Doping effect on the evolution of the pairing symmetry in n-type superconductor near antiferromagnetic phase boundary

Abstract

We present the investigation results of the in-plane ρ(T) resistivity tensor at the temperature range 0.4-40 K in magnetic fields up to 90kOe (H c, J ab) for electrondoped Nd 2−x Ce x CuO 4+δ with different degree of disorder near antiferromagneticsuperconducting phase boundary. We have experimentally found that for optimally doped compound both the upper critical field slope and the critical temperature decrease with increasing of the disorder parameter (d-wave pairing) while in the case of the underdoped system the critical temperature remains constant and (dH c2 /dT )| Tc increases with increasing of the disorder (s-wave pairing). These features suggest a possible implementation of the complex mixture state as the (s+id)-pairing.

Hall Resistivity Correlations in Disordered Electron-Doped $$\hbox {Nd}_{2-x}\hbox {Ce}_x\hbox {CuO}_{4+\delta }$$ Nd 2 - x

“…Temperature dependencies of the resistivity in external magnetic field up to B = 9 T for these types of the films were presented in [14]. In optimally -and non optimally reduced films we have found the sharp SC transition in zero magnetic field.…”

“…"Optimally reduced" film -T c = 18.8 K, k F ℓ = 10.8. In these underdoped films the critical temperature remains unchanged with the increase of the nonstochiometric disorder that may indicate a some change of the pairing symmetry (for example, assymetric s-wave pairing [14]). …”

“…Then the films were subjected to heat treatment (annealing) under various conditions to obtain samples with various oxygen content. As a result, three types of samples with x=0.15 were obtained: "as grown" samples, "optimally reduced" -after annealing in a vacuum and "non optimally reduced" samples [14]. For films with x = 0.14 were obtained two types of samples: "optimally reduced" and two samples "non optimally reduced" -non optimally annealed in vacuum [14,15].…”

“…The observed dependence T c from k F ℓ (which extracted as k F ℓ = hc 0 /e 2 ρ xx ) is associated in high-temperature superconductors with the manifestation of the d-wave pairing symmetry [14].…”

“…On the assumption of the possible coexistence of AF and SC we have obtained the a.c.susceptibility data (both χ ′ and χ ′′ ) for underdoped non optimally reduced single crystal film Nd 1.86 Ce 0.14 CuO 4+δ /SrTiO 3 with k F ℓ = 6.0 ( [14]). The onset of diamagnetic response occurs at T c ≃ 18.8 K. At the same temperature the sufficiently sharp resistivity SC transition is observed.…”