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.

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.

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 Early Results From the Cosmic Background Explorer (COBE)

1990 ◽  
Vol 123 ◽  
pp. 9-18
Author(s):  
J. C. Mather ◽  
M. G. Hauser ◽  
C. L. Bennett ◽  
N. W. Boggess ◽  
E. S. Cheng ◽  
...  
Keyword(s):  
Chemical Potential ◽  
Zero Point ◽  
Far Infrared ◽  
Strong Limit ◽  
Cosmic Background ◽  
Early Results ◽  
Local Sources ◽  
Infrared Background ◽  
Reduction Methods ◽  
Microwave Radiometers

AbstractThe Cosmic Background Explorer, launched November 18, 1989, has nearly completed its first full mapping of the sky with all three of its instruments: a Far Infrared Absolute Spectrophotometer (FIRAS) covering 0.1 to 10 mm, a set of Differential Microwave Radiometers (DMR) operating at 3.3, 5.7, and 9.6 mm, and a Diffuse Infrared Background Experiment (DIRBE) spanning 1 to 300 µm in ten bands. A preliminary map of the sky derived from DIRBE data is presented. Initial cosmological implications include: a limit on the Comptonization y parameter of 10−3, on the chemical potential μ parameter of 10−2, a strong limit on the existence of a hot smooth intergalactic medium, and a confirmation that the dipole anisotropy has the spectrum expected from a Doppler shift of a blackbody. There are no significant anisotropies in the microwave sky detected, other than from our own galaxy and a cosθ dipole anisotropy whose amplitude and direction agree with previous data. At shorter wavelengths, the sky spectrum and anisotropies are dominated by emission from ‘local’ sources of emission within our Galaxy and Solar System. Preliminary comparison of IRAS and DIRBE sky brightnesses toward the ecliptic poles shows the IRAS values to be significantly higher than found by DIRBE at 100 μm. We suggest the presence of gain and zero-point errors in the IRAS total brightness data. The spacecraft, instrument designs, and data reduction methods are described.

scholarly journals The gap amplification at a shape resonance in a superlattice of quantum stripes: A mechanism for high Tc

1996 ◽  
Vol 100 (3) ◽  
pp. 181-186 ◽  
Author(s):  
A. Perali ◽  
A. Bianconi ◽  
A. Lanzara ◽  
N.L. Saini
Keyword(s):  
Shape Resonance ◽  
High Tc

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.

The effect of magnetic field on RbCl quantum pseudodot qubit

2015 ◽  
Vol 29 (19) ◽  
pp. 1550098 ◽  
Author(s):  
Jing-Lin Xiao
Keyword(s):  
Magnetic Field ◽  
Probability Density ◽  
Chemical Potential ◽  
Zero Point ◽  
Strong Electron ◽  
Rbcl Quantum Pseudodot ◽  
Quantum Pseudodot ◽  
Dimensional Electron Gas ◽  
Increasing Function ◽  
Polaron Radius

Under the condition of strong electron–LO–phonon coupling in a RbCl quantum pseudodot (QPD) with an applied magnetic field (MF), the eigenenergies and the eigenfunctions of the ground and the first excited states (GFES) are obtained by using a variational method of the Pekar type (VMPT). A single qubit can be realized in this two-level quantum system. The electron’s probability density oscillates in the RbCl QPD with a certain period of [Formula: see text] fs when the electron is in the superposition state of the GFES. The results indicate that due to the presence of the asymmetrical structure in the z direction of the RbCl QPD, the electron’s probability density shows double-peak configuration, whereas there is only peak if the confinement is a symmetric structure in the x and y directions of the RbCl QPD. The oscillating period is an increasing function of the cyclotron frequency and the polaron radius, whereas it is a decreasing one of the chemical potential of the two-dimensional electron gas and the zero point of the pseudoharmonic potential (PP).

Temperature dependence of the chemical potential of high-Tc superconductors

1990 ◽  
Vol 165-166 ◽  
pp. 1605-1606 ◽  
Author(s):  
G. Rietveld ◽  
M.A. van Veenendaal ◽  
D. van der Marel ◽  
J.E. Mooij
Keyword(s):  
Temperature Dependence ◽  
Chemical Potential ◽  
High Tc Superconductors ◽  
High Tc
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