Effect of zero-point lattice vibrations on the scattered particle flux

1985 ◽  
Vol 90 (1-2) ◽  
pp. 85-92 ◽  
Author(s):  
A. I. Dodonov ◽  
V. A. Molchanov
Keyword(s):  
Particle Flux ◽  
Zero Point ◽  
Lattice Vibrations ◽  
Scattered Particle ◽  
Point Lattice

THEORY OF THE INTERACTION BETWEEN THE LATTICE VIBRATIONS AND THE ROTATIONAL MOTION IN SOLID HYDROGEN

1966 ◽  
Vol 44 (2) ◽  
pp. 313-335 ◽  
Author(s):  
J. Van Kranendonk ◽  
V. F. Sears
Keyword(s):  
Rotational Motion ◽  
Zero Point ◽  
Solid Hydrogen ◽  
The Self ◽  
Intermolecular Potential ◽  
Lattice Vibrations ◽  
Energy Effect ◽  
Self Energy ◽  
Blowing Up ◽  
Point Lattice

The effects of the interaction between the rotational motion of the molecules in solid hydrogen and the lattice vibrations, resulting from the anisotropic van der Waals forces, have been investigated theoretically. For the radial part of the anisotropic intermolecular potential an exp–6 model has been adopted. First, the effect of the lattice vibrations, and of the anistropic blowing up of the crystal by the zero-point lattice vibrations, is discussed. The effective anisotropic interaction resulting from averaging the instantaneous interaction over the lattice vibrations is calculated by assuming a Gaussian distribution for the modulation of the relative intermolecular separations by the lattice vibrations. Secondly, the displacement of the rotational levels due to the self-energy of the molecules in the lattice is calculated both classically and quantum mechanically, and the resulting shifts in the frequencies of the rotational transitions in solid hydrogen are given. Finally, the splitting of the rotational levels due to the anisotropy of the self-energy effect is calculated. The theory is applied to the calculation of the asymmetry of the S0(0) triplet in the rotational Raman spectrum of solid parahydrogen, and of the specific heat anomaly in solid hydrogen at low ortho-concentrations.

HIGH Tc SUPERCONDUCTIVITY IN DIBORIDES BY MICRO-STRAIN AND FERMI LEVEL TUNING

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1591-1598 ◽  
Author(s):  
A. BIANCONI
Keyword(s):  
Chemical Potential ◽  
Resonance Energy ◽  
Zero Point ◽  
Shape Resonance ◽  
Modulation Amplitude ◽  
Lattice Vibrations ◽  
High Tc ◽  
Critical Range ◽  
Ε Phase ◽  
Point Lattice

It is shown that the process of T c amplification in diborides occurs in a particular region of the (ρ,ε) phase diagram, where ρ is the charge density and ε is the micro-strain in the metallic boron plane. The T c (ρ,ε) shows that the superconducting phase occurs while the chemical potential is tuned near the "shape resonance" of the diboride superlattice and the micro-strain is in a critical range. The range of the high T c phase is determined by the modulation amplitude Δshape of the shape resonance energy due to the zero-point lattice vibrations Δu rms (ε), pointing towards an electronic or vibronic pairing mechanism. It has been discussed that the McMillan's formula breaks down for the diborides.

A practical approach to Rietveld analysis. Comparison of some programs running on personal computers

1999 ◽  
Vol 14 (3) ◽  
pp. 171-180 ◽  
Author(s):  
Lj. Karanović ◽  
I. Petrović-Prelević ◽  
D. Poleti
Keyword(s):  
Standard Procedure ◽  
Zero Point ◽  
Rietveld Analysis ◽  
Peak Shift ◽  
Cell Parameters ◽  
Large Correlation ◽  
Fourier Filtering ◽  
Two Samples ◽  
Using Data ◽  
Point Lattice

