I like to illustrate this question as below. In real solids, interactions of electrons and quasi- particles (phonon, spin (magnon), etc.,) are very important and that give rise to many important properties. For example, electron-phonon coupling gives superconducting property in some of the systems. Further, spin-phonon coupling gives rise to magnetic property in some of the magnetic materials. Similarly, the phonon-phonon coupling is responsible for anharmonicity which may give rise to the thermal expansion of the solids. Raman spectroscopy measurement gives the optical phonon energy of the systems. In addition, the width of the Raman peak is directly related to electron-phonon, phonon-phonon and spin-phonon coupling (interactions) exist in the system. Hence, the width of the Raman mode can measure (qualitatively) the interaction (electron-phonon, phonon-phonon and spin-phonon) of the system.
Whether, because of this interaction (electron-phonon, phonon-phonon, and spin-phonon coupling), the associated properties (superconductivity, thermal expansion, magnetic properties) are arising in material or vice versa?
In other words, is electron -phonon (phonon-phonon or spin-phonon) coupling cause or effect to give the associated property?
I kindly request you to answer this question and it will help my research work lot.
Thanks.
Dear Rajaji,
Welcome,
At first i would like to point out that i am an electronic engineer and a not physicist. So, one would understand my answer in this context.
When we have a solid , this solid contains electrons, the majority of them is bound to their parent atoms and the rest can move freely inside the solid. These free electrons are capable to move freely along the material.
The material contains also, thermal energy causing the vibration of the atoms leading to formation of phonons which are quantized thermal vibrations.
Both ensembles, the electrons and phonons interchange the energy and momentum as they share the same space. This interaction causes the two ensembles to get in equilibrium with each other. The interaction means the two sets of particles or quasiparicles collide with each other continuously leading to the phenomenon of scattering.
Let us give a specific example which is the mobility of free electrons in a conductor under an applied electric field E. If the material is pure, crystalline, and free from defects, and the temperature is zero kelvin which means that there is no phonons, the electrons will move inside the crystal with an effective mass as if it move in vacuum without any scattering. If the material is supplied with thermal energy to form phonons, then the electrons will be scattered on the photons and gets a limited mobility such that the drift velocity v= mobility x the applied electric field.
This example shows clearly the interaction between the free electrons and phonons in a solid causes the limited mobility of the electrons.
So, such coupling led to the limited mobility of free carriers in solids.
Hope this answer contributed to your question.
Best wishes
Hi Rajaji.
One can imagine this: in a certain volume water is poured, water molecules are electrons, waves on surface and in volume of water-phonons. Waves of energy density (fermions) in electronic structure determine different quantum characteristics. Solitons interact as particles, waves form in phases. As that is such a picture.
Thank you all ( Abdullah Hasan Jabbar , Abdelhalim Zekry , Konstantin Pavlov, and Amelia Carolina Sparavigna ) for useful discussion about this question.
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