Phase diagram and physical properties of NaFe1−xCuxAs single crystals

Abstract

A series of high quality NaFe1−xCuxAs single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature (Tc) is initially enhanced from 9.6 to 11.5 K by Cu doping, and then suppressed with further doping. A phase diagram similar to NaFe1−xCoxAs is obtained except that insulating instead of metallic behavior is observed in extremely overdoped samples. Tc's of underdoped, optimally doped, and overdoped samples are all notably enhanced by applying pressure. Although a universal maximum transition temperature (T max c ) of about 31 K under external pressure is observed in underdoped and optimally doped NaFe1−xCoxAs, T max c of NaFe1−xCuxAs is monotonously suppressed by Cu doping, suggesting that impurity potential of Cu is stronger than Co in NaFeAs. The comparison between Cu and Co doping effect in NaFeAs indicates that Cu serves as an effective electron dopant with strong impurity potential, but part of the doped electrons are localized and do not fill the energy bands as predicted by the rigid-band model.

Local breaking of fourfold rotational symmetry by short-range magnetic order in heavily overdoped Ba(Fe1−xCux)2As2Wang1, Song2, Hu3 et al. 2017Phys. Rev. B112101View full textAdd to dashboardCite

“…SG behavior seen in magnetization measurements is also reported for other heavily Cu-doped iron pnictides [10,16] and chalcogenides [19][20][21][22], pointing to the possible presence of shortrange magnetic order. Importantly, in both A(Fe 1−x Cu x ) 2 As 2 and NaFe 1−x Cu x As where SG behavior is observed, doped Cu is in a nonmagnetic 3d 10 configuration [10,18] and therefore any SG or short-range magnetic order must be due to Fe.…”

“…For BaFe 2−x T M x As 2 (T M = Co, Ni, Cu), while Co and Ni doping result in superconducting domes with optimal T c ∼ 20 K, optimal T c ∼ 2 K or no superconductivity is observed in AFe 2−x Cu x As 2 (A = Ba,Sr) [8][9][10]. This contrast points to the inadequacy of a simple rigid band picture [11][12][13] and highlights differences between dopants [14,15].Compared to AFe 2−x Cu x As 2 , superconductivity with optimal T c = 11.5 K is observed in NaFe 1−x Cu x As [16,17]. With increasing Cu concentration (x 10%), insulating-like transport and short-range magnetic order develop, evolving towards an insulator with long-range magnetic order and Fe-Cu ordering near x ≈ 50% [18].…”

“…1(c). The separation between ZFC and FC susceptibilities occurring at low temperatures indicates SG-like behavior, similar to other heavily Cu-doped iron pnictides and chalcogenides [10,16,[19][20][21][22].…”

“…Compared to AFe 2−x Cu x As 2 , superconductivity with optimal T c = 11.5 K is observed in NaFe 1−x Cu x As [16,17]. With increasing Cu concentration (x 10%), insulating-like transport and short-range magnetic order develop, evolving towards an insulator with long-range magnetic order and Fe-Cu ordering near x ≈ 50% [18].…”

Correlation-driven metal-insulator transition in proximity to an iron-based superconductor

“…Data after Ref. [21]. At high doping levels, NaFe 1−x Cu x As exhibits real-space ordering of copper and iron ions [see Fig.…”