Three computer programs for Rietveld analysis DBWS-9411, HILL-93.06, and FULLPROF-3.1 have been tested and compared using data for two samples of different complexity, spinel, and anglesite. The investigation shows that results are “program dependent.” The obtained R indices for spinel are in the ranges 10.60%–13.26%(Rwp) and 3.15%–5.25%(RB). Similarly, the ranges for anglesite are 9.76%–14.06%(Rwp) and 2.15%–5.06%(RB). Some atom and displacement parameters are significantly different, too. In attempt to define the standard procedure for Rietveld analysis, three parameters, n, BKPOS, and RLIM were examined. It was found that the most appropriate values for them are: n=8–10, BKPOS=90°, and RLIM=40° 2θ. Using Fourier filtering for background modeling, significantly lower R indices were obtained in comparison to polynomial and interpolated background. At the same time the great numbers of atom and cell parameters agree within ±3σmax and e.s.d.'s were identical or lower than those achieved for polynomial and interpolated background. It was found that the function given by Bérar and Baldinozzi (1993) (J. Appl. Crystallogr. 26, 128–129) much better described asymmetric peak profiles at low 2θ angles. This function and Fourier filtering were implemented only in FULLPROF, which has more possibilities and some advantages over the other two programs. In addition, the peak shift parameters (sample displacement and transparency) were tested. It was shown that under present circumstances these parameters do not have much effect on atom parameters and R indices. However, differences in unit cell parameters were considerable greater, most probably because of the large correlation between zero-point, lattice, and peak shift parameters.

scholarly journals Lifshitz transitions and zero point lattice fluctuations in sulfur hydride showing near room temperature superconductivity

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Antonio Bianconi ◽  
Thomas Jarlborg
Keyword(s):  
Critical Temperature ◽  
Fermi Surface ◽  
Fermi Energy ◽  
Room Temperature ◽  
Zero Point ◽  
Shape Resonance ◽  
Eliashberg Theory ◽  
Lifshitz Transitions ◽  
Point Lattice ◽  
Lattice Fluctuations

AbstractEmerets’s experiments on pressurized sulfur hydride have shown that H3S metal has the highest known superconducting critical temperature Tc = 203 K. The Emerets data show pressure induced changes of the isotope coefficient between 0.25 and 0.5, in disagreement with Eliashberg theory which predicts a nearly constant isotope coefficient.We assign the pressure dependent isotope coefficient to Lifshitz transitions induced by pressure and zero point lattice fluctuations. It is known that pressure could induce changes of the topology of the Fermi surface, called Lifshitz transitions, but were neglected in previous papers on the H3S superconductivity issue. Here we propose thatH3S is a multi-gap superconductor with a first condensate in the BCS regime (located in the large Fermi surface with high Fermi energy) which coexists with second condensates in the BCS-BEC crossover regime (located on the Fermi surface spots with small Fermi energy) near the and Mpoints.We discuss the Bianconi-Perali-Valletta (BPV) superconductivity theory to understand superconductivity in H3S since the BPV theory includes the corrections of the chemical potential due to pairing and the configuration interaction between different condensates, neglected by the Eliashberg theory. These two terms in the BPV theory give the shape resonance in superconducting gaps, similar to Feshbach resonance in ultracold fermionic gases, which is known to amplify the critical temperature. Therefore this work provides some key tools useful in the search for new room temperature superconductors.

scholarly journals Dispersion of Phonons in Ideal Crystals

1969 ◽  
Vol 22 (4) ◽  
pp. 471 ◽  
Author(s):  
NP Gupta
Keyword(s):  
Experimental Data ◽  
Phonon Dispersion ◽  
Zero Point ◽  
Lattice Vibrations ◽  
Rare Gases ◽  
Point Energy ◽  
Phonon Dispersion Curves ◽  
Debye Theory ◽  
Specific Heats ◽  
Theoretical Frequency

A quasiharmonic central force rigid-atom model has been used to study the lattice vibrations of frozen rare gases. The model takes care of interactions up to fourth neighbour and estimates zero-point energy and its volume derivatives by the Debye theory of specific heats. The theoretical frequency distribution and phonon dispersion curves are found to compare reasonably well with the available experimental data. Various causes of the discrepancies and possibilities of improvement of the results are discussed.

