Effects of Ru substitution on electron correlations and Fermi-surface dimensionality in Ba(Fe1−xRux)

Abstract

We report a systematic angle-resolved photoemission spectroscopy study on Ba(Fe1−xRux)2As2 for a wide range of Ru concentrations (0.15 ≤ x ≤ 0.74). We observed a crossover from twodimension to three-dimension for some of the hole-like Fermi surfaces with Ru substitution and a large reduction in the mass renormalization close to optimal doping. These results suggest that isovalent Ru substitution has remarkable effects on the low-energy electron excitations, which are important for the evolution of superconductivity and antiferromagnetism in this system. PACS numbers: 74.70.Xa, 71.18.+y, 74.25.Jb, Superconductivity in the iron-based materials usually emerges from a magnetic state by several kinds of routes leading to very similar phase diagrams of magnetism and superconductivity. In Ba 1−x K x Fe 2 As 2 [1] and Ba(Fe 1−x Co x ) 2 As 2 [2], the introduction of extra hole or electron carriers shifts the chemical potential so that the sizes of the hole and electron Fermi surface (FS) pockets evolve oppositely [3], which eventually suppresses the nesting between the hole and electron FS pockets that play a role in the formation of spin-density-wave (SDW) with exotic Dirac cone dispersion [4] in the parent compound. While it is generally believed that external pressure also changes the FS topology by modifying the chemical bonds [5], the role of isovalent element substitution is still debated. Various scenarios, for example changes of the FS topology by chemical pressure [6][7][8], the reduction of electron correlations [8,9], magnetic dilution [10], and even the addition of extra hole carriers [11], have been suggested to explain the suppression of the SDW order with isovalent element substitution in the BaFe 2 (As 1−x P x ) 2 and Ba(Fe 1−x Ru x ) 2 As 2 systems. Surprisingly, only little attention has been devoted to answer the reversed but somehow similarly important question: how does superconductivity is suppressed by increasing the substitution further than the optimal concentration?Since single-crystals can be grown for the entire phase diagram, the Ba(Fe 1−x Ru x ) 2 As 2 system is ideal to investigate the suppression of the SDW order, the emergence of superconductivity and its disappearance with isovalent-substitution. We expect that the electronic structure near the Fermi level (E F ) be substantially modified by the Ru substitution. Indeed, the isovalent Ru substitution at the Fe site leads to an anisotropic lattice distortion, resulting in a strong increase of the As-Fe(Ru)-As bond angle and a decrease of the As height from the Fe(Ru) plane [6,12,13]. The Hall coefficient, which is always negative and decreases with decreasing temperature in the parent compound BaFe 2 As 2 , increases with decreasing temperature in the Ru-substituted samples and even changes sign for large Ru concentrations [13]. With its capacity to resolve dispersive electronic states in the vicinity of E F , angleresolved photoemission spectroscopy (ARPES) is a powerful tool to determine which parameters drive the system from a SDW orde...

Fermiology of 122 family of Fe-based superconductors: An ab initio study

“…We show that there are no significant changes either in electronor hole-like FSs upon substantial Ru substitution and this observation is consistent with the observations of Dhaka et al [20]. But at about 50% doping there is significant change in the hole-like FSs which is also consistent with the experimental findings by N. Xu et al [25]. We study the nature of FSs when doped in any of the three sites mentioned above through first principles simulations.…”

Effect of Electron Correlations on Magnetic Excitations in the Isovalently Doped Iron-Based SuperconductorBa(Fe1−xRux)2<

“…We observe clear L modulations of the spin excitation intensities at both 2.5 meV and 6 meV. The K z dependence of the band structure revealed by ARPES further confirmed the 3D nature of the system [13,14]. We notice that the dynamical spin correlation lengths in this sample are much shorter than that characterizing the spin wave excitations in the ordered parent compounds [20][21][22][23].…”

“…The same measurements also find that the electron and hole Fermi surfaces are reasonably well nested over the whole phase diagram with Ru doping, in contrast to the carrier doped systems [13,14]. More interestingly, Hall and ARPES measurements have shown that the mobility of the carriers and the Fermi velocities in BaðFe 1Àx Ru x Þ 2 As 2 increase dramatically as compared with those of BaFe 2 As 2 , indicating that the electron-electron interactions are further reduced under Ru doping [13].…”

“…On the other hand, several ARPES measurements suggest that there are the same number of electrons and holes in BaðFe 1Àx Ru x Þ 2 As 2 , demonstrating that Ru doping indeed does not introduce extra holes or electrons [13,14]. The same measurements also find that the electron and hole Fermi surfaces are reasonably well nested over the whole phase diagram with Ru doping, in contrast to the carrier doped systems [13,14].…”

Effect of Electron Irradiation on Superconductivity in Single Crystals ofBa(Fe1−xRux)Prozorov1, Kończykowski2, Tanatar3 et al. 2014Phys. Rev. X7951213View full textAdd to dashboardCite

“…Angle-resolved photoemission spectroscopy (ARPES) measurements report no change in the shape of the Fermi surface and Fermi velocities up to x ¼ 0.55 [29] while other ARPES studies find a crossover from two-to three-dimensional geometry of some holelike pockets of the Fermi surface accompanied by the mass increase for the larger doping levels x [30]. These results were theoretically analyzed in a recent ab initio study [31].…”