Symmetry characterization of the collective modes of the phase diagram of the 
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 quantum Hall state in graphene: Mean-field phase diagram and spontaneously broken symmetries

Nova, Juan Ramón Muñoz de; Zapata, I.

doi:10.1103/physrevb.95.165427

Cited by 10 publications

(11 citation statements)

References 68 publications

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“…Both spin-up and spindown SWs can be transmitted and translate into VNL of opposite signs in the detection region. In a system with in-plane U(1) symmetry, the k = 0 mode is expected to be gapless [14,[26][27][28].…”

Section: Resultsmentioning

confidence: 99%

“…The large amplitude of the oscillations suggests long SW dephasing length of many micrometers in our devices, a necessary condition to explore spin superfluidity [14,16]. We focus on signals within ± Ez since in this range only excitations on the gapless CAF SW branch are allowed [26,27]. dVNL/dV at T = 0.33 K (blue) and 2 K (purple) with the mode numbers labeled in the plot.…”

Section: Resultsmentioning

confidence: 99%

“…Graphene materials enrich the physics and phenomenology of QHF by introducing isospins such as valley or layer/sublattice [19,20,22]. For instance, the E = 0 Landau levels of AB-stacked bilayer graphene is expected to support a spin-valley coherent, canted-antiferromagnetic (CAF) phase with in-plane rotational symmetry [22] and gapless, linearly dispersed SW excitations that correspond to an in-plane precession of the Néel vector [14,16,[26][27][28]. This gapless magnon mode is predicted to support spin superfluidity [12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

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Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet

Huang

Watanabe

et al. 2021

Phys. Rev. X

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In the Landau levels of a two-dimensional electron system or when flat bands are present, e.g. in twisted van der Waals bilayers, strong electron-electron interaction gives rise to quantum Hall ferromagnetism with spontaneously broken symmetries in the spin and isospin sectors. Quantum Hall ferromagnets support a rich variety of low-energy collective excitations that are instrumental to understand the nature of the magnetic ground states and are also potentially useful as carriers of quantum information. Probing such collective excitations, especially their dispersion 𝜔𝜔(𝑘𝑘), has been experimentally challenging due to small sample size and measurement constraints. In this work, we demonstrate an all-electrical approach that integrates a Fabry-Pérot cavity with non-equilibrium transport to achieve the excitation, wave vector selection and detection of spin waves in graphene heterostructures. Our experiments reveal gapless, linearly dispersed spin wave excitations in the E = 0 Landau level of bilayer graphene, thus providing direct experimental evidence for a predicted canted antiferromagnetic order. We show that the gapless spin wave mode propagates with a high group velocity of several tens of km/s and maintains phase coherence over a distance of many micrometers. Its dependence on the magnetic field and temperature agree well with the hydrodynamic theory of spin waves. These results lay the foundation for the quest of spin superfluidity in this high-quality material. The resonant cavity technique we developed offers a powerful and timely method to explore the collective excitation of many spin and isospin-ordered many-body ground states in van der Waals heterostructures and open the possibility of engineering magnonic devices.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet

Huang

Watanabe

et al. 2021

Phys. Rev. X

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“…The full dispersion relation of spin waves in graphene at ν = 0 has been studied in Refs. [51] and [52], while the low-energy dispersion and gaps of the KD and CAF state spin-waves was obtained using a non-linear sigma model in Ref. [53], which showed the presence of gapless linearly dispersing modes in these two phases.…”

Section: Introductionmentioning

confidence: 97%

SU(4) spin waves in the $ν=\pm1$ quantum Hall ferromagnet in graphene

Atteia,

Goerbig

2021

Preprint

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We study generalized spin waves in graphene under a strong magnetic field when the Landaulevel filling factor is ν = ±1. In this case, the ground state is a particular SU(4) quantum Hall ferromagnet, in which not only the physical spin is fully polarized but also the pseudo-spin associated with the valley degree of freedom. The nature of the ground state and the spin-valley polarization depend on explicit symmetry breaking terms that are also reflected in the generalised spin-wave spectrum. In addition to pure spin waves, one encounters valley-pseudo-spin waves as well as more exotic entanglement waves that have a mixed spin-valley character. Most saliently, the SU(4) symmetry-breaking terms do not only yield gaps in the spectra, but under certain circumstances, namely in the case of residual ground-state symmetries, render the originally quadratic (in the wave vector) spin-wave dispersion linear.

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“…In contrast, the non-local voltage signal is greatly suppressed by ν = 1|0|1 junctions. This finding requires an explanation since the ν m = 0 canted antiferromagnet also supports magnons [41][42][43].…”

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confidence: 95%

Scattering of magnons at graphene quantum-Hall-magnet junctions

Wei,

Huang,

MacDonald

2020

Preprint

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Motivated by recent non-local transport studies of quantum-Hall-magnet (QHM) states formed in monolayer graphene's N = 0 Landau level, we study the scattering of QHM magnons by gatecontrolled junctions between states with different integer filling factors ν. For the ν = 1| − 1|1 geometry we find magnons are weakly scattered by electric potential variation in the junction region, and that the scattering is chiral when the junction lacks a mirror symmetry. For the ν = 1|0|1 geometry, we find that kinematic constraints completely block magnon transmission if the incident angle exceeds a critical value. Our results explain the suppressed non-local-voltage signals observed in the ν = 1|0|1 case. We use our theory to propose that valley-waves generated at ν = −1|1 junctions and magnons can be used in combination to probe the spin/valley flavor structure of QHM states at integer and fractional filling factors.

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Symmetry characterization of the collective modes of the phase diagram of the ν=0 quantum Hall state in graphene: Mean-field phase diagram and spontaneously broken symmetries

Cited by 10 publications

References 68 publications

Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet

Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet

SU(4) spin waves in the $ν=\pm1$ quantum Hall ferromagnet in graphene

Scattering of magnons at graphene quantum-Hall-magnet junctions

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