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2Physics Quote:
"About 200 femtoseconds after you started reading this line, the first step in actually seeing it took place. In the very first step of vision, the retinal chromophores in the rhodopsin proteins in your eyes were photo-excited and then driven through a conical intersection to form a trans isomer [1]. The conical intersection is the crucial part of the machinery that allows such ultrafast energy flow. Conical intersections (CIs) are the crossing points between two or more potential energy surfaces."
-- Adi Natan, Matthew R Ware, Vaibhav S. Prabhudesai, Uri Lev, Barry D. Bruner, Oded Heber, Philip H Bucksbaum
(Read Full Article: "Demonstration of Light Induced Conical Intersections in Diatomic Molecules" )

Sunday, January 10, 2010

The Mechanism behind Superinsulation

From Left to Right: Valerii Vinokur, Tatyana Baturina and Nikolai Chtchelkatchev (photo courtesy: Argonne National Laboratory)

Scientists at the U.S. Department of Energy's Argonne National Laboratory have discovered the microscopic mechanism behind the phenomenon of superinsulation, the ability of certain materials to completely block the flow of electric current at low temperatures.

The essence of the mechanism is what the authors termed "multi-stage energy relaxation" in a recent paper [1] published in Physical Review Letters. An earlier paper [2] on the discovery of superinsulation was published in Nature in April, 2008.

Traditionally, energy dissipation accompanying current flow is viewed as disadvantageous, as it transforms electricity into heat and thus results in power losses. In arrays of tunnel junctions that are the basic building units of modern electronics, this dissipation permits the generation of current.

Argonne scientist Valerii Vinokour, along with Russian scientists Nikolai Chtchelkatchev (Moscow Institute of Physics and Technology) and Tatyana Baturina (Institute of Semiconductor Physics, Novosibirsk), found that at very low temperatures the energy transfer from tunneling electrons to the thermal environment may occur in several stages.

An electron microscopy image of titanium nitride, on which the effect of superinsulation was first observed [image courtesy: Argonne National Laboratory]

“First, the passing electrons lose their energy not directly to the heat bath; they transfer their energy to electron-hole plasma, which they generate themselves,” Vinokour said. “Then this plasma 'cloud' transforms the acquired energy into the heat. Thus, tunneling current is controlled by the properties of this electron-hole cloud.”

As long as the electrons and holes in the plasma cloud are able to move freely, they can serve as a reservoir for energy—but below certain temperatures, electrons and holes become bound into pairs. This does not allow for the transfer of energy from tunneling electrons and impedes the tunneling current, sending the conductivity of the entire system to zero.

“Electron-hole plasma disappears from the game and electrons cannot generate the energy exchange necessary for tunneling,” Vinokour said. Because the current transfer in thin films and granular systems that exhibit superinsulating behavior relies on electron tunneling, the multistage relaxation explains the origin of the superinsulators.

Superinsulation is the opposite of superconductivity; instead of a material that has no resistivity, a superinsulator has a near-infinite resistance. Integration of the two materials may allow for the creation of a new class of quantum electronic devices. This discovery may one day allow researchers to create super-sensitive sensors and other electronic devices.

Reference
[1] N. M. Chtchelkatchev, V. M. Vinokur, and T. I. Baturina, "Hierarchical Energy Relaxation in Mesoscopic Tunnel Junctions: Effect of a Nonequilibrium Environment on Low-Temperature Transport", Physical Review Letters, 103, 247003 (2009). Abstract.
[2] Valerii M. Vinokur, Tatyana I. Baturina, Mikhail V. Fistul, Aleksey Yu. Mironov, Mikhail R. Baklanov and Christoph Strunk, "Superinsulator and quantum synchronization", Nature, 452, 613-615 (3 April 2008). Abstract.

[We thank Argonne National Laboratory, IL, USA for materials used in this report]

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1 Comments:

At 4:37 PM, Blogger Macksb said...

Superinsulators are the exact opposite of superconductors. Fundamentally, we should ask whether they share the same basic explanation. I believe that they do: Art Winfree's theory of coupled oscillators, developed in the late 1960s and applied by him to biological systems, can also be applied to explain phases of matter and phase transitions. I have developed this point in the Aspen physics blog with posts dating back to 2007. The posts follow an article about Doug Scalapino and his theory of superconductivity.

My theory (which is simply Art Winfree's theory redirected from biology to physics) does not contradict the microscopic explanation set forth in the article above. Rather, it offers a deeper explanation. Readers who follow Steve Strogatz and his book Sync will understand the general outlines of my approach.

 

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