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Roman Pisarev, Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia

Linear and nonlinear optical spectroscopy in a complex magnetoelectric antiferromagnet CuB2O4


Copper metaborate CuB2O4 possesses unique noncentrosymmetric crystal structure -42m and in the unit cell magnetic Cu2+ (3d9) ions occupy nonequivalent 4b and 8d positions. Interactions within and between these sublattices lead to complicated phase diagram below TN=21 K with several commensurate and incommensurate phases. In the talk we will discuss optical studies of this material, in particular, its lattice dynamics ; unusual electronic absorption spectra characterized by six zero-phonon lines and unique vibronic structure ; and a resonance second harmonic generation. A strong spin-dependent photoluminescence was observed which is a very rare phenomenon in magnetically ordered materials. We also studied antiferromagnetic dichroism at zero-phonon lines [1], and these results allowed us to find new magnetic transitions below TN. Our experimental results allowed us to prove that magnetic field cannot induce crystallographic chirality contrary to claims in some publications [2] and in agreement with theoretical analysis [3].

 

[1] K. N. Boldyrev, R. V. Pisarev, L. N. Bezmaternykh, and M. N. Popova, Phys. Rev. Lett. 114, 247210 (2015).
[2] M. Saito, K. Ishikawa, K. Taniguchi, and T. Arima, Phys. Rev. Lett. 101, 117402 (2008).
[3] S. W. Lovesey and U. Staub, J. Phys. Condens. Matt. 21, 142201 (2009).

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