A solitary superconductor emerges under pressure

Jul 04, 2014
The diamond anvil cell used to induce superconductivity in a single-component nickel–organic molecule. Credit: Reproduced, with permission, from Ref. 1 © 2014 American Chemical Society

Three decades ago, researchers discovered that certain organic molecules become superconducting at low temperatures. This finding sparked numerous investigations into the properties of these lightweight, low-cost and easy-to-modify materials. Despite much recent progress, chemists remain puzzled by one aspect of these compounds: all known molecular superconductors need the cooperative action of two or more different molecular species to move electrons without resistance.

HengBo Cui and Reizo Kato from the RIKEN Condensed Molecular Materials Laboratory in collaboration with Hayao Kobayashi and Akiko Kobayashi from Nihon University have now realized a crucial goal in the search for metal-like by uncovering the first molecular superconductor containing only one component.

Superconducting organic crystals are designed around the principle of charge-transfer complexes, where strong interactions between distinct 'donor' and 'acceptor' components move electrons through normally insulating carbon bonds. By squeezing the charge-transfer structures together using diamond anvil cells—tools that allow crystals to be compressed at pressures of up to millions of atmospheres—resistance-free electrical transport can occur at temperatures near absolute zero.

The electron donors and acceptors in molecular are normally individual ionic compounds. However, Kobayashi's team has recently spearheaded investigations into metal–dithiolate complexes that contain a complete charge-transfer system in a single molecule. These crystals, in which a central gold or nickel acceptor atom is flanked on two sides by extended aromatic donor rings infused with sulfur atoms, have a high intrinsic conductivity and exhibit metallic behavior at .

The researchers partnered with Masaaki Sasa from Fujitsu to explore numerous metal–dithiolate synthetic derivatives. They eventually found a promising compound, nickel bis(trifluoromethyl)tetrathiafulvalenedithiolate (Ni(hfdt)2). This molecule has bulky fluorinated end-groups on its dithiolate rings that trigger two-dimensional layer stacking in the crystal state—a highly favorable arrangement for metal-like conductivity.

After carefully manipulating the tiny, submillimeter-sized Ni(hfdt)2 crystals into their diamond anvil cell device, the team measured how its electrical behavior changed with pressure and temperature. At a pressure of about 8.1 gigapascals, they found that the resistivity suddenly plunged to zero at a temperature of 5.5 kelvin—clear evidence that they had discovered a single-component molecular superconductor. High-level theoretical calculations confirmed these experimental findings by revealing the critical point at which pressure converts Ni(hfdt)2 from an insulator to a superconductor.

"This simple, single-component compound not only has the potential to bring about breakthroughs in organic solid-state devices, but will also help in the design of new superconducting systems," says Cui.

Explore further: Insights into the stages of high-temperature superconductivity

More information: Cui, H. B., Kobayashi, H., Ishibashi, S., Sasa, M., Iwase, F., Kato, R. & Kobayashi, A. A single-component molecular superconductor. Journal of the American Chemical Society 136, 7619–7622 (2014). DOI: 10.1021/ja503690m

add to favorites email to friend print save as pdf

Related Stories

Superconducting secrets solved after 30 years

Jun 17, 2014

(Phys.org) —A breakthrough has been made in identifying the origin of superconductivity in high-temperature superconductors, which has puzzled researchers for the past three decades.

Elusive metal discovered

Aug 22, 2012

Carnegie scientists are the first to discover the conditions under which nickel oxide can turn into an electricity-conducting metal. Nickel oxide is one of the first compounds to be studied for its electronic ...

Recommended for you

Physicist pursues superconductivity mysteries

51 minutes ago

More than a quarter of a century after its discovery, high-temperature superconductivity still challenges condensed matter physicists. For Binghamton's Pegor Aynajian, the key to unlocking the mystery—which will ultimately ...

Why does coffee spill more often than beer? (w/ Video)

1 hour ago

Watch even the most careful waiter bring a cup of coffee to your table, and you'll realize that carrying liquid is not easy. When set in motion, the coffee starts sloshing, little waves appear, and spilling ...

Measuring NIF's enormous shocks

1 hour ago

NIF experiments generate enormous pressures—many millions of atmospheres—in a short time: just a few billionths of a second. When a pressure source of this type is applied to any material, the pressure ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.