Effect of different impurity atoms on 1/<Emphasis Type="Italic">f</Emphasis><Superscript>α</Superscript> tunneling current noise characteristics on InAs(110) surface

The results of UHV STM investigations of tunneling current noise spectra in the vicinity of individual impurity atoms on the InAs(110) surface are reported. It was found that the power law exponent of 1/f ^α noise depends on the presence of an impurity atom in the tunneling junction area. This is consistent with the proposed theoretical model considering tunneling current through a two-state impurity complex model system taking into account many-particle interaction. The text was submitted by the authors in English.     

Overcoming of the gamow tunneling insufficiencies by maximizing the damp-matching resonant tunneling

The resonant quantum tunneling current through the barrier between two wells may be maximized when the damp (absorption) in one well matches the barrier parameters. The maximum resonant tunneling current is much greater than the conventional expectation by a factor ofθ (1/θ ² is the Gamow tunneling factor). It is shown that with all the established quantum mechanics, very much higher reaction probabilities between nuclei in contrary to the Gamow theory can be explained in agreement with experiments. Particularly, the resonance will select the sub-barrier fusion with a suitable fusion rate which matches the barrier parameters. This selective resonant tunneling model is able to explain both the hot fusion data (e.g. the width of resonance in¹¹B(p,α)2α reaction) and the cold fusion data (e.g. “excess heat” without any commensurate neutron andγ radiation). This work is supported by the State Commission of Science and Technology, the Natural Science Foundation of China (Contract #19645005), and the Fundamental Research Fund of Tsinghua University.     

Coexistence of superconductivity and ferromagnetism in ferromagnet/superconductor proximity structures

The Nambu spinor Green's function approach is applied to calculating the density of states (DOS) and superconducting order parameter in normal-metal/insulator/ferromagnet/superconductor (NM/I/FM/SC) junctions. It is found that the s-wave superconductivity and ferromagnetism can coexist near the FM/SC interface, which is induced by proximity effect. On the SC side, the spin-dependent DOS appears both within and without the energy gap. On the FM side, the superconducting order parameter displays a damped oscillation and the DOS exhibits some superconducting behavior. The calculated result for the DOS in FM for “0 state” and “π state” can reproduce recent tunneling spectra in Al/Al₂O₃/PdNi/Nb tunnel junctions. Received 1st July 2002 Published online 19 November 2002     

Time-dependent analysis of tunneling effect in the formation of ultracold molecules via photoassociation of laser-cooled atoms

The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs₂ and attributed to the 0_g ^-(6s, 6p _3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling is an efficient mechanism for transferring the population to the inner well (R < 15a ₀), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a ³Σ⁺ _u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances, and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels a ³Σ⁺ _u(6s, 6s)↦0_g ^-(6s, 6p _3/2) photoassociation at detunings around 2.9 cm^-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation), or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”). In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control the population of the inner well and hence the formation of ultracold molecules in low vibrational levels. Received 19 April 2002 Published online 1st October 2002 RID="a" ID="a"e-mail: francoise.masnou@lac.u-psud.fr     

Vibronic charge-transfer excitons: Possible nature of the unusual properties of virtual perovskitelike ferroelectrics

A vibronic charge-transfer exciton, which is a pair of Jahn-Teller electron and hole polarons, is considered as a possible cause of the appearance of the Müller phase in the virtual ferroelectric SrTiO₃ and the “green” luminescence in the virtual ferroelectric KTaO₃. The two “green” luminescence bands can be associated with emission from two states of a typical intrinsic defect, viz., a vibronic charge-transfer exciton trapped by an oxygen vacancy and an isolated vibronic charge-transfer exciton. In both cases the “green” luminescence corresponds to the recombination of the electron and the hole in the vibronic charge-transfer exciton, which is accompanied by the emission of light. The properties of the Müller phase can be attributed to mixing of the normal state and states of the vibronic charge-transfer exciton phase when they interact with polarization in the soft SrTiO₃ matrix under the conditions of a pseudo-Jahn-Teller (pseudo-JT) effect on a soft TO mode of the displacement type. In this case the vibronic charge-transfer exciton phase forming the low-lying excited states has “order-disorder” degrees of freedom and exists at temperatures significantly below the point of the order-disorder ferroelectric transition in SrTiO₃ at T=T Q≈37 K. The corresponding lowering of the symmetry of the vibronic charge-transfer exciton phase to polar symmetry leads to the possibility of a long-period incommensurate phase in such excited states, which arises as a result of the appearance of a Lifshitz invariant. The valence-band state making the largest contribution of the pseudo-JT effect corresponds to a wave vector equal to the critical wave vector of the incommensurate vibronic charge-transfer exciton phase. When the temperature is lowered, the pseudo-JT distortion increases down to ∼T _Q and subsequently saturates in accordance with the saturation of the dielectric constant. The basic assumption in the model is that the temperature T=T _Q corresponds to the narrow temperature range for the transition from an intermediate to a strong pseudo-JT effect under the conditions for the realization of polarization tunneling states. The appearance of a significant admixture of states of the modulated ferroelectric vibronic charge-transfer exciton phase to the ground state under the conditions for the realization of polarization tunneling states at low temperatures provides an explanation for the principal properties of the Müller phase. Fiz. Tverd. Tela (St. Petersburg) 40, 907–909 (May 1998)     

