On the occurrence of Berezinskii-Kosterlitz-Thouless behavior in highly anisotropic cuprate superconductors

Abstract

The conflicting observations in the highly anisotropic Bi2Sr2CaCu2O 8+δ , evidence for BKT behavior emerging from magnetization data and smeared 3D-xy behavior, stemming form the temperature dependence of the magnetic in-plane penetration depth are traced back to the rather small ratio, ξ [13,14,15,16,17,18,19,20,21] failed to observe any trace of the universal jump in the superfluid density around T c . Indeed, a systematic finite-size scaling analysis of in-plane penetration depth data taken on films and single crystals of the highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+δ reveal a smeared transition, consistent with an inhomogeneity induced finite-size effect [22]. Furthermore, there is evidence that in small thin-film samples on insulating substrates, edge effects modify the vortex-vortex interaction making it short-range, unlike the logarithmic long-range interaction needed for the BKT transition. This appears to make the BKT transition impossible in thin films of any size if they are supported by a non-superconducting substrate [23].In this work we attempt to unravel the conflicting observations on the highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+δ : evidence for BKT behavior emerging from the magnetization data of Li et al. [10] and evidence for smeared 3D-xy behavior, stemming form the temperature dependence of the magnetic in-plane penetration depth [13,16,22]. Although Bi 2 Sr 2 CaCu 2 O 8+δ is highly anisotropic [24], resistivity measurements [25] uncover clearly the three dimensional nature of the transition in this extreme type II superconductor. Accordingly, sufficiently close to T c homogeneous samples are expected to exhibit 3D-xy critical behavior. To explore how close this should be, we consider the magnetic in-plane penetration data shown in Fig. 1, derived from the complex conductivity measurements of Osborn et al.[16] on epitaxially grown Bi 2 Sr 2 CaCu 2 O 8+δ films, using a two-coil inductive technique at zero applied. For comparison we included the leading 3D-xy behavior given by the universal relation [5,22,26,27] withApparently, there is a rounded transition pointing to a finite size effect, preventing the c-axis correlation length ξ for the critical amplitude of the c-axis correlation length below T c and the limiting length L c set by inhomogeneities. The rather small value of ξ − c0 , reflecting the

Temperature dependence of the order parameter of cuprate superconductors

“…In underdoped cuprates, there is compelling evidence that T c is driven by phase fluctuations [2]. Uemura's empirical scaling law T c ∝ ρ ab s (T = 0) [3] and the observation of a superfluid density jump in ultrathin underdoped cuprate films [4,5,6,7] are consistent with the behavior of a bosonic superfluid, captured by an effective xy model. In this paper we calculate the temperature dependent order parameter of an effective Hamiltonian of charged lattice bosons (CLB).…”

Pseudogap formation and quantum phase transition in strongly-correlated electron systems

“…In addition, the spin anisotropy favours the directions of spins to point in the cooper-oxygen plane [3,20]. By the chemical doping, 3D AFM vanishes and antiferromagnetic (AF) correlation becomes short-ranged and highly anisotropic in space [21,22]. Due to the spin anisotropy, the remnant AF fluctuation can be described by a phase field φ(t, x) = (1/q)e iσ(t, x) .…”