Ab Initio Studies on Superconductivity in Alkali-Doped Fullerides

This book covers high-transition temperature ( T c ) s -wave superconductivity and the neighboring Mott insulating phase in alkali-doped fullerides. The author presents (1) a unified theoretical description of the phase diagram and (2) a nonempirical calculation of T c . For these purposes, the author employs an extension of the DFT+DMFT (density-functional theory + dynamical mean-field theory). He constructs a realistic electronphonon-coupled Hamiltonian with a newly formulated downfolding method. The Hamiltonian is analyzed by means of the extended DMFT. A notable aspect of the approach is that it requires only the crystal structure as a priori knowledge.

Remarkably, the nonempirical calculation achieves for the first time a quantitative reproduction of the experimental phase diagram including the superconductivity and the Mott phase. The calculated T c agrees well with the experimental data, with the difference within 10 K.

The book provides details of the computational scheme, which can also be applied to other superconductors and other phonon-related topics. The author clearly describes a superconducting mechanism where the Coulomb and electronphonon interactions show an unusual cooperation in the superconductivity thanks to the JahnTeller nature of the phonons.

Nominated as an outstanding Ph.D. thesis by The University of Tokyo's Applied Physics Department in 2014 Develops a novel downfolding scheme, constrained density functional perturbation theory, to construct realistic low-energy models for electronphonon coupled systems Reveals an effectively negative intramolecular exchange interactions realized by the JahnTeller phonons, which results in a surprising synergy of phonons and Coulomb correlations behind the exotic s-wave pairing Reproduces quantitatively the experimental transition temperature Tc of unconventional superconductivity by an ab initio theory without introducing any empirical/scaling parameters Includes supplementary material: sn.pub/extras

Auteur
Dr. Yusuke Nomura

Department of Applied Physics, The University of Tokyo

Texte du rabat

This book covers high-transition temperature (Tc) s-wave superconductivity and the neighboring Mott insulating phase in alkali-doped fullerides. The author presents (1) a unified theoretical description of the phase diagram and (2) a nonempirical calculation of Tc. For these purposes, the author employs an extension of the DFT+DMFT (density-functional theory + dynamical mean-field theory). He constructs a realistic electronphonon-coupled Hamiltonian with a newly formulated downfolding method. The Hamiltonian is analyzed by means of the extended DMFT. A notable aspect of the approach is that it requires only the crystal structure as a priori knowledge.

Remarkably, the nonempirical calculation achieves for the first time a quantitative reproduction of the experimental phase diagram including the superconductivity and the Mott phase. The calculated Tc agrees well with the experimental data, with the difference within 10 K.

The book provides details of the computational scheme, which can also be applied to other superconductors and other phonon-related topics. The author clearly describes a superconducting mechanism where the Coulomb and electron­phonon interactions show an unusual cooperation in the superconductivity thanks to the JahnTeller nature of the phonons.

Résumé

This book covers high-transition temperature (Tc) s-wave superconductivity and the neighboring Mott insulating phase in alkali-doped fullerides. The author presents (1) a unified theoretical description of the phase diagram and (2) a nonempirical calculation of Tc. For these purposes, the author employs an extension of the DFT+DMFT (density-functional theory + dynamical mean-field theory). He constructs a realistic electronphonon-coupled Hamiltonian with a newly formulated downfolding method. The Hamiltonian is analyzed by means of the extended DMFT. A notable aspect of the approach is that it requires only the crystal structure as a priori knowledge.

Remarkably, the nonempirical calculation achieves for the first time a quantitative reproduction of the experimental phase diagram including the superconductivity and the Mott phase. The calculated Tc agrees well with the experimental data, with the difference within 10 K.

The book provides details of the computational scheme, which can also be applied to other superconductors and other phonon-related topics. The author clearly describes a superconducting mechanism where the Coulomb and electron­phonon interactions show an unusual cooperation in the superconductivity thanks to the JahnTeller nature of the phonons.

Contenu

Introduction to superconductivity in alkali-doped fullerides.- Methods: Ab initio downfolding and model-calculation techniques.- Application of cDFPT to alkali-doped fullerides.- Analysis of low-energy Hamiltonians with extended DMFT.- Concluding remarks.