Semiconductor-metal phase transition under a strain induced by a spherical indenter

A semiconductor-metal phase transition is produced in samarium monosulfide under the action of the pressure of a spherical indenter in the region of quasiuniaxial compression of the sample material under the indenter and investigated. It is shown that the phase transition occurs when the decrease in the volume of SmS under the action of the applied field reaches a critical value of 4–5% at T=300 K. The temperature dependence of the critical volume decrease is recorded in the range 280–440 K. Zh. Tekh. Fiz. 68, 53–57 (March 1998)     

Effect of low-temperature compression on the parameters of the phase transition at 250–260 K in C60 single crystals

A thermodynamic transition in C₆₀ crystals, subjected beforehand to uniaxial compression at various temperatures and to thermal action, was investigated by differential scanning calorimetry. It was established that compression of the crystal at temperatures below the phase transition has a much smaller effect on the transition itself than a similar or even much weaker action at a temperature above the phase transition. A “quenching” effect was also found. This effect is probably due to the orientational order of individual fullerene molecules. A correlation was established between the magnitude of the effect and the preliminary deformation of C₆₀ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 550–553 (March 1999)     

Enhancement of the quantum characteristics of light from an inversionless three-level Λ-laser in cascade schemes

We show that when a three-level laser is excited by Poisson light the lasing remains sub-Poisson, as asserted by H. Ritsch, M. A. M. Marte, and P. Zoller [Europhys. Lett. 19, 7 (1992)], only if there is no reciprocal action on the exciting laser (weak coupling). In cascade schemes in which each three-level Λ-laser excites each succeeding Λ-laser with its light, any desired degree of shot-noise suppression can be achieved. Zh. éksp. Teor. Fiz. 114, 1971–1992 (December 1998)     

Two-photon Absorption Properties of 9,10-Disubstituted 2,6-Bis(p-dihexylaminostyryl)Anthracene Derivatives. Effect of 9,10-Substituents

A series of 2,6-bis(p-dihexylaminostyryl)anthracence derivatives having phenyl, styryl, and phenylethynyl groups at 9,10-positions (1−4) have been synthesized and their two-photon cross-sections were determined. Overall, the wavelengths of the longest wavelength absorption band and emission spectra increase with increase in the conjugation length and the electron withdrawing ability of the 9,10-substituents. All compounds show two-photon cross sections in the range of 740−3940 GM at 780−960 nm, which increase significantly by the donor and acceptor groups at 9,10-positions. In addition, Ph and phenylethynyl groups are better when compared to the styryl group at the 9,10-positions in terms of the two-photon action cross section. From a practical perspective, 1a, 2a–c, and 4b showed significant two-photon action cross-section and are most useful for applications that use two-photon excited fluorescence.     

A correction to the Hamiltonian of the QCD string with quarks due to the rigidity term

The correction to the Hamiltonian of a quark-antiquark system due to the rigidity term in the action of the gluodynamics string is found using the action obtained by D. V. Antonov et al., Mod. Phys. Lett. A 11, 1905 (1996) with the Hamiltonian obtained by A. Yu. Dubin et al., Phys. At. Nucl. 56, 1745 (1993); Phys. Lett. B 323, 41 (1994) and E. L. Gubankova and A. Yu. Dubin, Phys. Lett. B 334, 180 (1994); preprint ITEP 62-94. This correction contains additional contributions to the orbital momentum of the system and several higher derivative operators. The resulting Hamiltonian is used to evaluate the rigid-string-induced term in the Hamiltonian of the relativistic quark model for the case of large masses of the quark and antiquark. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 673–678 (10 May 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

The effective action of W 3-gravity

A new method for integrating anomalous Ward identities and finding the effective action is proposed. Two-dimensional supergravity and W ₃-gravity are used as examples to demonstrate its potential. An operator is introduced that associates each physical quantity with a Ward identity, i.e., a quantity that is transformed without anomalous terms and can be nullified in a consistent manner. A covariant form of the action for matter fields interacting with a gravitational and W ₃-gravitational background is proposed. Zh. éksp. Teor. Fiz. 111, 1537–1553 (May 1997)     

Asymptotic form of the nonsteady motion of a charged-particle gas

A solution is obtained for the problem of expansion of a gas of an inhomogeneous cloud of rotating particles under the action of its space charge. It is shown that with time the process of expansion of the cloud becomes self-similar. Zh. Tekh. Fiz. 69, 84–87 (June 1999)     

Amplification of the generation of the sum-frequency signal in multilayer periodic structures at the edges of the Bragg band gap

A new property of a one-dimensional periodic structure — amplification of the sum-frequency signal arising under the simultaneous action of two laser pulses on this structure with radiation frequencies corresponding to the edges of the fixed Bragg band gap — is experimentally observed and described. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 718–721 (10 December 1999)     

Time reversal in two-frequency NQR methods

A theoretical treatment is carried out for the time reversal of nuclear quadrupole resonance signals for nuclear spin 5/2 and two-frequency action. Fiz. Tverd. Tela (St. Petersburg) 39, 1358–1359 (August 1997)     

Symmetry and Topology in Quantum Logic

A test space is a collection of non-empty sets, usually construed as the catalogue of (discrete) outcome sets associated with a family of experiments. Subject to a simple combinatorial condition called algebraicity, a test space gives rise to a “quantum logic”—that is, an orthoalgebra. Conversely, all orthoalgebras arise naturally from algebraic test spaces. In non-relativistic quantum mechanics, the relevant test space is the set ℱ F(H) of frames (unordered orthonormal bases) of a Hilbert space H. The corresponding logic is the usual one, i.e., the projection lattice L(H) of H. The test space ℱ F(H) has a strong symmetry property with respect to the unitary group of H, namely, that any bijection between two frames lifts to a unitary operator. In this paper, we consider test spaces enjoying the same symmetry property relative to an action by a compact topological group. We show that such a test space, if algebraic, gives rise to a compact, atomistic topological orthoalgebra. We also present a construction that generates such a test space from purely group-theoretic data, and obtain a simple criterion for this test space to be algebraic. PACS: 02.10.Ab; 02.20.Bb; 03.65.Ta.     

