Mach-Zehnder Interferometry Using Spin- and Valley-Polarized Quantum Hall Edge States in Graphene

August 22, 2017

Fig. 5. Absence of equilibration between edge channels running along a gate-defined edge*.
[Reprinted under the Creative Commons Attribution-NonCommercial license.]

Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogs of monochromatic beams of light, providing a unique platform for studying electron interference. Electron interferometry is regarded as one of the most promising routes for studying fractional and non-Abelian statistics and quantum entanglement via two-particle interference. However, creating an edge-channel interferometer in which electron-electron interactions play an important role requires a clean system and long phase coherence lengths.

Physics research associate Toeno van der Sar, postdoc Javier Sanchez-Yamagishi, professors Bertrand Halperin and Amir Yacoby, and colleagues from SEAS, MIT, and the National Institute for Materials Science, Tsukuba (Japan), describe such an interferometer in a new research article in Science Advances. The scientists created electronic Mach-Zehnder interferometers with record visibilities of up to 98% using spin- and valley-polarized edge channels that copropagate along a pn junction in graphene. They discovered that interchannel scattering between same-spin edge channels along the physical graphene edge can be used to form beamsplitters, whereas the absence of interchannel scattering along gate-defined interfaces can be used to form isolated interferometer arms. Surprisingly, the authors found out that the interferometer is robust to dephasing effects at energies an order of magnitude larger than those observed in pioneering experiments on GaAs/AlGaAs quantum wells. These results shed light on the nature of edge-channel equilibration and open up new possibilities for studying exotic electron statistics and quantum phenomena.

*Read D.S. Wei1, T. van der Sar, J.D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, P. Jarillo-Herrero, B.I. Halperin, and A. Yacoby, "Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in graphene," Science Advances 3 (2017) DOI: 10.1126/sciadv.1700600.