Evidence for an exotic topological phase of matter in a system with 5-fold anisotropy!
The enigmatic even-denominator fractional quantum Hall state in the first-excited Landau level of two-dimensional electron systems are among the unsolved mysteries in condensed matter physics. Quasiparticles of its excitation are neither fermion nor boson but Majoranas supporting non-Abelian braiding which has amazing prospects in topological quantum computation. However, this state is fragile and theoretically expected to disappear in anisotropic systems. In my third paper, we contradict this expectation by experimentally demonstrating a robust, tunable even-denominator fractional quantum Hall state in an AlAs 2D electron systems with five-fold mass-anisotropy.
This result came entirely unanticipated. Since theories predict a nematic charge order where charges are expected to form a symmetry breaking spatial order, we were searching for its experimental evidence. As expected for a nematic order, we observed anisotropic longitudinal transport accompanied by a finite temperature transition. The anisotropic longitudinal transport sets in suddenly after this finite temperature transition. To our great surprise, however, we observed a well-developed half-integer quantized Hall plateau that is expected for an even-denominator fractional quantum Hall state.
The surprises did not stop there. Even-denominator fractional quantum Hall states such as 5/2 state in GaAs 2D electron systems are very susceptible to the exposure of in-plane magnetic fields and they disappear even after applying a small in-plane field. Contrary to this, the state that we observe is very robust as it remains unperturbed even in the presence of a 12 Tesla in-plane magnetic field. Moreover, we find that this state can be tuned by applying a uniaxial strain via piezo-electric actuators.
These unconventional properties suggest that the state we observe can be a novel phase of matter. The robustness of this state also encourages its potential use in future topological quantum computation. Given that the fractional quantum Hall state we observe is potentially non-Abelian and there is no prior theoretical work in the literature for such a state in mass-anisotropic systems, we believe that our results will attract theoretical and experimental attention. They are more than likely to foster the future search for a robust even-denominator fractional quantum Hall state in diverse material systems and promote efforts in realizing topological quantum computers.
Our findings were published in Physical Review Letters and featured on their homepage as Editor’s suggestion. Here is the link to the article:
Here is the arxiv link for those who do not have access to Phys. Rev. Lett.
