Nav: Home

Physicists solve decades-old scientific mystery of negative differential resistance

January 05, 2017

With a storied history that includes more than a half-century of research, a Nobel Prize, and multiple attempts at practical applications, the story of negative differential resistance--or NDR--reads like a scientific mystery, a mystery that University of Alberta physicists have at last succeeded in unraveling.

What does this mean? An opportunity to combine the knowledge with existing technology to create faster, cheaper, and smaller electronic devices, a boon to the continued boom of the digital era.

NDR is an odd effect. We can imagine it by thinking of water being pushed through a hose. The greater the pressure, the faster the flow. Electrons in a wire act similarly, except voltage is applied instead of pressure to induce flow. With water, increased pressure equals increased flow, but in special circumstances with electricity, there is sometimes a backwards and counterintuitive effect where flow slows: this is negative differential resistance.

The first attempt at a practical application for NDR, the Esaki Diode, named for inventor Japanese physicist Leo Esaki, was received in the 1950s with great excitement, some even proclaiming it to be more important than the transistor. The work was awarded a Nobel Prize. Soon after it became clear that mass production was too difficult, the once-heralded device was relegated to niche applications.

Replicating the NDR effect in a way that could be widely deployed remained an enticing goal. Alternatives to the Esaki Diode were found, but those too resisted mass production. The advent of scanning tunneling microscopes in the '80s and the access they provide to nanoscale material properties led to tantalizing NDR signatures from atom-scale structural irregularities in silicon. Excitement was re-kindled, but adequate understanding and manufacturability remained elusive.

Fast forward to the present, and a team of physicists led by Robert Wolkow from the University of Alberta have now discovered the precise atomic structure that gives rise to NDR. Furthermore, by accounting for the particular rules quantum mechanics enforces for electron flow through a single atom, Wolkow's colleague, theoretical physicist Joseph Maciejko, has succeeded in accounting for the at-first perplexing reduction in current with increasing voltage. These results point the way to practical and lucrative applications in everyday electronics such as phones and computers.

"It turns out that if you can easily see how to neatly and cheaply incorporate this NDR effect into existing electronic transistors, you can make smaller, faster, cheaper devices," says Wolkow. "The value of a hybrid transistor/NDR circuit has been known for decades, but no one has been able to do it efficiently or cheaply enough to make it worthwhile.

"Over the years, people have published papers on variants of the same atom-scale effect. Unfortunately, the riddle of the structure and its properties was never solved. But we now know exactly why it happens, we know exactly what constituents need to be there for it to be controlled. We have defined the exact atomic structure that gives rise to NDR, and luckily it is easy to make. As well, we have finally elucidated the mechanism at play-or should I say at work."

Wolkow explains that there's now a very realistic potential to combine this NDR phenomenon with everyday electronics in a practical, affordable way, an advance potentially worth billions for the technology industry.

"Negative Resistance with a Single Atom" was published December 30 in Physical Review Letters.
-end-


University of Alberta

Related Research Articles:

More Research News and Research Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 3: Shared Immunity
More than a million people have caught Covid-19, and tens of thousands have died. But thousands more have survived and recovered. A week or so ago (aka, what feels like ten years in corona time) producer Molly Webster learned that many of those survivors possess a kind of superpower: antibodies trained to fight the virus. Not only that, they might be able to pass this power on to the people who are sick with corona, and still in the fight. Today we have the story of an experimental treatment that's popping up all over the country: convalescent plasma transfusion, a century-old procedure that some say may become one of our best weapons against this devastating, new disease.   If you have recovered from Covid-19 and want to donate plasma, national and local donation registries are gearing up to collect blood.  To sign up with the American Red Cross, a national organization that works in local communities, head here.  To find out more about the The National COVID-19 Convalescent Plasma Project, which we spoke about in our episode, including information on clinical trials or plasma donation projects in your community, go here.  And if you are in the greater New York City area, and want to donate convalescent plasma, head over to the New York Blood Center to sign up. Or, register with specific NYC hospitals here.   If you are sick with Covid-19, and are interested in participating in a clinical trial, or are looking for a plasma donor match, check in with your local hospital, university, or blood center for more; you can also find more information on trials at The National COVID-19 Convalescent Plasma Project. And lastly, Tatiana Prowell's tweet that tipped us off is here. This episode was reported by Molly Webster and produced by Pat Walters. Special thanks to Drs. Evan Bloch and Tim Byun, as well as the Albert Einstein College of Medicine.  Support Radiolab today at Radiolab.org/donate.