The continuum limit and integer-valued vacuum charge

We consider a topologically trivial field theory defined in a large box of size L and exploit the enumeration of states to point out that the vacuum charge is integral, contrary to what a commonly used formula seems to suggest. We show that the large L limit is subtle: Standard anticommutation relations require the presence of a somewhat unfamiliar normalization factor which in turn leads to observable effects for the vacuum charge density. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 353–358 (10 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Stiffness of reinforced and unreinforced Bi2Te3 single crystals

We investigate the thermodynamics of Ω- and V-shaped bending of Bi₂Te₃ single crystals. To change the shape of the bending from Ω to V, the sample is reinforced with thin steel rods, arranged perpendicular to the cleavage planes. We find that reinforcement increases the ultimate strength of the samples by more than twofold. We show that the transition Ω→V leads to a substantial change in the spectrum of energy dissipation in the straining of the sample. Some aspects of the practical application of the observed effects are considered. Zh. Tekh. Fiz. 67, 50–54 (February 1997)     

Persistent spectral hole-burning in a -doped aluminosilicate glass from 8 to 295 K: Study of the burning and refilling kinetics, and of optical dephasing

High-temperature persistent spectral hole-burning (PSHB), up to room temperature, has been observed in a Eu ³⁺ -doped aluminosilicate glass using a high peak-power nanosecond dye laser. Spontaneous refilling as well as thermal cycling measurements show that at least two mechanisms, a fast and a slow one, are involved in our sample. We suggest that the fast or “easy” component may correspond to a non-photochemical local rearrangement of the host or to photoreduction of the Eu ³⁺ ions and that the second one leading to very stable photoproducts may correspond to transfer of an electron over a sizable distance through a several-step process. The mechanisms we suggest agree with light-induced hole refilling measurements. Line broadening mechanisms are discussed and the temperature-dependent part of the homogeneous width and of the spectral shift is interpreted in terms of a two-phonon (Raman) process involving pseudo-local phonons. Received 28 July 1999     

Vierbein walls in condensed matter

The effective field, which plays the part of the vierbein in general relativity, can have topologically stable surfaces, vierbein domain walls, at which the effective contravariant metric is degenerate. We consider vierbein walls separating domains with flat spacetime which are not causally connected at the classical level. The possibility of a quantum mechanical connection between the domains is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 705–710 (10 December 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (μSR). The alternation of a uniform state (with one μSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B ₂−B ₁≅30 Oe. Fiz. Tverd. Tela (St. Petersburg) 40, 524–526 (March 1998)     

Photoinduced domains in lithium niobate

We have observed the optically induced occurrence of domain structure with polarization opposite to the spontaneous polarization of a single-domain sample of lithium niobate. The appearance of the domains can be explained by a redistribution of the density of the Fe²⁺ and Fe³⁺ impurity ions under the action of the photoinduced field and subsequent additional inverse polarization of the environment surrounding the Fe²⁺ ions. Fiz. Tverd. Tela (St. Petersburg) 40, 531–533 (March 1998)     

Effect of mechanical stresses on the magnetoelastic properties of TmVO4

In this paper the influence of mechanical stress on magnetoelastic properties, i.e., magnetostriction and thermal expansion in the neighborhood of a structural phase transition of the Jahn-Teller crystal TmVO₄ is investigated experimentally and theoretically. It is shown that the magnetoelastic properties of TmVO₄ for a magnetic field H∥[001] do not change the domain structure of the sample, which is rather well described when mechanical stresses in the crystal are taken into account using the parameter . Conversely, for magnetic fields along the direction of spontaneous strain [110] the magnetoelastic properties are primarily caused by reorientation of the Jahn-Teller domains and short-range order effects. It is shown that the “true” magnetostriction of a single-domain crystal for H∥[110] diverges at the phase transition point T _c=2.15 K in the absence of mechanical stresses and is strongly decreased by these stresses. Fiz. Tverd. Tela (St. Petersburg) 40, 701–705 (April 1998)     

