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News from the March 2008 American Physical Society Meeting

The following scientific talks are among those that will be presented by researchers from the U.S. Department of Energy's Brookhaven National Laboratory at the American Physical Society meeting, March 10-14, 2008, at the Morial Convention Center, New Orleans, Louisiana. Please note that the content of each talk is embargoed until the time of that talk as noted below. All of the research described below was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science.

DNA-Guided Nanoparticle Assembly
Part 1: Embargoed for release on Monday, March 10, 2008, 8:12 a.m. Central Time (9:12 a.m. Eastern)

Brookhaven Lab scientists have developed a new method for controlling the self-assembly of nanometer and micrometer-sized particles. Based on designed DNA shells that coat a particle's surface, the method can be used to manipulate the structure of numerous materials. Such fine-tuning of materials at the molecular level may lead to numerous applications, including cell-targeted systems for drug-delivery and bio-molecular sensing for environmental monitoring or medical applications.

"Our method is unique because we attached two types of DNA to the particles' surfaces," said Brookhaven researcher Dmytro Nykypanchuk, who will give a talk about this work on Monday, March 10, at 8:12 a.m. Central Time in room R06. " The first type of DNA forms a double helix, while the second type is non-complementary, neutral DNA, so it provides a repulsive force. The addition of the repulsive force allows for regulating the size of particle clusters and the speed of self-assembly with more precision."

Part 2: Embargoed for release on Wednesday, March 12, 2008, 4:30 p.m. Central Time (5:30 p.m. Eastern)

In subsequent experiments, the researchers used DNA to guide the creation of three-dimensional, ordered, crystalline structures of nanoparticles. Engineering such 3-D structures is important for producing materials with unique properties that exist at the nanoscale, such as enhanced magnetism and improved catalytic activity. Brookhaven scientist Oleg Gang will present this research on Wednesday, March 12, at 4:30 p.m. Central Time in room 210.

This new assembly method relies on the attractive forces between complementary strands of DNA, but the scientists also heated the DNA-linked particles, then cooled them back to room temperature. "This 'thermal processing' allows the nanoparticles to unbind, reshuffle, and find more stable binding arrangements," Gang said.

A patent application has been filed for the technology.

Closing the "Pseudogap" on Superconductivity
Embargoed for release on Monday, March 10, 2008, 12:51 p.m. Central Time (1:18 p.m. Eastern)

One of the biggest mysteries in studying high-temperature (Tc) superconductors - materials that conduct electrical current with no resistance below a certain transition temperature - is the origin of a gap in the energy level of the materials' electronic spectrum. Brookhaven physicist Hongbo Yang will present his latest research on this "pseudogap" on Monday, March 10, 2008, at 12:51 p.m. Central Time in room RO8.

Understanding the pseudogap may help scientists understand the mechanism for high-temperature superconductivity, which in turn could lead to the strategic design of superconductors for practical applications such as high-capacity, highly efficient power transmission lines.

There are competing theories for the origin of the pseudogap. In one, the material is considered a normal metal from which superconductivity starts to emerge via the pairing of electrons. In another, the pseudogap is thought to reflect the competition between superconductivity and another condition of the material - some other "ground state."

"Our new results indicate that the first theory is clearly incorrect, these are not normal metals that simply become superconductors," said Yang.

Yang will present his results of how the gap changes at various temperatures and with various levels of doping - that is, with different amounts of various other atoms added to the material.

"The results show that the underdoped system in the normal state behaves differently from all regions of the phase diagram in the superconducting state, and point to potentially different origins for the pseudogap," he said.

Modeling How Electric Charges Move
Embargoed for release on Monday, March 10, 2008, 4:18 p.m. Central Time (5:18 p.m. Eastern)

Learning how to control the movement of electrons on the molecular and nanometer scales could help scientists devise small-scale circuits for many applications, including more efficient ways of storing and using solar energy. Marshall Newton, a theoretical chemist at Brookhaven Lab, will present a talk highlighting the theoretical techniques used to understand the factors affecting electron movement on Monday, March 10, 2008, at 4:18 p.m. Central Time in room RO4.

"Electron transfer plays a vital role in numerous biological processes, including nerve cell communication and converting energy from food into useful forms," says Newton. "It's the initial step in photosynthesis, as well, where charges are first separated and the energy is stored for later use - which is one of the concepts behind energy production using solar cells."

Newton will describe how combining electronic quantum mechanical theory with computational techniques has led to a unified, compact way to understand the nature of charge transfer in complex molecular aggregates.

"In essence," he explains, "the research has led to understanding electronic transport in terms of quantitative answers to a few basic mechanistic questions: namely, how far, how efficiently, and by which route (or molecular 'pathway') a charge moves from a 'donor' to an 'acceptor' in the molecular assembly." The answers come from detailed molecular quantum calculations of the energy gaps separating the relevant electronic states, and the strength of coupling between adjacent molecular units along the "pathways."

"This new approach may yield ways to predict and control electronic transport behavior by 'tuning' the molecular components, resulting in capabilities that can be used to design new solar-based energy schemes," Newton said.

Two-Dimensional Fluctuating Superconductivity
Embargoed for release on Thursday, March 13, 2008, 8:36 a.m. Central Time (9:36 a.m. Eastern)

Scientists at Brookhaven Lab have discovered a state of two-dimensional (2D) fluctuating superconductivity in a high-temperature superconductor with a particular arrangement of electrical charges known as "stripes." The finding was uncovered during studies of directional dependence in the material's electron-transport and magnetic properties. In the 2D plane, the material acts as a superconductor - conducts electricity with no resistance - at a significantly higher temperature than in the 3D state.

"The results provide many insights into the interplay between the stripe order and superconductivity, which may shed light on the mechanism underlying high-temperature superconductivity," said Brookhaven physicist Qiang Li, who will present this work in room RO7 on Thursday, March 13, 2008 at 8:36 a.m. Central Time.

Understanding the mechanism of high-temperature superconductivity is one of the outstanding scientific issues in condensed matter physics, Li said. Understanding this mechanism could lead to new strategies for increasing the superconducting transition temperature of other superconductors to make them more practical for applications such as electrical transmission lines.

"As electricity demand increases, the challenge to the national electricity grid to provide reliable power will soon grow to crisis levels," Li said. "Superconductors offer powerful opportunities for restoring the reliability of the power grid and increasing its capacity and efficiency by providing reactive power reserves against blackouts, and by generating and transmitting electricity."


Contact: Karen McNulty Walsh
DOE/Brookhaven National Laboratory

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