Browsing by Author "Giazotto, Francesco"
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- Heat Transistor: Demonstration of Gate-Controlled Electronic Refrigeration
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2007) Saira, Olli-Pentti; Meschke, Matthias; Giazotto, Francesco; Savin, Alexander M.; Möttönen, Mikko; Pekola, Jukka P.We present experiments on a superconductor–normal-metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor; i.e., the heat flux out from the normal-metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system. - Heat transistor: Demonstration of gate-controlled electronic refrigeration
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2007-07-09) Saira, Olli-Pentti; Meschke, Matthias; Giazotto, Francesco; Savin, Alexander; Möttönen, Mikko; Pekola, JukkaWe present experiments on a superconductor–normal-metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor; i.e., the heat flux out from the normal-metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system. - Influence of photon-assisted tunneling on heat flow in a normal metal-superconductor tunnel junction
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008-03-18) Kopnin, Nikolai; Taddei, Fabio; Pekola, Jukka; Giazotto, FrancescoWe have investigated theoretically the influence of an ac drive on heat transport in a hybrid normal metal-superconductor tunnel junction in the photon-assisted tunneling regime. We find that the useful heat flux out from the normal metal is always reduced as compared to its magnitude under the static and quasistatic drive conditions. Our results are useful to predict the operative conditions of ac-driven superconducting electron refrigerators. - Influence of photon-assisted tunneling on heat flow in a normal metal–superconductor tunnel junction
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008) Kopnin, Nikolai B.; Taddei, Fabio; Pekola, Jukka P.; Giazotto, FrancescoWe have investigated theoretically the influence of an ac drive on heat transport in a hybrid normal metal-superconductor tunnel junction in the photon-assisted tunneling regime. We find that the useful heat flux out from the normal metal is always reduced as compared to its magnitude under the static and quasistatic drive conditions. Our results are useful to predict the operative conditions of ac-driven superconducting electron refrigerators. - Josephson tunnel junction controlled by quasiparticle injection
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2005) Giazotto, Francesco; Pekola, Jukka P.A Josephson tunnel junction transistor based on quasiparticle injection is proposed. Its operationrelies on the manipulation of the electron distribution in one of the junction electrodes. This isaccomplished by injecting quasiparticle current through the junction electrode by two additionaltunnel-coupled superconductors. Both large supercurrent enhancement and fast quenching can beachieved with respect to equilibrium by varying quasiparticle injection for proper temperatureregimes and suitable superconductor combinations. Combined with large power gain, this makes thedevice attractive for applications where reduced noise and low-power dissipation are required. - Manipulation and generation of supercurrent in out-of-equilibrium Josephson tunnel nanojunctions
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008-08-14) Tirelli, S.; Savin, Alexander; Garcia, C.P.; Pekola, Jukka; Beltram, F.; Giazotto, FrancescoWe demonstrate experimentally the manipulation of supercurrent in Al−AlOx−Ti Josephson tunnel junctions by injecting quasiparticles in a Ti island from two additional tunnel-coupled Al superconducting reservoirs. Both supercurrent enhancement and quenching with respect to equilibrium are achieved. We demonstrate cooling of the Ti line by quasiparticle injection from the normal state deep into the superconducting phase. A model based on heat transport and the nonmonotonic current-voltage characteristic of a Josephson junction satisfactorily accounts for our findings. - Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2006) Giazotto, Francesco; Heikkilä, Tero T.; Luukanen, Arttu; Savin, Alexander M.; Pekola, Jukka P.This review presents an overview of the thermal properties of mesoscopic structures. The discussion is based on the concept of electron energy distribution, and, in particular, on controlling and probing it. The temperature of an electron gas is determined by this distribution: refrigeration is equivalent to narrowing it, and thermometry is probing its convolution with a function characterizing the measuring device. Temperature exists, strictly speaking, only in quasiequilibrium in which the distribution follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur due to slow relaxation rates of the electrons, e.g., among themselves or with lattice phonons. Observation and applications of nonequilibrium phenomena are also discussed. The focus in this paper is at low temperatures, primarily below 4K, where physical phenomena on mesoscopic scales and hybrid combinations of various types of materials, e.g., superconductors, normal metals, insulators, and doped semiconductors, open up a rich variety of device concepts. This review starts with an introduction to theoretical concepts and experimental results on thermal properties of mesoscopic structures. Then thermometry and refrigeration are examined with an emphasis on experiments. An immediate application of solid-state refrigeration and thermometry is in ultrasensitive radiation detection, which is discussed in depth. This review concludes with a summary of pertinent fabrication methods of presented devices. - Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications
A2 Katsausartikkeli tieteellisessä aikakauslehdessä(2006-03-17) Giazotto, Francesco; Heikkilä, Tero; Luukanen, Arttu; Savin, Alexander; Pekola, JukkaThis review presents an overview of the thermal properties of mesoscopic structures. The discussion is based on the concept of electron energy distribution, and, in particular, on controlling and probing it. The temperature of an electron gas is determined by this distribution: refrigeration is equivalent to narrowing it, and thermometry is probing its convolution with a function characterizing the measuring device. Temperature exists, strictly speaking, only in quasiequilibrium in which the distribution follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur due to slow relaxation rates of the electrons, e.g., among themselves or with lattice phonons. Observation and applications of nonequilibrium phenomena are also discussed. The focus in this paper is at low temperatures, primarily below 4K, where physical phenomena on mesoscopic scales and hybrid combinations of various types of materials, e.g., superconductors, normal metals, insulators, and doped semiconductors, open up a rich variety of device concepts. This review starts with an introduction to theoretical concepts and experimental results on thermal properties of mesoscopic structures. Then thermometry and refrigeration are examined with an emphasis on experiments. An immediate application of solid-state refrigeration and thermometry is in ultrasensitive radiation detection, which is discussed in depth. This review concludes with a summary of pertinent fabrication methods of presented devices. - Radio-Frequency Single-Electron Refrigerator
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2007) Pekola, Jukka P.; Giazotto, Francesco; Saira, Olli-PenttiWe propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of ∼kBT×f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of ∼kBT/Δ, where Δ is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation. - Radio-frequency single-electron refrigerator
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2007-01-16) Pekola, Jukka; Giazotto, Francesco; Saira, Olli-PenttiWe propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of ∼kBT×f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of ∼kBT/Δ, where Δ is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation. - Ultrasensitive proximity Josephson sensor with kinetic inductance readout
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008) Giazotto, Francesco; Heikkilä, Tero T.; Pepe, Giovanni Piero; Helistö, Panu; Luukanen, Arttu; Pekola, Jukka P.We propose a mesoscopic kinetic-inductance radiation detector based on a long superconductor-normal metal-superconductor Josephson junction. The operation of this proximity Josephson sensor relies on large kinetic inductance variations under irradiation due to the exponential temperature dependence of the critical current. Coupled with a dc superconducting quantum interference device readout, the PJS is able to provide a signal to noise (S/N) ratio up to ∼103 in the terahertz regime if operated as calorimeter, while electrical noise equivalent power as low as ∼7×10−20W/√Hz at 200mK can be achieved in the bolometer operation. The high performance together with the ease of fabrication make this structure attractive as an ultrasensitive cryogenic detector of terahertz electromagnetic radiation.