Nav: Home

Ultracold atoms used to verify 1963 prediction about 1D electrons

September 04, 2018

Rice University atomic physicists have verified a key prediction from a 55-year-old theory about one-dimensional electronics that is increasingly relevant thanks to Silicon Valley's inexorable quest for miniaturization.

"Chipmakers have been shrinking feature sizes on microchips for decades, and device physicists are now exploring the use of nanowires and nanotubes where the channels that electrons pass through are almost one-dimensional," said Rice experimental physicist Randy Hulet. "That's important because 1D is a different ballgame in terms of electron conductance. You need a new model, a new way of representing reality, to make sense of it."

With IBM and others committed to incorporating one-dimensional carbon nanotubes into integrated circuits, chip designs will increasingly need to account for 1D effects that arise from electrons being fermions, antisocial particles that are unwilling to share space.

The 1D implications of this standoffishness caught the attention of physicists Sin-Itiro Tomonaga and J.M. Luttinger, whose model of 1D electron behavior was published in 1963. A key prediction of Tomonaga-Luttinger liquid (TLL) theory is that exciting one electron in a 1D wire leads to a collective, organized response from every electron in the wire.

Stranger still, because of this collective behavior, TLL theory predicts that a moving electron in 1D will seemingly split in two and travel at different speeds, despite the fact that electrons are fundamental particles that have no constituent parts. This strange breakup, known as spin-charge separation, instead involves two inherent properties of the electron -- negative charge and angular momentum, or "spin."

In a study online this week in Physical Review Letters, Hulet, University of Geneva theoretical physicist Thierry Giamarchi and their colleagues used another type of fermion -- ultracold lithium atoms cooled to within 100 billionths of a degree of absolute zero -- to both verify the predicted speed that charge waves move in 1D and offer confirmation that 1D charge waves increase their speed in proportion to the strength of the interaction between them.

"In a one-dimensional wire, electrons can move to the left or to the right, but they cannot go around other electrons," said Hulet, Rice's Fayez Sarofim Professor of Physics. "If you add energy to the system, they move, but because they're fermions and can't share space, that movement, or excitation, causes a kind of chain reaction.

"One electron moves, and it nudges the next one to move and the one next to that one and so on, causing the energy you've added to move down the wire like a wave," Hulet said. "That single excitation has created a ripple everywhere in the wire."

In their experiments, Hulet's team used lithium atoms as stand-ins for electrons. The atoms are trapped and slowed with lasers that oppose their motion. The slower they go, the colder the lithium atoms become, and at temperatures far colder than any in nature, the atoms behave like electrons. More lasers are used to form optical waveguides, one-dimensional tubes wide enough for just one atom. Despite the effort needed to create these conditions, Hulet said the experiments offer a big advantage.

"We can use a magnetic field in our experiment to tune the strength of the repulsive interaction between the lithium atoms," Hulet said. "In studying these collective, or correlated electron behaviors, interaction strength is an important factor. Stronger or weaker electron interactions can produce wholly different effects, but it's extraordinarily difficult to study this with electrons because of the inability to directly control interactions. With ultracold atoms, we can essentially dial the interaction strength to any level we want and watch what happens."

While previous groups have measured the speed of collective waves in nanowires and in gases of ultracold atoms, none had measured it as a function of interaction strength, Hulet said.

"Charge excitations are predicted to move faster with increasing interaction strength, and we showed that," he said. "Thierry Giamarchi, who literally wrote the book on this topic, used TLL theory to predict how the charge wave would behave in our ultracold atoms, and his predictions were borne out in our experiments."

Having that ability to control interactions also sets the stage for testing the next TLL prediction: The speed of charge waves and spin waves diverge with increasing interaction strength, meaning that as electrons are made to repel one another with greater force, charge waves will travel faster and spin waves will travel slower.

Now that the team has verified the predicted behavior of charge waves, Hulet said they next plan to measure spin waves to see if they behave as predicted.

"The 1D system is a paradigm for strongly correlated electron physics, which plays a key role in many things we'd like to better understand, like high-temperature superconductivity, heavy fermion materials and more," Hulet said.
-end-
Hulet also is a member of the Rice Center for Quantum Materials. Giamarchi is a professor of condensed matter physics at the University of Geneva and a permanent member of the French National Center for Scientific Research.

