Detection of Rashba spin splitting in 2D organic-inorganic perovskite via precessional carrier spin relaxation

Abstract

The strong spin-orbit interaction in the organic-inorganic perovskites tied to the incorporation of heavy elements (e.g. Pb, I) makes these materials interesting for applications in spintronics. Due to a lack of inversion symmetry associated with distortions of the metal-halide octahedra, the Rashba effect (used e.g. in spin field-effect transistors and spin filters) has been predicted to be much larger in these materials than in traditional III-V semiconductors such as GaAs, supported by the recent observation of a near record Rashba spin splitting in CH 3 NH 3 PbBr 3 using angle-resolved photoemission spectroscopy (ARPES). More experimental studies are needed to confirm and quantify the presence of Rashba effects in the organic-inorganic perovskite family of materials. Here we apply time-resolved circular dichroism techniques to the study of carrier spin dynamics in a 2D perovskite thin film [(BA) 2 MAPb 2 I 7 ; BA = CH 3 (CH 2 ) 3 NH 3 , MA = CH 3 NH 3 ]. Our findings confirm the presence of a Rashba spin splitting via the dominance of precessional spin relaxation induced by the Rashba effective magnetic field. The size of the Rashba spin splitting in our system was extracted from simulations of the measured spin dynamics incorporating LO-phonon and electron-electron scattering, yielding a value of 10 meV at an electron energy of 50 meV above the band gap, representing a 20 times larger value than in GaAs quantum wells.The hybrid organic-inorganic perovskites have gained considerable attention in recent years due to their outstanding performance as absorbing layers in photovoltaics [1]. This success has led to a comprehensive research effort with the aim to unravel their photophysical properties [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], and to move beyond CH 3 NH 3 PbI 3 and explore other material compositions including 2D perovskites [19][20][21][22][23][24]. This burgeoning family of materials offers properties that can be tailored to a broad range of applications in opto-electronics, including photovoltaics [1,23,25], field-effect transistors [26,27], hard radiation detectors [28], light-emitting diodes [29][30][31], lasers [32], and optical sensors [33].The hybrid perovskites are characterized by strong spin-orbit coupling (SOC) tied to the constituent heavy elements [34]. These strong spin-orbit effects make the perovskite family of materials attractive for applications in semiconductor spintronics and spin optoelectronics [35][36][37][38][39][40][41][42][43][44][45]. SOC leads to a giant (∼1 eV) splitting of the lowest two conduction bands and influences the band gap and carrier effective masses [46,47]. In conjunction with a lack of inversion symmetry, SOC also leads to an effective magnetic field that lifts the degeneracy of the carrier spin states within each band [35]. While this effect has many origins in semiconductors tied to different sources of inversion asymmetry [48][49][50][51][52], it is most commonly referred to as the Rashba effect after Bychkov and Rashba analyzed the ...

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