Acoustoelectric effects in carbon nanotubes

We report observations of acoustoelectric effects in carbon nanotubes. We excite sound in &mgr;m long ropes of single walled carbon nanotubes suspended between two metallic contacts by applying radio-frequency electric field. The sound is detected by measuring either the dc resistance of the tubes in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. We show that, depending on the excitation power, the vibrations produce either electron heating or phase coherence breaking.     

Critical phenomena of thick branes in warped spacetimes

We have investigated the effects of a generic bulk first-order phase transition on thick Minkowski branes in warped geometries. As occurs in Euclidean space, when the system is brought near the phase transition an interface separating two ordered phases splits into two interfaces with a disordered phase in between. A remarkable and distinctive feature is that the critical temperature of the phase transition is lowered due to pure geometrical effects. We have studied a variety of critical exponents and the evolution of the transverse-traceless sector of the metric fluctuations.     

On the thermodynamics of the solidification of the Earth’s core

It has been shown that in the model of solidification in the inner solid Earth’s core, a phase transition at the interface between the solid core and outer liquid core is stepwise in the presence of a relatively small static shear modulus and shear acoustic vibrations in the inner core. The entropy and volume jumps, temperature hysteresis, and other thermodynamic derivatives certainly related to each other have been calculated taking into account the possible critical behavior of the system and using geophysical data.     

Description of Stabilization of Octupole Deformation in Alternating-Parity Bands of Heavy Nuclei

The angular-momentum dependences are analyzed for parity splitting and electric dipole transitions in alternating-parity bands of heavy nuclei. It is shown that these dependences can be treated universally by employing a single parameter taken to be a critical angular momentum that characterizes the phase transition from octupole vibrations to a stable octupole deformation. Analytic expressions for parity splitting and the electric dipole transitional moment are obtained on the basis of a simple model. The results are compared with experimental data for various barium, cerium, and neodymium isotopes.     

物理系统的稳定性与双稳现象(Ⅰ)

以力学系统（非线性振动），热力学系统（气液相变与铁磁相变）及光学系统中的几种双稳现象为实例，采用初等方法阐明系统的稳定性与双稳的基本原理。     

Analytical description of shape transition in nuclear alternating parity bands

The angular momentum dependencies of parity splitting and electric dipole transitions in the alternating parity bands of heavy nuclei have been analyzed. It is shown that these dependencies can be treated in a universal manner with a single critical angular momentum parameter, which characterizes phase transition from octupole vibrations to the stable octupole deformation. Using the simple but useful model of axially-symmetric reflectionasymmetric mode, the analytical expressions for parity splitting and electric dipole transitional moment have been obtained. The findings are in good agreement with the experimental data for various isotopes of Ra, Th, U, and Pu.     

Phase transition in liquid 3He in an aerogel at zero temperature

An expansion of the thermodynamic potential in powers of the order parameter of the superfluid phase transition is found for liquid ³He in an aerogel at T=0. The discontinuity in the compressibility (sound velocity), which is the analog of the discontinuity in the specific heat for second-order temperature phase transitions, is calculated. The magnitude of the critical quantum fluctuations (zero-point vibrations) of the order parameter is estimated. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 10, 655–660 (25 November 1997)     

Melting of metallic hydrogen at high pressures

The Lindemann equation was used to calculate the melting of metallic hydrogen. It is shown that, after transition from the molecular dielectric phase to the atomic metallic phase, hydrogen becomes a quantum liquid because of the atomic zero-point vibrations. The phase diagram of hydrogen is unique in that the molecular phase is the only solid phase of hydrogen.     

Lattice dynamics and Raman scattering spectrum of elpasolite Rb<Subscript>2</Subscript>KScF<Subscript>6</Subscript>: Comparative analysis

Raman scattering spectra of elpasolite Rb₂KScF₆ are studied in a wide temperature range including two phase transitions: from the cubic to the tetragonal phase and then to the monoclinic phase. The experimental Raman scattering spectrum is compared with the lattice vibration spectra of these phases calculated using an ab initio approach. A number of anomalies (caused by structural rearrangement during the phase transitions) are revealed and quantitatively analyzed in the ranges of both the intramolecular vibrations of the octahedron molecular ScF₆ ions and low-frequency intermolecular lattice vibrations. The interaction between low-frequency intramolecular vibrations and the intermolecular modes is found to be significant, and strong resonance interaction of the rotational soft modes (which are recovered below the phase transition points) with hard low-frequency vibrations of the rubidium ion sublattice is detected. These interactions are shown to substantially complicate the spectra.     

Calculations of Rms Velocities of Atomic Vibrations in the Mossbauer Experiment

To study mechanical and physical properties of solid bodies, it is important to know the behavior of rms velocities of atomic vibrations, especially accompanying changes in the ambient temperature. Therefore, we investigate binary iron alloys in the vicinities of phase transition temperatures using Mossbauer spectroscopy. The rms velocities of atomic vibrations demonstrate that 3d-3p direct chemical bonds for Si and 3d-4p direct chemical bonds for Ge are broken (formed) at the phase transition temperature; as a consequence, the velocities of atomic vibrations sharply increase.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 62–64, April, 2005.     

