Tuning the spin qubit property of diamagnetic Zn(II) metal– organic frameworks via Cu(II) doping

Abstract

With the aim of developing a general method for the synthesis of molecular spin qubits, this work demonstrates a spin-center doping method based on the use of a metal–organic framework (MOF). As the MOF host, perovskite-type [CH6N3][ZnII(HCOO)3] doped with 5%, 2%, and 1% mol of Cu(II) ions is used. An analysis including X-ray fluorescence spectroscopy, magnetism, and the complete active space self-consistent field calculation method confirm the presence of dopant Cu(II) sites with the S = 1/2 system. Magnetic dynamics indicate the occurrence of a slow magnetic relaxation via the Raman process under an applied field, with a relaxation time of 3.5 ms (5% Cu), 9.2 ms (2% Cu), and 15 ms (1% Cu) at 1.8 K. Furthermore, pulse electron spin resonance spectroscopy reveals spin qubit properties with a Hahn echo decay time of 0.24 µs (2% Cu) and 0.41 µs (1% Cu) at 4 K as well as Rabi oscillation between MS = ± 1/2 spin sublevels. These relaxation-extending effects stem from the weakening of the spin–spin interactions between the Cu(II) sites and can be tuned by adjusting the dopant concentration. This work demonstrates a new application of MOFs as quantum materials having fine-tuning ability for spin qubits.