While molecular spin qubits (MSQs) are a promising platform for quantum computing, read-out has been largely limited to electron paramagnetic resonance, which is often slow and requires a global system drive. Moreover, because one prerequisite for the Elzerman and Pauli spin blockade read-out mechanisms typical of semiconductor spin qubits is tunneling of electrons between sites, these read-out modalities are unavailable in MSQs. Here, we theoretically demonstrate electrical read-out of entangled MSQs via driven many-electron spin-unpolarized currents. In particular, using a time-dependent density matrix renormalization group approach, we simulate a maximally entangled MSQ pair between two electronic leads. Driving itinerant electrons between the two leads, we find that the conductance is greater when the MSQs are in the entangled singlet state compared to the entangled triplet state. This contrast in conductance is enhanced when the electronic density of states at the Fermi energy is large and for a narrow bandwidth. Our results are readily applicable to molecules supramolecularly functionalizing semiconductors with relatively flat bands, such as single-wall carbon nanotubes under a magnetic field.

In this work, we examine low-energy adsorption configurations of four dodecanuclear manganese single-molecule magnets [Mn_12O_12(O_2CR)_16(H_2O)_4] (Mn_12), where the ligand R being H, CH_3, CHCl_2 or C_6H_5, on a molybdenum disulfide (MoS_2) monolayer using force field and density functional theory calculations. The van der Waals interaction is shown to be crucial for determining the adsorption energy. Some electrons transfer from the substrate to the molecules upon surface adsorption, resulting in a reduction of the magnetic anisotropy energy of Mn_12. Since the lowest unoccupied molecular orbital of Mn_12 is close to the valence band of MoS_2, a negative electric field is more effective in modulating charge transfer and energy band alignment, and thus altering the magnetic anisotropy energy, compared with a positive electric field. A significant increase in the magnetic anisotropy energy of Mn_12 with the ligand R=CHCl_2 or R=C_6H_5 under a sufficiently high electric field has been predicted. Our calculations show that the molecules remain intact on the surface both before and after the electric field is applied. Finally, a two-level system formed by different adsorption configurations is evaluated, and the tunability of its energy barrier under an electric field is demonstrated. Our study sheds light on tuning the properties of single-molecule magnets using an electric field, when the molecules are supported on a surface.

We theoretically study Floquet engineering of magnetic molecules via a time-periodic magnetic field that couples to the emergent total electronic spin of the metal center. By focusing on the low-lying energy levels using an S = 1 spin Hamiltonian containing the zero-field and Zeeman terms, we demonstrate their continuous tunability under the Floquet field. Remarkably, under the action of linearly polarized Floquet controls, the energy levels of a clock transition qubit retain their stability against variations in an external static magnetic field. This property is closely linked to having a net-zero total Zeeman shift, which results from both static and effective dynamical contributions. Furthermore, using second-order Van Vleck degenerate perturbation theory, we derived an effective Hamiltonian analytically, which explicitly shows the dependence of the renormalized zero-field tensor on the driving field. Based on our theoretical predictions, experimentalists will be able to dynamically tune qubit energy gaps to values that are useful in their specific laboratory settings, while retaining the spin decoherence suppressing effect of maintaining a clock transition.

Spin decoherence poses a significant challenge in molecular magnets, with the nuclear spin bath serving as a prominent source. Intriguingly, spin qubits at the clock transition exhibit remarkable insensitivity to the surrounding nuclear spins. Recent experimental studies have unveiled a correlation between the decoherence time and the density of spin qubits, prompting our investigation into the contribution of the qubit bath to spin decoherence. In this paper, we present a comprehensive theoretical analysis of a few S=1 spin qubits, focusing on their interaction at the clock transition. Employing the exact diagonalization and the cluster correlation expansion (CCE) method, we simulate the dynamics of spin decoherence while varying the density of the qubit bath. To ensure the realism of our simulations, we incorporate structural and energetic parameters derived from previous studies on the HoW10 crystal. Our findings indicate that when the energy mismatch between the energy splittings of two qubits exceeds their interaction strength, they can become effectively insensitive to each other, offering an explanation for the absence of observed changes in the T2 time during experiments with lower qubit densities. Understanding the role of qubit bath density in spin decoherence at the clock transition not only advances our knowledge of decoherence mechanisms but also provides insights for the development of strategies to protect coherence in molecular magnets and other quantum systems. By optimizing the density of spin qubits, we can enhance the coherence properties and pave the way for improved performance of quantum devices. Overall, this study offers valuable insights into the relationship between qubit bath density and spin decoherence at the clock transition, contributing to the broader understanding and control of quantum systems in molecular magnets.

