Topic: Multiferroics by design with frustrated magnets with trimers

Speaker: Yoshi Kamiya (RIKEN)

Abstract:

Frustrated Mott insulators have been the focus of intense research over the past decades. When combined with other ingredients, such as strong quantum fluctuations, large spin-orbit coupling and charge fluctuations, frustration can lead to rich and fascinating phenomena including spin liquids and exotic spin textures. In this talk, as another illuminating example focusing on charge redistribution effects, we discuss multiferroics that arises from virtual charge fluctuations in Mott insulators, which in fact requires frustration as its precondition. We start from the simplest unit of geometrical frustration, that is, an equilateral triangle (“trimer”) of spins with S = 1/2, and show that it hosts built-in magnetic and electric dipoles arising from the frustrated exchange interaction [1]. Such trimers can be weakly coupled to make multiferroics by design [2]. After introducing a convenient effective operator formalism to describe perturbative electron fluctuations in Mott insulators with spin operators, we demonstrate that the organic molecular magnet TNN·CH₃CN provides an ideal experimental realization of our theory [3], predicting a very rich phase diagram resulting from an intriguing interplay between spin and effective orbital degrees of freedom. [Slides]

References:

[1] L. N. Bulaevskii, C. D. Batista, M. V. Mostovoy, and D. I. Khomskii, Phys. Rev. B 78, 024402 (2008).

[2] Y. Kamiya and C. D. Batista, Phys. Rev. Lett. 108, 097202 (2012).

[3] Y. Kamiya et al., in preparation.

Location: Classroom N306, UCAS Zhongguancun Campus, No. 3 Nanyitiao, Haidian District, Beijing

Time:  10:00am, Jun. 6 (Tue.), 2017