Fascinating structures have arisen from the study of the fractional quantum Hall effect (FQHE) at the even denominator fraction of 5/2 5 / 2 . We consider the FQHE at another even denominator fraction, namely \nu=2+3/8 ν = 2 + 3 / 8 , where a well-developed and quantized Hall plateau has been observed in experiments. We examine the non-Abelian state described by the `` \bar{3}\bar{2}^{2}1^{4} 3 ‾ 2 ‾ 2 1 4 " parton wave function and numerically demonstrate it to be a feasible candidate for the ground state at \nu=2+3/8 ν = 2 + 3 / 8 . We make predictions for experimentally measurable properties of the \bar{3}\bar{2}^{2}1^{4} 3 ‾ 2 ‾ 2 1 4 state that can reveal its underlying topological structure.
We consider the fractional quantum Hall effect at the filling $\ensuremath{\nu}=6/17$, where experiments have observed features of incompressibility in the form of a minimum in the longitudinal resistance. We propose a parton state denoted as ``
3213'' and show it to be a feasible candidate to capture the ground state at $\ensuremath{\nu}=6/17$. We work out the low-energy effective theory of the
3213 edge and make several predictions for experimentally measurable properties of the state which can help detect its underlying topological order. Intriguingly, we find that the
3213 state likely lies in the same universality class as the state obtained from composite-fermionizing the
1+1/5 Laughlin state.
The fractional quantum Hall effect (FQHE) in the second Landau level (SLL) likely stabilizes non-Abelian topological orders. Recently, a parton sequence has been proposed to capture many of the fractions observed in the SLL [A. C. Balram, SciPost Phys. 10, 083 (2021)]. We consider the first member of this sequence which has not yet been studied, which is a non-Abelian state that occurs at
4/11. As yet FQHE in the SLL at this fraction has not been observed in experiments. Nevertheless, by studying its competition with other candidate FQHE states in the SLL we show that this parton state might be viable. We also make predictions for experimentally measurable properties of the parton state which can distinguish it from other topological orders.
We review some theoretical progress towards understanding the origin of the fractional quantum Hall effect at filling factor 5/2 using numerical techniques. The leading candidate thought to describe the physics is the Moore-Read Pfaffian state which supports non-abelian anyonic excitations. Interestingly, these excitations have possible applications in topologically protected quantum information processing. Specifically, we discuss how the finite-thickness of realistic quasi-two-dimensional systems stabilizes the Moore-Read Pfaffian in the fractional quantum Hall effect at 5/2 and the use of bilayer systems in the second Landau level to investigate the possible quantum phase transition between abelian and non-abelian fractional quantum Hall states.
Interesting non-Abelian states, e.g., the Moore-Read Pfaffian and the anti-Pfaffian, offer candidate descriptions of the
ν=5/2 fractional quantum Hall state. But the significant controversy surrounding the nature of the
ν=5/2 state has been hampered by the fact that the competition between these and other states is affected by small parameter changes. To study the phase diagram of the
ν=5/2 state we numerically diagonalize a comprehensive effective Hamiltonian describing the fractional quantum Hall effect of electrons under realistic conditions in GaAs semiconductors. The effective Hamiltonian takes Landau level mixing into account to lowest-order perturbatively in
κ, the ratio of the Coulomb energy scale to the cyclotron gap. We also incorporate non-zero width
w of the quantum well and sub-band mixing. We find the ground state in both the torus and spherical geometries as a function of
κ and
w. To sort out the non-trivial competition between candidate ground states we analyze the following 4 criteria: its overlap with trial wave functions; the magnitude of energy gaps; the sign of the expectation value of an order parameter for particle-hole symmetry breaking; and the entanglement spectrum. We conclude that the ground state is in the universality class of the Moore-Read Pfaffian state, rather than the anti-Pfaffian, for
κ<κc(w), where
κc(w) is a
w-dependent critical value
0.6≲κc(w)≲1. We observe that both Landau level mixing and non-zero width suppress the excitation gap, but Landau level mixing has a larger effect in this regard. Our findings have important implications for the identification of non-Abelian fractional quantum Hall states.