A tetranuclear oxalate-bridged complex was synthesized by a reaction between the tris(oxalato)chromium(III), [Cr(C2O4)3]3-, and a 3-fold excess of the Ni2+ ion capped with a tetradentate 1,4,7,10-tetraazacyclododecane (cyclen) ligand. The structure of [Ni3(cyclen)3Cr(mu-C2O4)3](ClO4)3 (1), established by X-ray diffraction, features a triangle of the Ni2+ ions centered by the [Cr(C2O4)3]3- anion through bridging oxalate ligands. The Ni2+ and Cr3+ ions exhibit oxalate-mediated ferromagnetic exchange coupling, which leads to the S = 9/2 ground state. Both simulation of the magnetic data and theoretical calculations show that the exchange coupling is isotropic. Although the study of a model mononuclear complex [Ni(cyclen)(MeCN)2]2+ by high-field EPR spectroscopy reveals a substantial zero-field splitting on the Ni2+ ion, complex 1 exhibits weak magnetic anisotropy within a giant spin model. This difference is attributed to dilution of the single-ion anisotropies of the Ni2+ ions due to their nearly symmetrical (trigonal) arrangement around the central Cr3+ ion. CASSCF calculations provided reasonable zero-field splitting parameters and Lande g-factors for the Ni2+ and Cr3+ ions in complex 1.

A high-symmetry assembly of molecular spin qubits has been achieved in the metal-organic framework (MOF) [Ho(pzdo)4](ClO4)3 (1), where the eight-coordinate Ho3+ nodes are bridged by pyrazine-1,4-dioxide (pzdo) ligands. The approximate square-antiprismatic (D4d) coordination of the Ho3+ ion leads to the stabilization of the mJ = ±4 ground-state doublet due to crystal-field splitting of the J = 8 total angular momentum state. Mixing of the mJ = +4 and mJ = -4 projection states opens a zero-field energy gap (Δ) resulting in the spin clock transition (SCT) evident in the EPR spectra of 1. The SCTs are known to protect qubits from the surrounding magnetic noise to first order, thus enhancing the coherence time of the superposition states crucial for quantum information processing. Frequency-dependent EPR studies reveal that the Ho3+ centers in 1 exhibit a high-frequency SCT with ΔSCT = 54.6 GHz, which can be beneficial to minimizing second-order decoherence effects. The angular dependence of the resonance fields maps well onto the lattice symmetry, with two distinct orientations of the molecular anisotropy axes related to the tetragonal space group symmetry. All salient aspects of the magnetic and EPR measurements have been captured by a model that uses a new theoretical technique based on a constrained DFT derivation of the effective spin Hamiltonian. This work demonstrates the possibility of engineering SCTs in ordered arrays of molecular spin qubits, thus paving the way to scaling up molecular systems that are promising for applications in emerging quantum technologies.

The effective crystal field Hamiltonian provides the key description of the electronic properties of single-ion magnets, but obtaining its parameters from an ab initio computation is challenging. We introduce a simple approach to derive the effective crystal field Hamiltonian through density functional calculations of randomly rotated mean-field states within the low-energy manifold. In benchmarks on five lanthanide-based complexes, we find that we compute with mean-field cost an effective crystal field Hamiltonian that matches the state-of-the-art from much more expensive multiconfigurational quantum chemistry methods. In addition, we are able to reproduce the experimental low-energy spectrum and magnetic properties with an accuracy exceeding those of prior attempts. Due to its low cost, our approach provides a crucial ingredient in the computational design of single-ion magnets with tailored physical properties and low-energy spectra.

