Theory of Thermal Conductivity inYBa2Cu3O7−

Abstract

We calculate the electronic thermal conductivity in a d-wave superconductor, including both the effect of impurity scattering and inelastic scattering by antiferromagnetic spin fluctuations. We argue that phonons dominate heat transport near T c , but that electrons are responsible for most of the peak observed in clean samples, The peak position is predicted to vary nonmonotonically with disorder, in good agreement with experiments on YBa 2 ͑Cu 12x Zn x ͒ 3 O 72d . [S0031-9007(96)01535-9] PACS numbers: 74.72. Bk, 74.25.Fy, 74.62.Dh Analysis of transport experiments in the superconducting state of the high-temperature cuprate superconductors has already provided the most compelling evidence for electronic pairing in these materials. The collapse of the quasiparticle relaxation rate below T c , as observed in optical [1,2] and microwave [3] measurements, is not observed in classic superconductors, and is most naturally interpreted in terms of a gapping of the spectral density of electronic excitations responsible for inelastic scattering just above T c . This collapse is now understood to be responsible, e.g., for the peak at intermediate temperatures in the microwave conductivity of YBa 2 Cu 2 O 6.95 [3].Thermal conductivity measurements provide information on order parameter symmetry and quasiparticle relaxation and have the advantage that they are bulk probes not subject to extrinsic surface effects which have hampered the interpretation of the low-T microwave conductivity [3]. They have the disadvantage that the electronic contribution to the heat current must be separated from the phononic one. As pointed out by Yu et al. [4], the similarity between the microwave conductivity peak and measurements of the thermal conductivity k͑T ͒ in YBa 2 Cu 3 O 72d single crystals suggests that at least part of the thermal conductivity peak should be due to the electronic thermal conductivity k el ͑T ͒, in contrast to earlier analyses of this peak in terms of a phonon conductivity k ph ͑T ͒ alone [5,6]. In the work of Yu et al., the phononic mean free path ᐉ ph is assumed to vary only weakly with T , T c , whereas in the Peacor et al. approach [5], ᐉ ph is assumed to be dominated by phonon-electron relaxation, leading via the pair correlations in the electronic system to an exponential behavior below T c . In Ref.[5] it is assumed that k ph ¿ k el over the entire temperature range, whereas Yu et al. deduce k ph ͑T c ͒ Ӎ 2 2 3k el ͑T c ͒ using the measured s 1 ͑T c ͒ on similar quality crystals, and assuming the Wiedemann-Franz law k el L 0 T s 1 with the free electron Lorenz number L 0 .In this paper, we adopt a theoretical model of electronic transport in a d-wave superconductor limited by impurity and spin fluctuation scattering which has proven successful in describing many of the systematics of mi-crowave measurements, and apply it to calculate the electronic thermal conductivity. We analyze experiments on Zn doped YBa 2 Cu 3 O 72d to argue that (a) phonons do in fact dominate heat conduction at T c ; (b) a peak in ...

Breakdown of Universal Transport in Correlatedd-Wave Superconductors

“…2b), we show the low-T thermal conductivity for the case of n i = 2.5% (15%) scatterers with V imp /t = 10 (V imp /t = 3) averaged over 20 different random impurity configurations (which is enough for configurational convergence). For U = 0 the result in 2a agrees well with those obtained previously for the dilute impurity limit: in the non-self-consistent (NSC) calculation (with homogeneous ∆=0.4), κ(T )/T = κ 00 + αT 2 [31], whereas in the self-consistent (SC) case the spatial inhomogeneity of ∆ ij causes a reduction of α and leads to a more linear T dependence [9] of κ/T . The case with V imp /t = 3.0 in 2b is an example of one of the weak- est disorder potentials we are able to study since further reduced V imp leads to mean-free-path larger that our system.…”

Ab initiocalculation of impurity effects in copper oxide materials

“…[6] and suggested to correspond to Cu vacancies in the CuO 2 plane. While measured resonance energies on native defects and Zn are roughly consistent with fits to bulk transport measurements based on naive point-like potential scattering models 12 …”

Novel Anisotropy in the Superconducting Gap Structure ofBi2Sr2CaCu2Ando1, Takeya2, Abe3 et al. 2002Phys. Rev. Lett.444382View full textAdd to dashboardCite

“…The magnetic field is applied perpendicular to the ab plane and the H-dependence of κ is measured with the field-cooled procedure [9] to avoid complications that are associated with the vortex-pinning-related hysteresis [12]. Figure 2 displays the temperature dependences of ρ and κ for the a and b directions; the resistivity shows only a small, if any, in-plane anisotropy, while the thermal conductivity demonstrates a non-trivial anisotropy that cannot be attributed to an error in the geometrical factors; namely, the peak height at ∼70 K is smaller along the a axis and yet κ a becomes larger than κ b below ∼30 K. This anisotropy in κ(T ) suggests that the number of thermally-excited QPs is larger for the nodes along the a axis, because the QP population near the nodes is more directly reflected in κ at lower temperatures [13]. (The anisotropy in κ above T c is most likely due to phonons; it has been estimated [9] that phonons are responsible for roughly 2/3 of the total κ at T c .)…”