S. Sugai

Controlled vaporization of the superconducting condensate in cuprate superconductors by femtosecond photoexcitation.

We use ultrashort intense laser pulses to study superconducting state vaporization dynamics in La2-xSrxCuO4 (x=0.1 and 0.15) on the femtosecond time scale. We find that the energy density required to vaporize the superconducting state is 2.0+/-0.8 and 2.6+/-1.0 K/Cu for x=0.1 and 0.15, respectively. This is significantly greater than the condensation energy density, indicating that the quasiparticles share a large amount of energy with the boson glue bath on this time scale. Considering in detail both spin and lattice energy relaxation pathways which take place on the relevant time scale of approximately 10(-12) s, the experiments appear to favor phonon-mediated pair-breaking mechanisms over spin-mediated pair breaking.

Role of electron-electron and electron-phonon interaction effects in the optical conductivity of VO_2

We have investigated the charge dynamics of

Phonon, two-magnon, and electronic Raman scattering of Fe1+yTe1−xSex

{mathrm{VO}}_{2}

Bose peak in the Raman spectra of densified SiO2 and GeO2 glass under high pressure

by optical reflectivity measurements. Optical conductivity clearly shows a metal-insulator transition. In the metallic phase, a broad Drude-like structure is observed. On the other hand, in the insulating phase, a broad peak structure around

Separation of the charge and spin densities in La1.885Sr0.115CuO4

1.3phantom{rule{0.3em}{0ex}}mathrm{eV}

Impurity effect on charge-ordered and ferromagnetic–metallic state in manganese perovskites: Comparison between Cr and Al doping

is observed. It is found that this broad structure observed in the insulating phase shows a temperature dependence. We attribute this to the electron-phonon interaction as in the photoemission spectra.

Isotope Effect on Superconducting Transition Temperature of NaxCoO2 .yH2O

We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4 (T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5 and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree with the calculated results. Two-magnon excitation has been observed around 2300 cm-1 for both compounds. Temperature dependence between the electronic Raman spectra below and above T_c has been observed and 2Delta and 2Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.

Optical reflectivity study on magnetoresistive manganese perovskites: impurity effect on the ferromagnetic–metallic and charge-ordered states

Densified vitreous SiO2 and GeO2 recovered from various high pressures were measured by ambient-pressure Raman scattering. The phonon energies start to shift at the same pressures as the increase of coordination numbers of Si and Ge at high pressures. The correlation length is estimated from the energy of Bose peak, which is characteristic of disordered structure. The shortening of the correlation length in densified glass is in accordance with the mixed coordinations.

Zn-substitution effect on the optical properties of PrBa2Cu4O8

Abstract The dynamical stripes with separated charge and spin densities were investigated at the “1/8 problem” carrier concentration in La1.885Sr0.115CuO4 by Raman scattering. The splitting of the two-magnon peak, which is interpreted by the formation of the stripe structure, was observed below ∼350xa0K. This onset temperature is much higher than those obtained by low-frequency probes. The crossover from the instantaneous picture of the dynamical stripes characterized by the split two-magnon spectrum at high energies to the averaged picture of fluctuating stripes characterized by the metallic spectrum is observed at about 1100xa0cm−1. This energy coincides with the strong two-phonon scattering peak energy, 1145xa0cm−1. It indicates that stripes are fluctuating in cooperation with this 570xa0cm−1 (70xa0meV) phonon.

Dynamical Structural Instabilities in La1.9Sr0.1CuO4 Under Intense Laser Photoexcitation

The role of impurities in melting of the charge-ordered (CO) state in half-doped manganese perovskites is discussed based on the systematic study of Cr and Al doping on the CO state as well as on the ferromagnetic–metallic (FM) state. The CO state in Nd0.5Sr0.5MnO3 is destroyed and the FM state is restored by 2% high-spin (S=3/2) Cr3+, whereas the CO state survives doping of spinless Al3+. On the other hand, the doping effects on the FM state in La1−xSrxMnO3 are almost identical between Cr and Al, except that Cr degrades Curie temperature less. The slight resistance of the CO state against Cr doping can be explained by the magnetic interaction between the Cr and the Mnu2009t2g spins.