New unconventional plasmons in the N=1 Landau level*

In the partially filled second Landau level (SLL) emergent exotic quantum fluids overlap and interplay with fractional quantum Hall (FQH) liquids. Collective modes of the exotic quantum fluids uncover underlying physical mechanisms responsible for emerging new ground states [1-3]. Resonant inelastic light scattering (RILS) spectra access unprecedented collective modes in the FQH regime of the SLL: intra-Landau-level plasmons[3]. The plasmons herald rotational-symmetry-breaking (nematic) phases in the SLL and reveal the nature of long-range translational invariance in these phases. The intricate dependence of plasmon features on filling factor provides new insights on complex interplay between topological quantum Hall order and nematic electronic liquid crystal phases. A marked intensity minimum in the plasmon spectrum at Landau level filling factor v = 5/2 strongly suggests that the paired state, which may support non-Abelian excitations, overwhelms competing phases, revealing the robustness of the 5/2 superfluid state for small tilt angles. In contrast, a sharp and intense plasmon peak in the state at v=7/3 reveals that the macroscopic coherence of the FQH liquid coexists with nematic order, supporting the proposed model of a FQH nematic at 7/3. Other interpretations of the new collective mode, such as chiral graviton [4], will be discussed.

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[2]. A. L. Levy, et al, Phys. Rev. Lett. 116, 016801 (2016).
[3]. L. J. Du, et al, Science Advances 5, eaav3407 (2019).
[4]. S. F. Liou, et al, Phys. Rev. Lett. 123, 146801 (2019).