Controlling quantum materials with persistent optical effects: towards reconfigurable devices from topological and 2D materials

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Date/Time
Date(s) - May 23 2018
1:00 PM - 2:00 PM

Location
Shasta Room, Bldg. 40, Room 361

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Andrew L. Yeats

Joint Postdoctoral Appointee
Argonne National Laboratory & University of Chicago 

Controlling quantum materials with persistent optical effects: towards reconfigurable devices from topological and 2D materials

Topological insulators hold promise for applications in spintronics, metrology, and quantum computing. However, newly-synthesized research materials are often incompatible with traditional lithographic fabrication processes. We demonstrate an alternative optical approach to provide reconfigurable micron-scale control of both chemical potential and magnetization in ferromagnetic thin films of Cr-(Bi,Sb)2Te3 [1,2]. By optically manipulating a space charge layer in the underlying SrTiO3 substrates, we tune the local chemical potential of the films. This persistent “optical back-gating” effect allows us to write and erase p-n junctions in the films, which we study with photocurrent microscopy. Moreover, by optically modulating the magnetic coercivity of the films, we record and erase arbitrary patterns in their remanent magnetization, which we image with Kerr microscopy. Both effects are persistent and may be patterned and imaged independently on a few-micron scale. Dynamic optical control over both magnetization and chemical potential of a ferromagnetic TI may be particularly useful in efforts to understand and control the quantized chiral edge states that occur at magnetic domain walls in quantum anomalous Hall insulators. We also show that the substrate-based “optical back-gating” effect is generalizable to other ultra-thin materials such as monolayer MoS2 and graphene [3], and similar optical techniques can be applied to control the charge state of defect spin qubits in SiC [4].

[1] Yeats, et al., Science Advances (2015).

[2] Yeats, et al., PNAS (2017).

[3] Vincent, et al., in prep (2018).

[4] Wolfowicz, et al., Nature Communications (2017).