Pressure effects on the superconducting properties of single-crystalline Co doped NaFeAs

Abstract

Resistivity and magnetic susceptibility measurements under external pressure were performed on NaFe 1−x Co x As (x = 0, 0.01, 0.028, 0.075 and 0.109) single crystals. For both underdoped and optimally doped NaFe 1−x Co x As, the maximum T c reached as high as 31 K under certain pressures. Meanwhile the overdoped sample with x = 0.075 also exhibits a positive pressure effect on T c , and an enhancement of T c by 13 K is achieved under a pressure of 2.3 GPa. All of these superconducting samples show large positive pressure coefficients on superconductivity, being distinct from those of Ba(Fe 1−x Co x ) 2 As 2 . However, the superconductivity cannot be induced by pressure in heavily overdoped nonsuperconducting NaFe 0.891 Co 0.109 As. These studies reveal that the electronic structure is very different between superconducting and heavily overdoped non-superconducting NaFe 1−x Co x As, consistent with the observation of angleresolved photoemission spectroscopy.

Crystal structure and phase diagrams of iron-based superconductors

“…7a [112] that, in the majority of iron-pnictide systems, the application of pressure can enhance T c effici ently, provided the pressure is below a moderate value. The value of T c can then be suppressed as the pressure increases further, for example, in doped LaFeAsO [113], underdoped 122 systems [114], and doped NaFeAs [16,115,116]. In particular, superconductivity can be induced by pressure in non-superconducting LaOFeAs and AeFe 2 As 2 (Ae = Ca, Sr, Ba, Eu), which is accompanied by the suppression of the AFM/SDW transition in these systems [117,118].…”

Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure

“…The application of pressure on BaFe 1.92 Co 0.08 As 2 results in a very strong enhancement of T c from 11 to 21 K at 2.5 Gpa [25]. For Codoped NaFeAs, enhancement in T c is more than 14K at 2.5GPa due to optimization of the structural parameters of the FeAs layers [26]. The T c of FeSe is enhanced up to 37K at 7Gpa [27].…”

Hydrostatic pressure: A very effective approach to significantly enhance critical current density in granular iron pnictide superconductors

“…Pressure can result in improvement of T c from 28 to 43 K at 4 GPa for LaOFFeAs20. For Co doped NaFeAs, the maximum T c can reach as high as 31 K from 16 K at 2.5 GPa21. Pressure can also enhance the T c of La doped Ba-122 epitaxial films up to 30.3 K from 22.5 K, due to the reduction of electron scattering and increased carrier density caused by lattice shrinkage22.…”