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Manipulating optical and magnetic symmetry at the nanoscale in 2D semiconductors

Alex High, University of Chicago
Thursday, April 14, 2022 - 12:30pm to 1:30pm
PAB 421, TIQM meeting space

In this seminar I will present two experimental studies that leverage the optically-addressable valley degree of freedom in transition metal dichalcogenide monolayers (TMDs) to locally manipulate the  symmetry of optical and magnetic processes. First, I will discuss our realization of an electrically-tunable chiral nanophotonic interface with a TMD (1). We fabricate optical waveguides directly on the surface of low disorder, boron nitride-encapsulated tungsten diselenide (WSe2). The underlying excitonic states in the WSeenable scattering into the waveguide that can be electrically switched between directionally-biased and balanced. We also demonstrate that the optical modes of the waveguide can act as a local source for diffusive, spin-polarized excitonic fluxes. Second, I will discuss our observation that ferromagnetic order in electrostatically-doped TMDs – which arises due to interactions between conduction band electrons - can be stabilized and controlled at zero magnetic field by local optical pumping (2). We show that a diffraction-limited, circularly-polarized optical pump can break symmetry between oppositely-polarized magnetic states and stabilize long-range magnetic order, with carrier polarization exceeding 80% over an 8 µm x 5 µm extent. The local control of optical and magnetic symmetry in TMDs can unlock new spin and optical technologies and provide versatile tools in the study of correlated phases in two-dimensional electron gases.

Additionally, I will provide a brief overview our quantum research in diamond, and highlight our recent development of thin film diamond that hosts spin- and optically-coherent quantum states (3). We envision these films as a versatile platform for hybrid quantum devices.

  1. R. Shreiner, K. Hao, A. Butcher & A.A. High, "Electrically controllable chirality in a nanophotonic interface with a 2D semiconductor," Nature Photonics (2022).
  2. K. Hao, R.T. Shreiner, A. Kindseth & A.A. High, "Optically controllable magnetism in atomically thin semiconductors," arxiv: 2108.05931
  3. X. Guo, N. Delegan, J.C. Karsch, Z. Li, T. Liu, R. Shreiner, A. Butcher, D.D. Awschalom, F.J. Heremans & A.A. High, "Tunable and Transferable Diamond Membranes for Integrated Quantum Technologies," Nano Letters 21, 10392 (2021)