Russell W. Giannetta
Associate Professor of Physics
Professor Giannetta received his PhD from Cornell University in 1980. He was a postdoc at Bell Telephone Laboratories from 1980-1982. He served on the faculty of Princeton University as an assistant professor from 1982-1988, and as an associate professor at the City College of New York from 1989-1992. He joined the Department of Physics at the University of Illinois in 1993.
During the last five years, Professor Giannetta has been heavily involved in developing new techniques to unravel the mysteries of superconductivity and the physics of mesoscopic electronic devices. He has focused on precise measurements of the London penetration depth—the point at which a superconductor excludes magnetic fields from its interior—in a wide variety of recently synthesized superconducting materials. Perhaps his most significant work has been the development of a novel oscillator technique to measure with extremely high sensitivity penetration depth as a function of both temperature and magnetic field.
Research Area: Superconductivity, magnetic resonance, nanostructures
Description of Current Research
Since the initial discovery of high temperature superconductivity in 1986, a large number of new superconducting compounds have been discovered. These include electron doped copper oxides, heavy fermions, ruthenates, magnesium diboride and many new carbon-based organic superconductors. For many of these compounds, superconductivity coexists or competes with some form of magnetism.
To understand these complex materials, a window into the microscopic quantum mechanical state is needed. One feature common to all superconductors is the ability to screen out an applied magnetic field, a property known as the Meissner effect. The degree to which any superconductor performs this task is determined by a quantity known as the London penetration depth, l. Giannetta's lab employs high sensitivity electronic oscillator techniques to measure l in a variety of different superconductors. By studying how l changes with temperature, magnetic field, carrier concentration or pressure, we learn about the microscopic features of the superconducting state.
Some of our recent accomplishments have been (1) the discovery that magnetism can actually enhance the Meissner effect in SmCeCuO4, a copper oxide superconductor; (2) the demonstration that electron-doped copper oxide superconductors also possess a "d-wave" order parameter, similar to the more familiar hole-doped copper oxides; (3) measurements showing that the predictions of BCS theory do not hold in three different organic superconductors; (4) measurements demonstrating how the Meissner effect is altered when a superconductor contains vortex lines that are in a metastable state; and (5) the observation of a partial Meissner effect by the electrons of an ordinary metal in proximity with superconducting MgB2.
Experiments in the future will focus on organic conductors that exhibit both magnetism and superconductivity. Radio-frequency and microwave measurements under pressure will help us understand what kind of superconducting state evolves from magnetism and how the two phenomena may coexist.
The group has access to the very best organic crystals. Giannetta is also collaborating with Professor C.P. Slichter's group to perform low-temperature NMR experiments in organic superconductors. Nuclear magnetic resonance is an extremely powerful probe that yields information about the local electronic environment of particular atoms as the system transforms from magnetic to superconducting behavior. A goal over the next year is to extend this NMR capability to low temperatures, permitting measurements on new classes of materials, organic and otherwise.
Giannetta's group has also pursued research in nanoscience. In a collaboration with Professor I. Adesida's group in Electrical and Computer Engineering, they have measured the quantum mechanical transmission of heat and electricity through very small semiconducting devices. These structures contain a very high mobility two-dimensional gas of electrons. Using modern nanofabrication techniques, this electron gas can be patterned into wires, electron waveguides and tunneling structures. Measurements must be carried out at temperatures down to 50 mK to fully capture the quantum mechanical behavior in these devices. One recent accomplishment was the observation of a "zero bias peak" in which the electrical conductance through a quantum wire is enhanced, at very low temperatures, by a many-electron effect.
A more recent nanoscale project involved scanning tunneling microscopy (STM). An STM was used to initiate chemical reactions at the atomic scale with the intent of growing a superconducting "molecular" wire. By using the STM as both an electrochemical device and and an atomic scale probe of electrical conductance, we can study the nature of the superconductivity in an atomic-scale wire.
Recent Selected Publications
Giannetta, RW, et al. Conductance quantization and zero bias peak in a gated quantum wire. Physica E: Low-Dimensional Systems and Nanostructures. 27, 270-277 (2005).
Snezhko, A, et al. Nodal order parameter in electron-doped Pr2–xCexCuO4–d superconducting films. Phys. Rev. Lett. 92, 157005/1-4 (2004).
Prozorov, R, et al. Field-dependent diamagnetic transition in magnetic superconductor Sm1.85Ce0.15CuO4–y. Phys. Rev. Lett. 93, 147001/1-4 (2004).
Giannetta, RW, et al. London penetration depth in (BEDT-TTF)2 superconductors. Proc. of the Vth Intl. Symp. on Crystalline Organic Metals, Superconductors and Ferromagnets, ISCOM2003. (Port-Bourgenay, France; Sept. 21-28, 2003) J. de Phys. IV 114, 211-215 (2004).
Prozorov, R, et al. Campbell penetration depth of a superconductor in the critical state. Phys. Rev. B 67, 184501/1-4 (2003).
Guan, D, et al. Nonequilibrium Green's function method for a quantum Hall device in a magnetic field. Phys. Rev. B. 67, 205328/1-9 (2003).
Honors and Awards
Xerox Faculty Research Award, University of Illinois College of Engineering, 2003
Fellow, American Physical Society, 2007
