Research Highlights
Quantized Integrated Shift Effect in Multigap Topological Phases
Discovery of new quantized effects and sum rules
Quantised bulk photovoltaic shift currents induced by incident light. A second-order current density response of a multigap topological insulator with summed photo-conductivities quantises upon irradiating the system with circularly polarized light.
Quantized responses and topological matter are intricately related. Famously, quantum Hall effects and their topological character were discovered by observing quantized electric conductivities. Nonetheless, such quantized effects are still very scarce. We show that novel multigap phases, i.e. topological phases with electronic wavefunctions twisted across multiple gaps and within many bands, rather than in single ones, exhibit a quantized shift response, i.e. a higher-order quantized photovoltaic response upon shining light on the system. This provides a smoking gun experimental signature for these exotic multigap phases realizing torsion in momentum space. More generally, these results thus indicate that sets of bands can obey a quantised sum rule and provide a novel fundamental research direction.
Quantized Integrated Shift Effect in Multigap Topological Phases, Wojciech J. Jankowski and Robert-Jan Slager, Physical Review Letters 133, 186601 (2024).