Magnetic penetration depth in Ni- and Zn-dopedYBa2(Cu1−

Abstract

The penetration depth k(T) in YBa2(Cu& "M )307 films, with M=Ni or Zn and nominal concentrations, 0.02~x~0.06, is obtained from the mutual inductance of coaxial coils on opposite sides of the films. Both Ni and Zn increase A, (0) very rapidly, such that the superAuid density, n, (0) cc A, (0), decreases by a factor of 2 for each percent of dopant. The rapid increase in A, (0) implies that disorder fills in the superconducting density of states at low energy, so that Ns(0) is roughly 80 -95 % of the normalstate density of states. An analytic d-wave theory, valid at T =0, finds that A, (0) increases rapidly with disorder, but not as rapidly as observed. It is striking that the dependence of A, ( T/T, ) on T!T, does not change significantly as x increases from 2% to 6%, although it is different from undoped YBa2Cu307films. An ad hoc phenomenological model finds that one should expect this result. Finally, the values of Ns(0) deduced from A, are somewhat larger than values deduced from specific-heat measurements on Zn-doped YBa2Cu307 z, which also indicate increasing gaplessness with doping.

Metallic Nonsuperconducting Phase andD-Wave Superconductivity in Zn-SubstitutedLa1.85Sr0.15Karpińska1, Cieplak2, Guha3 et al. 2000Phys. Rev. Lett.Self Cite283230View full textAdd to dashboardCite

“…We note that nonmagnetic disorder should produce a rapid decrease of the zero-temperature value of the superfluid density, n S (0) ∼ λ(0) −2 , together with a steep decrease of T c [26]. Our results show that n S (0) decreases by a factor of 1.3 per percent of impurity, which is slightly slower than the rate reported for YBCO [25] but close to a theoretical predictions for a d-wave superconductor [26]. .…”

“…An attempt to fit a straight line to the low-temperature portion of the curves, as shown in the inset, leads to energy gaps decreasing with increasing y, inconsistent with the expectations for anisotropic s-wave symmetry. A similarly negligible effect of zinc doping on the T -dependence of λ has also been reported for YBCO [25]. We note that nonmagnetic disorder should produce a rapid decrease of the zero-temperature value of the superfluid density, n S (0) ∼ λ(0) −2 , together with a steep decrease of T c [26].…”

Critical temperature and superfluid density suppression in disordered high-Tccuprate superconductors

“…It has been noted that the experimentally observed T c is much more robust than one would expect from these simple models, when measured against the corresponding change in ρ s (0). Figure 1 illustrates this point by showing the experimental T c versus ρ s (0) for YBCO samples disordered by different types of disorder as obtained by various groups [9][10][11][12][13] and the corresponding theoretical prediction [5]. While there exists a considerable spread in the experimental data, it is quite evident that the theory systematically overestimates the suppression of T c , perhaps by as much as a factor of 2 in the cases of Refs.…”

Spin-orbit scattering in d -wave superconductors

“…The critical temperature T c and the superfluid density ρ s are lowered by non-magnetic impurity substitution [1,2,3,4] and disorder induced by irradiation [5,6]. Recent ARPES data show clearly how disorder leads to a redistribution of spectral intensity by adding new states at the Fermi level [6].…”