Two Young Physicists Honored with 2002 Apker Award

Kathryn Todd

Robert Wagner

Two promising undergraduate physics majors have been awarded the 2002 Apker Award. Robert E. Wagner of Illinois State University was honored for his thesis entitled, "Intense Laser Physics Theory." And Kathryn Todd of the California Institute of Technology was honored for her thesis entitled, "Studies of Two-Dimensional Electron Systems."

The Apker Award is given annually by the APS for physics research done by an undergraduate. The award was first given in 1978, and in recent years has been divided into two categories, depending on whether the institution has a PhD granting program or not. The winners, who will receive $5,000, were selected by a committee from among the seven finalists (see APS News, November 2001).

Wagner quickly distinguished himself at Illinois State as a gifted physics student, joining the laboratory of the Intense Laser Physics Theory Unit immediately after graduating from high school, learning a new computer language in less than a week. He then developed from scratch a computer simulation program to simulate the relativistic dynamics of atoms in strong laser and magnetic fields, resulting in his first peer-reviewed publication. His codes are still used by the group to explore theoretically novel mechanisms to generate new light sources exploiting resonance last-atom interactions.

Using his computer skills, Wagner has undertaken numerous research projects, including the exploration of a hydrogen atom in a laser field. He later added a strong, static magnetic field to the system, and found that the probability density function for the electron - which is initially the ground state of hydrogen - evolves over time to form a ring-shaped structure later dubbed a cycloatom. His most recent project concerns classical and quantum modeling of an electron-electron collision, with the objective of gaining a better understanding of the classical approximation in a two-electron system, which he hopes to apply to the study of a two-electron cycloatom.

Although just beginning his senior year, Wagner has presented more talks, published more papers and won more awards than any previous physics major, according to departmental chair Richard Martin. He has given 11 conference presentations and contributed to nine peer-reviewed publications, including a Physical Review Letters article on his development of a new Internet-based visualization software package that can generate 3D computer animated movies, which was featured in Physical Review Focus as well as Science News.

He has twice been selected to give invited talks at the APS Division of Atomic Molecular and Optical Physics' undergraduate research symposium, and presented a paper on high harmonic generation in ionization of magnetically dressed atoms at the APS Centennial Meeting in 1999. Wagner describes the past three years of research as "a very exciting and rewarding part of my undergraduate education" adding that he plans to pursue a career in physics. "I am looking forward to the new challenges offered by a physics graduate school."

Todd's thesis consisted of two main experimental research projects, both involving the physics of two-dimensional systems in semiconductor heterostructures. In the first, she studied the mobility of a 2D electron gas confined to an interface between gallium arsenide and an alloy. In such systems, the electrons are typically donated by silicon atoms deposited in a thin sheet some distance away from the interface on the alloy side. Todd added a narrow quantum well between the dopant sheet and the material interface in order to add a second layer of 2D electrons which could screen potential fluctuations of the donors. She then employed theoretical modeling to produce predictions of the electron densities in the quantum well and heterointerfaces as a function of various physical parameters.

In her second project, Todd examined the tunneling current that flows perpendicularly between two parallel 2D electron systems in a symmetrically doped double quantum well system. When a large magnetic field is perpendicularly applied to the 2D planes, tunneling at low interlayer voltages is heavily suppressed. Todd sought to examine this suppression and determine the exact shape of the nonlinear current voltage (I-V) characteristic at very low voltage. She succeeded in manufacturing tunnel junctions and measured the tunnel current down to values 100 times smaller than the research group had done in the past, concluding that the suppression effect deep in the gap was less rapid than it appears at higher energy. She is still pursuing the project, hoping to obtain a quantitative result for I-V deep in the gap.

James Eisenstein, her thesis advisor at CalTech, says he has watched Todd "mature from an inquisitive young undergraduate into an accomplished laboratory scientist," noting that in order to arrive at these scientific conclusions, she performed all aspects of the experiments and analyses herself, "at the level expected of an experienced graduate student." These included optical lithography, wet etching, thin film depositions, and low temperature, low noise electrical measurements. Todd is currently attending graduate school at Stanford University to pursue a PhD in physics.

Copyright 2001, The American Physical Society.
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