Microwave conductivity and superfluid density in strongly overdoped Tl2Ba2CuO6+δ

Abstract

We present measurements of the microwave surface impedance of the single-layer cuprate Tl2Ba2CuO 6+δ , deep in the overdoped regime, with Tc ≈ 25 K. Measurements have been made using cavity perturbation of a dielectric resonator at 17 discrete frequencies ranging from 2.50 to 19.16 GHz, and at temperatures from 0.12 to 27.5 K. From the surface impedance we obtain the microwave conductivity, penetration depth and superfluid density. The superfluid density displays a strong linear temperature dependence from 2 to 14 K, indicative of line nodes in the energy gap. The microwave data are compared with theoretical predictions for a d-wave superconductor with point-like impurities, with the conclusion that disorder in Tl2Ba2CuO 6+δ acts predominantly in the weak-to-intermediate-strength scattering regime, and that small-angle scattering is important. PACS numbers: 74.25.nn, 74.25.F-, 74.72.Gh arXiv:1312.6459v1 [cond-mat.supr-con]

Signatures of new d-wave vortex physics in overdoped Tl2Ba2CuO6+x revealed by TF-µ+SR

“…d + s, with separate order parameters on distinct Fermi surface sheets, has been advanced to explain the LSCO [11] and YBa 2 Cu 4 O 8 [12] results. However, Tl-2201 has only one FS sheet, and the pure d-wave symmetry and dissimilar microwave penetration depth at both lower and higher dopings [7,9] exclude such an origin. Second, the remarkable scaling seen in Fig.…”

“…A striking universal temperature dependence unambiguously confirms an unusual upturn in the in-plane penetration depth, now seen in at least four distinct material families, establishing that it is new physics generic to the cuprates. Fundamental differences from zero-field microwave measurements of nominally the same quantity [9] imply it is intrinsic to the d-wave vortices themselves. Aside from the substantial impacts of this result on vortex physics and what light this may shed on cuprate superconductivity, there are important ramifications for other techniques.…”

“…Pure d x 2 −y 2 -wave symmetry of the superconducting order in Tl-2201 has been conclusively established by observation of half-integer flux quanta at crystal boundaries in films [6]; line nodes are evident in microwave [7][8][9] and thermal transport [10] measurements; and the admixture of another pairing symmetry is unlikely because it would require spontaneous breaking of the crystal symmetry. However, some µSR measurements have suggested an additionial transition at low temperatures within the vortex state [11][12][13], which has been interpreted in terms of a multiple-component order parameter.…”

Superfluid density and carrier concentration across a superconducting dome: The case of strontium titanate

“…Where σ 1 (ω) is the real part of the optical conductivity. If we assume that σ 1 (ω) behave as a Lorentzian of width 1/τ and zero frequency value σ 0 = ne 2 τ /m as described by the Drude model we can simply integrate Eq.6: n s 2n π arctan 2π∆τ (7) Note that in the dirty limit (i.e. ∆τ → 0), leading to the Homes law which states that n s /m ∝ σ 0 T c [2,3].…”

Electronic structure and the structure of the order parameter in high-T c superconductors based on copper oxides and iron pnictides

“…This type of superconductivity is referred to as d wave superconductivity (by analogy with the nodal structure of d orbitals). Tl 2 Ba 2 CuO 6 + d is also a d wave superconductor, which follows, in particular, from the linear temperature dependence of its microwave conductivity and superconducting density [33].…”