Future Tuneable Correlated Spin System in Low-Cost Solution-Processed Perovskite Crystals?

We studied the implications of ligand size in solution-processed copper halide perovskite crystals to optical signatures and electronic modulations at various temperatures. The presence of local-induced antiferromagnetic interaction opens new venue in low-cost tuneable correlated spin systems.

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The combination of condensed matter physics, especially in correlated spin systems, and information science will address to the rise of quantum computations that are able to perform calculations and tasks of a complexity unattainable by systems that behave classically. For the qubits of the systems, most attention is strongly directed towards copper-based molecules, which usually have long-lived spin states. One important feature needed for the systems is that it needs to be stable enough so that one can enter and read out information. They are not so many copper molecules that are fulfil this requirement, and the available one is usually hard to synthesize.  Metal halide perovskite crystals have been long time subjected to various applications, from photovoltaics to radiation detectors since their almost cubical structures are easy to growth. The recent low-cost solution-processed method has been much evolved to yield high quality crystals and spin correlated plasmon was discovered in those grown copper halide perovskite samples. This is the first result to demonstrate the coupling between spin correlated-plasmons and electron−hole pairs together with spin-dependent exchange interactions in such crystals.     

To continue our research in the direction of correlated spin systems, here, we observed the structural transition, optical signature and electronic modulation are present in the copper chloride (A2CuCl4, A = MA, EA, PMA, PEA) single crystals under variable temperature using combined photoluminescence and high-resolution synchrotron spectroscopies. The main results of X-ray absorption spectra (XAS) of all investigated copper chloride perovskite crystals are shown in Figure 1. The spectra show several copper L2,3 edge peaks which demonstrated the implication of the ligand size and the observed temperature. In addition, some crystals did show the presence of local-induced antiferromagnetic interaction between the neighbouring copper-inorganic sheets. We also performed density functional theory calculations to prove such ligand effect to the electronic properties of our copper halide perovskite crystals, especially the odd-even effects of organic spacer in this copper halide perovskite crystals. The future applications such as quantum computations are very interesting due to the tuneable and correlated spin systems that can be offered by such stable perovskite structures.  

Figure 1. Temperature-dependent XAS spectra of copper halide perovskite crystals. The interactions in the absorption L-edge profile as function of temperatures were envisaged.

The collaborative project received technical supports from excellent people in the Surface Science Laboratory, NUS (Mr. Wong How Kwong) and Singapore Synchrotron Light Source (Dr. Xiaojiang Yu). Further information on our research groups can be found: https://phyweb.physics.nus.edu.sg/~surface/, https://www.ntu.edu.sg/cintra, and https://ssls.nus.edu.sg/.

For more information, please see our recent publication in Communication Materials:

Ligand size effects in two-dimensional hybrid copper halide perovskites crystals




Research Fellow , Surface Science Laboratory, Department of Physics, National University of Singapore

Current research theme is mainly to investigate the emergent two-dimensional layered materials span from hybrid and all-inorganic perovskites, transition metal dichalcogenides, and mxenes. In addition, the utilization of nc-AFM/LT-STM for on-surface synthesis.

Several expertise and experience: Scanning Electron Microscopy (SEM), Thermogravimetry Analysis (TGA), X-ray Diffraction (Bragg & Laue technique), UV-Vis spectroscopy, IR-Raman spectroscopy, Self-assembly monolayer fabrications, magnetic and capacitance measurements, “floating Zone” single crystal fabrication, X-ray/UV Photoelectron Spectroscopy (XPS/UPS) technique, Spectroscopic Ellipsometry, X-ray Absorption Spectroscopy, Near Edge X-ray Absorption Fine Structure, X-ray Circular Magnetic  Two-dimensional Materials, and Organic Thin Films deposition.