Redoubled effect of a neutron spin rotation in deformed noncentrosymmetric crystal for the Bragg diffraction scheme

JETP Letters - A doubled effect of a neutron spin rotation in a noncentrosymmetric quartz crystal for the Bragg reflected neutrons from the deformed exit crystal side is first observed. The effect...     

Depolarization of a neutron beam in Laue diffraction by a noncentrosymmetric crystal

The depolarization of a neutron beam executing Laue diffraction in a thick (～3.5 cm) noncentrosymmetric α-quartz crystal is observed. This effect was predicted by us earlier and suggested for measuring the electric dipole moment (EDM) of a neutron. The effect is due to an interaction of the magnetic moment of a moving neutron with a strong crystal electric field, as a result of which the neutron spin rotates in opposite directions for waves of two types excited in the crystal. The effect is studied for neutron diffraction by a system of crystallographic (110) planes at Bragg angles close to π/2, up to 87°. It is shown that, for a crystal of thickness L=3.5 cm, a direct beam initially polarized along the reciprocal lattice vector becomes depolarized upon diffraction, irrespective of the value of Bragg angle, whereas the beam polarized perpendicular to the diffraction plane retains its polarization. The Eτ value determining the sensitivity of the method to EDM is experimentally estimated.     

Selective spin coupling through a single exciton

We present a novel scheme for performing a conditional phase gate between two spin qubits in adjacent semiconductor quantum dots through delocalized single exciton states, formed through the interdot F?rster interaction. We consider two resonant quantum dots, each containing a single excess conduction band electron whose spin embodies the qubit. We demonstrate that both the two-qubit gate and arbitrary single-qubit rotations may be realized to a high fidelity with current semiconductor and laser technology.     

Electron spin resonance spectrum of trapped in a single crystal matrix

The radical , labelled with ¹³C in the position shown, has been prepared by X-irradiation of single crystals of . The ¹³C hyperfine coupling tensor of this radical confirms previous conclusions from a study of the corresponding unlabelled species that the electron is essentially localized on the carbon atom. At room temperature the methylene group undergoes rapid reorientation about the P-C bond while comparison of the ¹³C tensors at 300 K and 77 K suggests that the barrier to rotation has a strong two-fold component but contains intermediate minima.     

Positron annihilation study of voids in a neutron irradiated aluminum single crystal

We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·10²¹ n/cm² (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·10¹⁴ voids/cm³ with a mean diameter of 330 Å, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT ^1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum.     

Positron annihilation study of voids in a neutron irradiated aluminum single crystal

We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·10²¹ n/cm² (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·10¹⁴ voids/cm³ with a mean diameter of 330 ?, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT ^1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum. Research sponsored in part by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation.     

Surface bound states and spin currents in noncentrosymmetric superconductors

We investigate the ground state properties of a noncentrosymmetric superconductor near a surface. We determine the spectrum of Andreev bound states due to surface-induced mixing of bands with opposite spin helicities for a Rashba-type spin-orbit coupling. We find that the order parameter suppression qualitatively changes the bound state spectrum. The spin structure of Andreev states leads to a spin supercurrent along the interface, which is strongly enhanced compared to the normal state spin current. Particle and hole coherence amplitudes show Faraday-like rotations of the spin along quasiparticle trajectories.     

Martensitic transformation in a copper-aluminum-nickel alloy single crystal after short-term neutron irradiation

The influence of neutron irradiation on the temperature kinetics of thermoelastic martensitic transformation in a Cu-Al(13.4%)-Ni(5%) alloy single crystal is investigated by measuring the electrical resistivity directly under irradiation of the sample in a nuclear reactor channel. It is revealed that, after irradiation of the crystal in a martensitic or two-phase state, the temperature of the phase transition upon heating becomes 25–30 K higher than that prior to irradiation. This shift in the transition temperature is observed only upon the first heating, and the kinetics of martensitic transformation is restored in subsequent thermocycles. The shift in the transformation temperatures after irradiation increases with an increase in the fluence. The experimental results are explained by a disturbance of coherence at the interfaces in the irradiated crystals.     

Particle trajectories and interference in a time-dependent model of neutron single crystal interferometry

The de Broglie-Bohm interpretation of quantum mechanics is shown to provide an explanation of the observed spatial interference in neutron single crystal interferometers in terms of well-defined individual particle trajectories with continuously variable energy.     

Computer simulation of the dechanneling of low-energy protons and antiprotons passing through a crystal

A theoretical analysis is proposed for the CERN experimental data on the channeling of antiprotons with an energy of about 1 MeV. Computer simulation reproduces the basic regularities revealed by the experiment and points to a strong angular spread of antiprotons in dechanneling as compared to the dechanneling of protons.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Electronic conductivity in 1D Co spin chain single crystal

We have measured the transport and magnetic properties of the model spin chain single crystal Ca₃Co₂O₆ in high pulsed fields. A crossover between 1D and 3D transport is observed, with the opening of a Coulomb gap below the order temperature of the individual chains. The samples show changes in the variable range hopping transport dimensionality and gap; the magnetic field suppresses the gap, inducing a significant reduction of the resistance, while dimensionality seems governed by temperature. At fields associated with the levels of magnetization of the frustrated triangular lattice formed by the Co lines, and below the critical magnetic temperature, a further increase of the conductivity is observed. This effect is associated with planar magnetic states perpendicular to the lines.     

Control of the polarization properties of the supercontinuum generation in a noncentrosymmetric crystal

A systematic experimental study on the polarization properties of supercontinuum generation (SCG) in a noncentrosymmetric crystal (KDP) is reported. Our studies show that depolarization of the SCG is dependent on the plane of polarization of incident light as well as on the orientation of the crystal, allowing a better control of the polarization properties.     

