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The unbound excited states of the neutron drip-line isotope 240 have been investigated via the 240(p, p')230 + n reaction in inverse kinematics at a beam energy of 62 MeV/nucleon. The decay energy spectrum of 240* was reconstructed from the momenta of 230 and the neutron. The spin parity of the first excited state, observed at Ex = 4.65 ± 0.14 MeV, was determined to be Jπ = 2+ from the angular distribution of the cross section. Higher-lying states were also observed. The quadrupole transition parameter ß2 of the 2+1 state was deduced, for the first time, to be 0.15 ± 0.04. The relatively high excitation energy and small ß2 value are indicative of the N = 16 shell closure in 240. [ABSTRACT FROM AUTHOR]

The ferroelectric soft mode in a SrTiO3 thin film was impulsively driven to a large amplitude using intense picosecond terahertz pulses. As the terahertz electric field increased, the soft-mode absorption peak exhibited blueshifting and spectral narrowing. A classical anharmonic oscillator model suggests that the induced displacement is comparable to that of the ferroelectric phase transition. The spectral narrowing indicates that the displacement exceeds that induced by any inhomogeneities in the film, demonstrating that the method can be used to explore intrinsic quartic anharmonicity. [ABSTRACT FROM AUTHOR]

Coherent phonons were observed in perovskite dielectrics LaAlO3 and KMnF3 using ultrafast polarization spectroscopy. Ultrafast dynamics and softening of phonon modes, which contribute to structural phase transitions, were studied. The temperature dependences of the phonon frequency and relaxation rate were obtained from the observed damped oscillation of coherent phonons. In LaAlO3, typical softening of the phonon frequency was observed toward the phase-transition temperature Tc (~750 K). The observed relaxation for the soft-mode phonons is explained well by a population decay due to anharmonic phonon-phonon coupling. In KMnF3, two structural phase-transition temperatures, Tc (= 187 K) and Tcm (~81 K), were found through birefringence measurement. At temperatures below Tcm, three modes of coherent phonons were observed and the phonon modes were found to undergo softening toward Tcm. The observed dependences of the coherent phonon signal on the pumping polarization and the temperature suggest an orthorhombic structure, instead of a monoclinic structure, at temperatures below Tcm. The sudden decrease in the phonon frequency at Tcm indicates the first-order character of the phase transition at Tcm. Notable changes in birefringence and phonon frequency were observed at around 90 K, but no distinct anomaly is found, which suggests that the structure undergoes continuous change. Above 100 K, the Eg mode in the tetragonal symmetry is found to undergo softening toward Tc1. A coherent phonon signal of relaxation type appears at around Tc1 and survives even at near room temperature, which suggests the existence of structural disorder even in the cubic symmetry above Tc1. [ABSTRACT FROM AUTHOR]