Single-Crystal Study of a Low Spin Co(II) Molecular Qubit: Observation of Anisotropic Rabi Cycles.

A mononuclear low spin ( S = 1/2) Co(II) molecule crystallized in a 4-fold symmetry is fully investigated by CW and pulsed EPR on a single crystal sample. The quantum phase memory time of the molecule around 1 µs at 5 K is direction-independent, while the Rabi oscillation frequency is anisotropic. The spin Hamiltonian analyses reveal that the anisotropic Landé factor and hyperfine tensor do not influence the anisotropy apparently when the microwave magnetic field is applied along a certain direction. It is considered that the possibly involved nuclear spin forbidden transitions may be responsible for the small distinction of Rabi frequencies in two directions.

Qubit crossover in the endohedral fullerene Sc3C2@C80.

The core-shell structure of endohedral fullerenes results in good protection of the encapsulated spin carriers from the environment. In this research, the quantum coherence behavior of the endohedral fullerene Sc3C2@C80 in CS2 solution is characterized from 5 K to room temperature. Below the critical temperature of around 140 K, the inner group is hindered, and the EPR spectrum consists of a single broad line. The spin carriers display a maximum phase memory time of 17.2(7) µs at 10 K. In the high temperature region, the inner group is mobile, and the EPR spectrum consists of 22 homogeneously broadened lines due to isotropic hyperfine coupling. The maximum phase memory time for each transition is around 139(1) ns at 200 K which allows arbitrary superposition state manipulations to be performed. This research demonstrates that Sc3C2@C80 displays temperature-crossover behaviour due to weak interaction between the Sc3C2 core and the C80 shell.

Chemical Modification toward Long Spin Lifetimes in Organic Conjugated Radicals.

Organic semiconductors for spin-based devices require long spin relaxation times. Understanding their spin relaxation mechanisms is critical to organic spintronic devices and applications for quantum information processing. However, reports on the spin relaxation mechanisms of organic conjugated molecules are rare and the research methods are also limited. Herein, we study the molecular design and spin relaxation mechanisms by systematically varying the structure of a conjugated radical. We found that solid-state relaxation times of organic materials are largely different from that in solution state. We demonstrate that substitution of a lower gyromagnetic ratio nucleus (e. g. D, Cl) on the para-position of the aryl rings in the triphenylmethyl (TM) radical can significantly improve their coherence times (Tm ). Flexible thin films based on such radicals exhibit ultra-long spin-lattice relaxation times (T1 ) up to 35.6(6) µs and Tm up to 1.08(4) µs under ambient conditions, which are among the longest values in films. More importantly, using the TM radical derivative (5CM), we observed room-temperature quantum coherence and Rabi cycles in thin film for the first time, suggesting that organic conjugated radicals have great potentials for spin-based information processing.

A neutral auxiliary ligand enhanced dysprosium(iii) single molecule magnet.

An approximately equatorial three-coordinated dysprosium(iii) complex DyL2[N(SiMe3)2] (L = bis(2-(2,5-dimethyl-1H-pyrrol-1-yl)ethyl)amine) with an additional neutral auxiliary pyrrole ligand was synthesised and structurally characterized. The magnetic property measurement shows that it is an equatorial charge distributed field-induced single-molecule magnet. Ab initio calculations reveal that the neutral pyrrole ligand plays an important role in stabilizing the ground doublet and thus enhancing the magnetic anisotropy.

Magnetic anisotropy investigation on light lanthanide complexes.

Herein, a series of light lanthanide-based complexes, Ln(fdh)3(bpy) (Ln = CeIII, PrIII, and NdIII and fdh = 1,1,1-fluoro-5,5-dimethyl-hexa-2,4-dione, bpy = 2,2'-bipyridine), were synthesized and characterized. The angle-resolved magnetometry studies reveal that the three complexes have Ising-type anisotropy, and the magnetic easy axes orient along the negative charge dense direction in the crystal field. The results were consistent with the ab initio calculations. This research demonstrates that the crystal field electron density distribution determines the anisotropy of light lanthanides.