# Theoretical Physics

**30 April 2013**

**Time:**15:00 to 16:00

**Location:**SR 8.62

Stefanos Kourtis

Topologically and conventionally ordered phases from correlations in flat Chern bands

Several spinless-fermion models featuring topologically non-trivial and

flat bands have been recently studied as a potential host of lattice

fractional quantum-Hall (FQH) states in the absence of a magnetic field,

dubbed fractional Chern insulators (FCI). We introduce such an effective

model on the triangular lattice including short-range interactions,

originally derived from a 3-orbital model describing layered

transition-metal oxides [1,2], and study its ground states as a function

of filling, interaction strength and band dispersion using exact

diagonalization [3]. Using symmetry arguments as well as appropriate

observables, such as the Hall conductivity and the static

charge-structure factor, we identify FCI and charge-density wave (CDW)

ground states at various filling fractions and trace the phase diagram

of the model for some of these fillings. We show that FCI states survive

the competition against CDW states for a wide parameter range and that

they remain robust against disorder in the magnetic background. We also

compare to similar results obtained for a checkerboard-lattice model [4].

[1] J.W.F. Venderbos, M. Daghofer, and J. van den Brink, Phys. Rev.

Lett. 107, 116401 (2011).

[2] J.W.F. Venderbos, S. Kourtis, J. van den Brink, and M. Daghofer,

Phys. Rev. Lett. 108, 126405 (2012).

[3] S. Kourtis, J.W.F. Venderbos, and M. Daghofer, Phys. Rev. B 86,

235118 (2012).

[4] K. Sun, Z. Gu, H. Katsura, and S. Das Sarma, Phys. Rev. Lett. 106,

236803 (2011)

© Copyright Leeds 2011