Abstract
Two-dimensional topological materials bearing time reversal-breaking magnetic fields support protected one-way edge modes. Normally, these edge modes adhere to physical edges where material properties change abruptly. However, even in homogeneous materials, topology still permits a unique form of edge modes – kink modes – residing at the domain boundaries of magnetic fields within the materials. This scenario, despite being predicted in theory, has rarely been demonstrated experimentally. Here, we report our observation of topologically-protected high-frequency kink modes – kink magnetoplasmons (KMPs) – in a GaAs/AlGaAs two-dimensional electron gas (2DEG) system. These KMPs arise at a domain boundary projected from an externally-patterned magnetic field onto a uniform 2DEG. They propagate unidirectionally along the boundary, protected by a difference of gap Chern numbers (pm1) in the two domains. They exhibit large tunability under an applied magnetic field or gate voltage, and clear signatures of nonreciprocity even under weak-coupling to evanescent photons.
Highlights
Two-dimensional topological materials bearing time reversal-breaking magnetic fields support protected one-way edge modes
Protected one-way edge modes can exist in two-dimensional systems under a time-reversal-breaking magnetic field[1,2,3]
We find that the excitation frequencies of kink magnetoplasmons (KMPs) exhibit a unique dependence on an applied magnetic field or gate voltage, differing substantially from the conventional edge magnetoplasmons (EMPs)
Summary
Two-dimensional topological materials bearing time reversal-breaking magnetic fields support protected one-way edge modes. We report our observation of topologically-protected high-frequency kink modes – kink magnetoplasmons (KMPs) – in a GaAs/AlGaAs two-dimensional electron gas (2DEG) system These KMPs arise at a domain boundary projected from an externally-patterned magnetic field onto a uniform 2DEG. Protected one-way edge modes can exist in two-dimensional systems under a time-reversal-breaking magnetic field[1,2,3] Such modes usually arise at physical edges where material properties undergo a sudden change. Under a perpendicular magnetic field, the 2DEG hosts magnetoplasmons (MPs)—electron-density oscillations sustained by the longitudinal Coulomb force and subjected to a transverse Lorentz force—covering a broad spectral range from radio to microwave frequencies These MPs embody a prototypical band topology of bosonic excitations[5,17]. Previous studies of EMPs in any 2DEG systems all relied on sharp termination of electron density nðrÞ at sample edges[28,29,30]
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