Aslamazov-Larkin Term Research Articles

Fluctuation-Induced Conductivity above the Superconducting Transition Temperature in Thallium Films

Excess conductivity due to fluctuations above the superconducting transition temperature T c in two-dimensional systems is studied both theoretically and experimentally. Theoretically a small correction term added to the Maki-Thompson (MT) term is proposed. This correction term becomes not less important at relatively high temperatures. Experimental results on thallium films are as follows: (1) In the zero electric field limit excess conductivity is well described as the sum of the Aslamazov-Larkin (AL) and MT terms when T is close to T c . However at relatively high temperatures, \(\eta{\gtrsim}0.1\) (η=ln ( T / T c )), the contribution from the above-mentioned correction term is observed. (2) An empirical relation between the pair-breaking parameter δ and R N sq was found to be δ=δ 0 + const × R N sq . (3) When η is small excess conductivity in finite electric field is well expressed as the sum of the nonlinear AL and MT terms. (4) The characteristic electric field is observed to be proportional to η 3/2 .

Excess electrical conductivity due to fluctuations of quench-condensed superconducting Nb films

The resistive transition of superconducting Nb films evaporated onto a liquid-He-cooled substrate has been investigated, and shows a rounding characteristic of the thermal fluctuations. Transition curves have been measured above and below the superconducting transition temperatureTc in the absence of a magnetic field. The excess electrical conductivity due to fluctuations aboveTc of quench-condensed Nb films is well described in terms of the sum of the contributions from the Aslamazov-Larkin term and from the Maki-Thompson term, in contradistinction to the case of quench-condensed Bi, Ga, and Pb films. This suggests that thermal phonons play an important role in the contribution of the Maki term.

Fluctuations and the resistive transition in paramagnetically limited superconductors

We have studied, both theoretically and experimentally, the extra conductivity ${\ensuremath{\sigma}}_{\mathrm{fl}}$ due to thermal fluctuations in high-field superconductors in the Pauli-paramagnetic limit (SPPL). We first investigate theoretically the Aslamazov-Larkin (AL) term, and show that the Pauli-paramagnetic effect in the AL term can be included by renormalizing the thickness of the film. Then we calculate the pair-breaking function for the Maki-Thompson (MT) term in a magnetic field within the lowest-order approximation of Keller and Korenman and show that in contrast to ordinary superconductors the MT term in SPPL can be enhanced by a weak parallel field. We also report the first experimental measurements of ${\ensuremath{\sigma}}_{\mathrm{fl}}$ in SPPL. The angular dependence of the AL term is found to be essentially in agreement with the calculation of Aoi reported earlier. Near ${T}_{c0}$ the MT term is observed to be suppressed by a parallel field. We also study the effect of a perpendicular field, and find, both theoretically and experimentally, that in SPPL the MT term appears to be suppressed by a perpendicular field.

Contribution of the Anomalous Term to the Nonlinear Electrical Conductivity of Superconducting Aluminum Films

Experimental data on the nonlinear excess conductivity of Al films due to the fluctuation of the order parameter have been analyzed by taking account of the Aslamazov-Larkin term and the anomalous term proposed by Maki and Thompson. The analysis shows clearly the existence of a large contribution from the Maki-Thompson term to the nonlinear excess conductivity.

Nonlinear Field Dependence of Electric Conductivity above the Superconducting Transition

The nonlinear field dependence of the so-called anomalous term in the electric conduc­ tivity due to the fluctuation of the superconducting order parameter is studied theoretically. It is found that in the limit of a large electric field E (i.e. E'J:>Ec= y3/D s0(T)312je where c0 (T) =8/n(T-Tc) and D is the diffusion constant), the anomalous term becomes twice as large as the Aslamazov-Larkin term independenct of the dimensionality of the system and independ~nt of the pair-breaking parameter iJ.