Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Magnetic transistor could ’dial in’ quantum effects

13.12.2005


Physicists propose innovative probe for quantum criticalities



A team of theoretical and experimental physicists from Rice University is preparing a unique probe in hopes of "dialing in" elusive quantum states called "quantum criticalities." The team is using nanotechnology to create a probe capable of trapping and tuning a single electron to create the rarified physical state in nearby magnetic electrodes.

The probe, a transistor thousands of times smaller than a living cell, is described in research published online this week by the Proceedings of the National Academy of Sciences.


"The traditional theory of metals, which has held sway for 50 years and has fostered terrific technological advances in computing and materials science, breaks down completely in matter that exists in a ’quantum critical state,’" said Qimiao Si, professor of physics and astronomy at Rice and the lead theoretician on the project. "Previous experiments indicate that quantum criticality is characterized by the inherent quantum effect of entanglement, and the nanoscale magnetic probe we’ve proposed could provide a controlled and tunable setting to study entanglement at a quantum critical point."

The term "quantum critical point" refers to a phase transition. Just as water goes through a phase transition when it turns to ice or steam, all matter is subject to phase transitions due to fluctuations produced by the peculiar forces of quantum mechanics.

The probe proposed by Si and colleagues is based on a transistor with an active channel measuring just a few billionths of meter across. The transistor also uses a pair of electrodes made of ferromagnetic metal. The researchers plan to trap a single electron in the active channel between the electrodes. Then, they will capitalize on a uniquely quantum effect -- the tendency of a trapped electron to "tunnel," or wink out of existence in one place and appear in another -- to establish a quantum critical state in the metallic electrodes that trap the tiny particle.

"In principle, we can use the gate voltage in this setup to tune the physical state," said Douglas Natelson, assistant professor of physics and astronomy and of electrical and computer engineering. "We should be able to move the system from a quantum critical state and back again, simply by turning the knob on the voltage. That’s a level of precision that’s never been possible in another experimental system, and it’s really nanotechnology -- the control of matter at the atom-by-atom level -- that will make it possible."

Elementary particles like electrons have an intrinsic angular momentum known as spin. The probe’s design will allow the physicists to confine an electron with its spin on one molecule inside the transistor. In one quantum state, the tunneling effect causes the constrained electron spin to become "entangled" with the spins of electrons in the nearby metal electrodes. The magnetic nature of the electrodes also dictates the existence of a collective oscillation among the spins of electrons in the electrodes. These oscillations – known as "spin waves" -- will interact with the magnetic moment of the constrained electron’s spin and try to break the entanglement. The quantum critical point occurs when it is broken and the material transitions from one quantum phase to the next.

Natelson has already used the technique to study electron spin in similar molecules while using non-magnetic gold metal electrodes. Results of those experiments are due to be published shortly in the journal Physical Review Letters.

"The usage of the ferromagnetic electrodes in the proposed probe brings in spin waves, which couple to the local magnetic moment of the molecule as a fluctuating magnetic field," said theorist and co-author Stefan Kirchner, a postdoctoral fellow of physics and astronomy at Rice. "It is this coupling that gives rise to the ability to tune the degree of – and even destroy – the magnetic quantum entanglement."

The effect is manifested in the unique way that the electrical conductance of the transistor depends on temperature and frequency.

Though nano in scale, the new probe serves as a realistic model system to elucidate physics that cannot be explained by the traditional theory of metals, including phenomena associated with bulk materials like rare-earth-based heavy fermion metals and copper-based high temperature superconductors. For example, the nanoprobe allows the physicists to introduce competition between two quantum effects -- magnetic quantum entanglement and coupling with spin waves. By accessing the quantum critical point that lies at the phase change associated with these competing forces, the researchers can draw a direct linkage between the quantum criticality in the new probe and quantum criticalities in bulk materials like heavy fermion metals.

In a 2001 paper in Nature, Si and collaborators offered a new theory regarding a similar destruction of the magnetic quantum entanglement that appears at the quantum critical point of heavy fermion metals. The new probe could provide direct experimental evidence of this proposed effect.

"Based on previous experiments and theoretical predications, the new probe should provide us with much-anticipated evidence about the precise way that quantum criticality forms in nature," Si said. "With this unique experimental data, we hope to gain an in-depth understanding of the phenomena that may well be what engineers need in order to harness the power for high-temperature superconductivity."

Jade Boyd | EurekAlert!
Further information:
http://www.rice.edu

More articles from Physics and Astronomy:

nachricht First evidence on the source of extragalactic particles
13.07.2018 | Technische Universität München

nachricht Simpler interferometer can fine tune even the quickest pulses of light
12.07.2018 | University of Rochester

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Research finds new molecular structures in boron-based nanoclusters

13.07.2018 | Materials Sciences

Algae Have Land Genes

13.07.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>