M. Mehring

Short-wavelength cutoff effects in the ac fluctuation conductivity of superconductors

The short-wavelength cutoff has been introduced in the calculation of the ac fluctuation conductivity of superconductors. It is shown that a finite cutoff leads to a breakdown of the scaling property in frequency and temperature. Also, it increases the phase

Critical fluctuations and pseudogap observed in the microwave conductivity of BSCCO and YBCO thin films

ensuremath{varphi}

ROTATIONAL DYNAMICS OF C604- AND ELECTRONIC EXCITATION IN RB4C60

of the complex conductivity

Evidence for sp{sup 3} carbon atoms in the RbC{sub 60} dimer phase

(mathrm{tan}ensuremath{varphi}={ensuremath{sigma}}_{2}/{ensuremath{sigma}}_{1})

General solution for the complex frequency shift in microwave measurements of thin films

beyond

13C AND 23NA NMR STUDIES OF NA2C60 AND NA6C60 FULLERIDES

ensuremath{pi}/4

NMR investigation of the electronic structure of the RbC60polymer phase

at

87Rb NMR and the T' problem in Rb3C60.

{T}_{c}.

METALLIC PROPERTIES OF THE TERNARY FULLERIDES A BA2C60 (A = K, RB, CS)

Detailed expressions containing all essential parameters are derived for three-dimensional isotropic and anisotropic fluctuation conductivity. In the two-dimensional case we obtain individual expressions for the fluctuation conductivity for each term in the sum over discrete wave vectors perpendicular to the film plane. A comparison of the theory to the experimental microwave fluctuation conductivity is provided.

High-resolution 13C NMR investigation in Cs4C60.

Critical fluctuations have been studied in the microwave conductivity of Bi 2 Sr 2 CaCu 2 O 8 + δ , Bi 2 Sr 2 Ca 2 Cu 3 O 1 0 + δ , and YBa 2 Cu 3 O 7 - δ thin films above T c . It is found that a consistent analysis of the real and imaginary parts of the fluctuation conductivity can be achieved only if an appropriate wave vector or energy cutoff in the fluctuation spectrum is taken into account. In all of the three underdoped superconducting films one observes strong fluctuations extending far above T c . The coherence length inferred from the imaginary part of the conductivity exhibits the static critical exponent v= 1 very close to T c , and a crossover to the region with v=2/3 at higher temperatures. In parallel, our analysis reveals the absence of the normal conductivity near T c , i.e., fully opened pseudogap. Following the crossover to the region with v=2/3, the normal conductivity is gradually recovered, i.e., the closing of the pseudogap is monitored.