Gapless inhomogeneous topological superfluid found

Topological superfluids are recently discovered quantum systems that host topologically protected gapless edge states known as Majorana fermions - exotic quantum particles that act as their own anti-particles and obey nontrivial non-Abelian statistics. Their realisations are widely held to lie at the heart of future technologies such as fault-tolerant quantum computation. In the literature, it is commonly believed that a topological superfluid should be gapped in the bulk and that the nonzero energy gap is necessary for protecting Majorana fermions.

In two recent theoretical works reported by CQOS theorists, however, this common belief was challenged. By using an in-plane Zeeman field in a cold-atom setup of strongly interacting spin-orbit coupled atomic Fermi gases, CQOS theorists proposed a new scheme to induce the topological phase transition and discovered the existence of a new type of topological superfluid, which has a number of unique features that are absent in the previously known topological superfluids. These include the spatially inhomogeneous (Fulde-Ferrell) pairing order parameter, gapless excitations in the bulk, and unidirectional Majorana surface states at the edges. This conceptually new exotic state of matter - to be realised soon in cold-atom laboratories - may shed light on designing gapless topological materials in solid-state systems, whose potential applications are yet be understood.

These two works, describing the gapless topological superfluidity in 2D and 3D, have been published in Physical Review Letters and Physical Review A, respectively.

Link to papers:
[1] Y. Cao et al., Phys. Rev. Lett. 113, 115302 (2014)
[2] H. Hu et al. Phys. Rev. A 90, 033624 (2014).