This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The circular photogalvanic effect (CPGE), a phenomenon that generates helicity-dependent photocurrents in noncentrosymmetric materials, can originate purely from a crystal's internal structure without a contribution from the surface, a study from Science Tokyo reveals. Researchers demonstrated this effect in 2D organic–inorganic hybrid perovskites using circularly polarized light at normal incidence, which helped distinguish the bulk response from surface contributions.
The finding establishes a strategy for regulating spin-polarized photocurrents and advancing opto-spintronic technologies. The findings are published in Nano Letters. Most electronic devices we use today rely on electron charge to store, process and transmit information.
However, scientists are exploring another electron property, known as spin, to develop new ways to control electronic signals. These technologies, known as spintronics, could make electronic devices smaller and more energy-efficient. The circular photogalvanic effect (CPGE) has the potential to advance spintronics and provides a purely optical means to generate spin-polarized photocurrents in nonmagnetized materials.
When circularly polarized light falls on certain materials, it generates a photocurrent whose direction depends on the handedness (such as left- or right-handedness) of the light. This effect is particularly useful for generating and studying spin-dependent photocurrents in materials with strong spin–orbit interactions, where electron motion is closely linked to spin. In certain materials, circularly polarized light can generate a photocurrent whose direction changes depending on whether the light is right- or left-handed.
However, when designing such materials, an important question remains: Does the photocurrent originate from the polarity of the bulk of the material or from its surface? To address this question, researchers from Institute of Science Tokyo (Science Tokyo) in Japan demonstrate that CPGE originated from the bulk of two-dimensional organic–inorganic hybrid perovskite (2D-OIHP) crystals. The team was led by professor Kouji Taniguchi and included graduate student Ichi Naruse and assistant professor Po‑Jung Huang of the Department of Chemistry at Science Tokyo.
"CPGE is closely related to spin-polarized electronic states and has attracted attention as a route for generating spin-polarized photocurrents by light. However, in conventional CPGE measurements, signals originating from crystal surfaces and interfaces are often mixed with bulk contributions, making it difficult to determine the microscopic origin of the observed photocurrent," explains Taniguchi. The researchers demonstrated the effect in 2D-OIHP crystals made of alternating lead iodide layers and 1-(p-tolyl)ethylammonium cation layers.
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