Interactions in Noncommutative Dynamics

A mathematical notion of interaction is introduced for noncommutative dynamical systems, i.e., for one parameter groups of *-automorphisms of endowed with a certain causal structure. With any interaction there is a well-defined “state of the past” and a well-defined “state of the future”. We describe the construction of many interactions involving cocycle perturbations of the CAR/CCR flows and show that they are nontrivial. The proof of nontriviality is based on a new inequality, relating the eigenvalue lists of the “past” and “future” states to the norm of a linear functional on a certain C ^*-algebra. To the memory of Irving Segal Received: 12 October 1999 / Accepted: 21 October 1999     

A Fast Algorithm for Wave Propagation from a Plane or a Cylindrical Surface

The newly developed Taylor-Interpolation-FFT (TI-FFT) algorithm dramatically increases the computational speeds for millimeter wave propagation from a planar (cylindrical) surface onto a “quasi-planar” (“quasi-cylindrical”) surface. Two different scenarios are considered in this article: the planar TI-FFT is for the computation of the wave propagation from a plane onto a “quasi-planar” surface and the cylindrical TI-FFT is for the computation of wave propagation from a cylindrical surface onto a “quasi-cylindrical” surface. Due to the use of the FFT, the TI-FFT algorithm has a computational complexity of O(N ² log₂  N ²) for an N × N computational grid, instead of N ⁴ for the direct integration method. The TI-FFT algorithm has a low sampling rate according to the Nyquist sampling theorem. The algorithm has accuracy down to −80 dB and it works particularly well for narrow-band fields and “quasi-planar” (“quasi-cylindrical”) surfaces.     

Search for signatures of phase transition and critical point in heavy-ion collisions

The general concepts in the critical phenomena related with the notions of “scaling” and “universality” are considered. Behavior of various systems near a phase transition is displayed. Search for clear signatures of the phase transition of the nuclear matter and location of the critical point in heavy-ion collisions (HIC) is discussed. The experimental data on inclusive spectra measured in HIC at RHIC and SPS over a wide range of energies s _{N N} ^1/2 = 9–200 GeV are analyzed in the framework of z-scaling. A microscopic scenario of the constituent interactions is presented. Dependence of the energy loss on the momentum of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions described in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei by fractal dimensions. Preferable kinematical regions to search for signatures of the phase transition of the nuclear matter produced in HIC are discussed. Discontinuity of the “specific heat” is assumed to be a signature of the phase transition and the critical point.     

Intrinsic luminescence of amorphous and disordered crystalline systems

A unified method is developed for describing the steady-state luminescence of exciton fluctuation states for weak excitation in different disordered systems. The phononless luminescence band is found to be formed by “radiative” states of the fluctuation tail in the density of states, i.e., by states for which nonradiative states are either nonexistent or have a low probability. The shape of the emission spectra calculated including the phonon interaction is in good agreement with experimental luminescence spectra of α Si:H and of solid solutions of ZnSe_(1−c)Te_c and CdS_(1−c)Se_c. Fiz. Tverd. Tela (St. Petersburg) 40, 890–891 (May 1998)     

“Quasi-Planck” spectra of capillary turbulence on the surface of liquid hydrogen

We report the first observation of “quasi-Planck” spectra of capillary turbulence on the surface of liquid hydrogen in the dissipation domain. Capillary waves have been driven by low-frequency random force. We have observed that the frequency spectrum of surface elevation changes its dependence from power-like 〈|η_ω²|〉 ∼ ω^−2,8 at middle-frequency domain to “quasi-Planck” distribution ∼e ^ω/ω _d at higher frequencies. The frequency ω _d is proportional to the boundary frequency between inertial interval and dissipation domain and it is scaled up with the increase of driving force.     

