偶数分母分数量子霍尔态与自发破缺旋转对称性的相互作用
Even-denominator fractional quantum Hall states with spontaneously broken rotational symmetry
AI总结：
研究在垂直磁场中观察到偶数分母分数量子霍尔态，并发现其与自发对称破缺共存，揭示了单轴FQHS的出现及非阿贝尔准粒子激发。
摘要：
分数量子霍尔效应与单轴性之间的相互作用令人着迷，因为它将新兴的拓扑序与自发对称破缺联系起来。各向异性分数量子霍尔态（FQHSs）确实已在GaAs量子井中报告，但仅在倾斜的磁场中，其中平面内的磁场显式地破坏旋转对称性。在这里，我们报告了在纯垂直磁场中，在偶数分母朗德能级（LL）填充ν = 5/2和7/2的超高质量GaAs二维空穴系统中观察到具有高度各向异性纵向电阻的FQHSs。FQHSs与半填充处的自发对称破缺共存，表明了单轴FQHSs的出现，这可能也包含非阿贝尔准粒子激发。通过栅极调节空穴密度，我们观察到从各向异性发展中的FQHS到在ν = 7/2处各向同性的复合费米费米海的相变。我们的计算表明，部分占据的LL中的混合轨道成分在拓扑序和单轴序之间的竞争和相互作用中起关键作用。
英文摘要：
The interplay between the fractional quantum Hall effect and nematicity is intriguing as it links emerging topological order and spontaneous symmetry breaking. Anisotropic fractional quantum Hall states (FQHSs) have indeed been reported in GaAs quantum wells but only in tilted magnetic fields, where the in-plane field explicitly breaks the rotational symmetry. Here we report the observation of FQHSs with highly anisotropic longitudinal resistances in purely perpendicular magnetic fields at even-denominator Landau level (LL) fillings ν = 5/2 and 7/2 in ultrahigh-quality GaAs two-dimensional hole systems. The coexistence of FQHSs and spontaneous symmetry breaking at half fillings signals the emergence of nematic FQHSs which also likely harbor non-Abelian quasiparticle excitations. By gate tuning the hole density, we observe a phase transition from an anisotropic, developing FQHS to an isotropic composite fermion Fermi sea at ν = 7/2. Our calculations suggest that the mixed orbital components in the partially occupied LL play a key role in the competition and interplay between topological and nematic orders.
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