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The fractional quantum Hall (FQH) e ect emerges in high-quality two-dimensional electron systems exposed to a magnetic field when the Landau-level filling factor, ν e , takes on a rational value. Although the overwhelming majority of FQH states have odd-denominator fillings, the physical properties of the rare and fragile even-denominator states are most tantalizing in view of their potential relevance for topological quantum computation. For decades, GaAs has been the preferred host for studying these even-denominator states, where they occur at ν e = 5/2 and 7/2. Here we report an anomalous series of quantized evendenominator FQH states outside the realm of III-V semiconductors in the MgZnO/ZnO 2DES electron at ν e = 3/2 and 7/2, with precursor features at 9/2; all while the 5/2 state is absent. The e ect in this material occurs concomitantly with tunability of the orbital character of electrons at the chemical potential, thereby realizing a new experimental means for investigating these exotic ground states.T he framework for the wide range of ground states observed in two-dimensional electron systems (2DES) resides in the discretized energy spectrum with a high degeneracy of the allowed states which emerges with the addition of a perpendicular magnetic field, B p . A ladder of spin-split Landau-levels (LLs) results with B p , inducing quantization of the orbital motion and lifting of the spin degeneracy. Each level is characterized by its orbital index N e = 0, 1, . . . and spin orientation (↑ or ↓). These levels can host as many charge carriers as magnetic flux quanta thread the sample and the filling factor, ν e , indicates how many levels are occupied. With increasing B p these LLs are successively depopulated and, on emptying a level completely, ν e takes on an integer value and the bulk of the 2DES becomes incompressible (see ref. 1 for an overview). The system exhibits the integer quantum Hall effect: vanishing longitudinal resistance (R xx ) and a Hall resistance (R xy ) quantized in units of h/e 2 . Further incompressible ground states may form at fractional fillings p/q when the electron number and number of flux quanta are commensurable. In contrast to FQH states at odd-denominator fillings, where the anti-symmetry constraint on the many-particle wavefunction imposed by the Pauli exclusion principle for fermions is automatically fulfilled, the development of even-denominator states 2-11 requires some mechanism which either restores the anti-symmetry of the manyparticle wavefunction or simply lifts the need to fulfil the Pauli exclusion principle. For systems where the charge carriers possess another degree of freedom, such as a layer or subband index, the anti-symmetry issue at even-denominator fillings may be solved by a two-component wavefunction. Indeed, in wide GaAs quantum wells with two subbands or in double-layer systems evendenominator states have been observed 2-7 and consensus has been reached that they are described by many-particle wavefunctions like the two-component ψ 331 -Laughlin sta...

We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.