25 research outputs found
Superconductivity from Undressing. II. Single Particle Green's Function and Photoemission in Cuprates
Experimental evidence indicates that the superconducting transition in high
cuprates is an 'undressing' transition. Microscopic mechanisms giving
rise to this physics were discussed in the first paper of this series. Here we
discuss the calculation of the single particle Green's function and spectral
function for Hamiltonians describing undressing transitions in the normal and
superconducting states. A single parameter, , describes the strength
of the undressing process and drives the transition to superconductivity. In
the normal state, the spectral function evolves from predominantly incoherent
to partly coherent as the hole concentration increases. In the superconducting
state, the 'normal' Green's function acquires a contribution from the anomalous
Green's function when is non-zero; the resulting contribution to
the spectral function is for hole extraction and for hole
injection. It is proposed that these results explain the observation of sharp
quasiparticle states in the superconducting state of cuprates along the
direction and their absence along the direction.Comment: figures have been condensed in fewer pages for easier readin
Interplane Transport and Superfluid Density in Layered Superconductors
We report on generic trends in the behavior of the interlayer penetration
depth of several different classes of quasi two-dimensional
superconductors including cuprates, SrRuO, transition metal
dichalcogenides and organic materials of the -series. Analysis
of these trends reveals two distinct patterns in the scaling between the values
of and the magnitude of the DC conductivity: one realized in the
systems with a Fermi liquid (FL) ground state and the other seen in systems
with a marked deviation from the FL response. The latter pattern is found
primarily in under-doped cuprates and indicates a dramatic enhancement (factor
) of the energy scale associated with the formation of
the condensate compared to the data for the FL materials. We discuss
implications of these results for the understanding of pairing in high-
cuprates.Comment: 4 pages, 2 figure
Optical Sum Rule anomalies in the High-Tc Cuprates
We provide a brief summary of the observed sum rule anomalies in the
high-T cuprate materials. A recent issue has been the impact of a
non-infinite frequency cutoff in the experiment. In the normal state, the
observed anomalously high temperature dependence can be explained as a `cutoff
effect'. The anomalous rise in the optical spectral weight below the
superconducting transition, however, remains as a solid experimental
observation, even with the use of a cutoff frequency.Comment: 4 pages, 2 figures, very brief review of optical sum rule anomal
Superconducting Fluctuation investigated by THz Conductivity of LaSrCuO Thin Films
Frequency-dependent terahertz conductivities of LaSrCuO thin
films with various carrier concentrations were investigated. The imaginary part
of the complex conductivity considerably increased from far above a
zero-resistance superconducting transition temperature,
, because of the existence of the fluctuating
superfluid density with a short lifetime. The onset temperature of the
superconducting fluctuation is at most for
underdoped samples, which is consistent with the previously reported analysis
of microwave conductivity. The superconducting fluctuation was not enhanced
under a 0.5 T magnetic field. We also found that the temperature dependence of
the superconducting fluctuation was sensitive to the carrier concentration of
LaSrCuO, which reflects the difference in the nature of the
critical dynamics near the superconducting transition temperature. Our results
suggest that the onset temperature of the Nernst signal is not related to the
superconducting fluctuation we argued in this paper.Comment: J. Phys. Soc. Jpn. in pres
c-axis excitations in high-T-c superconductors detected by grazing incidence reflectivity measurements
Measuring absolute reflectivity at an angle of incidence of 80 degrees for Tl2Ba2CuO6, Bi2Sr2CuO6, Nd(1.85)Ce(0.15)CuO4 with p-polarized light (plane of incidence normal to the CuO2-planes), we were able to extract the c-axis longitudinal optical modes in the normal and superconducting state. Superconducting induced changes in the electronic c-axis properties will be discussed and compared to La2-xSrxCuO4 and YBa2Cu3Oy where a superfluid plasma edge is observed at low frequencies
Grazing incidence infrared reflectivity of La1.85Sr0.15CuO4 and NbN
Infrared reflectivity measurements, using p-polarized light at a grazing
angle of incidence, show an increased sensitivity to the optical conductivity
of highly reflecting superconducting materials. We demonstrate that when this
measurement technique is applied to the conventional s-wave superconductor NbN,
the results are in perfect agreement with BCS theory. For the in-plane response
of a LaSrCuO single crystal, in the superconducting
state, we find a reduction of the optical conductivity in the frequency range
below 20 meV. The observed frequency dependence excludes an isotropic s-wave
gap, but agrees well with model calculations assuming a d-wave order parameter.Comment: submitted to phys rev letters, 4 pages, 3 figures in postscrip