Pinning frequencies of the collective modes in alpha-uranium |
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Authors: | Mihaila B Opeil C P Drymiotis F R Smith J L Cooley J C Manley M E Migliori A Mielke C Lookman T Saxena A Bishop A R Blagoev K B Thoma D J Lashley J C Lang B E Boerio-Goates J Woodfield B F Schmiedeshoff G M |
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Institution: | Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. |
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Abstract: | Uranium is the only known element that features a charge-density wave (CDW) and superconductivity. We report a comparison of the specific heat of single-crystal and polycrystalline alpha-uranium. In the single crystal we find excess contributions to the heat capacity at 41 K, 38 K, and 23 K, with a Debye temperature ThetaD = 265 K. In the polycrystalline sample the heat capacity curve is thermally broadened (ThetaD = 184 K), but no excess heat capacity was observed. The excess heat capacity Cphi (taken as the difference between the single-crystal and polycrystal heat capacities) is well described in terms of collective-mode excitations above their respective pinning frequencies. This attribution is represented by a modified Debye spectrum with two cutoff frequencies, a pinning frequency V0 for the pinned CDW (due to grain boundaries in the polycrystal), and a normal Debye acoustic frequency occurring in the single crystal. |
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