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Pedrazzini, P., H. Wilhelm, D. Jaccard, T. Jarlborg, M. Schmidt, M. Hanfland, L. Akselrud, H. Q. Yuan, U. Schwarz, Yu. Grin et al. "Metallic State in Cubic FeGe Beyond Its Quantum Phase Transition." Physical Review Letters 98 (2007): 047204.
Abstract: We report on results of electrical resistivity and structural investigations on the cubic modification of FeGe under high pressure. The long-wavelength helical order (TC=280K) is suppressed at a critical pressure pc≈19GPa. An anomaly at TX(p) and strong deviations from a Fermi-liquid behavior in a wide pressure range above pc suggest that the suppression of TC disagrees with the standard notion of a quantum critical phase transition. The metallic ground state persisting at high pressure can be described by band-structure calculations if zero-point motion is included. The shortest FeGe interatomic distance display discontinuous changes in the pressure dependence close to the TC(p) phase line.
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Rus, T., H. Wilhelm, O. Stockert, T. Luhmann, N. Caroca-Canales, J. G. Sereni, C. Geibel, and F. Steglich. "Specific heat of CeIn3-xSnx single crystals in the vicinity of the quantum critical point." PHYSICA B-CONDENSED MATTER 359-361 (2005): 62–64.
Abstract: We report on results of low-temperature specific heat experiments on single crystals of the cubic alloy CeIn3-xSnx (x = 0.55,0.60, 0.65, and 0.80). The measurements support three-dimensional critical spin fluctuations in the vicinity of the magnetic instability, i.e. for x(c) approximate to 0.67, where the antiferromagnetic order vanishes. (c) 2005 Elsevier B.V. All rights reserved.
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Yadav, C. S., G. Seyfarth, P. Pedrazzini, H. Wilhelm, R. Cerný, and D. Jaccard. "Effect of pressure cycling on Iron: Signatures of an electronic instability and unconventional superconductivity." Physical Review B 88, no. 5 (2013): 054110–7.
Abstract: High pressure electrical resistivity and x-ray diffraction experiments have been performed on Fe single crystals. The crystallographic investigation provides direct evidence that in the martensitic $bcc \rightarrow hcp$ transition at 14 GPa the $\lbrace 110\rbrace{bcc}$ become the $\lbrace 002\rbrace{hcp}$ directions. During a pressure cycle, resistivity shows a broad hysteresis of 6.5 GPa, whereas superconductivity, observed between 13 and 31 GPa, remains unaffected. Upon increasing pressure an electronic instability, probably a quantum critical point, is observed at around 19 GPa and, close to this pressure, the superconducting $T{c}$ and the isothermal resistivity ($0<T<300\,$K) attain maximum values. In the superconducting pressure domain, the exponent $n = 5/3$ of the temperature power law of resistivity and its prefactor, which mimics $T{c}$, indicate that ferromagnetic fluctuations may provide the glue for the Cooper pairs, yielding unconventional superconductivity.
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