Přednášející: Laurent Bellaiche (University of Arkansas, USA)
Místo: Na Slovance, přednáškový sál v přízemí
Jazyk: anglicky
Pořadatelé:
Oddělení dielektrik
In 2004, the use of a first-principles-based effective Hamiltonian [1] led to the prediction of a novel structure in zero-dimensional ferroelectrics, in which the electric dipoles organize themselves to form a vortex [2]. Such structure exhibits the so-called spontaneous toroidal moment, rather than the spontaneous polarization, as its order parameter [2]. Subsequently, other phenomena, all related to vortices, were predicted in ferroelectric nanostructures. Examples of such phenomena are: (i) the existence of a new order parameter, denoted as the hypertoroidal moment, that is associated with many complex dipolar structures (such as double-vortex states) [3]; (ii) the possible control of single and double vortex states by electric fields, via the formation of original intermediate states [4-8]; (iii) the discovery of a new class of quantum materials (denoted as incipient ferrotoroidics), for which zero-point vibrations wash out the vortex state and yield a complex local structure [9]; (iv) the existence of chiral patterns of oxygen octahedral tiltings that originate from the coupling of these tiltings with the ferroelectric vortices [10]. These studies are done in collaboration with A.R. Akbarzadeh, H. Fu, I. Kornev, I. Naumov, I. Ponomareva, S. Prosandeev, Wei Ren and D. Sichuga, and are sponsored by NSF, ONR and DOE. References: [1] PRL 84, 5427(2000);[2] Nature 432, 737 (2004); [3] PRB 77, 060101 (2008);[4] PRL 96, 237601 (2006); [5] PRL 98, 077603 (2007); [6] PRL 101, 097203 (2008); [7] PRL 100, 047201 (2008); [8] PRL 101, 197601 (2008); [9] PRL 102, 257601(2009);[10] PRL 104, 207603 (2010).
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