scholarly journals Dispersion and Damping of Phononic Excitations in Fermi Superfluid Gases in 2D

2020 ◽  
Vol 5 (1) ◽  
pp. 13
Author(s):  
Lars-Paul Lumbeeck ◽  
Jacques Tempere ◽  
Serghei Klimin
Keyword(s):  
Sound Velocity ◽  
Collective Excitation ◽  
Binding Energies ◽  
Collective Excitations ◽  
Initial Increase ◽  
Response Functions ◽  
Action Functional ◽  
Integral Formalism ◽  
Damping Rate ◽  
Bogoliubov Excitations

We calculate the sound velocity and the damping rate of the collective excitations of a 2D fermionic superfluid in a non-perturbative manner. Specifically, we focus on the Anderson–Bogoliubov excitations in the BEC-BCS crossover regime, as these modes have a sound-like dispersion at low momenta. The calculation is performed within the path-integral formalism and the Gaussian pair fluctuation approximation. From the action functional, we obtain the propagator of the collective excitations and determine their dispersion relation by locating the poles of this propagator. We find that there is only one kind of collective excitation, which is stable at T = 0 and has a sound velocity of v F / 2 for all binding energies, i.e., throughout the BEC-BCS crossover. As the temperature is raised, the sound velocity decreases and the damping rate shows a non-monotonous behavior: after an initial increase, close to the critical temperature T C the damping rate decreases again. In general, higher binding energies provide higher damping rates. Finally, we calculate the response functions and propose that they can be used as another way to determine the sound velocity.

scholarly journals Simulation of Collective Excitations in Long Josephson Junction Stacks

2018 ◽  
Vol 173 ◽  
pp. 06011
Author(s):  
Ilhom Rahmonov ◽  
Yury Shukrinov ◽  
Pavlina Atanasova ◽  
Elena Zemlyanaya ◽  
Oksana Streltsova ◽  
...  
Keyword(s):  
Josephson Junction ◽  
Traveling Wave ◽  
Josephson Junctions ◽  
Collective Excitation ◽  
Radiation Power ◽  
Bias Current ◽  
Collective Excitations ◽  
Phase Dynamics

The phase dynamics of a stack of long Josephson junctions has been studied. Both inductive and capacitive couplings between Josephson junctions have been taken into account in the calculations. The IV-curve, the dependence on the bias current of the radiation power and dynamics of each JJs of the stack have been investigated. The coexistence of the charge traveling wave and fluxon states has been observed. This state can be considered as a new collective excitation in the system of coupled Josephson junctions. We demonstrate that the observed collective excitation leads to the decrease of radiation power from the system.

EELS white line intensities calculated for the 3d and 4d metals

1989 ◽  
Vol 47 ◽  
pp. 388-389
Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz
Keyword(s):  
Experimental Data ◽  
Line Intensity ◽  
Transition Probabilities ◽  
Initial Increase ◽  
White Line ◽  
Hartree Fock ◽  
Line Intensities ◽  
Integrated Intensity ◽  
X Ray Absorption ◽  
The Continuum

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.

Sound velocity of glassy Pd 80 Si 20 after heavy-ion irradiation at low temperatures

2002 ◽  
Vol 82 (11) ◽  
pp. 2333-2339
Author(s):  
G. Schumacher ◽  
R. C. Birtcher ◽  
D. P. Renusch ◽  
M. Grimsditch ◽  
L. E. Rehn
Keyword(s):  
Sound Velocity ◽  
Low Temperatures ◽  
Ion Irradiation ◽  
Heavy Ion ◽  
Heavy Ion Irradiation
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