Spinless composite fermions in an ultra-high quality strained Ge quantum well

We report on an observation of a fractional quantum Hall effect in an ultra-high quality two-dimensional hole gas hosted in a strained Ge quantum well. The Hall resistance reveals precisely quantized plateaus and vanishing longitudinal resistance at filling factors $ u = 2/3, 4/3$ and $5/3$. From the temperature dependence around $ u = 3/2$ we obtain the composite fermion mass of $m^star approx 0.4,m_e$, where $m_e$ is the mass of a free electron. Owing to large Zeeman energy, all observed states are spin-polarized and can be described in terms of spinless composite fermions.