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arXiv · 1403.4081

Entangled tetrahedron ground state and excitations of the magneto-electric skyrmion material Cu$_2$OSeO$_3$

Judit Romhányi·Jeroen van den Brink·Ioannis Rousochatzakis
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Abstract

The strongly correlated cuprate Cu$_2$OSeO$_3$ has recently been identified as the first insulating system exhibiting a skyrmion lattice phase. Using a microscopic multi-boson theory for its magnetic ground state and excitations, we establish the presence of two distinct types of modes: a low energy manifold that includes a gapless Goldstone mode and a set of weakly dispersive high-energy magnons. These spectral features are the most direct signatures of the fact that the essential magnetic building blocks of Cu$_2$OSeO$_3$ are not individual Cu spins, but rather weakly-coupled Cu$_4$ tetrahedra. Several of the calculated excitation energies are in nearly perfect agreement with reported Raman and far-infrared absorption data, while the magneto-electric effect determined within the present quantum-mechanical framework is also fully consistent with experiments, giving strong evidence in the entangled Cu$_4$ tetrahedra picture of Cu$_2$OSeO$_3$. The predicted dispersions along with the dynamical dipole and quadrupole spin structure factors call for further experimental tests of this picture.

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Judit Romhányi, Jeroen van den Brink, Ioannis Rousochatzakis. 2014-03-17. Entangled tetrahedron ground state and excitations of the magneto-electric skyrmion material Cu$_2$OSeO$_3$. https://doi.org/10.1103/physrevb.90.140404

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