Additional study co-authors include Rice graduate student Ya-Ting Chang; former Rice graduate students Tsung-Lin Yang, the study's lead author, and Zhenghao Zhao; former Rice visiting student researcher Chung-You Shih; and former University of Geneva research scientist Pjotrs Grisins. The research was supported by the Army Research Office's Multidisciplinary University Research Initiative, the Office of Naval Research, the National Science Foundation and the Swiss National Science Foundation.

The DOI of the Physical Review Letters paper is: 10.1103/PhysRevLett.121.103001

A copy of the paper is available at: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.103001

Related research from Rice:

Ultracold atom waves may shed light on rogue ocean killers -- April 28, 2017 http://news.rice.edu/2017/04/28/ultracold-atom-waves-may-shed-light-on-rogue-ocean-killers/

Simulating superconducting materials with ultracold atoms -- Feb. 23, 2015 http://news.rice.edu/2015/02/23/simulating-superconducting-materials-with-ultracold-atoms/

Ultracold disappearing act -- Nov. 2, 2014 http://news.rice.edu/2014/11/02/ultracold-disappearing-act/

One-dimensional window on superconductivity, magnetism -- Sept. 29, 2010 http://news.rice.edu/2010/09/29/one-dimensional-window-on-superconductivity-magnetism-2/

Rice physicists find reappearing quantum trios -- Dec. 11, 2009 http://news.rice.edu/2009/12/11/rice-physicists-find-reappearing-quantum-trios-2/

Rice awarded $5M for light-based crystal simulator -- Sept. 23, 2009 http://news.rice.edu/2009/09/23/rice-awarded-5m-for-light-based-crystal-simulator/

Ultracold test produces long-sought quantum mix -- Dec. 22, 2005 http://news.rice.edu/2005/12/22/ultracold-test-produces-long-sought-quantum-mix/

Rice physicists observe new 'atom wave' phenomena -- May 1, 2002 https://www.eurekalert.org/pub_releases/2002-05/ru-rpo043002.php

This release can be found online at news.rice.edu.

Follow Rice News and Media Relations via Twitter @RiceUNews.

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,970 undergraduates and 2,934 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction and No. 2 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.com/RiceUniversityoverview.

Rice University

Related Electrons Articles:

Deceleration of runaway electrons paves the way for fusion power
Fusion power has the potential to provide clean and safe energy that is free from carbon dioxide emissions.
Shining light on low-energy electrons
The classic method for studying how electrons interact with matter is by analyzing their scattering through thin layers of a known substance.
Ultrafast nanophotonics: Turmoil in sluggish electrons' existence
An international team of physicists has monitored the scattering behavior of electrons in a non-conducting material in real-time.
NASA mission uncovers a dance of electrons in space
NASA's MMS mission studies how electrons spiral and dive around the planet in a complex dance dictated by the magnetic and electric fields, and a new study revealed a bizarre new type of motion exhibited by these electrons.
'Hot' electrons don't mind the gap
Rice University scientists discover that 'hot' electrons can create a photovoltage about a thousand times larger than ordinary temperature differences in nanoscale gaps in gold wires.
Electrons used to control ultrashort laser pulses
We may soon get better insight into the microcosm and the world of electrons.
Supercool electrons
Study of electron movement on helium may impact the future of quantum computing.
Two electrons go on a quantum walk and end up in a qudit
There is a variety of physical systems that can be used to implement a separate quantum bit, but significantly less research has been done into systems of several qubits or qudits.
Radiation that knocks electrons out and down, one after another
Researchers at Japan's Tohoku University are investigating novel ways by which electrons are knocked out of matter.
Controlling electrons in time and space
A new method has been developed to control electrons being emitted from metal tips.

Related Electrons Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Setbacks
Failure can feel lonely and final. But can we learn from failure, even reframe it, to feel more like a temporary setback? This hour, TED speakers on changing a crushing defeat into a stepping stone. Guests include entrepreneur Leticia Gasca, psychology professor Alison Ledgerwood, astronomer Phil Plait, former professional athlete Charly Haversat, and UPS training manager Jon Bowers.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".