Signatures of filamentary superconductivity in antiferromagnetic BaFe 2 As 2 single crystals (original) (raw)
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Physical Review B, 2012
Resistivity, magnetization and microscopic 75 As nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe2As2 exhibit anomalous features that are consistent with the collective freezing of domain walls. Below T * ≈ 10 K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and 75 As NMR measurements reveal the presence of slow fluctuations of the hyperfine field. These features in both the charge and spin response are strongly field dependent, are fully suppressed by H * ≈ 15 T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.
Structural and Superconductivity Properties of BaFe2−x Pt x As2
Journal of Superconductivity and Novel Magnetism, 2016
Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample BaFe 2 As 2 and BaFe 2−x Pt x As 2 in the variation of x from 0 to 0.4 with the step of 0.1 were investigated. The bulk materials have been prepared by the solid-state reaction method and sealed into a quartz tube. The crystal structure of all samples exhibited the ThCr 2 Si 2-type crystal structure which is in harmony with earlier studies in the literature. The superconducting states with magnetization measurements have been detailed in the wide temperature range 5-170 K, up to a field of 20 Oe. Increasing Pt and decreasing Fe elements in the BaFe 2−x Pt x As 2 compound deteriorated superconductivity. Using magnetization measurement data, we present the variation of superconducting critical temperature (T c) correlating with a Pt dopant rate from x = 0 to x = 0.4. The dopant rate of x = 0.3 exhibited the limit rate for maximum T c ; deterioration of superconductivity was revealed with a dopant rate of more than x = 0.3.
Solid State Communications, 2018
Fluctuation conductivity measurements were carried out near the superconducting transition of a single-crystal sample of BaFe As P () 2 0.68 0.32 2. Experiments were performed in the presence of magnetic fields in the range 0-7 T applied perpendicular to the electrical current. The analysis of the results leads to the identification of an onedimensional Gaussian regime that remains stable up to the highest applied field. It is proposed that the fluctuations nucleate in a filamentary background formed by electron stripes reminiscent of the nematic ordering accompanying the spin-density-wave state characteristic of the undoped and slightly-doped ferro-pnictide compounds. The data also allowed the determination of the upper critical field for the studied system in the high temperature-low field limit.
Physical Review B, 2015
We study the antiferromagnetic (AFM) and structural phase transitions in single crystal BaFe 2 (As 1-x P x) 2 (0, 0.3 x =) at temperatures T N and T S , respectively, by high resolution ac microcalorimetry and SQUID magnetometry. The specific heat measurements of both as grown and annealed BaFe 2 As 2 display a sharp peak at the AFM/Structural transitions. A kink in the entropy of annealed BaFe 2 As 2 gives evidence for splitting of the two transitions by approximately 0.5K. No additional features could be identified in the specific heat of both BaFe 2 As 2 and BaFe 2 (As 0.7 P 0.3) 2 in the temperature regions around T* > T S where torque measurements [S. Kasahara et al., Nature 486, 382 (2012)] had revealed the "true" nematic phase transition, eventhough the Ginzburg-Landau model used to fit the magnetic torque data indicates that the expected thermal anomaly should be easily observable with our experimental resolution.
Applied Physics Letters, 2009
We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba(Fe 1-x Co x ) 2 As 2 . Unlike the high-temperature superconductor cuprates and 1111-phase oxypnictides, Ba(Fe 1-x Co x ) 2 As 2 showed practically no broadening of the resistive transitions under magnetic fields up to 45 T. We report the temperature dependencies of the upper critical field H c2 both parallel and perpendicular to the c-axis, the irreversibility field H irr c (T) and a rather unusual symmetric volume pinning force curve F p (H) suggestive of a strong pinning nanostructure. The anisotropy parameter γ = H c2 ab /H c2 c deduced from the slopes of dH c2 ab /dT = 4.9T/K and dH c2 c /dT = 2.5T/K decreases from ~2 near T c , to ~1.5 at lower temperatures, much smaller than g for 1111 pnictides and high-T c cuprates.
Magnetic imaging of antiferromagnetic and superconducting phases in RbxFe2−ySe2 crystals
Physical Review B, 2018
High-temperature superconducting (HTS) cuprate materials, with the ability to carry large electrical currents with no resistance at easily reachable temperatures, have stimulated enormous scientific and industrial interest since their discovery in the 1980's. However, technological applications of these promising compounds have been limited by their chemical and microstructural complexity and the challenging processing strategies required for the exploitation of their extraordinary properties. The lack of theoretical understanding of the mechanism for superconductivity in these HTS materials has also hindered the search for new superconducting systems with enhanced performance. The unexpected discovery in 2008 of HTS iron-based compounds has provided an entirely new family of materials for studying the crucial interplay between superconductivity and magnetism in unconventional superconductors. Alkali-metal-doped iron selenide (A x Fe 2−y Se 2 , A = alkali metal) compounds are of particular interest owing to the coexistence of superconductivity at relatively high temperatures with antiferromagnetism. Intrinsic phase separation on the mesoscopic scale is also known to occur in what were intended to be single crystals of these compounds, making it difficult to interpret bulk property measurements. Here, we use a combination of two advanced microscopy techniques to provide direct evidence of the magnetic properties of the individual phases. First, x-ray linear dichroism studies in a photoelectron emission microscope, and supporting multiplet calculations, indicate that the matrix (majority) phase is antiferromagnetic whereas the minority phase is nonmagnetic at room temperature. Second, cryogenic magnetic force microscopy demonstrates unambiguously that superconductivity occurs only in the minority phase. The correlation of these findings with previous microstructural studies and bulk measurements paves the way for understanding the intriguing electronic and magnetic properties of these compounds.
Effects of disorder on the superconducting properties of BaFe1.8Co0.2As2single crystals
Superconductor Science and Technology, 2009
Single crystals of superconducting BaFe 1.8 Co 0.2 As 2 were exposed to neutron irradiation in a fission reactor. The introduced defects decrease the superconducting transition temperature (by about 0.3 K) and the upper critical field anisotropy (e.g. from 2.8 to 2.5 at 22 K) and enhance the critical current densities by a factor of up to about 3. These changes are discussed in the context of similar experiments on other superconducting materials.