Scattering approach to the magnetic susceptibility of high-temperature superconductors

Abstract

We study the dc and ac magnetic susceptibility of high-temperature superconductors in weak magnetic fields. The high-resolution magnetic measurements were done using the non-commercial SQUID magnetometer with the sample in a properly quiet electromagnetic surrounding. The sample is in a residual external ac field smaller than 1 nT and the typical applied ac field is about 1 μT. We show that the interpretation of the temperature dependence of the susceptibility measured under these conditions cannot be based on temperature-dependent suprefluid density, but can be interpreted as due to temperature-dependent electron scattering.

High-resolution magnetic measurements of HTSC

“…(2) fits data recorded on K 3 C 60 too. Further, the resonance scattering model gives linear temperature dependence of resistivity r ab ðTÞ above T c and sign reversal of Hall effect below T c as a consequence of semitransparent gap related to modulated superlattice [14]. …”

Quasiparticle scattering in superconductors

“…The Im sðTÞ may be well approximated by Im sðTÞ / arctanð2ðT À T c Þ=GÞ; the Breit-Wigner resonance [7]. The S-shaped form with symmetry around T c and linear parts are inconsistent with the fluctuation model, which is widely used to explain the convex part.…”

Susceptibility of Superconductors via Scattering Approach

“…Unlike Pb, the data on La in 100 nT field fits rather the Lorentzian dependence, Reχ(T ) ∝ 1/(1 + ((T − T c )/Γ) 2 ), and data on YBCO fits Reχ(T ) ∝ arctan(2(T − T c )/Γ), the Breit-Wigner resonance [3]. Transitions in La and YBCO unlike in Pb have "linear" parts which is not consistent with the GL or BCS model.…”

“…Fluctuations should considerably broaden the transition and influence the phase diagram (B, T ) of vortex matter [2]. However, recent low field high-resolution magnetic measurements show a distinct character of SN transition in conventional BCS superconductors and cuprates [3]. Since the transition shape depends on the sample geometry (demagnetization factor) and experimental configuration, we approached to screen also these parameters.…”