Dynamic control of topological and ferroelectric properties in 2D materials

In two-dimensional layered quantum materials, the stacking order of the layers often determines the crystalline symmetry and associated properties such as Berry curvature, topology, and ferroelectricity. Electrical or optical stimuli can influence the free-energy landscape, making it possible to dynamically modify the stacking order and reveal hidden structures that host different quantum properties. In the first part of this talk I will discuss the application of terahertz frequency light pulses to drive interlayer shear excitations in WTe2, as probed by femtosecond electron diffraction techniques [1]. We find a new mechanism for directly modulating interlayer stacking and associated topological properties on picosecond time-scales. In the second part of this talk I will discuss the application of out-of-plane electric fields and electrostatic doping as a means of manipulating in-plane interlayer sliding to create multiple polar and centrosymmetric stacking orders in few layer WTe2. In-situ nonlinear Hall transport reveals that such stacking rearrangements result in a layer-parity-selective Berry curvature memory in momentum space, where the sign reversal of the Berry curvature and its dipole only occurs in odd-layer crystals. Our findings open an avenue towards exploring coupling between topology, electron correlations and ferroelectricity in hidden stacking orders and demonstrate a new low-energy-cost, electrically controlled memory in the atomically thin limit [2].

[1] E. Sie et al., “An ultrafast symmetry switch in a Weyl semimetal,”, Nature, 565, 61 (2019).

[2] J. Xiao et al., “Berry curvature memory through electrically-driven stacking transitions”, Nature Physics, 16, 1028 (2020).