Browsing by Author "Ronning, F."

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Anomalous effect of doping on the superconducting state of CeCoIn5 in high magnetic fields
(Amer Physical Soc, 2010)
Tokiwa, Yoshi
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Movshovich, R.
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Ronning, F.
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Bauer, E. D.
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Bianchi, A. D.
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Fisk, Z.
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Thompson, J. D.
We investigated the effect of electron and hole doping on the high-field low-temperature superconducting state in CeCoIn5 by measuring specific heat of CeCo(In1-xMx)(5) with M=Sn, Cd, and Hg and x up to 0.33% at temperatures down to 0.1 K and fields up to 14 T. Although both Cd and Hg doping (hole doping) suppresses the zero-field T-c monotonically, H-c2 increases with small amounts of doping and has a maximum around x=0.2% (M=Cd). On the other hand, with Sn doping (electron doping) both zero-field T-c and H-c2 decrease monotonically. The critical temperature for the high-field low-temperature superconducting state correlates with H-c2 and T-c, which we interpret in support of the superconducting origin of this state.
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Fully gapped superconductivity in Ni-pnictide superconductors BaNi2As2 and SrNi2P2
(2011)
Kurita, N.
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Ronning, F.
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Miclea, C. F.
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Tokiwa, Y.
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Bauer, E. D.
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Subedi, A.
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Singh, D. J.
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Sakai, H.
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Thompson, J. D.
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Movshovich, R.
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Kurita, N; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Ronning, F; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Miclea, C F; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Tokiwa, Y; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Bauer, E D; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Subedi, A; 4Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6114, USA
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Singh, D J; 4Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6114, USA
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Sakai, H; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Thompson, J D; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Movshovich, R; 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
We have performed low-temperature specific heat C and thermal conductivity κ measurements on the Ni-pnictide superconductors BaNi2As2 (Tc = 0.7K) and SrNi2P2 (Tc = 1.4K). The temperature dependences C(T) and κ(T) of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual κ for BaNi2As2 rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba0.6La0.4Ni2As2 shows a mild suppression of Tc and Hc2 relative to BaNi2As2.
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Quantum criticality in layered CeRhIn5-xSnx compared with cubic CeIn3-xSnx
(Epl Association, European Physical Society, 2009)
Donath, J. G.
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Steglich, Frank
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Bauer, E. D.
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Ronning, F.
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Sarrao, J. L.
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Gegenwart, Philipp
We report low-temperature thermal-expansion measurements on single crystals of the layered heavy fermion system CeRhIn5-xSnx (0.3 <= x <= 0.6) and compare it with a previous study on the related cubic system CeIn3-xSnx (Kuchler R. et al., Phys. Rev. Lett., 96 ( 2006) 256403). Both systems display a quantum critical point as proven by a divergent Gruneisen ratio. Most remarkably, the three-dimensional itinerant model explains quantum criticality in both systems, suggesting that the crystalline anisotropy in CeRhIn5-xSnx is unimportant. This is ascribed to the effect of weak disorder in these doped systems. Copyright (C) EPLA, 2009