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Jaime, M., R. Movshovich, G. R. Stewart, W. P. Beyermann, M. G. Berisso, and P. C. Canfield. "Specific heat of Ce3Bi4Pt3 at 60 T." PHYSICA B 294 (2001): 240–244.
Abstract: Kondo insulator materials such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3, and SmB6, are 3d, 4f and 5f intermetallic compounds. At high temperatures they behave like metals but a gap d in the conduction band opens at the Fermi energy as the temperature is reduced. It has been proposed that the formation of the low-temperature gap is a consequence of the hybridization between the conduction band and the f-electron levels. If this is true, Kondo metal physics should be recovered when the gap is closed at high magnetic fields. We report here specific heat results of Ce-3 Bi4Pt3 in DC and pulsed magnetic fields up to 60 T. We see evidence for the reduction of the gap in 18 T and a rapid increase of the Sommerfeld coefficient C-H/T\(T -->0) in 30 T > H > 40 T. Numerical results and the analysis of the data with the Coqblin-Schrieffer model prove a field-induced Kondo insulator-to-Kondo metal crossover. (C) 2001 Elsevier Science B.V. All rights reserved.
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Jaime, M., R. Movshovich, G. R. Stewart, W. P. Beyermann, M. G. Berisso, M. F. Hundley, P. C. Canfield, and J. L. Sarrao. "Closing the spin gap in the Kondo insulator Ce3Bi4Pt3 at high magnetic fields." Nature 405, no. 6783 (2000): 160–163.
Abstract: Kondo insulator materials(1)-such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3 and SmB6-are 3d, 4f and 5f intermetallic compounds that have attracted considerable interest in recent years(2-5). At high temperatures, they behave like metals. But as temperature is reduced, an energy gap opens in the conduction band at the Fermi energy and the materials become insulating. This contrasts with other f-electron compounds, which are metallic at all temperatures. The formation of the gap in Kondo insulators has been proposed to be a consequence of hybridization between the conduction band and the f-electron levels(6,7), giving a 'spin' gap. If this is indeed the case, metallic behaviour should be recovered when the gap is closed by changing external parameters, such as magnetic field or pressure. Some experimental evidence suggests that the gap can be closed in SmB6 (refs 5, 8) and YbB12 (ref. 9). Here we present specific-heat measurements of Ce3Bi4Pt3 in d.c. and pulsed magnetic fields up to 60 tesla. Numerical results and the analysis of our data using the Coqblin-Schrieffer model demonstrate unambiguously a field-induced insulator-to-metal transition.
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Kim, J., N. Haberkorn, K. Gofryk, M. J. Graf, F. Ronning, A. S. Sefat, R. Movshovich, and L. Civale. "Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals." Solid State Communications 201 (2015): 20–24.
Abstract: Abstract
We report the intrinsic superconducting parameters in a heavily overdoped Ba(Fe1−xCox)2As2 (x=0.14) single crystal and their influence in the resulting vortex dynamics. We find a bulk superconducting critical temperature of 9.8 K, magnetic penetration depth λab (0)=660±50 nm, coherence length ξab (0)=6.4±0.2 nm, and the upper critical field anisotropy γT→Tc≈3.7. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. The intrinsic pinning energy plays an important role in the resulting vortex dynamics as compared with similar pinning landscape and comparable intrinsic thermal fluctuations.
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Kim, J., N. Haberkorn, E. Nazaretski, R. de Paula, T. Tan, X. X. Xi, T. Tajima, R. Movshovich, and L. Civale. "Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film." Solid State Communications 204 (2015): 56–60.
Abstract: We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of λ=50±10 nm at T=4 K is related to a clean π-band. We find a high self-field critical current density Jc, which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the π-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson–Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field.
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