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Nanoscale amorphous marks have been produced in crystalline Ge2Sb2Te5 films using an atomic-force microscope (AFM) and a scanning-tunneling microscope (STM) through electrical phase changes. Voltage pulses with duration of 5–100 ns applied by metal probes of the AFM and the STM can produce, respectively, high-resistance regions and deformations, the smallest sizes being ∼10 and ∼100 nm in diameter. Raman-scattering spectra demonstrate that these marks are amorphous. The AFM mark can be erased by applying longer pulses. Formation processes of the marks are considered from electrothermal and thermodynamic aspects. [ABSTRACT FROM AUTHOR]

The temperature and the DC biasing field dependences of dielectric constants along the [011]- and [111]-directions of the cubic coordinate in 91%Pb(Zn1/3Nb2/3)O3–9%PbTiO3(PZN-9%PT) have been investigated. The temperature-field phase diagrams have been constructed in the field range below 15 kV/cm. It has been found that there exists the orthorhombic phase below the tetragonal phase as a ground state of the system in PZN-9%PT. The tetragonal phase disappears in the external field above about 11 kV/cm along the [011]- and [111]-directions. [ABSTRACT FROM AUTHOR]

We examined the phase coherence and power of auditory steady state responses (ASSRs) in magnetoencephalogram to an ongoing sinusoially amplitude modulated tone presented to the subject's one ear while bursts of white noise of various intensities were presented to the opposite ear. We also examined the real and imaginary parts of coherence between the ASSRs of the right and left auditory temporal regions. Stochastic resonance (SR) was seen in the phase coherence and power of the ASSR from the contralateral temporal area and in the real part of the right-left coherence. The results showed that the SR phenomenon occurred not in the periphery but in the central nervous system and suggested that it was not probably due to the interaction between the left and right auditory cortex. [ABSTRACT FROM PUBLISHER]

The kinetics of austenite-to-ferrite diffusional transformation in a medium carbon Fe-C-Mn steel was calculated based on classical nucleation and growth theory coupled with CALPHAD multicomponent thermodynamics. The description of the growth rate of proeutectoid ferrite includes a time dependence due to the carbon enrichment in the remaining austenite. The experimentally slower kinetics, especially a stagnating behavior at the later stage, was successfully reproduced when a transition from initial paraequilibrium (PE) to local equilibrium negligible partition (LENP) conditions at the austenite:ferrite ( γ/ α) interface was assumed. This transition is allowed when the velocity of the moving γ/ α interface is slow enough to be compared with Mn diffusivity, which leads to build up of a Mn spike in the interface. This assumption is consistent with a series of scanning transmission electron microscopy (STEM) analyses for Mn and C, which indicates that initial unpartitioned Mn ferrite growth is replaced by partitioned growth. [ABSTRACT FROM AUTHOR]

This paper presents temperature changes of the EPR lines in [P(CH 3 ) 4 ] 2 MnBr 4 in the vicinity of the ferroelastic phase transition temperature T c =376.5K. Significant changes in the EPR spectrum have been observed in the temperature range of 370-380K. It is suggested that the changes observed above T c are caused by rotations of the MnBr 4 groups loosely situated in the crystal lattice, whereas changes below T c are a direct result of rebuilding of the ferroelastic domain structure. [ABSTRACT FROM AUTHOR]

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]

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature 7* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at 7* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected tight polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (Tc), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders. [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]

Abstract: Laser-driven solid–solid phase transition is a new kind of manipulation of matter by light which offers fascinating possibilities for controlling macroscopic switching of materials at different time scales from hours down to femtosecond. Slow dynamics phenomena are illustrated by a photo-induced spin transition. A sub-nanosecond laser-induced ferroelectric ordering and the opposite transformation have been observed in a molecular charge-transfer material with a 100ps time resolution. New, exciting scientific challenges at 100fs such as the excitation of coherent phonons and non-thermal melting are also presented. [Copyright &y& Elsevier]

Phase transformation and defect structures in thin-film TaSi2 produced by co-sputtering have been investigated as a function of annealing temperature by transmission electron microscopy. Crystallization of amorphous TaSi2 thin films occurs at 400 °C without forming any metastable phases. Most of C40 TaSi2 crystallites contain planar faults parallel to (0001) basal planes. Convergent-beam electron diffraction (CBED) indicates that these planar faults are not simple stacking faults but are twin boundaries bounded by two adjacent enantiomorphically-related twin domains; i.e., domains belonging to the space groups P6222 (right-handed) and P6422 (left-handed) having the identical crystal orientation arrange alternatively separated by twin boundaries parallel to (0001). The formation of these enantiomorphically-related domains in TaSi2 thin films with the hexagonal C40 structures is discussed in comparison with the formation of twin-related domains in MoSi2 (the tetragonal C11b structure) and TiSi2 (the orthorhombic C54 structure) thin films. A new CBED method is proposed for identification of enantiomorphically-related crystals, in which asymmetry in the intensity of Bijvoet pairs of FOLZ disks in an experimental symmetrical zone-axis CBED pattern is compared with that in a computer simulated CBED pattern. [Copyright &y& Elsevier]

EPR measurements of a new two-component organic conductor, (CHTM-TTP)2TCNQ, were performed. This salt shows two drastic successive phase transitions at low temperatures. The electronic phases of the title salt are discussed by microscopic point of view. The contributions of the two-spin species of the magnetic properties are separated. Possibility of cooperative phenomena in the two-spin system with itinerant and localised moments is discussed. [Copyright &y& Elsevier]

Abstract: The introduction of a methyl group into ethylenedioxytetrathiafulvalene (EDO-TTF) greatly modified the molecular character as a component for the conducting complexes. While the pristine EDO-TTF almost exclusively formed head-to-tail type overlapping with the neighboring donor molecules in the complexes, the methyl substituted compound, MeEDO-TTF, showed both the head-to-head and head-to-tail overlapping patterns. In the former case, the donor molecules interacted with each other in a two-dimensional fashion to provide stable metals along with the charge-ordered complex which exhibited semiconductor-semiconductor first-order transition just above room temperature. The overlapping pattern of MeEDO-TTF directly corresponded to the electronic structure of the complex. In the case of head-to-tail packing patterns, the charge carriers were delocalized only in a quasi-one-dimensional column or in a multimer composed of the donor molecules. The comparison of the intermolecular overlap integrals calculated in the extended Hückel level suggested that at least the magnitude of ca. 10×10−3 is needed for the infinite chain or network of the conducting component molecules to exhibit metallic nature. [Copyright &y& Elsevier]