Anomalous Dispersion of LO Phonons in La 1.85 Sr 0.15 CuO 4 at Low Temperatures

摘要: Inelastic neutron scattering measurements of La1.85Sr0.15CuO4 show that a discontinuity in dispersion develops the middle highest energy LO phonon branch at low temperatures. The result suggests dynamic short range unit cell doubling CuO2 plane along direction Cu-O bond, such as charge ordering on every other row oxygen. Such is related to, but different from, stripe observed for nonsuperconducting cuprates. question influence electron-lattice interaction normal and superconducting electronic properties high temperature superconductors remains open. Perhaps most intriguing experimental evidence large anomalous comes from inelastic experiments various materials [1‐ 6]. A signature these strong renormalization longitudinal frequency (,80 meV) oxygen bond-stretching phonons when holes are doped into insulating compounds. doping causes decrease zone boundary s0.5, 0, 0d half-breathing mode (15%‐ 20% softening compared to compound), indicating there coupling holes. This effect seems be ubiquitous, has been single-crystal La22xSrxCuO4 [1], La2CuO41y [3], YBa2Cu3O61y [4,5], even Ba12xKxBiO3 [6]. There also indications this bands density states Pb2Sr2sCa,YdCu3O8 [7] Li11xTi22xO4 [8]. It proven quite difficult interpret results terms electron-phonon metal, especially since measured modes are, part, unaffected (especially breathing quadrupole modes). Typical electronphonon coupling, Kohn anomalies, seem inconsistent with wave vector affected phonon. Fermi surface should have nesting 2kf which close q › 0.5d, not 0d, demonstrated by local-density approximation calculation [9] ARPES [10]. We chosen investigate phenomena more closely discovered nature mysterious sample studied consisted two single crystals were comounted an aluminum can filled He exchange gas. Both samples grown floating method obtained same batch. total size approximately 3.8 3 1.5 0.8 cm . Previ