Quantitative determination of the hubbard model phase diagram from optical lattice experiments by two-parameter scaling

We propose an experiment to obtain the phase diagram of the fermionic Hubbard model, for any dimensionality, using cold atoms in optical lattices. It is based on measuring the total energy for a sequence of trap profiles. It combines finite-size scaling with an additional "finite-curvature scaling" necessary to reach the homogeneous limit. We illustrate its viability in the 1D case, simulating experimental data in the Bethe-ansatz local-density approximation. Including experimental errors, the filling corresponding to the Mott transition can be determined with better than 3% accuracy.     

Monochromatization of synchrotron radiation for nuclear resonant scattering experiments

An introduction to monochromatization of synchrotron radiation in the energy range of 5–30 keV is presented for applications involving nuclear resonant scattering. The relevant relationships of the dynamical theory of Xray diffraction are used to explain basic concepts of monochromatization. These relations are combined with raytracing techniques to design highenergyresolution monochromators. Transmissionoptimized and energyresolutionoptimized designs that achieve high energy resolutions (10⁶)< E/E < 10⁸) are discussed separately. Practical silicon monochromators of both types are presented for a variety of nuclear resonances in this energy range.     

Zero temperature phase diagram of a small metallic junction

We discuss the phase diagram for a metal tunnel junction with quasiparticle dissipation. We present some evidences of aT=0 phase transition induced by dissipation, by means of Monte Carlo simulation and studying the problem by means of a selfconsistent harmonic approximation. When the nominal conductance of the junctioin is large the predictions of the spin wave theory turn out to be correct and the algebraic decay of correlations implies quasi-long range order (phase with infinite susceptibility), this situation corresponds to the absence of a Coulomb blockade voltage threshold. The critical value of the nominal junction resistance is estimated to beR _t 0.6 k.     

Ultrasonic determination of the phase diagram in CsNiCl3

The phase diagram of CsNiCl₃ has been determined ultrasonically. There is a quadratic increase in the Néel temperature with increasing magnetic field. A possible spin-flop transition has been detected at approximately 22 kG.     

Protein crystal growth: An approach based on phase diagram determination

There is an increasing need to rationalize protein crystal growth, mostly carried out so far by trial-and-error. The phase rule gives the number of conditions necessary to specify the state of protein crystallization in equilibrium. Unsaturated and supersaturated regions are distinguished in phase diagrams. Examples of such diagrams for protein crystals are tabulated. To determine the phase diagrams reliably, the following items are discussed: (1) proper crystallization methods, (2) the length of time needed for establishing equilibrium, and (3) the importance of specifying the kind of solid state. Various crystallization methods are compared as to their effect on the solution system by using the phase diagrams, and the potential usefulness of the diagrams for crystallizing new proteins is discussed.     

Anisotropy-tuning by doping: phase diagram of CsNi0.98Fe0.02Cl3 measured by caloric experiments

The magnetic phase diagram of the Fe²⁺ doped hexagonal ABX₃ compound CsNi_0.98Fe_0.02Cl₃ is investigated measuring the specific heat capacity and the magnetocaloric effect. In contrast to earlier specific heat, ultrasound and NMR experiments our measurements identify transitions between three ordered phases with the field applied in the hexagonal plane. Since the pure compound, a Heisenberg antiferromagnet with weak Ising anisotropy, has only two ordered phases for this field direction, while three are predicted for weak easy-plane anisotropy, our data provide the unambiguous proof that the anisotropy of CsNiCl₃ can be effectively modeled by doping with Fe²⁺.     

Low-temperature photoluminescence of CoO excited by synchrotron radiation

We report the first observation of low-temperature luminescence of CoO crystals under synchrotron irradiation. At 8 K, the photoluminescence of CoO is characterized by smaller bandwidth and higher intensity relative to the corresponding photoluminescence band of NiO. The photoluminescence excitation spectra of CoO and NiO are similar. Position of the band related to charge transfer from oxygen ions to 3d-shell of cobalt ions is determined. The excitation energy is found to be 3.5 eV.     

Direct determination of the phase of reflectivity by means of modulation technique

A method is described by which the phase of reflectivity for cubic crystals is measured. It involves modulated piezo-reflectance at the frequency ω₁ and modulation of the polarization of light with a $\text{1}\text{2}$λ-plate rotating with the frequency ω₂. The signal of frequency 2ω₂ yields the phase, and the signals of frequencies (ω₁± 2ω₂) yield the derivative of the phase. We have applied this method to measure the exciton spectra of ZnTe. It turns out that the phase becomes negative in certain spectral regions. This behaviour is interpreted in terms of Hopfield and Thomas' model of exciton free surface layers.     

The impact of synchrotron radiation on biology

The speakers at the main session of the 2005 National Synchrotron Light Source (NSLS) Annual Users' Meeting, held on Tuesday, May 24, at Brookhaven National Laboratory (BNL), spoke on many different topics. But they all conveyed excitement for the science performed at the NSLS, and expressed enthusiasm for its proposed successor, the world-leading NSLS-II.

The incoming NSLS Users' Executive Committee Chair, Peter Stephens, welcomed the audience to the main meeting, setting a positive and enthusiastic tone for the day's events. He then opened the stage to BNL Director Praveen Chaudhari.

Chaudhari commended many attendees for their work to advance NSLS-II.     

Nuclear resonant scattering of synchrotron radiation by multilayer structures

Multilayer structures form a particular class of samples employed in nuclear resonant scattering of synchrotron radiation. Their specific properties lead to unusual energy and time characteristics of nuclear resonant scattering, which differ much from those of single crystals. The analysis of these distinctions is presented. Several approaches to achieve pure nuclear reflections with multilayers are discussed. Finally, we review the studies of multilayer structures with nuclear resonant scattering of synchrotron radiation.

     

浅谈偶极振子辐射的图示

指出了目前物理教学中在偶极振子辐射的图示方面存在的一些问题,并就这些问题进行了分析、探讨。     

Effect of synchrotron radiation on nuclear beta decay

The stimulation of the endothermic beta decay of stable nuclei by the field of synchrotron radiation has been analyzed theoretically in the framework of the photobeta decay mechanism. In contrast to works devoted to the effect of laser fields on beta decay, the action of the field directly on a nucleus rather than on a beta electron is considered (a sufficiently intense flux of hard photons whose energies exceed 60 keV allows this action). The rates of such a beta decay are calculated for a number of “parent nucleus-daughter nucleus” pairs for the relativistic case including Coulomb effects. For the most intense available sources of synchrotron radiation, the rate of stimulated beta decay for most nuclei under investigation appears to be characteristic of third-forbidden β^? transitions. The effect of synchrotron radiation on highly forbidden natural nuclear β^? decays is also analyzed. In particular, irradiation increases the rate of the β^? decay of the ₃₇ ⁸⁷ Rb and ₄₉ ¹¹⁵ In nuclei by 2% and by almost two orders of magnitude, respectively.