Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and X-ray scattering measurements of LaSrCuO

中性子及びX線非弾性散乱実験による銅酸化物高温超伝導体LaSrCuOにおける電荷モード

Park, S. R.*; 福田 竜生  ; Hamann, A.*; Lamago, D*; Pintschovius, L.*; 藤田 全基*; 山田 和芳*; Reznik, D.*

Park, S. R.*; Fukuda, Tatsuo; Hamann, A.*; Lamago, D*; Pintschovius, L.*; Fujita, Masaki*; Yamada, Kazuyoshi*; Reznik, D.*

In superconducting copper oxides, some Cu-O bond-stretching phonons around 70 meV show anomalous giant softening and broadening of electronic origin, and electronic dispersions have large renormalization kinks near the same energy. These observations suggest that phonon broadening originates from quasiparticle excitations across the Fermi surface and the electronic dispersion kinks originate from coupling to anomalous phonons. We measured the phonon anomaly in underdoped ( = 0.05) and overdoped ( = 0.20 and 0.25) LaSrCuO by inelastic neutron and X-ray scattering with high resolution. Combining these and previously published data, we found that doping dependence of the magnitude of the giant phonon anomaly is very different from that of the ARPES kink, i.e., the two phenomena are not connected. We show that these results provide indirect evidence that the phonon anomaly originates from novel collective charge excitations as opposed to interactions with electron-hole pairs. Their amplitude follows the superconducting dome so these charge modes may be important for superconductivity.