Observation of a Stripe/nematic Phase of Composite Fermions

TL;DR

This paper reports the unexpected discovery of a stripe/nematic phase in the lowest Landau level of hole systems at filling factor 5/8, indicating a novel state driven by residual interactions among composite fermions.

Contribution

It reveals a new stripe/nematic phase of composite fermions in the lowest Landau level, driven by residual long-range interactions, which was previously unobserved.

Findings

Observation of transport anisotropy at ν=5/8 in hole systems

Identification of a stripe/nematic phase in the lowest Landau level

Robustness of the phase up to ~100 mK

Abstract

Electronic stripe/nematic phases are fascinating strongly-correlated states characterized by spontaneous rotational symmetry breaking. In the quantum Hall regime, such phases typically emerge at half-filled, high-orbital-index ($N\geq2$) Landau levels (LLs) where the short-range Coulomb interaction is softened by the nodes of electron wave functions. In the lowest ($N=0$) LLs, these phases are not expected. Instead, composite fermion (CF) liquids and fractional quantum Hall states, which are well explained in the picture of weakly interacting CF quasiparticles, are favored. Here we report the observation of an unexpected stripe/nematic phase in the \textit{lowest} LL at filling factor $\nu=5/8$ in ultrahigh-quality GaAs two-dimensional \textit{hole} systems, evinced by a pronounced in-plane transport anisotropy. Remarkably, $\nu=5/8$ can be mapped to a half-filled, high-index CF LL ($N_{\text{CF}}=2$), analogous to the $N=2$ hole LL. Our finding signals a novel stripe/nematic phase of CFs, driven by the residual long-range interaction among these emergent quasiparticles. This phase is surprisingly robust, surviving up to $\sim$100 mK. Its absence in electron-type systems suggests that severe LL mixing stemming from the large hole effective mass and non-linear LL fan diagram plays a crucial role in modifying the CF-CF interaction.