Pinning frequencies of the collective modes in alpha-uranium

• Published in: Physical review letters Vol. 96; no. 7; p. 076401
• Main 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
• Format: Journal Article
• Language: English
• Published: United States 24.02.2006
• ISSN: 0031-9007
• DOI: 10.1103/PhysRevLett.96.076401

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.