Molecular lanthanide (Ln) complexes are promising candidates for the development of next-generation quantum technologies. High-symmetry structures incorporating integer spin Ln ions can give rise to well-isolated crystal field quasi-doublet ground states, i.e., quantum two-level systems that may serve as the basis for magnetic qubits. Recent work has shown that symmetry lowering of the coordination environment around the Ln ion can produce an avoided crossing or clock transition within the ground doublet, leading to significantly enhanced coherence. Here, we employ single-crystal high-frequency electron paramagnetic resonance spectroscopy and high-level ab initio calculations to carry out a detailed investigation of the nine-coordinate complexes, [(HoL1L2)-L-III], where L-1 = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane and L-2 = F- (1) or [MeCN](0) (2). The pseudo-4-fold symmetry imposed by the neutral organic ligand scaffold (L-1) and the apical anionic fluoride ion generates a strong axial anisotropy with an m(J) = +/- 8 ground-state quasi-doublet in 1, where m J denotes the projection of the J = 8 spin-orbital moment onto the similar to C-4 axis. Meanwhile, off-diagonal crystal field interactions give rise to a giant 116.4 +/- 1.0 GHz clock transition within this doublet. We then demonstrate targeted crystal field engineering of the clock transition by replacing F- with neutral MeCN (2), resulting in an increase in the clock transition frequency by a factor of 2.2. The experimental results are in broad agreement with quantum chemical calculations. This tunability is highly desirable because decoherence caused by second-order sensitivity to magnetic noise scales inversely with the clock transition frequency.

Experimental results on two supramolecular complexes in which a CrIII or FeIII d-orbital single-ion magnet center is embedded between a pair of FeII spin-crossover moieties make those two complexes interesting as possible candidates for use in quantum information technologies. We report detailed computational results for their structure and electronic properties and use the resulting data to parametrize a spin Hamiltonian that facilitates comparison with experimental results and their interpretation. Consistent with experimental results on decoherence in [Fe(ox)3]@[Fe2L3]+, we find it to be easy-plane type while the [Cr(ox)3]@[Fe2L3]+ system is easy-axis type.

Supplemental Figure S3. Graph derived from the scientific literature (24) that shows a linear correlation between 18F-FPP(RGD)2 uptake and tumor volume in HCT116 human colon cancer xenografts.

Supplemental Figure S5. Bar graphs showing effect of BAY 87-2243 on RT-PCR expression profiles for (A) SLC16A, (B) ITGB1, (C) IGF-2 and (D) TK-1

List of legend for supplementary files. Description list for supplementary files

We report on the fabrication and characterization of vertical tunnel heterojunctions in which sublimated phthalocyanine (Pc) films (H2Pc, CoPc, and MnPc) as thin as 1 nm are sandwiched between conducting bottom-layer base electrodes and top-layer soft-landing eutectic GaIn (EGaIn) electrodes. The heterojunctions can be reliably cycled to temperatures as low as 2 K and are remarkably robust, showing little evidence of pinhole shorts over a wide temperature range. Ultraslow sublimation of Pc powders (at rates of & ANGS;/min) onto temperature-regulated substrates for the most part produced ultrasmooth films with 100% coverage. As an example, atomic force microscopy in combination with X-ray diffraction showed that CoPc films with subnanometer roughness deposited onto conducting substrates had the crystalline ordering of lying-down planar molecules. The current-voltage (I-V) characteristics, obtained to temperatures as low as 2 K, reveal the onset of a subgap reduction in the density of states due to the appearance of superconductivity at T (c) = 6 K in the top EGaIn electrode. Together with the higher temperature fitting of a modified Simmons model, these behaviors provide incontrovertible evidence for direct quantum mechanical tunneling processes rather than thermally activated hopping through the transition-metal ions and associated satellite ligands of the Pc molecules in our heterojunctions. Our use of thermally stable soft landing EGaIn counter electrodes preserves the fragility of the underlying organic Pc molecules down to few-layer thicknesses at low temperatures where quantum properties can be exploited for molecular electronic applications.

Supplemental Figure S2. Dose-dependent effect of BAY 87-243 on (A) 18F-FAZA uptake and (B) tumor volume for PC3 xenografts of nude, murine models.

Supplemental Figure S7. Dose-dependent effect of BAY 87-243 (1 and 9 mg/kg) on (A) 18F-FAZA uptake and (B) tumor volume for H460 xenografts of nude, murine models. For (A), *- p<0.001 for 2-way ANOVA of vehicle vs. BAY 87-2243, n=6 tumors and for (B) *-P<0.01 for 2-way ANOVA of vehicle vs. BAY 87-2243, n=6 tumors.

