Strong coupling of the proton-phonon system in KDP

Ferroelectric KDP is best described through an Ising Hamiltonian in a transverse field, coupled linearly to the phonon system. The soft optical mode is coupled to the order parameter, whereas the dependence of the transition temperature on deuteration follows from the coupling of the tunneling frequency to another optical branch. After unitary transformations of the Hamiltonian, in which parts of the phonon coupling are dealt with, an analytic upper bound for the free energy of the KDP system is found using Bogoliubov's inequality. This allows a choice from the class of different canonical transformations of that one leading to the lowest free energy bound. Then, in a mean field approximation, the effective coupling constant is found to be a solution of an implicit analytic function, which is solved numerically for different coupling strengths. In the ferroelectric region a strong temperature dependence of the effective coupling is found; crossing into the paraelectric region, its value changes smoothly for weak and abruptly for medium coupling strengths. These results parallel the behavior found in phonon coupled exciton systems.

show abstract

scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.

Contact Info

hi@scite.ai

10624 S. Eastern Ave., Ste. A-614

Henderson, NV 89052, USA

Blog Terms and Conditions API Terms Privacy Policy Contact Cookie Preferences Do Not Sell or Share My Personal Information

Made with 💙 for researchers

Part of the Research Solutions Family.

Strong coupling of the proton-phonon system in KDP

Abstract: A mixed mode model for KDP is proposed, which includes beside the coupling to the c-mode the coupling to a local mode in the x-y plane. The transition temperature and the spectrum of the collective excitations are obtained.

Cited by 2 publications

References 8 publications

Energy band calculations on helical systems

Energy band calculations on helical systems

Variational treatment of the proton–phonon system in KDP

Contact Info

Product

Resources

About