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Local photo-excitation of shift current in noncentrosymmetric systems
摘要： Photocurrent in solids is an important phenomenon with many applications including the solar cells. In conventional photoconductors, the electrons and holes created by light irradiation are separated by the external electric field, resulting in a current flowing into electrodes. Shift current in noncentrosymmetric systems is distinct from this conventional photocurrent in the sense that no external electric field is needed and, more remarkably, is driven by the Berry phase inherent to the Bloch wavefunction. It is analogous to the polarization current in the ground state but is a dc current continuously supported by the nonequilibrium steady state under the pumping by light. Here we show theoretically, by employing Keldysh–Floquet formalism applied to a simple one-dimensional model, that the local photo excitation can induce the shift current which is independent of the position and width of the excited region and also the length of the system. This feature is in stark contrast to the conventional photocurrent, which is suppressed when the sample is excited locally at the middle and increases towards the electrodes. This finding reveals the unconventional nature of shift current and will pave a way to design a highly efficient photovoltaic effect in solids.
关键词： nonequilibrium Green’s function method,shift current,photovoltaic effect
更新于2025-09-23 15:21:21
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Strong bulk photovoltaic effect in chiral crystals in the visible spectrum
摘要： Structurally chiral materials hosting multifold fermions with large topological number have attracted considerable attention because of their naturally long surface Fermi arcs and bulk quantized circular photogalvanic effect (CPGE). Multifold fermions only appear in metallic states, and therefore most studies so far have only focused on the semimetals in compounds with chiral crystal structures. In this work, we show that the structurally chiral topological trivial insulators are also exotic states, which is interesting from the application point of view, owing to their natural advantage to host a large bulk photovoltaic effect in the visible wavelength region. In recent decades, the shift current in the visible wavelength region was limited to be 10 μA/V2 in all the experimentally measured reports. By scanning the insulators with chiral structure, we found a class of compounds with photoconductivity ranging from ～20 to ～80 μA/V2, which is comparable to the largest reported shift current. This work illustrates that the compounds with chiral structure can host both quantum CPGE and a strong shift current in the second-order optical response. Moreover, this work offers a good platform for the study of the shift current and its future application by putting the focus on insulators with chiral lattices, so far overlooked in photovoltaic technologies.
关键词： photoconductivity,chiral crystals,shift current,bulk photovoltaic effect,visible spectrum
更新于2025-09-12 10:27:22
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Impact of electrodes on the extraction of shift current from a ferroelectric semiconductor SbSI
摘要： Noncentrosymmetric bulk crystals generate photocurrent without any bias voltage. One of the dominant mechanisms, shift current, comes from the quantum interference of electron wave functions being distinct from the classical current caused by electrons’ drift or diffusion. The dissipation-less nature of shift current, however, has not been fully veri?ed, presumably due to the premature understanding of the role of electrodes. Here, we show that the photocurrent dramatically enhanced by choosing electrodes with large work functions for a p-type ferroelectric semiconductor SbSI. An optimized device shows a nearly constant zero-bias photocurrent despite the signi?cant dependence of photocarrier mobility on temperature, which could be a clear hallmark for the dissipation-less nature of shift current. Distinct from conventional photovoltaic devices, the shift current generator operates as a majority carrier device. The present study provides fundamental design principles for energy-harvesting and photo-detecting devices with novel architectures optimal for the shift current photovoltaic effect.
关键词： SbSI,electrodes,ferroelectric semiconductor,photocurrent,shift current
更新于2025-09-09 09:28:46