Using first-principles methods and spin models, we investigate the magnetic properties of transition-metal trimers Cr3 and Cu3. We calculate exchange coupling constants and zero-field splitting parameters using density functional theory and, with these parameters, determine the ground spin state as well as thermodynamic properties via spin models. Results for Cr3 indicate uniaxial magnetic anisotropy with a magnetic easy axis aligned along the 3-fold rotational symmetry axis and a mostly isotropic exchange interaction. The Cu3 molecule lacks rotational symmetry and our results show strong antisymmetric interactions for three distinct exchange couplings within the molecule. We are able to reproduce experimental findings on magnetic susceptibility and magnetization of Cr3 with the first-principles spin-Hamiltonian parameters. Our results show no presence of a toroidal ordering of spins for Cr3 and a finite toroidal moment for Cu3 in the ground state. We apply an external electric field up to 0.08 V/Å to each system to reveal the field dependence of exchange coupling as magnetoelectric effects. Finally, we scan the parameter space of a spin Hamiltonian to gain insights into which parameters would lead to a sizable toroidal moment in such systems.

Supplemental Figure S4. Chemical Structure of 18F-fluoroazomycin arabinoside (18F-FAZA). Nucleoside analog contains nitroimidazole ring in α-position of arabinose ring.

We study intramolecular electron transfer in the single-molecule magnetic complex [Mn12O12(O2CR)16 (H2O)4] for R = -H, -CH3, -CHCl2, -C6H5, and -C6H4F ligands as a mechanism for switching of the molecular dipole moment. Energetics is obtained using the density functional theory (DFT) with onsite Coulomb energy correction (DFT + U). Lattice distortions are found to be critical for localizing an extra electron on one of the easy sites on the outer ring in which localized states can be stabilized. We find that the lowest-energy path for charge transfer is for the electron to go through the center via superexchange-mediated tunneling. The energy barrier for such a path ranges from 0.4 to 54 meV depending on the ligands and the isomeric form of the complex. The electric field strength needed to move the charge from one end to the other, thus reversing the dipole moment, is 0.01-0.04 V/Å.

We study bilayer manganese phthalocyanine (MnPc) molecules and MnPc polymeric sheets using first-principles simulations with a focus on the magnetic interactions between Mn atoms. We find that the most stable position of the upper layer with respect to the lower layer is shifted about 1/8 of a lattice vector from the center of the bottom layer along the direction toward a nearest-neighbor N atom. The magnetic ground state is the Neel antiferromagnetic (AFM) configuration within a layer and ferromagnetic (FM) between Mn atoms in adjacent layers. In this state, the system becomes a semiconductor with an indirect band gap of 11 meV. The strongest interaction is the interlayer coupling between the closest Mn atoms. A maximally localized Wannier analysis suggests that the dominant coupling pathway is Mn-(N,C)-Mn rather than a direct Mn-Mn coupling. The maximum calculated magnetic anisotropy energy is found to be 1.0 meV per Mn atom. We also find that the bilayer molecule shows a significant stacking angle change from FM to AFM configurations accompanied by a change of orbital filling ordering.

Magic-angle twisted bilayer graphene (MATBG) is notable as a highly tunable platform for investigating strongly correlated phenomena such as unconventional superconductivity and quantum spin liquids, due to easy control of doping level through gating and sensitive dependence of the magic angle on hydrostatic pressure. Experimental observations of correlated insulating states, unconventional superconductivity and ferromagnetism in MATBG indicate that this system exhibits rich exotic phases. In this work, using density functional theory calculations in conjunction with the effective screening medium method, we find the MATBG under pressure at a twisting angle of 2.88∘and simulate how its electronic states evolve when doping level and electric field perpendicular to plane are tuned by gating. Our calculations show that, at doping levels between two electrons and four holes per moiré unit cell, a ferromagnetic (FM) solution with spin density localized at AA stacking sites is lower in energy than the nonmagnetic solution. The magnetic moment of this FM state decreases with both electron and hole doping and vanishes at four electrons/holes doped per moiré unit cell. Hybridization between the flat bands at the Fermi level and the surrounding dispersive bands can take place at finite doping. On increasing the out-of-plane electric field at zero doping, a transition from the FM state to the nonmagnetic one is seen. An investigation of impurity effects shows that both absorption ofO2molecules and occurrence of Stone-Wales impurities suppress the FM state, and the mechanisms are understood from our calculations. We also analyze the interlayer bonding character due to flat bands via Wannier functions. Finally, we report trivial band topology of the flat bands in the FM state at a certain doping level.