Variation in Electronic State of Ba(Fe_1-xCo_x)₂As₂Alloy as Investigated in Terms of Transport Properties

Abstract

We investigate the in-plane transport properties of the electron-doped iron arsenide superconductor Ba(Fe 1Àx Co x ) 2 As 2 (0 x 1). We observe a non-Fermi-liquid behavior characterized by an incoherent resistivity and a low-temperature increase in Hall coefficient (R H ) at x 0:14. We discuss this feature in terms of antiferromagnetic fluctuations. We find that the effective carrier density per Fe/Co atom n eff ¼ ÀV=ðeR H Þ (V is the volume per Fe/Co atom and e is the elementary electric charge) at 250 K exhibits a nonmonotonic x dependence with a minimum value at x $ 0:1, which is considered to reflect the disappearance of hole Fermi surfaces. We discuss the interrelationships among superconductivity, magnetism, and band nesting.The recent discovery of superconductivity with a high critical transition temperature (T c ) in F-doped LaFeAsO has sparked much interest in materials containing FeAs layers. 1) Among several series of iron arsenide superconductors, one of the most investigated systems is Ba(Fe 1Àx Co x ) 2 As 2 owing to its ease of crystal growth. 2) Its parent compound BaFe 2 As 2 (x ¼ 0) undergoes a magnetic transition into a stripe-type order at T N ¼ 140 K, which is accompanied by a tetragonal-orthorhombic structural transformation. [3][4][5] Despite the first-order nature of the transition, anisotropic spin fluctuations are observed above T N . 4,5) This antiferromagnetic transition is considered to be triggered by the nesting character of the Fermi surface, which consists of three hole cylinders at the zone center and two electron cylinders at the zone corner. 6-8) The Fermi surfaces of holes and electrons have identical areas ($0:15/Fe); 6-9) this is characteristic of a compensated metal. Owing to the antibonding character of bands, the band mass of electrons is lower than that of holes. The other limit, BaCo 2 As 2 (x ¼ 1), exhibits no magnetic transition. 10) However, its high Wilson ratio R W ¼ 7 {10 indicates that the system is close to ferromagnetic instability. Superconductivity with a maximal T c ¼ 24 K is observed at intermediate compositions of 0:04 x 0:15. 9,[11][12][13][14] Even though extensive studies have been carried out, there still remain fundamental problems concerning the electronic states of Ba(Fe 1Àx Co x ) 2 As 2 . One naive but important question is whether the substituted Co atom having a larger atomic number than the Fe atom indeed offers one conducting electron to the system. A recent angle-resolved photoemission study revealed the doping variation of the Fermi surface; 15) however, the validity of the rigid-band picture is not yet clarified. It is expected that there is a unique Co concentration at which hole bands disappear; how such modification of the Fermi surface topology affects the electronic ground states as well as fluctuations from them should be clarified. Moreover, Co atoms substituted for Fe atoms likely introduce randomness to the system; how this affects the electronic properties should also be unraveled. In order to tackle these issues, we report on the...

Doping evolution of superconducting gaps and electronic densities of states in Ba(Fe 1−x Co x ) 2 As 2 iron pnictides

“…[18]). Our phase diagram is very similar to previous reports, except that superconductivity disappears at a lower Co concentration (x ≈ 0.125) than previously reported from transport and magnetization measurements [19][20][21][22]. We also observe that superconductivity emerges already in the magnetic phase, at a concentration x ≈ 0.04, and T c increases to 24.2 K at x ≈ 0.575.…”

Transport and magnetic properties of Co-doped BaFe2As2epitaxial thin films grown on MgO substrate

“…The value of R H at 300 K is three times larger than that just above T c . The values of R H agree quite well with that in slightly overdoped single crystals [23]. Magneto-optical (MO) images were captured using the local-field dependent Faraday rotation of linearly polarized light in an in-plane magnetized garnet film placed above the sample.…”

Interplane resistivity of isovalent doped BaFe2(As1−xPxTanatar1, Hashimoto2, Kasahara3 et al. 2013Phys. Rev. B265221View full textAdd to dashboardCite

“…The crossover temperature is rapidly suppressed with doping in BaCo122, it is preceded by metallic temperature dependence at high temperatures above a minimum in ρ c (T ) for heavily doped BaCo122. A close to Tlinear ρ c (T ) dependence is found at a critical concentration x=0.313 [14], and normal metallic ρ c (T ), and temperature-independent Pauli susceptibility, χ(T ), and Hall constant are restored for x >0.313 [14,30].…”