Possible restoration of particle-hole symmetry in the 5/2 Quantized Hall State at small magnetic field

Motivated by the experimental observation of a quantized 5/2 thermal conductance at filling $\nu =5\mathrm{/}2$, a result incompatible with both the Pfaffian and the Antipfaffian states, we have pushed the expansion of the effective Hamiltonian of the $5\mathrm{/}2$ quantized Hall state to third-order in the parameter $\kappa =E_c\mathrm{/}\mathrm{\hslash }{\omega }_c\propto 1\mathrm{/}\sqrt{B}$ controlling the Landau level mixing , where $E_c$ is the Coulomb energy and ${\omega }_c$ the cyclotron frequency. Exact diagonalizations of this effective Hamiltonian show that the difference in overlap with the Pfaffian and the AntiPfaffian induced at second-order is reduced by third-order corrections and disappears around $\kappa =0.4$, suggesting that these states are much closer in energy at smaller magnetic field than previously anticipated. Furthermore, we show that in this range of $\kappa$ the finite-size spectrum is typical of a quantum phase transition, with a strong reduction of the energy gap and with level crossings between excited states. These results point to the possibility of a quantum phase transition at smaller magnetic field into a phase with an emergent particle-hole symmetry that would explain the measured $5\mathrm{/}2$ thermal conductance of the $5\mathrm{/}2$ quantized Hall state.