Strongly resonant p-wave superfluids

We study theoretically a dilute gas of identical fermions interacting via a p-wave resonance. We show that, depending on the microscopic physics, there are two distinct regimes of p-wave resonant superfluids, which we term "weak" and "strong." Although expected naively to form a paired superfluid, a strongly resonant p-wave superfluid is in fact unstable toward the formation of a gas of fermionic trimers. We examine this instability and estimate the lifetime of the p-wave molecules due to the collisional relaxation into trimers. We discuss consequences for the experimental achievement of p-wave superfluids in both weakly and strongly resonant regimes.     

Detectors for nuclear resonant scattering experiments

Ferrite samples of Zn_0.5Cu_0.5Al _x Fe_2?x O₄, 0≤x≤1 were studied using Mössbauer, X-ray and infrared spectra. Mössbauer spectra taken at room temperature show signs of relaxation for all samples. The obtained spectra were analysed into two Zeeman magnetic patterns assigned to the tetrahedral A- and octahedral B-sites and a paramagnetic phase C (quadrupole doublet ΔE). ΔE and the doublet area, which increase with x and the oxygen parameter u are studied. The quadrupole shift is small and may be ignored within experimental error. The isomer shift of the B-sites increases, with x while that of the A-sites does not change. The hyperfine magnetic field of the A-site (H _A) is higher than that of the B-sites (H _B). H _B decreases for x≤0.8 and increases at x=1 while H _A decreases for x≤0.4 and increases for x>0.4. This behaviour is discussed. The cation distribution has been estimated. The linewidth of the outermost A and B-sites and the calculated magnetization have been studied as functions of x for all samples. The B-sites show a composite pattern that has been successfully analysed into separate components. The obtained hyperfine parameters are discussed. The oxygen parameter, the ionic radius and the metal-oxygen bonds of the A- and B-sites were calculated for all samples. The infrared spectra show three vibration bands υ₁, υ₂ and υ₄. The bands υ₁ and υ₂ show a shoulder, splitting and increasing overlap. Their behaviour has been discussed as a function of x. They show the same behaviour of magnetization and area ratio as the B- to A-sites. All parameters show a different behaviour at x=0.4, which is assigned to higher fraction of the Cu²⁺ ions in the A-site at this composition.     

Tuning p-wave interactions in an ultracold Fermi gas of atoms

We have measured a p-wave Feshbach resonance in a single-component, ultracold Fermi gas of 40K atoms. We have used this resonance to enhance the normally suppressed p-wave collision cross section to values larger than the background s-wave cross section between 40K atoms in different spin states. In addition to the modification of two-body elastic processes, the resonance dramatically enhances three-body inelastic collisional loss.     

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.     

Polaron effects in resonant Raman scattering

Loudon's resonant Raman scattering theory is reconsidered by including polaron effects in the intermediate electron states. The Fröhlich Hamiltonian is used to derive the polaron propagators. Numerical calculations were carried out for CdS which show that polaron effects produce a large enhancement of the scattered intensity, improving the agreement between theoretical and experimental results.     

Many-body effects in resonant pion-nucleus scattering

The many-body approach of Barshay et al. for resonant pion-nucleus scattering is extended to non-uniform density distribution s and compared with recent total cross section data for ¹²C, ³²S, ¹²⁰Sn and ²⁰⁸Pb. For light nuclei the shapes and magnitudes are very well reproduced and represents an improvement over fits not using many-body corrections. A recent modification suggested by linearing the Low equation is seen to be not very significant for these calculations.     

General properties of nuclear resonant scattering

The process of nuclear resonant scattering resonant scattering is considered on the basis of an optical model. The coherent properties coherent properties of the radiation and scattering mechanism are described. The complementary pictures of γ-ray resonant scattering in energy and time domains are presented. Special attention is paid to scattering of a γ quantum by an ensemble of nuclei. The central concept of the theory of nuclear resonant scattering, the nuclear exciton, nuclear exciton as a delocalized nuclear excitation, is described in detail. It is shown that both temporal and spatial aspects of coherence play a crucial role in the evolution of the nuclear exciton. A large place is given to the analysis of resonant scattering of synchrotron radiation by nuclear ensembles.

