Increased Crystal Field Drives Intermediate Coupling and Minimizes Decoherence in Tetravalent Praseodymium Qubits

Abstract

Crystal field (CF) control of rare-earth (RE) ions has been employed to minimize decoherence in qubits and to enhance the effective barrier of single-molecule magnets. The CF approach has been focused on the effects of symmetry on dynamic magnetic properties. Herein, the magnitude of the CF is increased via control of the RE oxidation state. The enhanced 4f metal− ligand covalency in Pr 4+ gives rise to CF energy scales that compete with the spin−orbit coupling of Pr 4+ and thereby shifts the paradigm from the ionic ζ SOC ≫ V CF limit, used to describe trivalent RE-ion, to an intermediate coupling (IC) regime. We examine Pr 4+ -doped perovskite oxide lattices (BaSnO 3 and BaZrO 3 ). These systems are defined by IC which quenches orbital angular momentum. Therefore, the single-ion spin−orbit coupled states in Pr 4+ can be chemically tuned. We demonstrate a relatively large hyperfine interaction of A iso = 1800 MHz for Pr 4+ , coherent manipulation of the spin with Q M = 2Ω R T m , reaching up to ∼400 for 0.1Pr:BSO at T = 5 K, and significant improvement of the temperature at which T m is limited by T 1 (T* = 60 K) compared to other RE ion qubits.

A tetravalent praseodymium complex with field-induced slow magnetic relaxation

“…The χT value of 0.46 cm 3 K mol −1 at 300 K is significantly smaller than the calculated value of 0.80 cm 3 K mol −1 for Ce( iii ) of the same 4f 1 configuration but in a much weaker crystal field typical of a trivalent lanthanide complex, 11,49 which can be understood as a result of the aforementioned competition between the strong crystal field of 1·Tol and the spin–orbit coupling of Pr( iv ). 45,46 The χT value decreases with decreasing temperature, reaching a value of 0.09 cm 3 K mol −1 at 2 K. The inverse susceptibility ( χ −1 ) also decreases upon cooling (Fig. S6†), showing a similar magnetic behavior to that of a solid featuring Pr( iv ) in a pure inorganic lattice, 45,46 where the crystal-field and spin–orbit coupling interactions of Pr( iv ) are generally competing.…”

“…45,46 The χT value decreases with decreasing temperature, reaching a value of 0.09 cm 3 K mol −1 at 2 K. The inverse susceptibility ( χ −1 ) also decreases upon cooling (Fig. S6†), showing a similar magnetic behavior to that of a solid featuring Pr( iv ) in a pure inorganic lattice, 45,46 where the crystal-field and spin–orbit coupling interactions of Pr( iv ) are generally competing. The field-dependent magnetization intensity was measured from 0 to 7 T at 2 K, 3 K, and 5 K (Fig.…”

“…As recently demonstrated by La Pierre and coworkers, the strong crystal field experienced by a Pr( iv ) in an inorganic environment can compete effectively with the spin–orbit coupling interactions. 45,46 This particular piece of result is stimulating as it points to the possibility of realizing Pr( iv )-based SMMs with high energy barriers. Great prospects notwithstanding, the research has been challenged by the availability of Pr( iv ) complexes limited only to the original [Pr(OSiPh 3 ) 4 (MeCN) 2 ] and [Pr(OSiPh 3 ) 4 (OPPh 3 )(MeCN)] reported by Mazzanti and coworkers.…”

Siloxide tripodal ligands as a scaffold for stabilizing lanthanides in the +4 oxidation state

“…Until 2019, molecular complexes containing lanthanides in the +4 oxidation state have been limited to cerium (Ce), 3–8 for which the readily accessible Ce( iii )/Ce( iv ) couple has resulted in a broad range of applications in organic synthesis 9 and in catalysis. 10–17 In contrast, although the +4 oxidation state had been identified for Pr, Nd, Tb, and Dy in solid state compounds, 18–24 and in the gas phase ( via mass spectrometry and/or vibrational spectroscopy in matrix isolation) for Pr, Nd, Tb, and Dy, 25–27 where even Pr( v ) was observed, 28–30 the high Ln( iii )/Ln( iv ) oxidation potential of these ions prevented their isolation in molecular complexes. The electrochemical oxidation of Tb( iii ) and Pr( iii ) to Tb( iv ) and Pr( iv ) in concentrated aqueous carbonate solutions was reported in the 1980s, 31 but seminal attempts to isolate molecular complexes of Tb( iv ) and Pr( iv ) using chemical oxidation in organic solutions were unsuccessful.…”

Much more to explore with an oxidation state of nearly four: Pr valence instability in intermetallic m -Pr 2 Co 3 Ge 5

“…Valence instabilities in lanthanide compounds can have substantial impacts on crystal structure and physical properties (13)(14)(15)(16). Targeting systems with structural phase transformations can provide an exciting path forward for strongly correlated materials, specifically in identifying valence-unstable states in dominantly trivalent lanthanides like Pr with the opportunity to access technologically relevant quantum states (17)(18)(19)(20). Still, Pr compounds are typically trivalent, with only a small number of dominantly tetravalent Pr-containing oxides and fluorides reported (21).…”