Thermal Dephasing in the Laughlin Quasiparticle Interferometer

We report experiments on thermal dephasing of the Aharonov-Bohm oscillations in the novel Laughlin quasiparticle (LQP) interferometer, [1] where quasiparticles of the 1/3 FQH fluid execute a closed path around an island of the 2/5 fluid. In the $10.2 \leq T \leq 141$ mK temperature range, qualitatively, the experimental results follow a thermal dephasing dependence expected for an electron interferometer, and show clear distinction from the activated behavior observed in resonant tunneling and Coulomb blockade devices, both in the chiral Luttinger liquid ($\chi$LL) and the Fermi liquid regimes. The data fit very well the $\chi$LL dependence predicted for a $g=1/3$ two point-contact LQP interferometer. [2] The fit yields a value of the chiral edge excitation velocity, $u=1.4\times 10^4$ m/s obtained for the first time for a continuous FQH edge excitation spectrum. The small deviation from the zero-bias theory seen below 20 mK indicates yet unrecognized source of experimental decoherence, not included in theory. \newline \noindent [1] F. E. Camino et al., Phys. Rev. B $\bf 72$, 075342 (2005). \newline \noindent [2] C. de C. Chamon et al., Phys. Rev. B $\bf 55$, 2331 (1997).