Stochastic theory of ferroelectric domain structure formation dominated by quenched disorder

A self-consistent stochastic model of domain structure formation in a uniaxial ferroelectric, quenched from a high-temperature paraelectric phase to a low-temperature ferroelectric phase, is developed with an account of the applied electric field and the feedback effect via local depolarization fields. Both polarization and field components are considered as Gauss random variables. A system of integro-differential equations for correlation functions of all involved variables is derived and solved analytically and numerically. Phase diagram in terms of the average value and dispersion of polarization reveals different possible equilibrium states and available final single-domain and multi-domain states. The time-dependent evolution of the average polarization and dispersion discloses a bifurcation behavior and the temperature-dependent value of the electric field, deciding between the single-domain and multi-domain final states, which can be interpreted as the coercive field. Analytical and numerical results for the time-dependent correlation length and correlation functions exhibit plausible agreement with available experimental data.Comment: 33 pages, 10 figure

Resonances in Exotic 7^7He Nucleus within the No-Core Shell Model

We present ab initio calculations of resonances for $^7$He, a nucleus with no bound states, using the realistic nucleon-nucleon interaction Daejeon16. For this, we evaluate the $n{-}{^6\rm He}$ elastic scattering phase shifts obtained within an $S$-matrix analysis of no-core shell model results for states in the continuum. We predict new broad resonances likely related to fragmentary experimental evidence.Comment: 6 pages, 3 figure

Visible And Near-Infrared Responsivity Of Femtosecond Laser-Structured Photodiodes

We investigated the current-voltage characteristics and responsivity of photodiodes fabricated with silicon that was microstructured by use of femtosecond-laser pulses in a sulfur-containing atmosphere. The photodiodes that we fabricated have a broad spectral response ranging from the visible to the near infrared (400-1600 nm). The responsivity depends on substrate doping, microstructuring fluence, and annealing temperature. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, 2 orders of magnitude higher than for standard silicon photodiodes. For wavelengths below the bandgap we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm

SS-HORSE Extension of the No-Core Shell Model: Application to Resonances in 7He^7{\mathrm He}

Theoretical ab initio studies of resonances in the unbound ${\rm^{7}He}$ nucleus are presented. We perform no-core shell model calculations with $NN$ interactions Daejeon16 and JISP16 and utilize the SS-HORSE method to calculate the $S$ matrix for two-body channels $n{-}{\rm^{6}He}$ and $n{-}{\rm^{6}He^{*}}$ with ${\rm^{6}He}$ respectively in the ground and excited $2^{+}$ states as well as for the four-body democratic decay channel ${{\rm^{4}He}+n+n+n}$. The resonant energies and widths areobtained by numerical location of the $S$-matrix poles. We describe all experimentally known ${\rm^{7}He}$ resonances and suggest an interpretation of an observed wide resonance of unknown spin-parity.Comment: 10 pages, 2 figure

Femtosecond Laser-Induced Formation Of Submicrometer Spikes On Silicon In Water

We fabricate submicrometer silicon spikes by irradiating a siliconsurface that is submerged in water with 400 nm, 100 fs laser pulses. These spikes are less than a micrometer tall and about 200 nm wide—one to two orders of magnitude smaller than the microspikes formed by laser irradiation of silicon in gases or vacuum. Scanning electron micrographs of the surface show that the formation of the spikes involves a combination of capillary waves on the molten siliconsurface and laser-induced etching of silicon. Chemical analysis and scanning electron microscopy of the spikes show that they are composed of silicon with a 20-nm-thick surface oxide layer

A Quantum Mechanical Model of the Reissner-Nordstrom Black Hole

We consider a Hamiltonian quantum theory of spherically symmetric, asymptotically flat electrovacuum spacetimes. The physical phase space of such spacetimes is spanned by the mass and the charge parameters $M$ and $Q$ of the Reissner-Nordstr\"{o}m black hole, together with the corresponding canonical momenta. In this four-dimensional phase space, we perform a canonical transformation such that the resulting configuration variables describe the dynamical properties of Reissner-Nordstr\"{o}m black holes in a natural manner. The classical Hamiltonian written in terms of these variables and their conjugate momenta is replaced by the corresponding self-adjoint Hamiltonian operator, and an eigenvalue equation for the ADM mass of the hole, from the point of view of a distant observer at rest, is obtained. Our eigenvalue equation implies that the ADM mass and the electric charge spectra of the hole are discrete, and the mass spectrum is bounded below. Moreover, the spectrum of the quantity $M^2-Q^2$ is strictly positive when an appropriate self-adjoint extension is chosen. The WKB analysis yields the result that the large eigenvalues of the quantity $\sqrt{M^2-Q^2}$ are of the form $\sqrt{2n}$, where $n$ is an integer. It turns out that this result is closely related to Bekenstein's proposal on the discrete horizon area spectrum of black holes.Comment: 37 pages, Plain TeX, no figure

Ultrafast Electronic Disordering During Femtosecond Laser Melting of GaAs

We have observed an ultrarapid electronic phase transformation to a centrosymmetric electronic state during laser excitation of GaAs with intense femtosecond pulses. Reflection second-harmonic intensity from the upper 90 atomic layers vanishes within 100 fs; reflectivity rises within 0.5 ps to a steady value characteristic of a metallic molten phase, long before phonon emission can heat the lattice to the melting temperature

Iordanskii Force and the Gravitational Aharonov-Bohm effect for a Moving Vortex

I discuss the scattering of phonons by a vortex moving with respect to a superfluid condensate. This allows us to test the compatibility of the scattering-theory derivation of the Iordanskii force with the galilean invariance of the underlying fluid dynamics. In order to obtain the correct result we must retain $O(v_s^2)$ terms in the sound-wave equation, and this reinforces the interpretation, due to Volovik, of the Iordanskii force as an analogue of the gravitational Bohm-Aharonov effect.Comment: 20 pages, LaTe