Direct Observation of Majorana Mode

Direct Observation of Majorana Mode

topological order of the 5/2 FQHE state

Moty Heiblum

Braun Center for Sub-Micron Research, Department of Condensed Matter Physics, 

Weizmann Institute of Science, Rehovot, Israel 76100

Quantum Hall states – the progenitors of the growing family of topological insulators – are also a source of exotic quantum states. These states can be abelian (e.g., integers & fractions) or non-abelian (e.g., special fractions)., and thus may host electrons, fractionally charged quasiparticles, and neutral bosonic or Majorana (in general, para-fermionic) quasiparticles. Since the bulk is insulating (with the quasiparticles localized), counter-propagating gapless edge modes mirror the bulk’s topological order (due to ‘bulk-edge’ correspondence).

The most theoretically studied non-abelian state has a filling =5/2. The state supports charge-neutral quasiparticles accompanied by e/4 charges. This filling, however, permits different topological orders, which can be abelian or non-abelian. While numerical calculations favor the non-abelian Anti-Pfaffian (A-Pf) order, our recent thermal conductance measurements found the unexpected order, Particle-Hole Pfaffian (PH-Pf). Employing a novel interface method, where the bulk of the =5/2filling was interfaced with a bulk of integer filling =2 or =3, an isolated interface channel of =1/2 emerged. Studying the latter via measuring heat flow, we re-verified the PH-Pf order of the =5/2 state (and its non-abelian nature).

Identifying the correct topological order is crucial in testing the numerical predictions. While such experiments are more complicated than the ubiquitous conductance measurements, their ‘power’ is already evident. Moreover, isolating the fractional channel can be most helpful in complex interference (braiding) experiments.

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