Home > Press > Forced to insulate: Substrate-induced strain can be used to switch an organic superconductor into an insulator that responds to the application of a v
 |
| Figure 1: Images of the device investigated. The left panel shows a κ-Br single crystal film deposited on a SiO2/Si substrate with pre-patterned gold contacts. The right panel shows the same device after a pulsed laser has been used to shape the κ-Br crystal into a more regular geometry. |
Abstract:
Scientists at the RIKEN Advanced Science Institute, Wako, Saitama University, Saitama, and the National Institute of Advanced Industrial Science and Technology, Tsukuba, have demonstrated that an organic film can be switched from being a superconductor to an insulator through the proper choice of substrate1. In addition, the researchers have shown that the electrical conductivity of the film can be tuned by an external voltage, which is necessary to realize transistors.
Forced to insulate: Substrate-induced strain can be used to switch an organic superconductor into an insulator that responds to the application of a v
Japan | Posted on October 25th, 2008
When the film of a molecular conductor is deposited on a substrate of an organic electronic device, considerable strain can arise that dramatically affects its transport properties, particularly when the temperature varies owing to differences in thermal contraction between film and substrate.
In demonstrating the switch from superconductor to insulator, Yoshitaka Kawasugi and colleagues focussed on the well-known organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br—κ-Br in short—that has a 2.93% thermal contraction when cooled from room temperature (~300 K) to 20 K. At room temperature, the material is an insulator, but when cooled it becomes a metal at approximately 50 K, and eventually a superconductor at 11 K.
The researchers examined the κ-Br film deposited on a silicon-based (SiO2/Si) substrate (Fig. 1), which is nominally unshrinkable and therefore hinders thermal contraction. Their transport measurements show that resistance increases with decreasing temperature, from 300 K to below 10 K, which means that the silicon-based substrate has made the film an insulator throughout this temperature range.
To explain these results, Kawasugi and colleagues compared the effect of the non-shrinking substrate with that of pressure. Using a phase diagram of compounds similar to κ-Br, the researchers assumed that although the material is a superconductor below 11 K at ambient pressure, it becomes an insulator when negative pressure is applied. By hindering thermal contraction, the SiO2/Si substrate has the same effect as negative pressure, so when the sample is cooled, the pressure effectively decreases, and the sample stays insulating.
Kawasugi and colleagues also verified that the strain-induced insulator exhibits a field effect, which is variable conductance with an applied gate voltage. As Kawasugi explains, "The gate voltage applied to the film enhanced its conductivity by several orders of magnitude, and the field-effect mobility reached a very high value as an organic transistor, 94 cm2/Vs at low temperature." From the phase diagram, the insulating film is in the proximity of the superconducting phase, and with even higher gate voltages it may switch to a superconductor. "The results open the way to field-induced superconductivity in organic materials," says Kawasugi.
Reference
1. Kawasugi, Y., Yamamoto, H.M., Hosoda, M., Tajima, N., Fukunaga, T., Tsukagoshi, K. & Kato, R. Strain-induced superconductor/insulator transition and field effect in a thin single crystal of molecular conductor. Applied Physics Letters 92, 243508 (2008).
The corresponding author for this highlight is based at the RIKEN Condensed Molecular Materials Laboratory
####
For more information, please click here
Copyright © Riken
If you have a comment, please
Contact us.
Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Bookmark:
article
News and information
Sound waves precisely position nanowires June 19th, 2013
Scientists Use Nanotechnology to Increase Thermal Stability of Essential Oils June 19th, 2013
Production of Bioactive Material for Quick Treatment of Bone Damages June 19th, 2013
Nanometrics Announces Participation in 5th Annual CEO Investor Summit: Accredited Investor and Publishing Research Analyst Event to be Held Concurrently With SEMICON West and Intersolar 2013 in San Francisco June 19th, 2013
Chip Technology
Sound waves precisely position nanowires June 19th, 2013
Nanometrics Announces Participation in 5th Annual CEO Investor Summit: Accredited Investor and Publishing Research Analyst Event to be Held Concurrently With SEMICON West and Intersolar 2013 in San Francisco June 19th, 2013
Which qubit my dear? New method to distinguish between neighbouring quantum bits June 18th, 2013
SEMATECH to Address Critical Supply Chain Challenges and Present Latest Technology Advances at SEMICON West 2013 June 17th, 2013
Discoveries
Sound waves precisely position nanowires June 19th, 2013
Scientists Use Nanotechnology to Increase Thermal Stability of Essential Oils June 19th, 2013
Production of Bioactive Material for Quick Treatment of Bone Damages June 19th, 2013
New Method to Synthesize Zinc Oxide Nanoparticles with High Catalytic Activity June 18th, 2013
Announcements
Sound waves precisely position nanowires June 19th, 2013
Scientists Use Nanotechnology to Increase Thermal Stability of Essential Oils June 19th, 2013
Production of Bioactive Material for Quick Treatment of Bone Damages June 19th, 2013
Nanometrics Announces Participation in 5th Annual CEO Investor Summit: Accredited Investor and Publishing Research Analyst Event to be Held Concurrently With SEMICON West and Intersolar 2013 in San Francisco June 19th, 2013