Low-energy phonon excitations in superconducting RNiB2C (R = Lu, Y)

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Bullock, M.
Zarestky, J.
Stassis, C.
Honda, Z
Shirane, G.
Shapiro, S. M.
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American Physical Society
Goldman, Alan
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Canfield, Paul
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Inelastic neutron-scattering techniques have been used to study the low-energy phonon excitations in superconducting RNi2B2C (R = Lu, Y) to further characterize the anomalous features observed by Kawano et al. [Phys. Rev. Lett. 77, 4628 (1996)] for R = Y and Stassis et al. [Phys. Rev. B 55, R8678 (1997)] for R = Lu, when these systems enter the superconducting ground state. We find that above T, the frequencies of the Delta(4)[xi 00] lowest-lying acoustic and optic phonon modes decrease with decreasing temperature, for xi close to the nesting vector xi(m). In addition there is a shift of intensity from the upper to the lower mode, an effect characteristic of mode coupling. The observed intensity transfer between these modes above T-c can be described satisfactorily in both compounds by a coupled-mode model. Below T-c the observed spectrum changes dramatically: it consists of a sharp peak at approximately 4 meV with a broad weak shoulder at higher energies. The experimental results unambiguously show that this dramatic change is due to the onset of superconductivity in these compounds. In this temperature region, the results are in qualitative agreement with recent theoretical calculations.
This article is published as Bullock, M., J. Zarestky, C. Stassis, A. Goldman, P. Canfield, Zentaro Honda, Gen Shirane, and S. M. Shapiro. "Low-energy phonon excitations in superconducting R Ni 2 B 2 C (R= Lu, Y)." Physical Review B 57, no. 13 (1998): 7916. DOI: 10.1103/PhysRevB.57.7916. Copyright 1998 American Physical Society. Posted with permission.