Exploring novel states of matter induced by electron correlation and the phase transitions between them has been one of the major topics in the field of condensed matter physics. While most of the earlier works were concerned with ferromagnetism and superconductivity, which are well described by Ginzburg-Landau-Wilson theory, later studies on frustrated magnets and discovery of high- T c superconductors have turned the spotlight onto a novel class of phases that are not described by a local order parameter. Recent discoveries of spin-ice compounds and other geometrically frustrated magnets have set a good testing ground for possible realization of these exotic phases. At the same time, discoveries of metallic magnets on pyrochlore and triangular lattices have opened another aspect in the study of geometrically frustrated magnets. In these systems, the coupling between itinerant electrons and localized spins induces effective spin-spin interactions, which have crucial effects on the magnetic behavior. On the other hand, the electronic and transport properties are strongly affected by its magnetic texture.
Motivated by these experiments, recently, we theoretically studied spin-charge coupled systems. Our model is a Kondo lattice-type model in which itinerant electrons are coupled with localized Ising spins on a frustrated lattice, such as triangular, kagome, and pyrochlore lattices. By using exact diagonalization, unbiased Monte Carlo simulation, and perturbation, we present that these models show peculiar electronic and magnetic states at low temperatures. For instance, we clarify that a two-dimensional partially-disordered state is stabilized in the triangular and kagome lattice models. We also argue emergence of massless Dirac fermions under a three-sublattice ferrimagnetic order on a triangular lattice. For the case in which the localized Ising spin has a noncoplanar anisotropic axis of spin ice type, we find that a new 32-sublattice order emerges and its spin and charge pattern is switched by applied magnetic field. We also discuss a topological Hall effect due to local noncoplanar magnetic textures.
H. Ishizuka, M. Udagawa, and Y. Motome, preprint (arXiv:1107.4174).
H. Ishizuka and Y. Motome, Phys. Rev. Lett. 108 , 257205 (2012).
H. Ishizuka and Y. Motome, preprint (arXiv:1206.1721).
H. Ishizuka, M. Udagawa, and Y. Motome, J. Phys. Soc. Jpn. 81 , 113706 (2012).
H. Ishizuka and Y. Motome, preprint (arXiv:1210.6700).