With one bit per molecule, the potential of single-molecule magnets (SMMs) for ultra-high density magnetic memory devices is extraordinary, plus these systems have been proposed as qubits for quantum computation and information processes. Due to their unique magnetic behavior, the use of SMMs in nanoscale spintronic devices is expected to be transformative in that they would lead to novel characterization and technological tools, such as high-sensitivity local magnetic field sensors and ultra-fast writing/reading memory units.
So far the quantum properties of SMMs have been typically studied in experiments with macroscopic single crystals containing a large number of nearly identical and decoupled SMMs. Thus the magnetic response of the crystal tends to reflect the quantum properties associated to each individual SMM within the sample. Perhaps the most striking property of SMMs is the presence of steps in the magnetic hysteresis loops that are attributed to resonant quantum tunneling of the magnetization (QTM). This unique feature of SMMs is a consequence of the quantum superposition of high-spin states of the molecule and has led to the observation of a variety of fundamental phenomena, such as quantum (Berry-phase) interference between equivalent QTM trajectories. Berry phase interference in SMMs permits fast tuning of the energy associated with a quantum superposition between spin states (see figure above). This effect has been proposed for the implementation of two-qubit quantum logic gates in dimeric SMMs where the exchange interaction between opposite sides of the dimer could be tuned. In addition, quantum interference in SMMs would lead to extremely sensitive magnetic sensors at the molecular level, which could be integrated in nanoscale spintronic devices. Novel features of QTM are expected to manifest themselves in other observables as well. In particular, the effects of QTM on electronic transport remain to be explored in depth both experimentally and theoretically. Novel and exciting applications are expected to arise from a deeper understanding of the electronic transport properties of SMMs.
The study an isolated individual SMM is both of fundamental and technological interest since the ability to control decoherence processes in nanoscale systems is a prerequisite for using SMMs in quantum information processing devices. For this, we make use of an experimental approach that mixes the chemical functionalization of SMMs with the use of single-electron transistors (SETs) to access the high-spin states of an isolated SMM through transport measurements. The broad goal of this project is to investigate the interplay between high-spin states of an individual SMM and conduction electrons in a three-terminal SET and to develop molecular electronic devices for innovative technological applications. This study involves electronic transport over a wide range of experimental conditions, such as low electronic temperature (T > 100 mK), high magnetic fields oriented in arbitrary directions, continuous-wave and pulsed high-frequency microwave excitations, and ultra-fast pulsed voltage gating.
Works on this project:
Haque, M. Langhirt (UG), E. del Barco, T. Taguchi and G. Christou
“Magnetic field dependent electronic transport through a Mn4 single-molecule magnet”
J. Appl. Phys. 109, 07B112 (2011).