Spin Selectivity in Electron Transfer in Photosystem I

Abstract

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons’ spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high‐spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high‐spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.

Circuit-model analysis for spintronic devices with chiral molecules as spin injectors

“…Therefore, the CISS-related spin signals in Ref. 26 was at least two orders of magnitude lower than the measured value. In fact, if we consider a realistic situation where PSI units do not form a fully-oriented and densely-packed layer on silver and |η| < 1, the actual CISS signals should be even smaller.…”

“…For Ref. 26 the value should be on the same order of magnitude due to the large similarities between the two experiments. However, this value is still two orders of magnitude slower than the most ideal scenario that we have assumed.…”

“…For the envisioned spintronic behavior in Ref. 26, this model captures all relevant aspects for spintronic signals in the linear transport regime, without making assumptions that restrict its validity. It is thus suited for describing the observed spin signals in a quantitative manner when the values of the circuit parameters are available.…”

“…[14][15][16][17][18][19][20][21][22] Building on CISS, hybrid devices with efficient molecular spin injectors and detectors were realized. [23][24][25][26][27][28][29][30][31][32] However, a full understanding of the signals produced by these devices is still lacking, and thereby the understanding of CISS largely hindered.…”

“…While generally applicable, we take the device reported in Ref. 26 as a case study for demonstrating our approach. In comparison to our recent analysis using electron-transmission modeling, 36 the circuit-model approach is more suited for including a role for optically driven chiral molecules, and for electron transport outside the linear-response regime.…”