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Unconventional Magnetic and Electronic States in Doped Frustrated Magnets

March 26, 2013 4:00PM to 5:00PM
Sanjeev Kumar, Indian Institute of Science Education and Research
Building 223, Room S105
Materials Science Seminar
A large class of electronic systems can be described in terms of localized core spins and itinerant fermions. A well-known example is that of manganites where the half-filled t2g levels on Mn give rise to S=3/2 magnetic moments which are well localized, and a partially filled eg band contains the mobile electrons. The superexchange coupling between localized spins competes with the coupling induced via the Kondo-term. The Interplay between these two typically gives rise to very interesting magnetic states, such as the canted state recently observed in manganite heterostructures [1].

The generic starting point for a theoretical investigation of such systems is the Kondo-lattice-model (KLM). Partly motivated by the observation of anomaleous Hall effect in pyrochlore magnets [2], we begin by asking a simple question: what happens if the underlying lattice of the KLM is geometrically frustrated? In this seminar I will describe our work that tries to answer the above question. We study the KLM on two frustrated lattices, namely, triangular lattice and checkerboard lattice [3,4].

Our results show that the electronic degrees of freedom can provide a unique way for the magnetic subsystem to release its frustration, leading to unconventional magnetic states and in-turn to novel electronic properties. In case of the checkerboard lattice, a novel connection to graphene and topological insulating states is uncovered.

[1] T. Santos et al., Phys. Rev. Lett. 107, 167202 (2011).
[2] Y. Taguchi et al., Science 291, 2573 (2001); S. Iguchi et al., Phys. Rev. Lett. 102, 136407 (2009).
[3] S. Kumar and J. van den Brink, Phys. Rev. Lett. 105, 216405 (2010).
[4] J. Venderbos et al., Phys. Rev. Lett. 109, 166405 (2012).