Bloch oscillations {sinusoidal sweeps between alternate extremes of a particle in a lattice} arise in the presence of a field, but the understanding of how the compact localized states perform these oscillations under some perturbation is far from being clear. Previous studies have found Bloch oscillations of quantum particles but only on a very basic level; namely, in one-dimensional lattice systems with an applied electric field. Although those resulting Bloch oscillations were common, more in depth research involving more complex structures had not been attempted before the IBS report.

The IBS Center for PCS engineered Bloch oscillations within an intricate lattice structure that demonstrated a very intriguing anharmonic structure under electric and magnetic fields. An anharmonic structure concerns an oscillation which drastically differs from the gentle dynamics of a well-known pendulum. This result is quite interesting as Bloch oscillations are typically symmetric, without such dramatic behavior. It is accomplished by precisely manipulating the electric and magnetic perturbing fields and controlling the degeneracies. An almost complete halt is achieved during the initial flat stage. The following scan of the whole band structure follows the Bloch oscillation scenario which is harvesting on tunneling between energy levels or Landau-Zener tunneling, before returning to the flat band state to repeat the sweep again. However, under a precise tuning of the magnetic field strength, the structure can be made to be gapless again and almost flat. In this case, Landau-Zener tunneling is enforced and drives the Bloch oscillations. The resulting asymmetric and anharmonic diagram is both a novel and promising discovery.

Speaking from the Center’s base in KAIST’s Munji Campus, PCS Director Sergey Flach, and co-author of the manuscript published in Physical Review Letters, said: “The result demonstrates, not only the potential of this research direction to allow for the engineering of new qualitative states of quantum matter, but an elegant implementation to an old problem, how to arrest a quantum particle in a highly localized way on a lattice structure through the application of external fields.”

Neil Mannix

Notes for editors

- References
Ramaz Khomeriki, Sergej Flach (2016) Landau-Zener Bloch Oscillations with Perturbed Flat Bands. Physical Review Letters, DOI: http://dx.doi.org/10.1103/PhysRevLett.116.245301

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