Chernful multiplet excitations in the breathing kagome model

Rövid cím: 
Chernful multiplet excitations
2017. 12. 22. 10:15
BME Fizikai Intézet, Elméleti Fizika Tanszék, Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba
Judit Romhányi (Okinawa Inst. Sci. Tech.)

We study the topologically nontrivial multiplet excitations of the antiferromagnetic spin-1/2 kagome system with breathing anisotropy. We show that in the chiral magnetic ground state the excitations can be characterized by a low-energy spin-1/2 doublet and a high-energy spin-3/2 quartet. A small magnetic field removes the degeneracy of the multiplets and the excitations become topologically nontrivial with Chern numbers C_m = 2m, the spin-3/2 manifold thus having large Chern numbers -3, -1, 1, 3. Increasing the magnetic field above a critical point, the bands undergo a topological transition when a novel spin-3/2 Dirac cone is formed by the touching of four bands. Above the critical field the bands become trivial. Before a similar topological transition occurred for the lower spin-1/2 doublet, at a higher magnetic field value, a conventional symmetry breaking transition takes place to the 1/3-plateau phase in which all bands are topologically trivial.