| Summary: | In this work, we studied, at low temperature, the coherent evolution of the localized electron and hole spins in a polycrystalline film of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPI) by using a picosecond-photo-induced Faraday rotation technique in an oblique magnetic field. We observed an unexpected anisotropy for the electron and hole spin. We determined the electron and hole Landé factors when the magnetic field was applied in the plane of the film and perpendicular to the exciting light, denoted as transverse <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>⊥</mo><mo> </mo></mrow></semantics></math></inline-formula> factors, and when the magnetic field was applied perpendicular to the film and parallel to the exciting light, denoted as parallel <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo> </mo><mo>∥</mo><mo> </mo></mrow></semantics></math></inline-formula> factors. We obtained <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mo>|</mo><mrow><msub><mi>g</mi><mrow><mi>e</mi><mo>,</mo><mo>⊥</mo></mrow></msub></mrow><mo>|</mo></mrow><mo>=</mo><mn>2.600</mn><mo> </mo><mo>±</mo><mo> </mo><mn>0.004</mn></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mo>|</mo><mrow><msub><mi>g</mi><mrow><mi>e</mi><mo>,</mo><mo>∥</mo></mrow></msub></mrow><mo>|</mo></mrow><mo>=</mo><mn>1.604</mn><mo> </mo><mo>±</mo><mo> </mo><mn>0.033</mn></mrow></semantics></math></inline-formula> for the electron and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mo>|</mo><mrow><msub><mi>g</mi><mrow><mi>h</mi><mo>,</mo><mo>⊥</mo></mrow></msub></mrow><mo>|</mo></mrow><mo>=</mo><mn>0.406</mn><mo> </mo><mo>±</mo><mo> </mo><mn>0.002</mn></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mo>|</mo><mrow><msub><mi>g</mi><mrow><mi>h</mi><mo>,</mo><mo>∥</mo></mrow></msub></mrow><mo>|</mo></mrow><mo>=</mo><mn>0.299</mn><mo> </mo><mo>±</mo><mo> </mo><mn>0.007</mn></mrow></semantics></math></inline-formula> for the hole. Possible origins of this anisotropy are discussed herein.
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