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Condensed Matter Seminar: Screening of charge and structural motifs in oxides

SpeakerPeter B. Littlewood - Assoc. Director - Physical Sciences and Engineering - Argonne National Laboratory Prof of Physics - James Franck Institute - University of Chicago
Date Mar 8, 2013
Time 1:00 pm  
Location 190 Engineering Sciences Bldg - corner Goodwin & Springfield 
Sponsor Physics
Contact Peggy Pennell
Phone 217/244-7636
Event type CM Seminar
Views 1421

Heterostructure oxides offer the opportunity to build in electric fields by precise control of chemistry on the atomic scale, used recently to generate modulation doping of two- dimensional electron gases (2DEG) in oxides. The origin of the 2DEG, whether in pristine or defected materials, is under debate. I will discuss the role of surface redox reactions, in particular O vacancies, as the source of mobile carriers, and also discuss their role in the switching of ferroelectricity in ultra-thin films.

While electric charges can be screened by mobile carriers, 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, eg 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.

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