Spin-resolved tunneling in the fractional quantum Hall effect regime*

Strong Coulomb interactions and internal spin degrees of freedom lead to a plethora of correlated electronic phases in quantum Hall (QH) systems. Despite the successes of nuclear magnetic resonance and optical techniques, spin-sensitive measurements have remained challenging, particularly at low carrier density or in higher Landau levels (LLs). Here we introduce a new method, spin-resolved tunneling, that can probe the spin texture of both the ground and excited states of QH systems. We establish a complete phase diagram of the ground-state spin in a wide range of filling factors ν and magnetic fields. Our phase diagrams show the detailed structure of the composite fermion (CF) phases in the lowest LL, in which the changes in the Zeeman energy and ν drive phase transitions between the spin-unpolarized, the spin-polarized, and the topological spin skymion states. On the other hand, the non-Laughlin correlated behavior, such as the absence of spin transitions at ν = 2 + 1/2 and 2 + 2/3 states, is observed in the first excited LL, where the conventional CF picture is no longer valid due to the softened pair interactions.