scholarly journals On the Effective Coupling Strength in the Static Pion Theory

1957 ◽  
Vol 18 (1) ◽  
pp. 89-91
Author(s):  
Tetsuro Kobayashi ◽  
Jun'ichi Osada ◽  
Smio Tani
Keyword(s):  
Coupling Strength ◽  
Effective Coupling

Analysis of effective coupling strength in high‐frequency SQUIDs

1995 ◽  
Vol 78 (10) ◽  
pp. 6276-6282 ◽  
Author(s):  
M. Gottschlich ◽  
E. Sodtke ◽  
Y. Zhang ◽  
A. M. Portis
Keyword(s):  
Coupling Strength ◽  
High Frequency ◽  
Effective Coupling

scholarly journals Unconventional Superconductivity in Samarium Nitride

2021 ◽  
Author(s):  
◽  
William Doonan
Keyword(s):  
Fermi Level ◽  
Coupling Strength ◽  
Band System ◽  
Pair Potential ◽  
Effective Model ◽  
Unconventional Superconductivity ◽  
Effective Coupling ◽  
Triplet Pairing ◽  
Nitrogen Ion ◽  
Special Case

<p>We have studied the nature of unconventional superconductivity in the rare-earth nitride (REN) samarium nitride (SmN) for the purposes of providing a deeper understanding of the mechanisms that lead to such a phenomenon in an already extremely interesting material. An approximate low energy model has been introduced for SmN based on previous bandstructure calculation and recent experimental results. This consists of the non-dispersive 4f band associated with the samarium ion crossing through the dispersive 5d band associated with the nitrogen ion. Due to large spin polarisation in the bandstructure we need only consider the majority-spin 5d and 4f bands which lead to an essentially spinless two band system. Starting from this two band system, we apply the k dot p method to it in order to create an effective model for the system. This effective model for the material acts as the platform from which we study the possible triplet superconducting pairing. Basing our pairing on the electron-phonon interaction we have postulated the existence of triplet pairing in the 5d band, from which we have successfully characterised the pair potential in this system through the self-consistency equation. The pair potential Delta_d could be solved analytically in a special case where the Fermi level was equal to the 4f band. In this case we find that above a threshold effective coupling strength the superconducting state is established and analytically known. In contrast to this result for the more general case where the Fermi level is different to the 4f band we numerically recover a solution that was exponential in the effective coupling strength which is similar to the pairing as we expect from the single band case. Analytic solutions in this case were not able to be found, however, we know that from our numerical investigations there will exist a solution for any effective coupling strength, contrasting with the special case where the pairing amplitude can disappear below a certain threshold. In conjunction to these results we also examined the situation where the 5d and 4f bands have hybridised together in order to search for unique pairing that may be resistant to disorder. By keeping the triplet pairing only in the 5d band, this translates to hybrid pairing between electrons in the two hybridised bands. Results from the hybridised bands system show a new singlet-like pairing Delta_S which is even in k and singlet in the hybridised band indices. Preliminary numerical results suggest that this pairing indeed exists and occurs only near the avoided crossing of the hybridised bands. The existence of such a pairing, originating from triplet pairing, has exciting implications for the robustness of the superconductivity in the presence of disorder and/or impurities.</p>

scholarly journals Unconventional Superconductivity in Samarium Nitride

2021 ◽  
Author(s):  
◽  
William Doonan
Keyword(s):  
Fermi Level ◽  
Coupling Strength ◽  
Band System ◽  
Pair Potential ◽  
Effective Model ◽  
Unconventional Superconductivity ◽  
Effective Coupling ◽  
Triplet Pairing ◽  
Nitrogen Ion ◽  
Special Case

<p>We have studied the nature of unconventional superconductivity in the rare-earth nitride (REN) samarium nitride (SmN) for the purposes of providing a deeper understanding of the mechanisms that lead to such a phenomenon in an already extremely interesting material. An approximate low energy model has been introduced for SmN based on previous bandstructure calculation and recent experimental results. This consists of the non-dispersive 4f band associated with the samarium ion crossing through the dispersive 5d band associated with the nitrogen ion. Due to large spin polarisation in the bandstructure we need only consider the majority-spin 5d and 4f bands which lead to an essentially spinless two band system. Starting from this two band system, we apply the k dot p method to it in order to create an effective model for the system. This effective model for the material acts as the platform from which we study the possible triplet superconducting pairing. Basing our pairing on the electron-phonon interaction we have postulated the existence of triplet pairing in the 5d band, from which we have successfully characterised the pair potential in this system through the self-consistency equation. The pair potential Delta_d could be solved analytically in a special case where the Fermi level was equal to the 4f band. In this case we find that above a threshold effective coupling strength the superconducting state is established and analytically known. In contrast to this result for the more general case where the Fermi level is different to the 4f band we numerically recover a solution that was exponential in the effective coupling strength which is similar to the pairing as we expect from the single band case. Analytic solutions in this case were not able to be found, however, we know that from our numerical investigations there will exist a solution for any effective coupling strength, contrasting with the special case where the pairing amplitude can disappear below a certain threshold. In conjunction to these results we also examined the situation where the 5d and 4f bands have hybridised together in order to search for unique pairing that may be resistant to disorder. By keeping the triplet pairing only in the 5d band, this translates to hybrid pairing between electrons in the two hybridised bands. Results from the hybridised bands system show a new singlet-like pairing Delta_S which is even in k and singlet in the hybridised band indices. Preliminary numerical results suggest that this pairing indeed exists and occurs only near the avoided crossing of the hybridised bands. The existence of such a pairing, originating from triplet pairing, has exciting implications for the robustness of the superconductivity in the presence of disorder and/or impurities.</p>

scholarly journals Dipole radiation and beyond from axion stars in electromagnetic fields