Ionization of atoms in electric and magnetic fields and the imaginary time method

A semiclassical theory is developed for the ionization of atoms and negative ions in constant, uniform electric and magnetic fields, including the Coulomb interaction between the electron and the atomic core during tunneling. The case of crossed fields (Lorentz ionization) is examined specially, as well as the limit of a strong magnetic field. Analytic equations are derived for arbitrary fields ℰ and ℋ that are weak compared to the characteristic intraatomic fields. The major results of this paper are obtained using the “imaginary time” method (ITM), in which tunneling is described using the classical equations of motion but with purely imaginary “time.” The possibility of generalizing the ITM to the relativistic case, as well as to states with nonzero angular momentum, is pointed out. Zh. éksp. Teor. Fiz. 113, 1579–1605 (May 1998)     

Collectivity in the optical response. of small metal clusters

The question of whether the linear absorption spectra of metal clusters can be interpreted as density oscillations (collective “plasmons”) or can only be understood as transitions between distinct molecular states is still a matter of debate for clusters with only a few electrons. We calculate the photo-absorption spectra of Na₂ and Na₅ ⁺ comparing two different methods: quantum fluid dynamics and time-dependent density functional theory. The changes in the electronic structure associated with particular excitations are visualized in “snapshots” via transition densities. Our analysis shows that even for the smallest clusters, the observed excitations can be interpreted as intuitively understandable density oscillations. For Na₅ ⁺, the importance of self-interaction corrections to the adiabatic local density approximation is demonstrated. Received: 1 July 2001 / Published online: 10 October 2001     

Dependences of the drift velocity of electrons and the magnetoresistance effect on the ionization-degrees and the active radii of the Coulomb force of an ion sphere in an intermediately ionized plasma of a helium gas

Two weakly ionized plasmas (the ionization-degree a′′ = 10^-6 and 10^-5) and an intermediately ionized plasma (a′′ = 10^-4) are investigated. In previous work, the negative magnetoresistance effect (the increase-phenomenon of the discharge current) in a gas plasma in the case where electrons are scattered only by heavy neutral atoms was only touched upon. In this work, under the condition that electrons are scattered by heavy neutral atoms and by the Coulomb force of heavy helium ions, the dependences of “the drift velocity of electrons” and “the increase-phenomenon of the discharge current in the magnetoresistance effect” on the ionization-degrees and the active radii of the Coulomb force of a helium ion are examined. And it is pointed out that the increase-phenomenon of the discharge current in the magnetoresistance effect appears from neither the wellknown Langevin equation nor the Fokker-Planck equation.     

Thermal hopping ofμ + between “FμF” centres in NaF

Strongly hydrogen-bonded diamagnetic “FμF” centres are formed by theμ ⁺ in a wide variety of fluoride crystals. Hydrogen atoms are expected to form similar “FHF” complexes. Through the “motional narrowing” of the zero-field muon relaxation function in NaF, we have observed an Arrhenius temperature dependence of the dissociation rate of theFμF complex, yielding a binding energy of 1700 (200) K for theμ ⁺ in theFμF centre.     

Irreducible tensor operators and selective/hard single and double resonance experiments in insulators: Applications to NMRON and MQ-NMR

Recently, pulsed NMRON experiments have been carried out on trace amounts of radioactive⁵⁴Mn in the antiferromagnet MnCl₂4H₂O at 500 MHz (Le Gros et al. [1]). In this compound, the quadrupole splitting between the two lowest NMR transitions is ≈3 MHz, which precludes the use of non-selective (hard) rf pulses. Yet within the restricted 2*2 manifold, associated with a given transition, the nuclear rotation is “hard”. In this paper, the theory of “selective-hard” NMRON and MQ-NMR experiments is developed within the framework of irreducible tensor operators. In essence, the theory extends the early work of Jaynes [4] to deal with the higher-order multipolar states created during the course of a given NMR experiment. Several new pulsed NMRON and MQ-NMR experiments are proposed. For example, it is demonstrated how “ouble resonance”, “selective-hard” experiments on the pseudo spin-1 manifold spanned by |±1> and |0> Zeeman states of any integer spinI could be used to extract small chemical shifts in the face of very large quadrupole splittings.     

