Seminar "Spin-wave excitations in the multiferroic compound Ba2CoGe2O7" by Karlo Penc

Seminar Announcement by Theory of Quantum Matter Unit:

• Date: Wednesday, 17th June
• Time: 11:00-12:00
• Venue: D014, Lab1
• Speaker: Professor Karlo Penc (Institute for Solid State Physics and Optics)

Spin-wave excitations in the multiferroic compound Ba2CoGe2O7

Karlo Penc

Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungary

We studied spin excitations in the magnetically ordered phase of the noncentrosymmetric Ba2CoGe2O7 in high magnetic fields up to 33 T. In the electron spin resonance and far infrared absorption spectra we found several spin excitations beyond the two conventional magnon modes expected for such a two-sublattice antiferromagnet. We show that a multiboson spin-wave theory describes these unconventional modes, including spin-stretching modes, characterized by an oscillating magnetic dipole and quadrupole moment. In particular, the lack of inversion symmetry allows each mode to become electric dipole active and interact with light. Finally, we discuss the signatures of higher energy excitations in inelastic neutron spectrum.