Figure 1. (a) 3D pseudo-color plot of left- (σ⁺) and right-circularly (σ⁻) polarized PL spectra in magnetic fields from −16 T to 16 T at T = 4.2 K. (b) Peak energy of the σ⁺ and σ⁻ polarized PL and energy splitting (ΔE) versus B. The inset illustrates the excitons energy levels, where the magneto-PL arises from the Zeeman splitting of J_z = ±1 states. The reversal of the +1 and −1 states, due to the highly localized Cu²⁺ ions, leads to the giant Zeeman splitting. (c) Schematic diagram of the transport and recombination of carriers with electrical excitation under the magnetic field. (d) P_EL versus B, with the solid curves fitted.

Background

The integration of electrical, magnetic, and optical properties within semiconductor nanostructures is pivotal for the advancement of spintronics. However, establishing efficient coupling between excitons and magnetic ions remains challenging. This is primarily due to the weakly bound nature of Wannier excitons and the significant luminescence quenching typically associated with magnetic doping. In this context, low-dimensional cesium copper halides offer a solution. These materials host highly localized, Frenkel-type self-trapped excitons (STE), which confine excitons at the atomic scale. Crucially, they enable the in situ formation of magnetic centers via the photoinduced conversion of Cu⁺(3d¹⁰) into Cu⟡⁺(3d⁹) states. This unique combination of features facilitates efficient exciton-spin coupling without emission loss, thus establishing copper halides as promising candidates for spin-optoelectronic applications.

What we discover?

Within the zero-dimensional lattice of Cs₃Cu₂I₅, the Jahn–Teller distortions induce the formation of localized Cu⟡⁺ centers which facilitate spin-exciton interactions, and lead to pronounced Zeeman splitting. As shown in Fig. 1a, the σ⁺- and σ⁻-polarized PL show opposite tendencies with increasing magnetic field in both intensity and peak energy, and both tendencies reverse when the field changes its polarities. The field-dependent E⁺, E⁻, and ΔE are shown in Fig. 1b, ΔE increases with B and saturates at |B| ≥ 15 T, with a saturation value of −53 meV. In the linear region at low fields (|B| ≤ 10 T), an effective exciton g-factor (g_eff) of −93.5 could be obtained. This giant Zeeman splitting significantly exceeds that observed in lead-based perovskites and comparable with that of some diluted magnetic semiconductor (DMS) nanostructures. Within the established sp-d exchange model for DMS, the effect in Cs₃Cu₂I₅ originates from strong sp-d coupling between tightly bound STE and spatially confined spin-1/2 Cu²⁺ centers. This coupling induces an imbalance in spin-level occupancy, enhancing spin-polarized emission. Leveraging this mechanism, utilizing the Cs₃Cu₂I₅ thin films as the active region, a heterostructure of ITO/ZnO/Al₂O₃/Cs₃Cu₂I₅/MCP/TAPC/HAT-CN/Al is fabricated. The working principle of spin-polarized electroluminescence (EL) is illustrated in Fig. 1c. According to the optical selection rules and conservation of angular momentum in the optical transitions, the excitonic recombination would produce circularly polarized luminescence, which attributed to the imbalanced population of electrons on the two pairs of Zeeman energy levels. These devices achieve a saturated circular polarization degree in electroluminescence (P_EL) of up to 44.5% at low temperature, while retaining significant spin polarization (~8%) even at room temperature (Fig. 1d).

Why is this important?

The cesium copper halide system demonstrates strong spin-carrier interactions, remarkable luminescence properties, and flexibility in spin-electronic manipulation. This positions it as a novel platform for developing efficient, spin-tunable, and environmentally friendly semiconductor optoelectronic materials, thereby opening a new pathway toward identifying optimal candidates for spin–photonics applications.

Who did the research?

Ruiqin Huang¹, Longbo Yang², Feng Yang¹, Yuttapoom Puttisong³, Qingsong Hu⁴, Guixian Li¹, Jingnan Hu¹, Zhaobo Hu⁵, Liang Li¹, Jiang Tang², Weimin Chen³, Yibo Han^1*, Jiajun Luo^2*, Feng Gao^3*

(1) Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan, 430074, China

(2) Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, China

(3) Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden.

(4) Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices, Hubei University of Arts and Science, Xiangyang, 441053, China

(5) School of Chemistry and Chemical Engineering, Jiangxi Provincial Key Laboratory of Functional Crystalline Materials Chemistry, Jiangxi University of Science and Technology, Ganzhou 341000, China

Nature Communications, 2025, 16: 7264

https://www.nature.com/articles/s41467-025-62704-y

Funding

This study was supported by the National Key R&D Program of China (grant no. 2022YFA1602702) and the Natural Science Foundation of China (grant no. 11974126).