ICQM faculty member publishes an article in Physical Review Letters reporting ‘Chern Kondo Insulator in an Optical Lattice’

Recently, a postdoc Dr. Hua Chen, Prof. Xiong-Jun Liu and Prof. X. C. Xie at International Center for Quantum Materials, Peking University published a paper titled “Chern Kondo Insulator in an Optical Lattice” in Physical Review Letters 116, 046401 (2016).

The work is motivated by the recently progress of time-reversal invariant topological Kondo insulators (TKIs), which were predicted in a few heavy-fermion materials like SmB6. The topological Kondo insulators originate from the hybridization between itinerant conduction bands and strong correlated f electrons. The proposed scenario of TKIs is consistent with the transport measurement, angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy. Nevertheless, the TKIs share the same topological classification as conventional TIs, and the essential difference is that in a TKI it is the strongly correlated Kondo effect that leads to the insulating gap. Measuring such strong correlation physics (for f electrons) can directly distinguish a TKI from conventional TIs, while this might be a challenging task for condensed matter systems. This motivates us to consider Kondo insulators with nontrivial topology in cold atoms, which may allow for an exact study with full controllability.

In our work, we propose to realize and observe a strongly correlated quantum anomalous Hall phase, called Chern Kondo insulator, in an optical lattice, motivated by the recent rapidly developing new technologies for cold atoms. Compared with solid state systems, the cold atoms can offer extremely clean platforms with full controllability to study many-body physics and topological phases. Here, we consider a double-well square lattice with Raman-coupling-assisted s-p orbital hybridization to observe Chern Kondo insulating phases. Due to the strong Hubbard interaction of s orbital states, the Kondo screening is achieved when the applied Raman coupling exceeds a critical value, and then a nonzero renormalized s-p orbital hybridization drives the system into a fully gapped Chern Kondo phase.

Figure: Main panel: (a) Image map of Kondo temperature and (b) direct band gap as a function of hopping integral and gauge field. Subfigure: (a) Kondo temperature and (b) band gap (open square), Chern number (open circle) versus gauge field with tsp=0.8.

We show that the predicted CK insulator can be identified by three characteristic features, namely, the existence of a critical s-p coupling strength for the CK phase transition, the nontrivial topology in the bulk band, and the Mott behavior of the s orbital. These features distinguish the strongly correlated CK insulating phase from the single-particle QAH states. The experimental schemes are proposed for such detection.

This work is supported by the National Basic Research Program of China (Grant No. 2015CB921102) and the National Natural Science Foundation of China (Grants No. 11534001 and No. 11574008).