Europhys. Lett.
Volume 48, Number 5, December 1999
Page(s) 568 - 572
Section Condensed matter: electronic structure, electrical, magnetic and optical properties
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00521-4

Europhys. Lett, 48 (5), pp. 568-572 (1999)

Resonant defect scattering in thorium-doped $\rm UBe_{13}$

T. Schreiner 1, E.-W. Scheidt 1 and G. R. Stewart 1,2

1 Institut für Physik, Universität Augsburg
Universitätsstrasse 1, 86159 Augsburg, Germany
2 Department of Physics, University of Florida
Gainesville, Florida 32611-8440, USA

(received 1 June 1999; accepted in final form 30 September 1999)

PACS. 74.25Bt - Thermodynamic properties.
PACS. 74.70Tx - Heavy-fermion superconductors.


Low-temperature specific-heat measurements on ${\rm U}_{1-x}{\rm Th}_x{\rm Be}_{13}$reveal a linear contribution $C_{\rm lin} = \gamma_{\rm rest}(x)\cdot T$ at lowest temperatures which varies systematically with thorium concentration. Size and concentration dependence of this contribution can be explained by resonant defect scattering of the Th impurities in an anisotropic superconductor with gap nodes. The most meaningful observation, however, is that $\gamma_{\rm rest}(x)$ shows relatively sharp minima at both critical concentrations ( $x_{\rm C1}\approx 1.8$ at%, $x_{\rm
C2}\approx 4.5$ at%) in the phase diagram of ${\rm U}_{1-x}{\rm Th}_x{\rm Be}_{13}$; in between these concentrations a double-maximum structure in the temperature-dependent specific heat is observed. These sharp minima are strong indications of a sudden change in the superconducting ground state at the critical concentrations. This direct information about the gap nodes is important for theory to explain the complex phase diagram of ${\rm U}_{1-x}{\rm Th}_x{\rm Be}_{13}$.


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