Vortex Crystals, Spintronics And Electron-Pair Puddles At World's Largest Physics Meeting
College Park, MD---February 9, 1998---The March Meeting of The American Physical Society (APS), annually the largest physics meeting in the world, will be held March 16-20, 1998 at the Los Angeles Convention Center in Los Angeles, California. Approximately 5000 papers will be delivered. The APS, with over 40,000 members, is the largest professional organization in the world devoted to physics.
WHAT KIND OF MEETING? The March Meeting is the chief gathering place for many APS divisions and topical groups, including condensed matter physics, materials physics, chemical physics, polymer physics, and biological physics. Much of the physics behind the technological innovations we now take for granted---such as smart materials, rapid telecommunications, and mass storage of data---emerged at past March APS meetings.
In addition to the many technical sessions, numerous other sessions are devoted to subjects of a more general nature, such as arms control, energy-efficient windows, the possibilities for storing nuclear waste safely over the long term, and global change issues.
APS PRESSROOM The meeting newsroom will be located in room 517 of the Los Angeles Convention Center, while news conferences will be held in room 516. The address of the Convention Center is 1201 South Figueroa Street. The hours will be as follows: 8 AM until 5 PM, Monday-Wednesday (March 16-18) and 8 AM until noon on Thursday (March 19). Reporters attending the meeting should first come to the newsroom, where they can obtain registration badges and various news releases. Several news conferences will be held during the week of the meeting on subjects soon to be decided. A fax machine will be available in the pressroom.
FURTHER INFORMATION AND VIRTUAL PRESSROOM Reporters interested in attending the meeting or in obtaining further information should return the form at the end of this press release. In early March we will issue an additional press release about the meeting, including a list of prospective news conferences and more detailed descriptions of specific sessions and papers.
Moreover, this information and a variety of lay-language papers and news releases will be added to a "Virtual Pressroom" for the meeting located at http://www.aps.org/BAPSMAR98/vpr/ on the World Wide Web. Abstracts of the talks at the meeting can be accessed right now on the Web at this address.
PRESS TOUR We have plans to visit the nearby campus of Caltech to see some world- class laboratories. The itinerary will include the labs of Michael Roukes, maker of tiny suspended silicon structures (one of which is, in effect, the fastest oscillating physical object) and Jeff Kimble, an expert on squeezed light and quantum computers. Other stops may be scheduled.
SESSION HIGHLIGHTS AT THE MEETING
---Vortex Crystals. Many fluids in nature move principally in two dimensions; one example is the Great Red Spot of Jupiter, the hurricane-like tempest on the giant planet. Amazingly, the mathematical equations describing ideal, frictionless versions of these two-dimensional fluids are identical to those governing the movement of charged particles trapped in a strong magnetic field. Exploiting this connection, Fred Driscoll and his colleagues at UC-San Diego (619-534-2489) have recently built an apparatus that for the first time allows a full spatial imaging of the flow of electrons trapped in a magnetic field. The density of electric charge in such flows is directly analogous to the density of vortices, the whirlpool-like eddies that can exist in a fluid. This approach has enabled them to study phenomena such as the formation of "vortex crystals," repeating patterns of vortices that can stay frozen in place in the fluid. (Paper C6.02, March 16, 11 AM)
---Weird Behavior in Quantum Dots. Interesting things happen when particles are confined in a tiny box. Researchers at MIT led by Raymond Ashoori (617-253-5585) make themselves such a box, a quantum dot, out of semiconductors---a layer of gallium arsenide between layers of aluminum gallium arsenide. On top of this sandwich sits a metal gate electrode which feeds electrons into the dot and controls the arrival or departure of electrons one at a time. Building up from just one electron, the MIT physicists collect a puddle of electrons and observe how the arrival of each newcomer must overcome (with the help of an increasing voltage) the mutual repulsion ("Coulomb blockade") of those already in place. For small dots (0.2 microns across) a graph of charge-vs-voltage would look like a staircase. Such an effect is at the heart of single-electron transistors (SET), which act as sensitive detectors of electrical charge (just as superconducting quantum interference devices---SQUIDS---are sensitive detectors of magnetic flux). For larger dots (1 micron across) the MIT scientists were astonished to observe an unexpected and mysterious pairing: for each stepwise voltage increase not one but two electrons were able to join the puddle. The pairing has not yet been explained but might have something to do with the electrons' spins. For medium-sized dots (0.5 microns) the physics gets even weirder: the pairing occurs only for every fourth or fifth electron. The goal now is to understand how small puddles coalesce into larger puddles and how the pairing comes about. (Paper K3.01, March 17, 2:30 PM)
