Stripe-Nematic Phase of Composite Fermions

Area of Science:

• Condensed Matter Physics
• Quantum Hall Effect
• Strongly Correlated Electron Systems

Background:

• Electronic stripe-nematic phases involve spontaneous rotational symmetry breaking in strongly correlated states.
• These phases usually occur in high-orbital-index (N≥2) Landau levels (LLs) in the quantum Hall regime.
• They are not typically expected in the lowest (N=0) LLs, where composite fermion (CF) liquids and fractional quantum Hall states are favored.

Purpose of the Study:

• To investigate the unexpected emergence of a stripe-nematic phase in the lowest Landau level.
• To understand the role of composite fermion interactions in this novel phase.
• To explore the influence of system parameters, such as LL mixing, on the observed phenomena.

Main Methods:

• Fabrication and characterization of ultra-high-quality GaAs two-dimensional hole systems.
• Measurement of in-plane transport anisotropy at a filling factor of ν=5/8 in the lowest LL.
• Analysis of the observed anisotropy in the context of composite fermion theory and Landau level mixing.

Main Results:

• Observation of a pronounced in-plane transport anisotropy, indicating a stripe-nematic phase at ν=5/8 in the lowest LL.
• This filling factor maps to a half-filled, high-index CF LL (N_{CF}=2), analogous to higher LLs.
• The stripe-nematic phase is robust, persisting up to approximately 100 mK.
• The phase's absence in electron systems suggests LL mixing plays a critical role.

Conclusions:

• A novel stripe-nematic phase of composite fermions has been identified in the lowest Landau level.
• This phase is driven by residual long-range interactions among composite fermions, modified by LL mixing.
• The findings challenge existing theories and highlight the importance of hole effective mass and LL mixing in exotic quantum Hall states.