Theory of crystal-field interactions in solid hydrogen. I. Single ortho impurities in solid parahydrogen

1979 ◽  
Vol 57 (7) ◽  
pp. 933-943 ◽  
Author(s):  
S. Luryi ◽  
J. Van Kranendonk
Keyword(s):  
Crystal Field ◽  
Pair Potential ◽  
Zero Point ◽  
Debye Model ◽  
Lattice Vibrations ◽  
Sound Waves ◽  
Quantum Crystal ◽  
Energy Effect ◽  
Out Of Plane ◽  
The Difference

The theory of the crystal-field splitting, Ve, of the J = 1 level of an ortho impurity in a parahydrogen matrix, due to the coupling of the rotational motion of the ortho molecule to the lattice vibrations, is developed taking due account of the quantum-crystal nature of the solid. Two contributions to Ve are identified, both arising from the anisotropy in the lattice vibrations. One contribution is due to the difference in the relative zero-point motion of the molecules in in-plane and out-of-plane pairs in the hcp lattice, and is parametrized in terms of the second moments of the pair distribution function. The other contribution is due to the local, quasi-state distortion of the lattice around the impurity induced by the terms in the coupling linear in the phonon variables. This self-energy effect is calculated using a generalized Debye model for the self-consistent harmonic phonons, in which the anisotropy of the velocity and of the polarization of the sound waves is parametrized in terms of the elastic constants of the crystal. The theory is compared with that of Raich and Kanney, which is shown to be based on unrealistic assumptions. The remaining uncertainties in the anisotropic pair potential and the phonon renormalization factors are discussed in connection with the available experimental data.

On the photoconductivity of hot electrons in semiconductors at low temperatures

1983 ◽  
Vol 61 (6) ◽  
pp. 821-824
Author(s):  
E. F. El-Wahidy
Keyword(s):  
Low Temperatures ◽  
Theoretical Study ◽  
Zero Point ◽  
Potential Scattering ◽  
Hot Electrons ◽  
Average Lifetime ◽  
Deformation Potential ◽  
Acoustic Phonons ◽  
Temperature Dependences ◽  
Point Lattice

A theoretical study is made of the photoconductivity of hot photoelectrons interacting with acoustic phonons in n-type germanium at low temperature, T = 4 K, when the equipartition of the energy of phonons is not obeyed. Assuming that the energy relaxation of photoelectrons takes place by the spontaneous emission of acoustic phonons, the energy distribution of photoelectrons is obtained using the deformation potential scattering by acoustic phonons for the zero point lattice. The distribution function is then used in calculating the photoconductivity and average lifetime of photoelectrons. New temperature dependences of the photoconductivity and average lifetime arc obtained. It is shown that the new results differ from those reported when equipartition is obeyed.

scholarly journals Structure and thermal properties associated with some hydrogen bonds in crystals, II. Thermal expansion

1939 ◽  
Vol 170 (941) ◽  
pp. 241-251 ◽  
Keyword(s):  
Thermal Expansion ◽  
Thermal Properties ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Zero Point ◽  
Lattice Vibrations ◽  
Point Energy ◽  
Binding Forces ◽  
Anisotropy Of Thermal Expansion ◽  
Made In

One of the most important thermodynamic properties of a crystal in relation to its structure is the thermal expansion, which provides information on the lattice vibrations, and thus indirectly on the binding forces. The experiments described in this paper were carried out with a view to obtaining fresh information on hydrogen and hydroxyl bonds in crystals from measurements of the thermal expansion. A comparison of the thermal expansion of corresponding- hydrogen and deuterium compounds from about 90° K to room temperature was made in order to distinguish between lattice deformations due to zero point energy and thermal energy respectively. The marked anisotropy of thermal expansion in crystals containing hydrogen bonds throws interesting light on the structure.

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