Capabilities of a muon method for studying the diamagnetic domains accompanying the de Haas-van Alphen effect

This paper analyzes the capabilities of a muon (μSR) method for studying the de Haas-van Alphen effect and the diamagnetic domain structure accompanying it. It is shown that, unlike the NMR method, the μSR method makes it possible to observe the formation of a diamagnetic domain structure in all metals. It is not currently known what type of domain structure accompanies the de Haas-van Alphen effect: one-dimensional (laminar) or two-dimensional. It is shown that the line shape of the Fourier spectrum of the signal makes it possible to determine both the character of the domain structure (two-dimensional or laminar) and the magnetic field distribution in the domains. Zh. éksp. Teor. Fiz. 111, 250–261 (January 1997)     

Muon spin echo

A muon spin echo method is proposed for determining the contributions of the static and dynamic local fields in muon experiments. It is shown that if for each muon which has stopped in the sample a rf pulse of fixed duration is applied to the sample at a time τ after the muon entered the sample, then after a sufficient number of muon-positron decays have been accumulated a muon spin echo can appear at time 2τ. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 500–503 (10 October 1996)     

Effects of charge-density-wave depinning on the low frequency shear compliance of NbSe3

We report on measurements of the voltage dependence of the complex shear compliance of two crystals of the charge-density-wave (CDW) conductor NbSe₃, for torsional frequencies between 1 Hz and 71 Hz. For both samples, there is a frequency independent, ∼1% increase of the magnitude of the compliance when the voltage exceeds the threshold for CDW depinning, but the internal friction has a striking sample dependence which we do not understand. For one sample, there is a frequency independent decrease in internal friction with CDW depinning, suggesting that the elastic changes are not relaxational and might reflect changes in the screening of the crystal strain by the CDW. For the second sample, the sign and magnitude of the change in internal friction is strongly frequency dependent, which we associate with a change in screening due to the finite electron diffusion time. The second sample also exhibits a frequency dependent peak in internal friction near threshold that may reflect relaxation of the CDW phase. Received 14 August 2001 and Received in final form 3 October 2001     

Can Spacetime be a Condensate?

We explore further the proposal [Hu, B. L. (1996). General relativity as geometro-hydrodynamics. (Invited talk at the Second Sakharov Conference, Moscow, May 1996); gr-qc/9607070.] that general relativity is the hydrodynamic limit of some fundamental theories of the microscopic structure of spacetime and matter, i.e., spacetime described by a differentiable manifold is an emergent entity and the metric or connection forms are collective variables valid only at the low-energy, long-wavelength limit of such micro-theories. In this view it is more relevant to find ways to deduce the microscopic ingredients of spacetime and matter from their macroscopic attributes than to find ways to quantize general relativity because it would only give us the equivalent of phonon physics, not the equivalents of atoms or quantum electrodynamics.It may turn out that spacetime is merely a representation of certain collective state of matter in some limiting regime of interactions, which is the view expressed by Sakharov [Sakharov, A. D. (1968). Soviet Physics-Doklady 12, 1040–1041; Sakharov, A. D. (1967). Vacuum quantum fluctuations in curved space and the theory of gravitation. Doklady Akad. Nauk S.S.R. 177, 70; Adler, S. L. (1982). Reviews of Modern Physics 54, 729]. In this talk, working within the conceptual framework of geometro-hydrodynamics, we suggest a new way to look at the nature of spacetime inspired by Bose–Einstein condensate (BEC) physics. We ask the question whether spacetime could be a condensate, even without the knowledge of what the‘atom of spacetime’ is. We begin with a summary of the main themes for this new interpretation of cosmology and spacetime physics, and the ‘bottom-up’ approach to quantum gravity. We then describe the ‘Bosenova’ experiment of controlled collapse of a BEC and our cosmology-inspired interpretation of its results. We discuss the meaning of a condensate in different context. We explore how far this idea can sustain, its advantages and pitfalls, and its implications on the basic tenets of physics and existing programs of quantum gravity.     

