Structural fluctuations cause spin-split states in tetragonal (CH₃NH₃)PbI₃ as evidenced by the circular photogalvanic effect

Niesner D, Hauck M, Shrestha S, Levchuk I, Matt G, Osvet A, Batentschuk M, Brabec C, Weber HB, Fauster T (2018)


Publication Language: English

Publication Type: Journal article, Original article

Publication year: 2018

Journal

Book Volume: 115

Pages Range: 9509-9514

Journal Issue: 38

URI: https://www.pnas.org/doi/epdf/10.1073/pnas.1805422115

DOI: 10.1073/pnas.1805422115

Open Access Link: https://www.pnas.org/doi/epdf/10.1073/pnas.1805422115

Abstract

Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic{ extendash}tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry.

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APA:

Niesner, D., Hauck, M., Shrestha, S., Levchuk, I., Matt, G., Osvet, A.,... Fauster, T. (2018). Structural fluctuations cause spin-split states in tetragonal (CH₃NH₃)PbI₃ as evidenced by the circular photogalvanic effect. Proceedings of the National Academy of Sciences of the United States of America, 115(38), 9509-9514. https://dx.doi.org/10.1073/pnas.1805422115

MLA:

Niesner, Daniel, et al. "Structural fluctuations cause spin-split states in tetragonal (CH₃NH₃)PbI₃ as evidenced by the circular photogalvanic effect." Proceedings of the National Academy of Sciences of the United States of America 115.38 (2018): 9509-9514.

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