Collaborative Research: Molecular Spintronics with Single-Molecule Magnets

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The broad goal of this proposal is to explore the interplay between localized high-spin states of an individual molecule and conduction electrons in order to develop molecular electronic devices for local magnetic field sensing, ultra-high-density information storage, and quantum information processing. Single-molecule magnets are characterized by a large total spin and a strong intrinsic anisotropy. They present some unique characteristics, such as quantum tunneling of the magnetization and Berry phase interference. Although extensively studied in crystalline form, some of their key properties remain elusive. For instance, it is unclear how quantum tunneling of the magnetization influences electronic conduction through these molecules. Understanding this property is crucial for any electronic device development. The proposed research program addresses these issues by combining chemical synthesis with experimental and theoretical physics to probe quantum properties of isolated single-molecule magnets. The molecules will be attached to nanometer-gapped metal electrodes and gated electrically to form a single-electron transistor. Device fabrication will make use of lithographic and electromigration techniques. The molecule?s electric conduction will be studied both statically and dynamically to reveal excited molecular states, the effect of different ligands, the Kondo effect, spin-polarized transport, the Berry-phase blockade, quantum oscillations of the magnetization, and decoherence,. The proposed study emphasizes exploring these phenomena toward practical devices. In particular: (i) to employ the intense magnetic field tunability of the Berry phase to obtain high-sensitivity local magnetic field nanosensors; (ii) to develop reading and writing procedures for molecular bits in high-density magnetic memories; and (iii) to demonstrate quantum logic gate operations in a molecular qubit. The team has extensive experience with single-molecule magnets and in quantum electronic transport. Preliminary results have demonstrated the team?s ability to fabricate suitable devices and to measure the IV characteristics of isolated molecules in the Coulomb blockade regime. Available facilities permit efficient device fabrication with a short turnover time. The facilities available to the team include low temperatures, high magnetic fields oriented in arbitrary directions, continuous-wave and pulsed high-frequency microwave excitations, and ultra-fast pulsed voltage gating.Intellectual Merit: Molecular electronics is rapidly becoming a separate research field within Applied Sciences and Engineering. The main effort so far has been on carbon-based systems or isotropic molecules containing a small net spin. This proposal focuses on molecules that are intrinsically magnetic due to their large spin and strong axial anisotropy. The research encompasses chemistry, physics, device fabrication and development, as well as fundamental studies at low temperatures and high magnetic fields. The proposed studies will lead to a better understanding of the quantum properties of isolated single-molecule magnets and how magnetism can be combined with electronic transport in a single-electron transistor setup.Broader Impact:The proposal will advance our knowledge of single molecule-based electronic devices. These devices have great potential for ultra-high density integration and quantum information processing, which may lead to new and revolutionary technologies. Several graduate and undergraduate students will be trained in the interface between inorganic chemistry and fundamental and applied physics within an environment that constantly crosses the boundaries of these disciplines.