The paleoinformation value of natural remanent magnetization of several traps in Yakutia

Research was carried out to estimate the possibility of determining the direction and strength of the ancient geomagnetic field (H _an ) by natural remanent magnetization (I _n ) of nine oriented samples from traps of the Minor Botuoba Region (Yakutia) aged 260 Ma. Five samples (Pi-10, K-4, K-6, 315–13, and Ki-2) are characterized by negative polarity of In, while four samples (nos. 334-5, 331–2, 315–11, 299–2) have positive polarity as does the recent geomagnetic field in this region. The ferrimagnetic constituent of the samples with reverse I _n polarity appears to be quite variable: samples K-4 and K-5 are characterized by low Curie points (T _c ≈ 200°C) of the ferrimagnetic phase, sample Ki-2 contains single-phase oxidized titanomagnetite with T _c ≈ 310°C, and the T _c of the Pi-10 ferrimagnetic phase is 540°C. Hence, it may be concluded that the primary remanent magnetization of the first two samples was formed in a reverse polarity field. These samples also may be used to determine the paleostrength of the geomagnetic field. The properties of traps containing single-phase oxidized (sample Ki-2) and disintegrated (sample Pi-10) titanomagnetite require additional investigation. Samples with positive In polarities are characterized by the self-reversal phenomenon upon thermal demagnetization of the natural remanent magnetization, which was most likely caused by the occurrence of titanomagnetite exsolution textures in ferrimagnetic grains. The paleoinformation value of the I _n of these samples is doubtful.     

Studies of parity and time reversal symmetries in neutron scattering from165Ho

We describe searches for parity and time reversal violations in the scattering of polarized neutrons from polarized and aligned¹⁶⁵Ho targets. We have completed a search with 7.1 and 11.0 MeV neutrons for P_oddT_odd terms in the elastic scattering forward amplitude of the form s. (I×K), wheres is the neutron spin,I is the target spin andk is the neutron momentum vector. The target was a single crystal of holmium, polarized horizontally along itsb axis by a 1 Tesla magnetic field. The neutrons were polarized vertically. Differences in the neutron transmission were measured for neutrons with spins parallel (antiparallel) toI×k. The P,T violating analyzing powers were found to be consistent with zero at the few 10⁻³ level: ρ_P,T(7.1 MeV)=−0.88 (±2.02) x 10⁻³, ρ_P,T(11.0 MeV)=−0.4 (±2.88) x 10⁻³. We have also attempted to find enhancements with MeV neutrons in P-violation due to the term s\k. We are preparing an aligned target cryostat for investigations of P_evenT_odd terms {bd(I\k)(I×k)\s} in neutron scattering. The target will be a single crystal cylinder of¹⁶⁵Ho cooled to 100 mK in a bath of liquid helium and rotated by a shaft from a room temperature stepping motor. The cylinder will be oriented vertically and the alignment (c) axis oriented horizontally. Warming or rotation of the sample allows one to separate effects that mimic the sought-after time reversal violating term.     

Giant magnetoacoustic effect in KMnF3 due to nuclear spin waves

An explanation is proposed for the gigantic magnetoacoustic effect that we observed in KMnF₃ in previous work {Kh. G. Bogdanova, V. A. Golenishchev-Kutuzov, M. I. Kurkin et al., Zh. éksp. Teor. Fiz. 112, 1830 (1997) [JETP 85, 1001 (1997)]}. The effect entails a tenfold amplitude reduction of an acoustic pulse in a magnetic field that varies over the range 0–8 kOe. It is shown that this effect is due to the interference of two nuclear magnetoelastic waves propagating in the sample under magnetoacoustic resonance conditions, if this resonance occurs in the region of strong spatial dispersion of nuclear spin waves. The effect is said to be gigantic because it exceeds in magnitude the magnetoacoustic effects observed previously in magnetically ordered materials even though it is due to nuclear magnetism, which is 10⁵ times weaker than electronic magnetism. We observe a concomitant anomalous dependence of the dispersion of the velocity of sound on the external magnetic field. Zh. éksp. Teor. Fiz. 115, 1727–1739 (May 1999)     

