d

Para una película delgada epitaxial superconductora de Bi2Sr2CaC2O8+d crecida sobre un substra-to de LaAlO3, por el método de pulverización catódica a altas presiones de oxígeno, se comparan las mediciones de la resistividad dc en el plano ab con los valores encontrados al calcular la con-ductividad infraroja, cuando la frecuencia tiende a cero, a través del cálculo del peso espectral, después de aplicar la regla de la suma de Ferrell-Glover-Tinkham (FGT), considerando el modelo de Drude-Lorentz-London. La conductividad óptica fue obtenido de la medida de la reflectividad entre 30-25000 cm-1 y temperaturas entre 20 y 30K

Etude des proprietes electromagnetiques des couches minces et monocristaux supraconducteurs a haute temperature critique

Available from INIST (FR), Document Supply Service, under shelf-number : AR 16161 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEMinistere de la Recherche et de l'Espace (MRE), 75 - Paris (France)FRFranc

Investigation de divers procédés de texturation de céramiques supraconductrices à haute Tc{T_{\rm c}}

We have invetigated three processes of texturing high $T_{\rm c}$ superconducting ceramics based on : alignment of paramagnetic grains in a high magnetic field, sintering under a heavy load (creep-sintering) and oriented solidification. After recalling the principle and analyzing the controling mechanisms of each process, microstructural, magnetic and electrical characterization of the best produced samples are presented.Nous avons étudié trois procédés de texturation des céramiques supraconductrices à haute température critique basés sur : l'alignement de grains paramagnétiques dans un champ magnétique intense, le frittage sous forte charge (frittage-fluage) et la solidification dirigée. Après avoir rappelé le principe et analysé les méchanismes contrôlant chacun de ces procédés, on présente les caractérisations microstructurales, magnétiques et électriques des meilleurs échantillons produits