Equilibrium and response properties of a many-polaron gas

Serghei Klimin (U Antwerpen)

Dec 13. 2019, 09:00 — 09:40

Many-body effects such as quantum statistics, particle-particle interaction, correlation, exchange and screening, play a crucial role in the physics of the many-polaron systems. Here, we report on our theoretical studies of several problems related to interacting polarons of different types. The talk is particularly focused on an interacting polaron gas in complex polar crystals and rather unconventional many-polaron systems of ripplonic polarons which are formed near a liquid helium surface. First, we address on superconductivity in doped strontium titanate and at a SrTiO3/LaAlO3 interface. Strontium titanate is known as the most dilute superconductor and exhibits many unusual properties. It is at the moment probably the only superconductor where superconductivity is provided by the electron-phonon interaction with optical phonons. Their energies are comparable with the Fermi energy of electrons, so that the Migdal-Eilashberg theory is not applicable. We calculated the transition temperature as a function of the electron concentration [1, 2] using the Kizhnits-Maksimov-Homskii dielectric function method. We have obtained a good agreement with experimental results and have got an anomalous sign of the isotope effect, in line with experimental observations. Second, the optical conductivity in complex polar crystals, particularly in doped strontium titanate, exhibits mid-infrared band convincingly described within the many-polaron picture [3, 4]. Our recent investigations refine previous results, explaining the low-energy features of the optical conductivity in terms of dynamic screening [4]. We consider also specific many-polaron states which arise from the interaction of electrons confined to the liquid helium surface with the vibrations of the surface – ripplonic polarons in multielectron bubbles [5] and at a flat helium surface [6]. Different phase states and phase diagrams of ripplonic-polaron gas are obtained, such as electron liquid, polaron liquid and Wigner solid of polarons or electrons. [1] S. N. Klimin, J. Tempere, J. T. Devreese and D. van der Marel, J. Sup. Nov. Magn. 30, 757 (2017), [2] S. N. Klimin, J. Tempere, J. T. Devreese, J. He, C. Franchini and G. Kresse, J. Sup. Nov. Magn. 32, 2739 (2019). [3] J. T. Devreese, S. N. Klimin, J. L. M. van Mechelen and D. van der Marel, Phys. Rev. B 81, 125119 (2010) [4] S. N. Klimin, J. Tempere, J. T. Devreese, C. Franchini and G. Kresse (to be published) [5] J. Tempere, S. N. Klimin, I. F. Silvera and J.T. Devreese, Eur. Phys. J. B 32, 329 (2003) [6] S. N. Klimin, J. Tempere, V. R. Misko and M. Wouters, Eur. Phys. J. B 89, 172 (2016)

Further Information
ESI Boltzmann Lecture Hall
Associated Event:
Polarons in the 21st Century (Workshop)
Jozef Devreese (U Antwerpen)
Cesare Franchini (U of Vienna)
Georg Kresse (U of Vienna)
Jacques Tempere (U Antwerpen)