Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 69: Other Low Temperature Topics: Cold Atomic Gases

TT 69.15: Talk

Wednesday, March 18, 2015, 18:45–19:00, A 053

Dirac cones merging transition and geometric phase in Stuckelberg interferometer with cold atoms — •Lih-King Lim — MPI PKS, Dresden, Germany — Institut d’Optique, Palaiseau, France

Dirac cones in the energy spectrum lies at the heart of many interests in studying two-dimensional crystals such as graphene or MoS₂. Besides its unusual density-of-states, a Dirac cone possesses geometric information hidden in the wavefunction, e.g., Berry phase and mass. The latter determines the type of topological state of matter. Thanks to recent progresses in engineering two-dimensional topological band structure with cold atoms, we study a Stuckelberg interferometer realized via Bloch-oscillations-type experiment. The paths that bring Bloch waves to interfere are made of the two energy levels in between a pair of Dirac cones. We show that the interference pattern contains an extra phase shift that has a geometric origin, in the form of an open path Berry phase of the wavefunction. It is revealed in the final inter-band transition probability and hence, it is a gauge invariant quantity. This phase can serve as a robust bulk probe for topological band structures realized with artificial crystals.

[1] L.-K. Lim, J.N. Fuchs, G. Montambaux,

Phys. Rev. Lett. 112, 155302 (2014).