title: Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.
abstract: Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.
authors.affiliation: Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Lykkebo
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Romano
authors.affiliation: Technische Universität München, Electrical Engineering and Information Technology, Arcisstr. 21, 80333 München, Germany.
authors.forename: Alessio
authors.initials: A
authors.lastname: Gagliardi
authors.affiliation: Consiglio Nazionale delle Ricerche, ISMN, Via Salaria Km 29.6, 00017 Monterotondo, Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pecchia
authors.affiliation: Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark.
authors.forename: Gemma C
authors.initials: GC
authors.lastname: Solomon