Ferroelectricity by Bose-Einstein condensation in a quantum magnet.
The Bose-Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose-Einstein condensates. Realization of Bose-Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose-Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose-Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl3, leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose-Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets.
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
S
S
Kimura
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
K
K
Kakihata
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Y
Y
Sawada
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
K
K
Watanabe
Department of Physics, Shizuoka University, Shizuoka 422-8529, Japan.
M
M
Matsumoto
Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan.
M
M
Hagiwara
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
H
H
Tanaka
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