Excitons in monoclinic zinc diphosphide. Longitudinal exciton and the mixed mode

Exciton absorption spectra in high-quality β-ZnP₂ single crystals have been investigated at T=1.7 K for various directions of the wave vector and various polarization states of the radiation. It has been unambiguously established that the additional high-energy A series, which in some works has been called a D series and ascribed to ZnP₂ crystals, of so-called “rhombic” symmetry,^1,8,10,11 is an intrinsic exciton of the β-ZnP₂ series. A mixed mode has been detected for the first time, and the energy of the longitudinal exciton has been determined. The selection rules for the exciton transitions have been analyzed by a group-theoretical approach, and the symmetry of the nS states of the single exciton has been established on the basis of the experimental data — Γ ₂ ⁻ (z). Fiz. Tverd. Tela (St. Petersburg) 41, 193–202 (February 1999)     

Correlations of polarizations and entangled states in the two-photon system

The correlations of the linear and circular polarizations in the system of two photons have been theoretically investigated. The polarization of a two-photon state is described by the one-photon Stokes parameters and by the components of the correlation “tensor” in the Stokes space. It is shown that in the case of two-photon decays π⁰ → 2γ, η → 2γ, K _L ⁰ → 2γ, K _S ⁰ → 2γ and the cascade process |0〉 → |1〉 + γ → |0〉 + 2γ(|0〉 and |1〉 are states with the spin 0 and 1, respectively) the final two-photon state represents a characteristic example of the entangled (nonfactorizable) state, and the correlations between the Stokes parameters in all these decays have the purely quantum character: the incoherence inequalities of the Bell type for the components of the correlation “tensor”, established previously for the case of classical “mixtures”, are violated. The general analysis of the registration procedure for two correlated photons by two one-photon detectors is performed.     

AC conductivity of porous silicon: A fractal and surface transport mechanism?

Summary In this paper we report on the frequency dependence of the AC conductivity of porous silicon in the range 10 Hz-100 kHz. Two types of testing devices have been fabricated on three different series of samples formed electrochemically using as a starting materialptype,n ⁻-type andn ⁺-type silicon substrates. For frequencies less than 20-40 kHz the conductivity is found to follow a sublinear frequency dependence. This behaviour is typical of a carrier transport mechanism determined by an anomalous diffusion process. At higher frequencies we find that surface states influence the transport mechanism. This suggests a double-channel transport mechanism: one related to porous-silicon “volume” properties and the other more connected to the “surface” itself. Paper presented at the III INSEL (Incontro Nazionale sul Silicio Emettiore di Luce) Torino, 12–13 October 1995.     

On the static permittivity of the Coulomb system in the long-wavelength limit

The general expression for the static permittivity ε(q, 0) of the Coulomb system in the region of small wave vectors was derived based on exact limit relations. The relation obtained describes the function ε(q, 0) in both “metal” and “dielectric” states of the Coulomb system. On this basis, the concept of the “true” dielectric is introduced and the definition of the “true” screening length was discussed. Exact relations were derived for the function ε(q, 0) in the region of small wave vectors q within the random phase approximation at an arbitrary degeneracy.     

Super Universality of the Quantum Hall Effect and the?“Large N Picture” of the ? Angle

It is shown that the “massless chiral edge excitations” are an integral and universal aspect of the low energy dynamics of the ϑ vacuum that has historically gone unnoticed. Within the SU(M+N)/S(U(M)×U(N)) non-linear sigma model we introduce an effective theory of “edge excitations” that fundamentally explains the quantum Hall effect. In sharp contrast to the common beliefs in the field our results indicate that this macroscopic quantization phenomenon is, in fact, a super universal strong coupling feature of the ϑ angle with the replica limit M=N=0 only playing a role of secondary importance. To demonstrate super universality we revisit the large N expansion of the CP ^N−1 model. We obtain, for the first time, explicit scaling results for the quantum Hall effect including quantum criticality of the quantum Hall plateau transition. Consequently a scaling diagram is obtained describing the cross-over between the weak coupling “instanton phase” and the strong coupling “quantum Hall phase” of the large N theory. Our results are in accordance with the “instanton picture” of the ϑ angle but fundamentally invalidate all the ideas, expectations and conjectures that are based on the historical “large N picture.”