Interplay of charge and structure in transition metal oxides
Event details
| Date | 06.03.2017 |
| Hour | 13:15 › 14:15 |
| Speaker | Prof. Peter B. Littlewood, University of Chicago, USA |
| Location | |
| Category | Conferences - Seminars |
The boundary between metal and insulator remains a fruitful source of emergent phenomena in materials, ranging from oxides, to cold atoms. Typically the insulating side of this boundary is occupied by an electronic crystal (though often disordered), and at higher temperatures a polaronic liquid or bad metal. While the paradigm Hamiltonian for this transition involves only short –range electronic correlations, in practice the transition is tuned by disorder, by screening of longer range Coulomb forces, and by coupling to the lattice.
I will discuss the physics of small polarons in SrTiO3, and in particular the collapse of strong Frohlich coupling with increasing metallicity as the long-range Coulomb mediated interaction with optic phonons is screened out. SrTiO3 is an unusually good metal and an enigmatic superconductor at very low carrier concentrations.
While electric charges can be screened, the same is not true of strain fields, which have intrinsic long-range interactions that cannot be screened. When strain fields are produced as a secondary order parameter in phase transitions - as for example in ferroelectrics - this produces unexpected consequences for the dynamics of order parameter fluctuations, including the generation of a gap in what would otherwise have been expected to be Goldstone modes. In some cases, e.g. manganites and nickelates, other intra-cell modes can nonlinearly screen the order parameter, which produces a strong sensitivity of ordering to octahedral rotations, essentially a jamming transition. This is relevant for tuning entropic effects at phase transitions, perhaps to enhance electro-caloric and magneto-electric effects. Wang et al. Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid. Nature Materials (2016). DOI: 10.1038/NMAT4623 Elastic interactions and control of the Mott transition, G. G. Guzmán-Verri, R. T. Brierley, P. B. Littlewood arXiv:1701.02318 Why is the electrocaloric effect so small in ferroelectrics? G. G. Guzmán-Verri, P. B. Littlewood, APL Mater. 4, 064106 (2016)
Bio: Peter B. Littlewood is a condensed matter theorist at the University of Chicago who is a Professor in Physics, the James Franck Institute, and the College. His research interests include superconductivity and superfluids, strongly correlated electronic materials, collective dynamics of glasses and density waves in solids, neuroscience, and applications of materials for energy and sustainability.
Dr. Littlewood came to Chicago and to Argonne in 2011 after being appointed associate laboratory director of the lab’s Physical Sciences and Engineering directorate, and served from 2014 to 2016 as Laboratory DIrector. He spent the previous 14 years at the University of Cambridge, where he last served as the head of the Cavendish Laboratory and the Department of Physics. He began his career with almost 20 years at Bell Laboratories, ultimately serving for five years as head of Theoretical Physics Research.
Dr. Littlewood holds six patents, has published more than 250 articles in scientific journals and has given more than 300 invited talks at international conferences, universities and laboratories. He is a fellow of the Royal Society of London, the Institute of Physics, the American Physical Society, and TWAS (The World Academy of Sciences). He serves on advisory boards of research and education institutions and other scientific organizations worldwide. He holds a bachelor's degree in natural sciences (physics) and a doctorate in physics, both from the University of Cambridge.
I will discuss the physics of small polarons in SrTiO3, and in particular the collapse of strong Frohlich coupling with increasing metallicity as the long-range Coulomb mediated interaction with optic phonons is screened out. SrTiO3 is an unusually good metal and an enigmatic superconductor at very low carrier concentrations.
While electric charges can be screened, the same is not true of strain fields, which have intrinsic long-range interactions that cannot be screened. When strain fields are produced as a secondary order parameter in phase transitions - as for example in ferroelectrics - this produces unexpected consequences for the dynamics of order parameter fluctuations, including the generation of a gap in what would otherwise have been expected to be Goldstone modes. In some cases, e.g. manganites and nickelates, other intra-cell modes can nonlinearly screen the order parameter, which produces a strong sensitivity of ordering to octahedral rotations, essentially a jamming transition. This is relevant for tuning entropic effects at phase transitions, perhaps to enhance electro-caloric and magneto-electric effects. Wang et al. Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid. Nature Materials (2016). DOI: 10.1038/NMAT4623 Elastic interactions and control of the Mott transition, G. G. Guzmán-Verri, R. T. Brierley, P. B. Littlewood arXiv:1701.02318 Why is the electrocaloric effect so small in ferroelectrics? G. G. Guzmán-Verri, P. B. Littlewood, APL Mater. 4, 064106 (2016)
Bio: Peter B. Littlewood is a condensed matter theorist at the University of Chicago who is a Professor in Physics, the James Franck Institute, and the College. His research interests include superconductivity and superfluids, strongly correlated electronic materials, collective dynamics of glasses and density waves in solids, neuroscience, and applications of materials for energy and sustainability.
Dr. Littlewood came to Chicago and to Argonne in 2011 after being appointed associate laboratory director of the lab’s Physical Sciences and Engineering directorate, and served from 2014 to 2016 as Laboratory DIrector. He spent the previous 14 years at the University of Cambridge, where he last served as the head of the Cavendish Laboratory and the Department of Physics. He began his career with almost 20 years at Bell Laboratories, ultimately serving for five years as head of Theoretical Physics Research.
Dr. Littlewood holds six patents, has published more than 250 articles in scientific journals and has given more than 300 invited talks at international conferences, universities and laboratories. He is a fellow of the Royal Society of London, the Institute of Physics, the American Physical Society, and TWAS (The World Academy of Sciences). He serves on advisory boards of research and education institutions and other scientific organizations worldwide. He holds a bachelor's degree in natural sciences (physics) and a doctorate in physics, both from the University of Cambridge.
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- Michele Ceriotti & Esther Amstad
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- Michele Ceriotti & Esther Amstad