**Физика Низких Температур: ***Том ***32**, Выпуск **4-5** (Апрель 2006), c. 641-650
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### Investigation of the superconducting energy gap in the compound LuNi_{2}B_{2}C by the method of point contact spectroscopy: two-gap approximation

**N.L. Bobrov, S.I. Beloborod`ko, L.V. Tyutrina, V.N. Chernobay, and I.K. Yanson**

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Lenin Ave., Kharkov 61103, Ukraine

E-mail: bobrov@ilt.kharkov.ua

**D.G. Naugle and K.D.D. Rathnayaka**

Department of Physics, Texas A&M University, College Station TX 77843-4242, USA

*Received October 26, 2005*

**Аннотация**

It is shown that the two-gap approximation is applicable for describing the *dV*/*dI*(*V*) spectra of LuNi_{2}B_{2}C–Ag point contacts in a wide interval of temperatures. The values and the temperature dependences of the large and the small gaps in the *ab* plane and in the *c* direction were estimated
using the generalized BTK model [A. Plecenik, M. Grajacar, S. Benacka P. Seidel, A. Pfuch, *Phys. Rev*. **B49**, 10016 (1994)]] and the equations of [S.I. Beloborodko, *Fiz. Nizk. Temp*. **29**, 868 (2003) [*Low Temp. Phys*. **29**, 650 (2003)]. In the BCS extrapolation the critical temperature of the small gap is 10 K in the *ab* plane and 14.5 K in the *c* direction. The absolute values of the gaps are D_{0}^{ab} = 2.16 meV and D_{0}^{c} = 1.94 meV. For the large gaps the critical temperature *T*_{c} coincides
with the bulk, *T*_{c}^{bulk} = 16.8 K, and their absolute values are very close, being about 3 meV in both orientations. In the *c* direction the contributions to the conductivity from the small and the large gaps remain practically identical up to 10–11 K. In the *ab* plane the contribution from the small gap is much smaller and decreases rapidly as a temperature rises.

**PACS:**

63.20.Kr - Phonon-electron and phonon-phonon interactions

72.10.Di - Scattering by phonons, magnons, and other nonlocalized excitations (see also 71.45.-d Collective effects in electronic structure of bulk materials)

73.40.Jn - Metal-to-metal contacts

**Ключевые слова: **point contacts, two-gap approximation.