Formation of nanometer ordered defect-deformational structures induced by energy fluxes in solids

A defect-deformational theory is constructed for the hierarchic formation of nanometer clusters in periodic structures of point defects under the action of an energy flux. The theoretical results obtained are compared with experimental results on the formation of nanometer pore lattices in metals under the action of particle beams and the laser-induced structural modification of semiconductor surfaces. Good agreement between the theory and experiment is obtained. Fiz. Tverd. Tela (St. Petersburg) 39, 2029–2035 (October 1997)     

Coleman–de Luccia Instanton of the Second Order in a Brane World

The second order Coleman–de Luccia instanton and its action in the Randall–Sundrum type II model are investigated and the comparison with the results in Einstein’s general relativity is done in the present paper. PACS Numbers: 98.80.Cq.     

Nature of the microwave response of a YBaCuO Josephson junction on a bicrystalline substrate

The response of YBaCuO Josephson junctions on a bicrystalline substrate to the action of microwave radiation is found to contain, besides the Josephson response, a contribution associated with the tunneling of quasiparticles through channels formed by localized states in the region of the Josephson junction. It is shown that this contribution is associated with an increase in the conduction through these channels under the action of the radiation on the junction. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 416–420 (25 September 1996)     

Four-photon polarization spectroscopy of water in a millimeter-wave radiation field

Resonance (frequency 1.4 cm⁽⁻¹) changes induced in the four-photon optical spectrum of water by a millimeter-wave electromagnetic field are observed experimentally. Comparison with the spectrum of ice in the range 0‒2 cm⁽¹ shows that the action of such a field is of a structure-forming character. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 266–268 (25 August 1998)     

Application of symmetry operations for construction of quasiperiodic structures in a plane

A method is proposed for constructing a quasiperiodic structure of symmetry elements — regular pentagons and five-pointed stars — in a plane. The growth of the structure is determined by the action of the symmetry operations, whose effect is not completely identical to that of similar operations in classical crystallography. The tiling (“flower of pentagons”), consisting of a central pentagon and five side pentagons joined along the edges, is studied. The growth of this tiling is accompanied by the appearance of a “flower of stars” and by the formation of isolated pores in the form of rhombi. The relation between the obtained structure and Penrose tiling is examined, and it is noted that some vertices of the Penrose tiling coincide with all vertices of the polygons of the packing obtained. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 635–640 (25 April 1997)     

Laser acceleration of electrons in a thin metal film

A mechanism acceleration of electrons to relativistic velocities in a thin metal film irradiated with ultrashort (τ _L ≤1 ps) high-power (I>¹⁶ W/cm²) laser pulses is proposed. The acceleration is due to a resonance action of the nonuniform field on a portion of the electrons, viz., those which oscillate in the direction transverse to the film with a frequency close to the frequency of the field. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 8–12 (10 July 1997)     

From effective BCS action to vortex dynamics

The topological term in the effective action for the electrically neutral BCS system is discussed. It is applied for the calculation of the transverse force acting on a vortex in the limit of a smooth vortex core and vanishing interlevel distance in the vortex core. The controversy between the topological terms in the articles by I. J. R. Aitchison et al., Phys. Rev. B 51, 6531 (1995) and A. van Otterlo et al., cond-mat/9703124 is resolved. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 641–646 (25 April 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Hamiltonian dynamics of vortex lines in hydrodynamic-type systems

It is shown that the degeneracy of the noncanonical Poisson bracket operating on the space of solenoidal vector fields that arises due to the freezing-in of the curl of the velocity [E. A. Kuznetsov and A. V. Mikhailov, Phys. Lett. A 77, 37 (1980)] is lifted when the vorticity Ω is represented in terms of vortex lines. This representation makes it possible to integrate the equation of motion of the vorticity for a system with the Hamiltonian H=∫∣Ω∣d r. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 1015–1020 (25 June 1998)     

Conformal blocks and correlators in a bosonized WZNW model

The solutions of the Knizhnik-Zamolodchikov equations as conformal blocks of the Wess-Zumino-Novikov-Witten SU(2) model on a sphere are examined. An action that permits finding the N-point correlators of the model, which are constructed in a natural manner from the conformal blocks, is proposed. This is an action of three free fields perturbed by a special marginal operator. The construction described should extend to the case of other groups and surfaces of higher genus. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 648–653 (25 November 1999)     

The effect of short-range repulsion of electronic shells on the energy spectrum of ions desorbed under the influence of electronic transitions: A relaxation model

A relaxation model is used to investigate the effect of repulsion of electron shells, which is modeled by introducing an initial velocity of the desorbed particles, on the energy distributions of ions desorbed under the action of electronic transitions. The role of reneutralizing processes is considered. Fiz. Tverd. Tela (St. Petersburg) 39, 1679–1682 (September 1997)