     

Time-delayed interferometry with nuclear resonant scattering

Hyperfine Interactions - Experimental results of “time-delayed interferometry” with nuclear resonances at KEK are reported. Mössbauer nuclei were used as a cavity for X-rays in...     

Polarization effects in resonant nuclear scattering

Polarization phenomena are present in every radiative transition, whether it is of atomic or nuclear origin. Nuclear resonant scattering of synchrotron radiation is an ideal technique for their study because (a) the probing radiation is in a well characterized polarization state, in most cases linear, (b) the scattered radiation can be efficiently analyzed with polarization filters, and (c) synchrotron pulses are very short compared to the lifetime of a nuclear resonance, resulting in a clean signal. In the following article we describe experimental and theoretical studies of the 14.4 keV Mössbauer resonance of ⁵⁷Fe and its transitions with linear and circular polarization. After introducing the required instrumentation a formalism to calculate time dependent polarization phenomena is derived. With the help of different scattering geometries we illustrate various aspects, such as polarization mixing and selective excitation of subsets of the resonance. Perhaps the most fascinating example is the Faraday geometry where the E-vector rotates several 360^ο turns during the lifetime of the resonant scattering. A comparison of this phenomenon with the optical Faraday effect is given. New powerful synchrotron radiation sources will enable researchers to exploit polarization phenomena in nuclear resonant scattering to detect subtle changes in physically and chemically relevant systems.

     

Double resonant raman scattering in graphite

We find that the electronic dispersion in graphite gives rise to double resonant Raman scattering for excitation energies up to 5 eV. As we show, the curious excitation-energy dependence of the graphite D mode is due to this double resonant process resolving a long-standing problem in the literature and invalidating recent attempts to explain this phenomenon. Our calculation for the D-mode frequency shift ( 60 cm(-1)/eV) agrees well with the experimental value.     

Multiphonon resonant Raman scattering in GaSe

Multiphonon resonant Raman scattering up to 4 phonons in GaSe has been measured. The results are interpreted by a simple cascade theory. It is shown that the dispersion of RRS here is dominated by resonances with the exciton states.     

N-d elastic scattering and polarization calculations with tensor force and p-wave interaction

Three-body calculations for the n-d elastic scattering are preformed at E_n = 14.1 MeV with s and p-wave N-N interaction and tensor force. The tensor force is not able to reproduce even the order of magnitude of the elastic neutron polarization. It is also shown that the p-wave N-N interactions have an important effect on the neutron polarization.     

Nuclear resonant scattering of synchrotron radiation

The principal ideas of the theory and the main results of the experimental studies of the coherent resonant scattering of-radiation by nuclear ensembles in matter are briefly over-viewed. An analysis of transmission of the Mössbauer-radiation and of synchrotron radiation through a nuclear resonant medium is suggested using an approach based on the optical theory. The feasibilities of the nuclear resonant scattering of synchrotron radiation as a new technique for studying the hyperfine interactions and some other phenomena of the physics of condensed matter are considered.     

Nuclear resonant scattering of annihilation quanta

Resonant scattering by ¹⁰⁶Pd nuclei of γ-quanta produced by positron annihilation in metallic copper has been observed. The differential cross section of this process for a scattering angle of 120° was found to be 0.27 ± 0.05 mb/sr.     

Nuclear resonant scattering using synchrotron radiation

A one-dimensional quantum model for nuclear resonant scattering using synchrotron radiation has been developed. This model gives a clear physical interpretation of the most prominent features of the coherent forward scattering process namely, the “speed-up” and “dynamical beat” effects. The form of the solution, for the time-dependent forward scattered intensity of the resonant radiation from the resonant medium after synchrotron radiation excitation, is a finite series. This unique solution can be interpreted in terms of a summation over all multiple forward scattering paths the radiation takes in reaching the detector. The resonant medium is represented by a linear chain of N effective resonant nuclei. The analysis starts from a coupled set of quantum mechanical equations for the relevant amplitudes in frequency space. Transformation to the time domain gives an analytical expression for the forward scattered intensity. The contribution of every order of the multiple scattering processes from the N effective nuclei appears naturally. The expression gives a clear physical understanding of all relevant aspects of resonant forward nuclear scattering. Furthermore, the present formalism allows the consideration of incoherent processes. This permits the study of processes in which there is gamma emission with recoil or emission of internal-conversion electrons. This revised version was published online in August 2006 with corrections to the Cover Date.