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arXiv · 2607.25128

Field-Induced Dissociation Reveals Excitonic Long-Range Photocarrier Transport in Bulk-Insulating Bi2Se3 Nanoribbons

Rodrigo Becerra Silva·Xiang Yi·Ziyi Song·Dong Yu
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Abstract

Photoexcited charge carriers in topological insulators display anomalously long-range transport at cryogenic temperatures, but the underlying mechanism remains under debate. Here we use a transverse electric field as a discriminating probe of photocarrier dynamics in bulk-insulating Sb-doped Bi2Se3 nanoribbons, combining scanning photocurrent microscopy (SPCM) with ultrafast transient photovoltage (TPV) measurements. SPCM shows that suppression of the photocurrent requires a transverse electric field nearly 50 times larger than that needed to deflect free carriers, yet comparable to the expected exciton dissociation field. TPV measurements at 12 K and low excitation fluence reveal that the photocarrier diffusivity exceeds the value implied by the Einstein relation and the measured drift mobility by more than an order of magnitude, a bound that holds even at the lower end of the fitting uncertainty. Together, these observations indicate that the long-range photoresponse is not carried by free charge carriers but by a charge-neutral correlated state.

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Rodrigo Becerra Silva, Xiang Yi, Ziyi Song, Dong Yu. 2026-07-27. Field-Induced Dissociation Reveals Excitonic Long-Range Photocarrier Transport in Bulk-Insulating Bi2Se3 Nanoribbons. https://arxiv.org/abs/2607.25128

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