UC's Spintronics Team: Cross-college collaboration puts a new spin on electronics

(PhysOrg.com) -- For decades, the transistors inside radios, televisions and other everyday electronic items have transmitted data by controlling the movement of the charge of an electron. Scientists have since discovered that transistors that function by controlling an electron’s spin instead of its charge would use less energy, generate less heat and operate at higher speeds.

This has resulted in a new field of research — spin electronics or spintronics — that offers one of the most promising paradigms for the development of novel devices for use in the post-CMOS (complementary metal-oxide-semiconductor) era. And the multidisciplinary spintronics research team at the University of Cincinnati is leading the way.

With so many people working on the project, one almost needs a program to keep the cast of characters straight.

UC’s team brings together researchers from the Department of Physics in the McMicken College of Arts & Sciences, the Department of Electrical Engineering and Computer Science in the College of Engineering, as well as several other universities and institutes.

The physics group is led by Philippe Debray and Richard Newrock, while Marc Cahay heads the effort from electrical engineering. In addition to the faculty, the team includes graduate student Saydur Rahman and currently includes postdoctoral fellow Krishna Chetry from physics and graduate students Junjun Wan and Partha Pratim Das from electrical engineering.

The team also collaborates with Steven Herbert of Xavier University (a close collaborator who provides access to his sample processing and characterization facilities) and Sergio Ulloa of Ohio University, who often offers his theoretical support.

“Frequent consultation with him has been a source of encouragement for us,” says Philippe Debray.

Mark Johnson, a well-known spintronics researcher at the Naval Research Laboratory, has provided appropriate semiconductor materials and helped with useful experimental suggestions.

The experimental work of all-electric spintronics is carried out in the laboratory for research on charge and spin transport in one-dimensional electron systems located in the Department of Physics. Newrock heads this laboratory.

“Before I came to UC in 2004, the laboratory was focused on experimental investigations of statistical mechanics, using large arrays of classical Josephson junctions to study low-dimensional phase transitions,” says Debray. “When Professor Newrock, a pioneer in this research area, became Dean of the College of Applied Science, he transferred the responsibility for the operations of his laboratory to me, but he maintained his interest in the work being done.”

Debray, who had published many papers on transport in nanoscale devices (such as quantum dots and quantum point contacts) in international journals, reoriented the laboratory’s research efforts to spin and charge transport in nanoscale one-dimensional semiconductor devices.

Debray, Newrock and coworkers’ experimental work on Coulomb drag between parallel quantum wires to obtain experimental evidence of the Luttinger liquid state remains unmatched by any other research laboratory.

“Mustafa Muhammad, a graduate student in physics, obtained his PhD in this research area and was almost immediately hired by the National Institute of Nanotechnology, at the University of Alberta in Canada,” says Richard Newrock. The work on Coulomb drag was supported by a National Science Foundation (NSF) grant with Newrock as the principal investigator (PI) and Debray and Xavier’s Steven Herbert as co-PIs.

In early 2006, Debray met Marc Cahay of the Electrical Engineering Department in the corridors of the Physics Department, which he calls “an unplanned, fortuitous meeting” that led to the creation of this multidisciplinary research team.
Cahay is a well-known spintronics theorist specializing in theoretical modeling of spin devices using non-equilibrium Greens function techniques. He has published a large number of papers in peer-reviewed journals. He has co-authored the only introductory textbook on spintronics, “Introduction to Spintronics” (with Prof. Bandyopadhyay from Virginia Commonwealth University). Cahay and his graduate student, Junjun Wan, provide the theoretical underpinnings of the form the theoretical pillar of the spintronics effort.

About two decades ago, in a pioneering work, two researchers called Datta and Das had proposed a one-dimensional spin field-effect transistor or FET, based on creating spin-polarized electrical current using ferromagnetic contacts. The UC team decided, in 2007, to implement a Datta-Das spin FET without the use of ferromagnetic materials or external magnetic field to create spin polarization, beginning the search for all-electric spintronics or spintronics without ferromagnetism.

A proposal for developing an All-Electric Datta-Das Spin FET was submitted to NSF in early 2007 (with Debray as the PI and, Cahay, Newrock and Herbert as co-PIs). The proposal was acclaimed by the review panel as creative, interesting and — if successful — was expected to be ground-breaking. It was funded.

In early 2008, the team was the first to use a novel method to produce completely spin-polarized current. They used a quantum point contact — a short quantum wire — to generate strongly spin-polarized current by tuning the electrons’ confinement in the wire by bias voltages of the gates that create it. The key condition for success was that the potential confinement must be asymmetric — the transverse opposite edges of the quantum point contact must be asymmetrical. An important finding of this work is that a strong spin-orbit coupling is not essential for achieving spin polarization; the electron-electron interaction is more important. This work was published in “Nature Nanotechnology.” Saydur Rahman contributed significantly to the experimental work as a graduate student and Junjun Wan did the same for the theoretical analysis. Rahman received his PhD in 2008 and moved to Queen’s University in Canada, where he is doing research in nanomechanics and nanoelectronics.

The team continues its powerful work in spintronics, with new developments in the future.

Provided by University of Cincinnati