---Magnetic Refrigeration. In a new type of refrigerator, physicists have exploited the fact that the rare earth element gadolinium (Gd) has a large "magnetocaloric effect": applying a magnetic field to a chunk of gadolinium will heat it up, while removing the magnetic field will cool it down and enable it to absorb heat from its surroundings. Not only is this process more efficient than conventional refrigeration (in which the compressing and expanding fluid refrigerants lose energy to processes like turbulence), it is more environmentally friendly: the solid Gd material can't leak out, and the only working fluid is water, which carries heat to the Gd refrigerant from the objects to be cooled. Carl Zimm of Astronautics Corporation (608-221-9001) in Wisconsin will describe a Gd-based magnetic refrigerator, built in collaboration with the Ames DOE Laboratory, that has efficiency rivaling that of a conventional unit and has been operating for more than a year. Other physicists at session Q5 will discuss similar approaches. This potentially more efficient design can be used in places like supermarkets, which could conceivably lower the cost of groceries by using less energy-hungry refrigerators. (March 18, 2:30 PM)
---Smaller, Faster, Cheaper. Microelectromechanical systems (MEMS) are just what NASA needs to explore the solar system with softball-sized spacecraft. Often built with the same materials and lithographic techniques used in making integrated circuits, micron-sized MEMS motors, pumps, resonators, actuators, and sensors have been developed in the lab but not yet much deployed in marketable devices. But this may change soon. Michael Roukes of Caltech (818-395-2916) will describe the effort to coax small suspended columns of silicon into vibrations at GHz frequencies making them into possible radio wave transmitters. Thomas Kenny of Stanford will report on the use of slender cantilevers in atomic force microscopes to measure forces at the attonewton (10^-18 newton) level. JPL scientist William Tang (818-354-2052) will describe the integration of microgyroscopes, microseismometers, micropropulsion engines and other pint-sized gadgets on future space missions. (Session E5, March 16, 2:30 PM)
---Spintronics. Consumer devices such as computers work by controlling the movements of electrons through circuits. These electrons are typically influenced by applying some sort of electric field which attracts or repels the electron's negative charge. However, the movement of an electron in a circuit can also be manipulated by properties other than its charge. One example is spin, a quantity which describes how the electron responds to a magnetic field. Stuart Wolf of the Naval Research Laboratory and DARPA (202-767-4163) will describe several spin-dependent phenomena which can potentially be exploited in electronic devices. Two examples are giant magnetoresistance, in which the electrical resistance that electrons experience in a multilayered material can be substantially changed by the magnetic field within the material, and spin-dependent tunneling, in which an electron can move through a normally impenetrable barrier if it has the right spin value. Wolf will also describe spin injection devices, in which the spin of an electron can modify the properties of a material into which it is injected. These spin-dependent devices are expected to become very important for future high-performance electronics. (Paper K5.04, March 17, 4:18 PM)
---Liquefied Particle Physics. One of the most complex processes known to physicists is the process of turbulence, in which a fluid exhibits irregular flow patterns that vary randomly in space and time. A Cornell group (Eberhard Bodenschatz and Jim Alexander, 607-255-0794) is applying particle physics detection technology to fluid mechanics, by installing a silicon-strip detector also used in Cornell's CLEO accelerator. The detector can make up to 100,000 measurements per second of a particle--and can track perhaps up to 6 particles at a time, promising insights into such questions as how two particles that are initially close together in an extremely turbulent fluid fly apart. Such studies may aid understanding of problems such as the transport of pollutants in the atmosphere. (Paper A6.05, March 16, 10:24 AM)
---Quick as a Flash: Femtosecond Lasers. New discoveries often happen at the frontiers of physics. Examples include the discovery of the top quark at Fermilab (the highest obtained particle collision energies) and Bose-Einstein condensates of gases inside magneto-optic traps (the lowest obtained temperatures). A relatively new frontier area is the domain of short-time 100 femtosecond), high-intensity (terrawatts/cm^2) bursts of laser light. Pulses generated by femtosecond lasers can almost instantly destabilize a semiconductor, turning it into something like a metal, at least temporarily. Papers in the session O4 consider what happen what these pulses do in a variety of materials, including C-60 molecules (buckyballs), and human-vision (retinal) and photosynthesis complexes (Roland E. Allen, Texas A&M, 409-845-2590). (Session O4, March 18, 11 AM)
