Short-Time Dynamics and Electron-Lattice Interaction in Iron Based Superconductors
Final Report Abstract
Understanding quantum materials is at the forefront of fundamental condensed matter physics research. These materials have large number of degrees of freedom that interact strongly. The latter leads to a variety of functional properties interesting from applications point of view. Examples include high temperature superconductivity, in the iron-based superconductors. The overall objective of the project was two-fold. (i) Staying within the realm of equilibrium physics study how crucial electron-phonon interaction and spin-orbit coupling is in these materials. The question is non-trivial because electrons are the main actors here, and effect of electron-electron interaction is where focus is mostly given. Likewise, being single-electron property, spin-orbit is often neglected. (ii) Study out-ofequilibrium dynamics such as in pump-probe spectroscopy. This is a more recently developed experimental tool that promises to give complementary information compared to more traditional equilibrium probes. The theoretical tools used here are standard methods of many-body physics such as quantum field theory. For out-of-equilibrium problems we used both Equation of motion method and Keldysh two-time field theory formalism. Our results showed that electron-phonon interaction can have profound effect on electronic phase transitions. We also showed how out-of-equilibrium pumpprobe spectroscopy can be used to reveal competing phases that occur often in correlated systems. Both these conclusions are rather general, and the lessons learnt here can be useful to other materials. Methodology: Many-body field theory techniques in and out of equilibrium. From a technical point of view the tasks were of two varieties. (i) Study of equilibrium properties of many-body electronic systems. In this case one can use standard techniques of quantum field theory to implement quantum statistics correctly. A second technique which is often used in such problems is to simplify the microscopic description by invoking an "effective field theory" that is appropriate to study low-energy properties. The foundation of it is based on renormalization group ideas, and it involves keeping only the essential degrees of freedom and "integrating out" the non-essential variables. (ii) Study of out-of-equilibrium dynamics where standard field theory techniques fail because the density matrix is not that in equilibrium and is often unknown a priori, and also because time translation symmetry is, by definition, broken. We used two tools, namely Equation of motion method and Keldysh two-time formalism, which are standard to deal with out-of-equilibrium problems. Note, the challenge of the tasks was not to develop technical tools, but rather to use standard well-known tools to extract important physics.
Publications
- Comptes Rendus Physique 17, 113 (2016)
Gallais and I. Paul
(See online at https://doi.org/10.1016/j.crhy.2015.10.001) - Phys. Rev. B 96, 014517 (2017)
J. Boeker, P.A. Volkov, K.B. Efetov, and I. Eremin
(See online at https://doi.org/10.1103/PhysRevB.96.014517) - Phys. Rev. B 96, 195146 (2017)
D. Labat and I. Paul
(See online at https://doi.org/10.1103/PhysRevB.96.195146) - Phys. Rev. Lett. 118, 227601 (2017)
I. Paul and M. Garst
(See online at https://doi.org/10.1103/PhysRevLett.118.227601) - Phys. Rev. B 98, 024522 (2018)
M. A. Müller, P. Shen, M. Dzero, I. Eremin
(See online at https://doi.org/10.1103/PhysRevB.98.024522) - New J. Phys. 21, 083021 (2019)
J. Böker, P. A. Volkov, P. J. Hirschfeld, I. Eremin
(See online at https://doi.org/10.1088/1367-2630/ab2a82) - Phys. Rev. B 100, 140501 (2019)
M. A. Müller, P. A. Volkov, I. Paul, I. Eremin
(See online at https://doi.org/10.1103/PhysRevB.100.140501) - Phys. Rev. B 99, 035131 (2019)
M. Lakehal and I. Paul
(See online at https://doi.org/10.1103/PhysRevB.99.035131)
