Abstract:We have studied the anisotropy in the in-plane resistivity and the electronic structure of isovalent Ru-substituted BaFe 2 As 2 in the antiferromagnetic-orthorhombic phase using well-annealed crystals. The anisotropy in the residual resistivity component increases in proportional to the Ru dopant concentration, as in the case of Co-doped compounds. On the other hand, both the residual resistivity and the resistivity anisotropy induced by isovalent Ru substitution is found to be one order of magnitude smaller t… Show more
“…For ρ ab (T ), it has turned out that the predominant effect of substitution is to introduce disorder, leading to an increase in the RR component. 8,20,21 A large increase is indeed observed for Co substitution [Fig. 3(f)], in agreement with the previous study.…”
Section: B Evolution With Chemical Substitutionsupporting
confidence: 92%
“…38 It is also worth noting that, among the three isovalent substitutions, the in-plane scattering induced by P atoms is not intermediate in magnitude between those by Ru and Sr but comparable with that for Ru substitution. 21 This is counterintuitive because Ru substitution, which introduces disorder in the conduction layer, is expected to cause the strongest scattering. The strengths of the out-of-plane scattering for P and Ru substitution are also comparable.…”
Section: Substitution Effect In the Afo Phasementioning
We investigated the out-of-plane transport properties of parent and chemically substituted BaFe2As2 for various types of substitution. Based on the studies of Hall coefficient and chemicalsubstitution effect, we have clarified the origin for the unusual temperature dependence of outof-plane resistivity ρc(T ) in the high-temperature paramagnetic-tetragonal phase. Electron (hole) carriers have an incoherent (coherent) character, which is responsible for non-metallic (metallic) ρc(T ). Although both of electron and hole contributions are almost comparable, a slightly larger contribution comes from electrons at high temperatures, while from holes at low temperatures, resulting in a maximum in ρc(T ). In the low-temperature antiferromagnetic-orthorhombic phase, the major effect of substitution is to increase the residual-resistivity component, as in the case for the in-plane transport. In particular, Co atoms substituted for Fe give rise to strong scattering with large ac anisotropy. We found that K substitution induces a non-metallic behavior in ρc(T ) at low temperatures, which is likely due to a weakly localized nature along the c-axis direction.
“…For ρ ab (T ), it has turned out that the predominant effect of substitution is to introduce disorder, leading to an increase in the RR component. 8,20,21 A large increase is indeed observed for Co substitution [Fig. 3(f)], in agreement with the previous study.…”
Section: B Evolution With Chemical Substitutionsupporting
confidence: 92%
“…38 It is also worth noting that, among the three isovalent substitutions, the in-plane scattering induced by P atoms is not intermediate in magnitude between those by Ru and Sr but comparable with that for Ru substitution. 21 This is counterintuitive because Ru substitution, which introduces disorder in the conduction layer, is expected to cause the strongest scattering. The strengths of the out-of-plane scattering for P and Ru substitution are also comparable.…”
Section: Substitution Effect In the Afo Phasementioning
We investigated the out-of-plane transport properties of parent and chemically substituted BaFe2As2 for various types of substitution. Based on the studies of Hall coefficient and chemicalsubstitution effect, we have clarified the origin for the unusual temperature dependence of outof-plane resistivity ρc(T ) in the high-temperature paramagnetic-tetragonal phase. Electron (hole) carriers have an incoherent (coherent) character, which is responsible for non-metallic (metallic) ρc(T ). Although both of electron and hole contributions are almost comparable, a slightly larger contribution comes from electrons at high temperatures, while from holes at low temperatures, resulting in a maximum in ρc(T ). In the low-temperature antiferromagnetic-orthorhombic phase, the major effect of substitution is to increase the residual-resistivity component, as in the case for the in-plane transport. In particular, Co atoms substituted for Fe give rise to strong scattering with large ac anisotropy. We found that K substitution induces a non-metallic behavior in ρc(T ) at low temperatures, which is likely due to a weakly localized nature along the c-axis direction.
“…The anisotropy or direction-dependence of resistivity in the thermal hysteresis region of a single crystal of SrFeO 2.81 is not mostly explained by the coexistence of antiferromagnetic and paramagnetic phases, by the incommensurate-to-commensurate CO transition 5, 6, 13 , or in terms of the charge-disproportionation or CDW state 3, 19 . Several theoretical and experimental studies of single crystals and thin films of various materials have established that the anisotropy of resistivity is associated with OO or with the preferential occupation of orbitals, is primarily controlled by doping or lattice distortion/strains 21, 23, 26, 29–33 . Accordingly, the anisotropy of resistivity both in the ab -plane and along the c -axis in SrFeO 2.81 crystal in the thermal hysteresis region is closely related to the changes in electronic and lattice structures.Figure 2Temperature-dependence of resistivity of a single crystal of SrFeO 2.81 , measured in ab -plane and along c -axis.…”
Section: Resultsmentioning
confidence: 99%
“…They further noted that such preferable orbital states can be identified by x-ray linear dichroism (XLD) 23 . However, the complex interplay between the mechanisms that drive OO and cause these orbital effects remains unresolved 24–26 . As discussed above, the tetragonal phase of SrFeO 3-δ undergoes a first-order spin-charge ordering transition that is accompanied by a change in lattice structure, which exhibits exotic electrical and magnetic properties 1 .…”
The local electronic and atomic structures of the high-quality single crystal of SrFeO3-δ (δ~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L
3,2-edge X-ray linear dichroism results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d e
g states remain in persistently out-of-plane 3d
3z
2
-r
2 orbitals. In contrast, in the warming process below the transition temperature, they change from 3d
3z
2
-r
2 to in-plane 3d
x
2
-y
2 orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3d
x
2
-y
2 and out-of-plane 3d
3z
2
-r
2 orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-δ (δ~0.19) single crystal.
“…The magnitude of the anisotropy strongly depends on sample residual resistivity, as found in the study on the annealed samples [9][10][11]. It was argued [8] that the sign change of the resistivity anisotropy can be caused by a dramatic difference in the levels of disorder scattering on the electron-doped side * tanatar@ameslab.gov in Ba(Fe 1−x T M x ) 2 As 2 (T M = Co, Ni, Rh, Ir [12,13]) and the hole-doped side in Ba 1−x K x Fe 2 As 2 [14][15][16][17], as summarized in the bottom panel of Fig.…”
In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped Ba1-xKxFe2As2 in the composition range 0.21 <= x <= 0.26 where anisotropy changes sign. Low-temperature (similar to 20 K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to the conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic C-2 phase above the reentrant tetragonal transition. Unusual T-linear dependence of the anisotropy Delta rho rho(a) (T)rho(b) (T) is found in pristine samples with x = 0.213 and x = 0.219, without similar signatures in either rho(a) (T) or rho(b) (T). We show that this feature can be reproduced by a phenomenological model of R. M. Fernandes et al. [Phys. Rev. Lett. 107, 217002 (2011)]. We speculate that onset of fluctuations of nematic order on approaching the instability towards the reentrant tetragonal phase contributes to this unusual dependence.
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