At high magnetic fields, monolayer graphene hosts competing phases distinguished by their breaking of the approximate SU(4) isospin symmetry. Recent experiments have observed an even denominator fractional quantum Hall state thought to be associated with a transition in the underlying isospin order from a spin-singlet charge density wave at low magnetic fields to an antiferromagnet at high magnetic fields, implying that a similar transition must occur at charge neutrality. However, this transition does not generate contrast in typical electrical transport or thermodynamic measurements and no direct evidence for it has been reported, despite theoretical interest arising from its potentially unconventional nature. Here, we measure the transmission of ferromagnetic magnons through the two-dimensional bulk of clean monolayer graphene. Using spin polarized fractional quantum Hall states as a benchmark, we find that magnon transmission is controlled by the detailed properties of the low-momentum spin waves in the intervening Hall fluid, which is highly density dependent. Remarkably, as the system is driven into the antiferromagnetic regime, robust magnon transmission is restored across a wide range of filling factors consistent with Pauli blocking of fractional quantum Hall spin-wave excitations and their replacement by conventional ferromagnetic magnons confined to the minority graphene sublattice. Finally, using devices in which spin waves are launched directly into the insulating charge-neutral bulk, we directly detect the hidden phase transition between bulk insulating charge density wave and a canted antiferromagnetic phase at charge neutrality, completing the experimental map of broken-symmetry phases in monolayer graphene.

中文翻译：

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单层石墨烯中的强磁场磁子传输

在高磁场下，单层石墨烯承载竞争相，其特征在于它们破坏了近似的 SU(4) 同位旋对称性。最近的实验观察到一个偶数分母分数量子霍尔态被认为与从低磁场下的自旋单重态电荷密度波到高磁场下的反铁磁体的基本同位旋顺序的转变有关，这意味着必须发生类似的转变在电荷中性。然而，这种转变不会在典型的电传输或热力学测量中产生对比，并且没有直接的证据报告，尽管其潜在的非常规性质引起了理论上的兴趣。在这里，我们测量了铁磁磁振子通过干净的单层石墨烯的二维体的传输。使用自旋极化分数量子霍尔态作为基准，我们发现磁振子传输受中间霍尔流体中的低动量自旋波的详细特性控制，这是高度依赖于密度的。值得注意的是，随着系统被驱动到反铁磁状态，在与分数量子霍尔自旋波激发的泡利阻塞和它们被限制在少数石墨烯亚晶格的传统铁磁磁控器的替代一致的广泛填充因子上恢复了强大的磁控管传输。最后，使用将自旋波直接发射到绝缘电荷中性体中的装置，我们直接检测到体绝缘电荷密度波与电荷中性时倾斜的反铁磁相之间的隐藏相变，