---Polymer LECs. Alan Heeger of UC-Santa Barbara (805-893-3184) will describe a new type of light-emitting device based on a semiconducting polymer. In this design, known as a light-emitting electrochemical cell (LEC), researchers create a blend of a light-emitting polymer material and a solid electrolyte, a substance that transports ions. According to Heeger, polymer LECs have important advantages over polymer LEDs. For example, the way in which electrical charge is injected into the semiconducting polymer is the same for all LECs independent of the color of the emitted light, and the performance of LECs is insensitive to the thickness of the material. (Paper A11.01, March 16, 8 AM)
---Quantum Computers. Physicists will discuss the latest efforts towards building a practical quantum computer, a device that uses quantum particles (such as ions or photons) to represent the 0s and 1s (the binary digits, or "bits") employed in computations. Unlike ordinary bits, quantum bits (or "qubits") can represent 0 and 1 simultaneously--opening possibilities for powerful computers that can carry out multiple calculations at the same time. Although primitive quantum computers have already been built, a likely scheme for an advanced design would be to trap a string of ions with electromagnetic fields and then use laser beams to manipulate the ions' quantum states and carry out calculations. Peter Zoller (Peter.Zoller@uibk.ac.at), a University of Innsbruck theorist who co-authored this proposal in 1995, will describe this approach. Richard Hughes of Los Alamos (505-667-3876) will describe experimental progress towards realizing this scheme. Having cooled and trapped a string of 5 ions, Hughes and his Los Alamos colleagues have impressively demonstrated that they can point a laser beam at an ion without disturbing its neighbors (the closest of which are 20 microns away). Jeff Kimble of Caltech (818-395-8340) will describe experimental progress towards realizing an alternate approach in which the qubits are photons trapped between a pair of mirrors. Anupam Garg of Northwestern University (847-491-3229) will show how large-scale quantum computers may be disrupted most by quantum zero-point motion, in which the unavoidable vibrations of quantum particles (even those cooled to near absolute zero temperatures) can disturb the calculations in progress. (Session I2, March 17, 11 AM)
---Laser Medicine. If you have ever been the beneficiary of laser surgery, thank a physicist--such as Rangaswamy Srinivasan (914-941-9411) of UVTech Associates in New York. To be honored at the APS Division of Biological Physics Prize session, Srinivasan showed at IBM in the early 1980s that ultrashort laser pulses could vaporize specific regions of biological material without damaging the surrounding material, helping to lead to the use of lasers in medicine. The Prize session will feature numerous talks on this topic. Michael Berns of UC-Irvine (714-824-6291) will discuss how "laser scissors" and "optical tweezers" can now cut and paste chromosomes and sequence genes. Alexander Oraevsky of the University of Texas will discuss how aiming laser light at skin lesions can induce sound waves that provide information on whether the lesion is benign or cancerous. Srinivasan will describe the physical explanations of how laser beams can safely remove tissue. (Session I12, March 17, 11AM)
---The Mysteries of Water. Essential for life on Earth and the beautiful geological features on the surface of our planet, water has many unusual properties which are not completely understood. For example, heating water shrinks it, unlike most other liquids. Three sessions at the meeting (A10, C10, G10) deal with the physics and chemistry of water. Scheduled to describe the latest quantum-mechanics based simulations of water, David Clary of University College in London (d.c.clary@ucl.ac.uk) was part of the team that recently discovered that water only begins to act like the liquid with which we are familiar when at least six molecules of H20 are clustered together. (A10.05, March 16, 10 AM) Gene Stanley of Boston University (617-353-2617) will discuss a hypothesis that predicts a previously unknown, low-temperature "critical point" for water in which two liquid phases--a higher-density liquid and a lower-density liquid--can coexist. (A10.01, March 16, 8 AM)
---Making Nanopattern Surfaces. Researchers are pursuing an important new frontier in nanotechnology: to make nanometer-scale patterns of two or more chemically and physically distinct materials. Such nanopattern surfaces could be used as chemical and biological sensors or the "masks" that etch tiny circuit patterns in computer chips. Martin Moeller of Ulm University in Germany (martin.moeller@chemie.uni-ulm.de) will describe a new technique for creating such surfaces. The technique involves embedding a metal or semiconducting nanoparticle inside a polymer whose interior acts as a "nanocompartment." Subsequently, these nanoparticle-containing polymers are deposited onto polymer films. Afterwards, the polymer shells can be removed by using plasma beams similar to those used to etch patterns in computer chips. This leaves metal or semiconducting nanoparticles (1-20 nm in size, depending upon the amount of space in the nanocompartment) which can be separated by 10-200 nm (depending on the overall size of the polymer which embeds the nanoparticle). (Paper E11.02, March 16, 3:06PM)
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APS 1998 MARCH MEETING PRESS REGISTRATION FORM
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