Café com Física



05 de julho de 2017
Sala 146 (LEF)

Willian M. H. Natori

Dynamics of a j =3/2 quantum spin liquid

Mott insulators that retain orbital degeneracy and display strong spin-orbit coupling (SOC) are a new focus of research in the field of strongly correlated systems. Most of this interest is traced back to the seminal work of Jackeli and Khaliullin [1], who showed that the interplay of lattice geometry and SOC in specific transition metal compounds generates a solid state platform to the exactly solvable Kitaev model [2]. One can show through a simple Majorana fermion representation that this j=1/2 spin model has a quantum spin liquid (QSL) ground state with Majorana fermions and vison excitations. The line of research opened by Ref. [1] has proved very fruitful to discover new and exotic magnetic phases. Unfortunately, the studies also showed that the Kitaev QSL is not sufficiently stable to usual realistic perturbations. In this Colloquium, I will present an alternative way to search for QSLs using the Jackeli-Khaliullin mechanism to derive j=3/2 exchange-frustrated spin-orbital models. Then, I propose a Majorana QSL [3] in analogy with Kitaev's work and analyze its experimental responses [4]. In this seminar, I focus on the resonant inelastic x-ray scattering (RIXS) results. I will show how symmetry arguments can be used to link photon-polarization factors and RIXS probed excitations. It is then proved that RIXS cross sections supply important information of j=3/2 systems that remain hidden in neutron scattering. Comparison between theoretical and experimental results of the QSL candidate Ba2YMoO6 will be shown. In the end of the seminar I will give perspectives for this field, both in theory and experiments.

[1] G. Jackeli and G. Khaliullin. PRL, 102, 017205 (2009)
[2] A. Kitaev. Ann. Phys., 321, 2 (2006)
[3] W. M. H. Natori, E. C. Andrade, E. Miranda, and R. G. Pereira., PRL, 117, 017204 (2016)
[4] W. Natori, M. Daghofer, and R. Pereira., ArXiv e-prints, 1704.06134 (2017).