Double Poincaré sections of a quasi-periodically forced,chaotic attractor

A nonlinear mechanical oscillator is forced with two incommensurate harmonic signals and chaotic vibrations are experimentally observed. The fractal nature of this strange attractor in four-dimensional phase space is revealed by using a double Poincaré section. This section involves a narrow timing pulse on one harmonic driving signal and a wider phase window on the other forcing harmonic signal. The resulting two-dimensional map shows a Cantor set structure characteristic of strange attractors. The transition from quasi-periodic to chaotic vibrations is also observed.     

The cubic-to-monoclinic phase transition in (NH4)3ScF6 cryolite: A Raman scattering study

This paper reports on a Raman study of the cubic-to-monoclinic phase transition in (NH₄)₃ScF₆ cryolite. We observed sharp anomalies in the frequencies and half-widths of the Raman lines corresponding to internal vibrations of the ScF ₆ ³⁺ ions and to lattice vibrations; no soft lattice mode condensation was revealed. It is concluded that the phase transition studied is related primarily to the orientational ordering of these ions.     

Raman spectroscopic study of the phase transitions induced by hydrostatic pressure in a Rb2KScF6 crystal

The Raman spectra of Rb₂KScF₆ elpasolite crystals are studied in the pressure range up to 7 GPa. A phase transition is revealed at a pressure of approximately 1 GPa. Analysis of the changes in the spectral parameters shows that the phase transition is accompanied by a doubling of the volume of the primitive cell in the initial cubic phase. Judging from the character of the variations in the pressure dependences of the frequency of the observed vibrations, there can exist another transition to the phase with a lower symmetry at a pressure of approximately 2.1 GPa.     

Reflection of elastic waves in a crystal of Heusler alloy Ni<Subscript>2</Subscript>MnGa in the phase transition range

The reflection of longitudinal and transverse acoustic waves from the free surface of the ferromagnetic shape memory alloy Ni₂MnGa that is located in the ranges of the premartensite and martensite phase transformations is considered. The propagation directions and amplitudes of the waves reflected in the (001) plane of the crystal are determined. They acquire the character of substantially quasi-longitudinal and quasi-transverse vibrations rather than being pure modes. The angles of wave reflection and conversion are shown to be effectively controlled by temperature and a magnetic field due to the colossal acoustic anisotropy of the crystal over the wide range of its phase transitions. Beginning from a certain critical angle of incidence of a quasi-transverse wave, the quasi-longitudinal wave having appeared upon reflection becomes an accompanying surface vibration, and it can be emitted into the bulk of the crystal when the phase transition point is approached. Two angles of full conversion of an incident quasi-longitudinal wave into a quasi-transverse wave are established, and their temperature dependences are found. Trivisonno’s experimental data for the ultrasound velocity and absorption in an Ni₂MnGa crystal are used to numerically estimate these acoustic effects.     

Isostructural phase transitions in solids

A model of electrons interacting with lattice vibrations is shown to exhibit an isostructural phase transition as a function of applied force by relating the Hamiltonian to that of an Ising model in magnetic field.     

Hydrodynamical description of a hadron-quark first-order phase transition

Solutions of hydrodynamical equations are presented for the equation of state of the Van der Waals type allowing for a first-order phase transition. As an example we consider the hadron-quark phase transition in heavy-ion collisions. It is shown that fluctuations dissolve and grow as if the fluid is effectively very viscous. In the vicinity of the critical point even in spinodal region seeds are growing slowly due to viscosity, surface tension and critical slowing down. These non-equilibrium effects prevent enhancement of fluctuations in the near-critical region, which in thermodynamical approach is frequently considered as a signal of the critical endpoint in heavy-ion collisions.     

Manifestation of a ferroelectric-antiferroelectric phase transition in Li<Subscript>0.12</Subscript>Na<Subscript>0.88</Subscript>Ta<Subscript>0.4</Subscript>Nb<Subscript>0.6</Subscript>O<Subscript>3</Subscript> in its Raman scattering spectra

The ferroelectric-antiferroelectric phase transition in the Li_0.12Na_0.88Ta_0.4Nb_0.6O₃ ceramic solid solution has been studied by the Raman scattering technique. As the temperature approached the transition point from below, we observed an appreciable broadening of the lines associated with the vibrations of the cations occupying octahedral and cubooctahedral cavities of the structure and with the oxygen network vibrations (which implies a substantial increase in disorder on the cation sublattices), as well as a decrease to zero intensity of the 875-cm^?1 line corresponding to stretch vibrations of the bridging oxygen in the BO₆ octahedral anion in the vicinity of the transition. The temperature dependence of the 875-cm_?1 line intensity near the transition was used to study the behavior of the phase transition order parameter η. The behavior of η was found to disagree markedly with the Landau theory of second-order phase transitions. It is shown that discrepancies originate from the increase in disorder in the niobium and tantalum sublattices in the Li_0.12Na_0.88Ta _y Nb_1-y O₃ solid solution system with increasing y. The order of the transition is lowered.     

Quantum phase transitions and backbending in even-even N ∼ 90 nuclei

We extend the classical Landau theory for rotating nuclei and show that the backbending in ¹⁶²Yb, which comes about as a result of the two-quasiparticle alignment, is identified with the second-order phase transition. We found that the backbending in ¹⁵⁶Dy, caused by the instability of γ vibrations in the rotating frame, corresponds to the first-order phase transition. We suggest an empirical rule to determine the type of the phase transition in rotating nuclei undergoing backbending. The text was submitted by the authors in English.