μ + Knight shift and spin relaxation in indium single crystalKnight shift and spin relaxation in indium single crystal

μ ⁺ SR measurements have been performed in a single crystal indium sample between 12 K and 300 K with a stroboscopic μSR spectrometer. The muonic Knight shiftK _μ and the muonic depolarization rate σ were obtained for various angles θ between the tetragonal crystallinec-axis and the direction of the external field. The isotropic part ofK _μ is only weakly temperature dependent and is consistent with the estimated Pauli spin susceptibility value. At a temperature of 12 K the angular dependence ofM ₂ (the second moment of the field distribution at the muon, obtained from the measured σ(θ) values) allows a clear determination of the muon location — the symmetric tetrahedral site. The observed anisotropicK _μ cannot be explained by the dipoles at the In atoms responsible for the bulk magnetic susceptibility but probably originates from an anisotropic Pauli spin susceptibility.     

Electron spin resonance in X-irradiated single crystal of strontium tartrate tetrahydrate

The electron spin resonance spectra of an irradiated single crystal of strontium tartrate tetrahydrate (SrC₄H₄O₆·4H₂O) grown from silica gel have been investigated. Two species of free radical were observed at room and liquid nitrogen temperatures. The free radicals were found to be the result of the splitting of a C-H bond of the tartrate ions contained in the unit cell. The unpaired electron of each radical specie interacts with two nonequivalent protons giving rise to hyperfine splittings of relatively small magnitude. The g factors of the radicals were found to be almost isotropic and have similar values and it was very difficult to determine the ESR parameters from experimental patterns directly. A least-squares method, proposed earlier, was used to analyze the observed experimental patterns at various orientations.The existence of two nonequivalent radicals is believed to be the result of the nonplanarity of the two halves of the tartrate ions. The H nuclei giving rise to the hyperfine splittings are the protons of the hydroxyl groups attached directly to the unsaturated carbon atoms and those attached directly to the other asymmetric carbon atoms (β protons). The principal elements of the hyperfine splittings for the observed radicals were: Radical I: ?9.02, ? 2.84, ?0.47 and ?1.66, ?1.54, ?0.89. Radical II: ?10.16, ?7.83, ? 1.51 and 0.00, ?1.58, ?1.06. The radicals were found to be very stable, the ESR patterns being undiminished for more than six months after the irradiation.     

Ultrasound effect on neutron Bragg diffraction in a perfect and deformed silicon single crystal

The features of neutron Bragg diffraction in a perfect and bent (deformed) silicon single crystal have been studied under ultrasound excitation. In contrast to a perfect crystal where an increase in the diffraction intensity has been observed with an increase in the ultrasound wave’s amplitude, in a deformed silicon crystal the intensity sharply decreases (two times) already at small voltages on a piezoelectric transducer. The depth and position of minima of the total intensity depend on the ultrasound wave’s amplitude and the bending radius of a crystal. To explain the observed effects the modified Penning-Polder-Kato model has been successfully used, in which the role of ultrasound is reduced to the formation of resonance transitions of imaging points between different sheets of dispersion surface. Experimental proofs of validity of the used model are presented. Estimations of the probabilities of one- and multiphonon scattering processes obtained from experimental data have a good agreement with theoretical ones.     

93Nb NMR spin echo spectroscopy in single crystal NbSe3

We report electric field induced phase displacements of the charge density wave (CDW) in a single crystal of NbSe3 using 93Nb NMR spin-echo spectroscopy. CDW polarizations in the pinned state induced by unipolar and bipolar pulses are linear and reversible up to at least E = (0.96)ET. The polarizations have a broad distribution extending up to phase angles of order 60 degrees for electric fields close to threshold. No evidence for polarizations in excess of a CDW wavelength or for a divergence in polarization near ET are observed. The results are consistent with elastic depinning models, provided that the critical regime expected in large systems is not observable.     

Effect of neutron spin rotation at Laue diffraction in a deformed transparent crystal with no center of symmetry

The effect of neutron spin rotation at Laue diffraction in a noncentrosymmetric weakly deformed neutron-transparent crystal has been studied experimentally. The effect appears because of two phenomena: (i) the interaction of the magnetic moment of a moving neutron with the crystalline electric field and (ii) bending of trajectories of the neutron in a deformed crystal; as a result, the amplitudes of two waves excited at Laue diffraction, which propagate in the crystal in opposite electric fields, at the output of the crystal are not equal.     

Longitudinal ultrasonic attenuation in the spin spiral state of single crystal holmium

Ultrasonic attenuation experiments have been performed using 15–255 MHz longitudinal sound waves along the c-axis of single crystal holmium. Without an external magnetic field, the attenuation increases in the spin-spiral state. This anomalous increase originates, at least in part, from the spin-phonon relaxation mechanism we have proposed, which states that the attenuation coefficient Δα₁ ∞ ω²/(1+ω²τ²) where τ is the longitudinal spin phonon relaxation time. The frequency dependence of the attenuation varies from ω^1·0 to ω^1·5 which suggests a frequency-dependent character for the spin-phonon relaxation time τ. A broad longitudinal attenuation maximum, which presumably is due to the competing processes between $\overline{S}$, J and τ, is observed in the spin-spiral state, where $\overline{S}$ is the thermal average of the spin angular momentum per trivalent ion and J the Fourier transform of the exchange integral. An anomalous suppression of the longitudinal attenuation spike at T_N for frequencies higher than 165 MHz is unexplainable at present. The longitudinal attenuation spike at T_N for frequencies higher than 165 MHz is unexplainable at present. The longitudinal spin-phonon relaxation time for Ho has been determined using experimental data. It has a T^?3 temperature dependence. In the presence of an external magnetic filed in the basal plane the attenuation is decreased and a new peak and a plateau appear at the intermediate phase transitions.