Non-equilibrium phase transitions
Final Report Abstract
Phase transitions rank among the most fascinating phenomena of statistical physics. Therefore, understanding phase transitions has attracted a great deal of research interest throughout the last century. By now, we are using the knowledge steaming from this research in everyday life, such as in classical antifreeze substances. Especially fascinating are the phase transitions found in quantum systems, as they often defy our intuition. Exploring phase transitions in those quantum systems had an immense impact on applications, leading to the development of, e.g,. phase change materials, phase change memories or superconductors. From a theorist’s point of view phase transitions in strongly correlated quantum system pose a formidable task, even after powerful tools, such as the Ginsburg-Landau approach and the renormalization group theory, have been developed. Thus even today phase transitions in those systems are an active field of research. The description of phase transitions has focused mainly on equilibrium, but recently controlled experimental realizations of non-equilibrium quantum many-body systems were devised as well. Therefore, non-equilibrium has increasingly shifted into the focus of research attention. Within this project I aimed to contribute to the understanding of non-equilibrium quantum phase transitions. I contributed to this by providing a mechanism of how such transitions can be tuned in optically addressed electron-phonon systems. This work might open up the intriguing possibility of non-equilibrium controlled transient superconductivity at unprecedentedly high temperatures. I also pushed the boundaries of methods able to describe strongly correlated physics (as needed to interrogate generic phase transitions) in periodically driven scenarios, by extending the functional renormalization group to this physical realm. In equilibrium the functional renormalization group has been vital for the understanding of phase transitions in two-dimensional systems. Therefore, by the extension of the method to periodically driven systems I hope to contribute to the understanding of non-equilibrium phase transitions under periodic drive in the future. Deviating from the original proposal, triggered by the opportunity to collaborate closely with multiple experimental groups, I started to run time-dependent Ginzburg-Landau simulations which provide phenomenologically motivated insights into the non-equilibrium physics of phase transitions. I have explained the observation of a particularly puzzling short life time of optically excited modes in pyrochlore oxids as well as some recently obtained experimental results pertaining to the nature of two-dimensional superconductors under the influence of non-equilibrium drive. In the future I plan to continue exploring the highly exciting field of non-equilibrium phase transitions from a ”quantum matter on demand perspective”, that is the question of how to engineer quantum properties at will by non-equilibrium means, such as optical excitation. The research project has put me in a natural position to do so, as I can contribute to the field from multiple angles: (i) using a functional renormalization group devised for periodically driven systems, (ii) exploring the non-equilibrium physics of driven electron-phonon systems as well as by (iii) a strong network with experimental groups leading in the field of non-equilibrium quantum matter on demand.
Publications
- “Functional renormalization group in Floquet space”. Phys. Rev. B 94, 245116 (2016)
A.K. Eissing, V. Meden and D.M. Kennes
(See online at https://doi.org/10.1103/PhysRevB.94.245116) - “Electromagnetic Response during a Quench Dynamics to Superconducting State: Time-Dependent Ginzburg-Landau Analysis”. Phys. Rev. B 96, 064507 (2017)
D.M. Kennes, A. J. Millis
- “Non-equilibrium Optical Conductivity: General Theory and Application to Transient Phases”. Phys. Rev. B 96, 054506 (2017)
D.M. Kennes, E.Y. Wilner, D.R. Reichman, A.J. Millis
(See online at https://doi.org/10.1103/PhysRevB.96.054506) - “Small quenches and thermalization”. Phys. Rev. B 95, 035147 (2017)
D.M. Kennes, J.C. Pommerening, J. Diekmann, C. Karrasch, V. Meden
(See online at https://doi.org/10.1103/PhysRevB.95.035147) - “The Adiabatically Deformed Ensemble: Engineering Non-Thermal States of Matter”. Phys. Rev. B 96, 024302 (2017)
D.M. Kennes
- “Transient superconductivity from electronic squeezing of optically pumped phonons”. Nature Physics 13, 479 (2017)
D.M. Kennes, E.Y. Wilner, D.R. Reichman, A.J. Millis
(See online at https://doi.org/10.1038/NPHYS4024) - “Transport in quasiperiodic interacting systems: from superdiffusion to subdiffusion”. EPL 119 (2017) 37003
Y. Bar Lev, D.M. Kennes, C. Klckner, D.R. Reichman, C. Karrasch
(See online at https://doi.org/10.1209/0295-5075/119/37003) - “Evidence of an improper displacive phase transition in Cd2 Re2 O7 via time-resolved coherent phonon spectroscopy”. Phys. Rev. Lett. 120, 047601 (2018)
J.W. Harter, D.M. Kennes, H. Chu, A. de la Torre, Z.Y. Zhao, J.-Q. Yan, D.G. Mandrus, A.J. Millis, and D. Hsieh
(See online at https://doi.org/10.1103/PhysRevLett.120.047601)
