Reports

An on/off Berry phase switch in circular graphene resonators

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Science  26 May 2017:
Vol. 356, Issue 6340, pp. 845-849
DOI: 10.1126/science.aal0212

Flicking the Berry phase switch

When an electron completes a cycle around the Dirac point (a particular location in graphene's electronic structure), the phase of its wave function changes by π. This so-called Berry phase is tricky to observe directly in solid-state measurements. Ghahari et al. built a graphene nanostructure consisting of a central region doped with positive carriers surrounded by a negatively doped background. Scanning tunneling spectroscopy revealed sudden jumps in conductivity as the external magnetic field was increased past a threshold value. The jumps occurred when electron orbits started encompassing the Dirac point, reflecting the switch of the Berry phase from zero to π. The tunability of conductivity by such minute changes in magnetic field is promising for future applications.

Science, this issue p. 845