Giant growth of quantum oscillations in an inhomogeneous 2D electron system

It is detected experimentally for the first time that the connection of 2D electron systems with different electrochemical potentials results in long-range (τ 50 μm) electron density disturbances. When a gated region of a Corbino sample is strongly depleted, the amplitude of the magnetoresistance oscillations caused by high density ungated regions is found to increase in direct proportion to the sample resistance, which is dominated by low-density regions with small conductivity. Experiments on samples with an artificial potential profile (antidots and etched rings) below the gate show that the observed effects are not due to contact effects. Pis’ma Zh. Eksp. Teor. Fiz. 63, No. 1, 55–60 (10 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Feasibility of measuring the average sizes of diamagnetic domains by the μSR 2 method

Abtract One of the simplest examples of possible application of the μSR ² method for estimating the sizes of diamagnetic domains is analyzed in detail. The domains have been observed for the first time by means of the μ SR method in beryllium [G. Solt, C. Baines, V. S. Egorov et al., Hyperfine Interactions 104, 257 (1997)]. Results are given from a computer simulation of a μSR ² experiment to measure domain sizes in Be. An algorithm is described for processing the experimental results. It is graphically demonstrated that domain sizes can be estimated within the accelerator operating time allocated for an ordinary μSR experiment. Zh. éksp. Teor. Fiz. 115, 2133–2142 (June 1999)     

Spatial correlation study of internal magnetic fields in magnets by μSR2-technique

It is shown that using position-sensitive detectors in μSR experiments to determine the muon stopping site in a target permits one to study correlation effects in μSR time histograms produced by the decay of muons stopping in the same domain, i.e. to obtain time correlators of μSR histograms of decays from a small region. These correlators contain information on the spatial correlation of magnetic fields in the sample under study. The proposed method (μSR²-technique) allows measuring correlation radii (r _c ) down to 10⁻⁵ cm in a bulk sample. Among interesting physical phenomena occuring overr _c≥3×10⁻⁶ cm are, for instance, long wavelength fluctuations of the order parameter near the phase transition point in ferromagnets and antiferromagnets and magnetic field correlations in magnet domains and spin glasses. One may use this method also on heavy-current accelerators producing pulsed muon beams to investigate the variation in time of spatial correlations in magnets, spin glasses and superconductors.     

Absence of neutron emission during interaction of deuterium with metal at low energies

Technique and instrumentation to detect reliably, multiplicity of neutrons emitted in sharp bursts (≤100 μs) has been developed where a burst of as low as 15 neutrons and continuous emission of ⋍10⁻¹ neutron/s may be detected. Using this technique, attempts were made to detect neutron emission from various experiments in which anomalous nuclear effects (or what is commonly referred to as cold fusion) may be expected to occur. No neutrons, above our detection threshold, were detected in the recent series of experiments.     

Diffraction of picosecond bulk longitudinal and shear waves in micron thick films

Investigation of thin metallic film properties by means of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies. Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal to the film free surface has been demonstrated. Such measurements cannot provide complete information about properties of anisotropic films. Extreme focusing of a laser pump beam (≈0.5 μm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting longitudinal and shear wavefronts propagate at group velocity through the bulk of the film. To interpret the received signals, source directivity diagrams are calculated taking into account material anisotropy, optical penetration, and laser beam width on the sample surface. It is shown that acoustic diffraction increases with optical penetration, so competing with the increasing of directivity caused by beam width. Reflection with mode conversion at the film-substrate interface is discussed.