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Mustafa A. Amin ◽  
Andrew J. Long ◽  
Zong-Gang Mou ◽  
Paul M. Saffin
Keyword(s):  
Electromagnetic Fields ◽  
Parametric Resonance ◽  
Coupling Strength ◽  
Coupling Parameter ◽  
Strong Dependence ◽  
Dipole Radiation ◽  
Large Coupling ◽  
External Electromagnetic Fields ◽  
Order Of Magnitude ◽  
Dimensionless Coupling

Abstract We investigate the production of photons from coherently oscillating, spatially localized clumps of axionic fields (oscillons and axion stars) in the presence of external electromagnetic fields. We delineate different qualitative behaviour of the photon luminosity in terms of an effective dimensionless coupling parameter constructed out of the axion-photon coupling, and field amplitude, oscillation frequency and radius of the axion star. For small values of this dimensionless coupling, we provide a general analytic formula for the dipole radiation field and the photon luminosity per solid angle, including a strong dependence on the radius of the configuration. For moderate to large coupling, we report on a non-monotonic behavior of the luminosity with the coupling strength in the presence of external magnetic fields. After an initial rise in luminosity with the coupling strength, we see a suppression (by an order of magnitude or more compared to the dipole radiation approximation) at moderately large coupling. At sufficiently large coupling, we find a transition to a regime of exponential growth of the luminosity due to parametric resonance. We carry out 3+1 dimensional lattice simulations of axion electrodynamics, at small and large coupling, including non-perturbative effects of parametric resonance as well as backreaction effects when necessary. We also discuss medium (plasma) effects that lead to resonant axion to photon conversion, relevance of the coherence of the soliton, and implications of our results in astrophysical and cosmological settings.

scholarly journals Control of the coupling strength and linewidth of a cavity magnon-polariton

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Isabella Boventer ◽  
Christine Dörflinger ◽  
Tim Wolz ◽  
Rair Macêdo ◽  
Romain Lebrun ◽  
...  
Keyword(s):  
Coupling Strength

Complex projection synchronization of fractional order uncertain complex-valued networks with time-varying coupling

2019 ◽  
Vol 33 (29) ◽  
pp. 1950351 ◽  
Author(s):  
Dawei Ding ◽  
Xiaolei Yao ◽  
Hongwei Zhang
Keyword(s):  
Fractional Order ◽  
Coupling Strength ◽  
Dynamic Networks ◽  
Sufficient Conditions ◽  
Feedback Gain ◽  
Time Varying ◽  
Order Complex ◽  
Unknown Parameters ◽  
Synchronization Problem ◽  
Complex Valued

In this paper, the complex projection synchronization problem of fractional complex-valued dynamic networks is investigated. Considering the time-varying coupling and unknown parameters of the fractional order complex network, several decentralized adaptive strategies are designed to adjust the coupling strength and controller feedback gain in order to investigate the complex projection synchronization problem of the system. Moreover, based on the designed identification law, the uncertain parameters in the network can be estimated. Using adaptive law which balances the time-varying coupling strength and the feedback gain of the controller, some sufficient conditions are obtained for the complex projection synchronization of complex networks. Finally, numerical simulation examples are provided to illustrate the efficiency of the complex projection synchronization strategies of the fractional order complex dynamic networks.

TRANSITION FREQUENCY OF STRONG-COUPLING IMPURITY BOUND POLARON IN AN ASYMMETRIC QUANTUM DOT

2012 ◽  
Vol 11 (03) ◽  
pp. 1250026 ◽  
Author(s):  
CHENG-SHUN WANG ◽  
YU-FANG CHEN ◽  
JING-JIN XIAO
Keyword(s):  
Excited State ◽  
Coupling Strength ◽  
State Energy ◽  
Transition Frequency ◽  
Phonon Coupling ◽  
Excited State Energy ◽  
Bound Polaron ◽  
Asymmetric Quantum Dot ◽  
Asymmetric Quantum ◽  
Electron Phonon Coupling

Properties of the excited state of strong-coupling impurity bound polaron in an asymmetric quantum dot are studied by using linear combination operator and unitary transformation methods. The first internal excited state energy, the excitation energy and the transition frequency between the first internal excited and the ground states of the impurity bound polaron as functions of the transverse and the longitudinal effective confinement lengths of the dot, the electron–phonon coupling strength and the Coulomb bound potential were derived. Our numerical results show that they will increase with decreasing the effective confinement lengths, due to interesting quantum size confining effects. But they are an increasing functions of the Coulomb bound potential. The first internal excited state energy is a decreasing function of the electron–phonon coupling strength whereas the transition frequency and the excitation energy are an increasing one of the electron–phonon coupling strength.

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