High-precision measurement of the Ferrell-Glover-Tinkham sum rule in a cuprate high-temperature superconductor

Abstract

The Ferrell-Glover-Tinkham (FGT) sum rule in superconductors defines the superfluid density, ρs, as the optical conductivity spectral weight (SW) that transfers into a δ function at ω=0 due to the opening of the energy gap below Tc. In high-Tc superconductors, strong electron-boson coupling, self-energy effects, and intertwining of energy scales can link ρs to various high-energy processes, making the question of whether or not the FGT sum rule is valid in cuprates, and at what energy scale, central to a full understanding of the pairing mechanism. Here, we report high-precision measurements of the FGT sum rule in near-optimally doped DyBa2Cu3O7−δ thin films. We resolve the low-energy balance of SW by combining submillimeter-microwave interferometry, terahertz time-domain spectroscopy, and infrared ellipsometry to independently obtain the real and imaginary parts of the complex dielectric function between 0.8 meV and 1.1 eV (6–9000 cm−1). By applying a Kramers-Kronig consistency analysis to the measured spectra we find that the FGT sum rule is obeyed, and the total intraband SW is conserved to within ±0.2% below an energy scale ∼0.6 eV. We attribute specific anomalies observed in the conductivity spectra below ∼0.6 eV to coupling of charge carriers to the spectrum of collective antiferromagnetic spin fluctuations. The procedure presented here, applied to near-optimally doped DyBa2Cu3O7−δ, lays out a protocol for how the FGT sum rule should be studied in other doping levels and compounds.

Source-reported materials — not catalogue approval

Similar papers