| Summary: | Measurement of the ground-state spin polarization of quantum systems offers great potential for the discovery and characterization of correlated electronic states. However, spin polarization measurements have mainly involved optical1–3 and NMR4,5 techniques that perturb the delicate ground states and, for quantum Hall systems, have provided conflicting results1,4,6. Here we present spin-resolved pulsed tunnelling (SRPT) that precisely determines the phase diagram of the ground-state spin polarization as a function of magnetic field and Landau level (LL) filling factor (ν) with negligible perturbation to the system. Our phase diagram shows a variety of polarized, unpolarized and topological spin states in the lowest (N = 0) LL, which can largely be described by a weakly interacting composite fermion (CF) model7. However, the phase diagram shows unexpected behaviour in the N = 1 LL. We observe fully polarized ν = 5/2 and 8/3 states but a partially depolarized ν = 7/3 state. This behaviour deviates from the conventional theoretical picture7,8 of weakly interacting fractional quasiparticles, but instead suggests unusual electronic correlations and the possibility of new non-Abelian phases9–11. The results establish SRPT as a powerful technique for investigating correlated electron phenomena. ©2020, The Author(s), under exclusive licence to Springer Nature Limited.
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