Absolute value and temperature dependence of the magnetic penetration depth in Ba(Co 0.074 Fe 0.926 ) 2 As 2 (original) (raw)
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Physical Review B, 2009
We have performed transverse field muon spin rotation measurements of single crystals of Ba(Fe0.93Co0.07)2As2 with the applied magnetic field along theĉ direction. Fourier transforms of the measured spectra reveal an anisotropic lineshape characteristic of an Abrikosov vortex lattice. We have fit the µSR spectra to a microscopic model in terms of the penetration depth λ and the Ginzburg-Landau parameter κ. We find that as a function of temperature, the penetration depth varies more rapidly than in standard weak coupled BCS theory. For this reason we first fit the temperature dependence to a power law where the power varies from 1.6 to 2.2 as the field changes from 200G to 1000G. Due to the surprisingly strong field dependence of the power and the superfluid density we proceeded to fit the temperature dependence to a two gap model, where the size of the two gaps is field independent. From this model, we obtained gaps of 2∆1 = 3.7kBTc and 2∆2 = 1.6kBTc, corresponding to roughly 6 meV and 3 meV respectively.
Physical Review B, 2010
The zero temperature value of the in-plane London penetration depth, λ ab (0), has been measured in single crystals of Ba(Fe1−xCox)2As2 as a function of the Co concentration, x, across both the underdoped and overdoped superconducting regions of the phase diagram. For x 0.047, λ ab (0) has been found to have values between 120 ± 50 nm and 300 ± 50 nm. A pronounced increase in λ ab (0), to a value as high as 950 ± 50 nm, has been observed for x 0.047, corresponding to the region of the phase diagram where the itinerant antiferromagnetic and superconducting phases coexist and compete. Direct determination of the doping-dependent λ ab (0) has allowed us to track the evolution of the temperature-dependent superfluid density, from which we infer the development of a pronounced superconducting gap anisotropy at the edges of the superconducting dome.
Physical Review B, 2011
Measurements of the magnetic penetration depth λ in the Fe-based superconductor Ba1−xRbxFe2As2 (x = 0.3, 0.35, 0.4) were carried out using the muon-spin rotation (µSR) technique. The temperature dependence of λ is well described by a two-gap s+s-wave scenario with a small gap ∆1 ≈ 1-3 mev and a large gap ∆2 ≈ 7-9 mev. By combining the present data with those obtained for RbFe2As2 a decrease of the BCS ratio 2∆2/kBTc with increasing Rb content x is observed. On the other hand, the BCS ratio 2∆1/kBTc is almost independent of x. In addition, the contribution of ∆1 to the superfluid density is found to increase with x. These results are discussed in the light of the suppression of interband processes upon hole doping.
Physical review. …, 2010
Superfluid density and field-induced magnetism in Ba(Fe1-xCox)2As2 and Sr(Fe1-xCox)2As2 measured with muon spin relaxation Williams, T. J.; Aczel, A. A.; Baggio-Saitovitch, E.; Bud'ko, S. L.; Canfield, P. C.; Carlo, J. P.; Goko, T.; Kageyama, H.; Kitada, A.; Munevar, J.; Ni, N.; Saha, S. R.; Kirschenbaum, K.; Paglione, J.; Sanchez-Candela, D. R.; Uemura, Y. J.; Luke, G. M. Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca. http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc\_cp.jsp?lang=fr L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site
Physical Review B, 2011
Low-temperature specific heat (SH) is measured on Ba(Fe1−xCox)2As2 single crystals in a wide doping region under different magnetic fields. For the overdoped sample, we find the clear evidence for the presence of T 2 term in the data, which is absent both for the underdoped and optimal doped samples, suggesting the presence of line nodes in the energy gap of the overdoped samples. Moreover, the field induced electron specific heat coefficient ∆γ(H) increases more quickly with the field for the overdoped sample than the underdoped and optimal doped ones, giving another support to our arguments. Our results suggest that the superconducting gap(s) in the present system may have different structures strongly depending on the doping regions.
Microscopic Coexistence of Superconductivity and Magnetism in Ba_{1-x}K_{x}Fe_{2}As_{2}
Physical Review Letters, 2011
We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe1−xRux)2As2 (x = 0.23). We find two phase transitions, to antiferromagnetism at TN ≈ 60 K and to superconductivity at TC ≈ 15 K. Below TN , our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 µB/Fe. The spin-lattice relaxation rate 1/ 75 T1 is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below TC, 1/ 75 T1 on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity. In the iron-based superconductors, superconductivity (SC) is achieved on suppressing a long-ranged antiferromagnetic order [1] by doping or pressure. At this phase boundary, much attention has been drawn to the question of whether SC may coexist with antiferromagnetism (AFM). Proposals for possible coexisting phases have included commensurate [2] and incommensurate [3-5] magnetic structures, competition between AFM and SC , and variations in the size of the ordered moment or the pairing symmetry . No consensus has yet been reached on the pairing mechanism or the possible phenomena arising from the interplay of AFM and SC. For most materials, local-probe studies on high quality samples are required as a matter of urgency to distinguish the key properties of microscopic coexistence from any form of phase separation.
Physical Review Letters, 2010
We report muon spin rotation (µSR) and infrared (IR) spectroscopy experiments on underdoped BaFe1.89Co0.11As2 which show that bulk magnetism and superconductivity (SC) coexist and compete on the nanometer length scale. Our combined data reveal a bulk magnetic order, likely due to an incommensurate spin density wave (SDW), which develops below T mag ≈ 32 K and becomes reduced in magnitude (but not in volume) below Tc = 21.7 K. A slowly fluctuating precursor of the SDW seems to develop alrady below the structural transition at T s ≈ 50 K. The bulk nature of SC is established by the µSR data which show a bulk SC vortex lattice and the IR data which reveal that the majority of low-energy states is gapped and participates in the condensate at T ≪ Tc.