Navigation Links
Laser mastery narrows down sources of superconductivity
Date:2/24/2013

UPTON, NY Identifying the mysterious mechanism underlying high-temperature superconductivity (HTS) remains one of the most important and tantalizing puzzles in physics. This remarkable phenomenon allows electric current to pass with perfect efficiency through materials chilled to subzero temperatures, and it may play an essential role in revolutionizing the entire electricity chain, from generation to transmission and grid-scale storage. Pinning down one of the possible explanations for HTSfleeting fluctuations called charge-density waves (CDWs)could help solve the mystery and pave the way for rapid technological advances.

Now, researchers at the Massachusetts Institute of Technology and the U.S. Department of Energy's Brookhaven National Laboratory have combined two state-of-the-art experimental techniques to study those electron waves with unprecedented precision in two-dimensional, custom-grown materials. The surprising results, published online February 24, 2013, in the journal Nature Materials, reveal that CDWs cannot be the root cause of the unparalleled power conveyance in HTS materials. In fact, CDW formation is an independent and likely competing instability.

"It has been difficult to determine whether or not dynamic or fluctuating CDWs even exist in HTS materials, much less identify their role," said Brookhaven Lab physicist and study coauthor Ivan Bozovic. "Do they compete with the HTS state, or are they perhaps the very essence of the phenomenon? That question has now been answered by targeted experimentation."

Custom-grown Superconductors

Electricity travels imperfectly through traditional metallic conductors, losing energy as heat due to a kind of atomic-scale friction. Impurities in these materials also cause electrons to scatter and stumble, but superconductors can overcome this hurdleassuming the synthesis process is precise.

For this experiment, Bozovic used a custom-built molecular beam epitaxy system at Brookhaven Lab to grow thin films of LaSrCuO, an HTS cuprate (copper-oxide) compound. The metallic cuprates, assembled one atomic layer at a time, are separated by insulating planes of lanthanum and strontium oxides, resulting in what's called a quasi-two-dimensional conductor. When cooled down to a low enough temperatureless than 100 degrees Kelvinstrange electron waves began to ripple through that 2D matrix. At even lower temperatures, these films became superconducting.

Electron Sea

"In quasi-two-dimensional metals, low temperatures frequently bring about interesting collective states called charge-density waves," Bozovic said. "They resemble waves rolling across the surface of a lake under a breeze, except that instead of water, here we actually have a sea of mobile electrons."

Once a CDW forms, the electron density loses uniformity as the ripples rise and fall. These waves can be described by familiar parameters: amplitude (height of the waves), wavelength (distance between waves), and phase (the wave's position on the material). Detecting CDWs typically requires high-intensity x-rays, such as those provided by synchrotron light sources like Brookhaven's NSLS and, soon, NSLS-II. And even then, the technique only works if the waves are essentially frozen upon formation. However, if CDWs actually fluctuate rapidly, they may escape detection by x-ray diffraction, which typically requires a long exposure time that blurs fast motion.

Measuring Rolling Waves

To catch CDWs in action, a research group at MIT led by physicist Nuh Gedik used an advanced ultrafast spectroscopy technique. Intense laser pulses called "pumps" cause excitations in the superconducting films, which are then probed by measuring the film reflectance with a second light pulsethis is called a pump-probe process. The second pulse is delayed by precise time intervals, and the series of measurements allow the lifetime of the excitation to be determined.

In a more sophisticated variant of the technique, largely pioneered by Gedik, the standard single pump beam is replaced by two beams hitting the surface from different sides simultaneously. This generates a standing wave of controlled wavelength in the film, but it disappears rapidly as the electrons relax back into their original state.

This technique was applied to the atomically perfect LaSrCuO films synthesized at Brookhaven Lab. In films with a critical temperature of 26 degrees Kelvin (the threshold beyond which the superconductivity breaks down), the researchers discovered two new short-lived excitationsboth caused by fluctuating CDWs.

Gedik's technique even allowed the researchers to record the lifetime of CDW fluctuationsjust 2 picoseconds (a millionth of a millionth of a second) under the coldest conditions and becoming briefer as the temperatures rose. These waves then vanished entirely at about 100 Kelvin, actually surviving at much higher temperatures than superconductivity.

Ruling out a Suspect

The researchers then hunted for those same signatures in cuprate films with slightly different chemical compositions and a greater density of mobile electrons. The results were both unexpected and significant for the future of HTS research.

"Interestingly, the superconducting sample with the highest critical temperature, about 39 Kelvin, showed no CDW signatures at all," Gedik said.

The consistent emergence of CDWs would have bolstered the conjecture that they play an essential role in high-temperature superconductivity. Instead, the new technique's successful detection of such electron waves in one sample but not in another (with even higher critical temperature) indicates that another mechanism must be driving the emergence of HTS.

"Results like this bring us closer to understanding the mystery of HTS, considered by many to be one of the greatest problems in physics today," Bozovic said. "The source of this extraordinary phenomenon is slowly but surely running out of places to hide."


'/>"/>

Contact: Justin Eure
jeure@bnl.gov
631-344-2347
DOE/Brookhaven National Laboratory
Source:Eurekalert  

Related biology technology :

1. X-ray laser sees photosynthesis in action
2. NTU research embraces laser and sparks cool affair
3. INRS develops a nanohybrid with remarkable properties using a new laser-plasma process
4. Recently FDA-Approved Full Neck Treatment for Sagging Skin Now Available at Maryland Laser Skin and Vein Institute
5. X-ray laser helps fight sleeping sickness
6. Researchers create laser the size of a virus particle
7. From lectures to explosives detection: Laser pointer identifies dangerous chemicals in real-time
8. Worlds smallest semiconductor laser created by University of Texas scientists
9. Calmar Laser Growth Reinforced by ISO 9001:2008 Certification
10. JPSA Introduces Picosecond Laser Micromachining System
11. CU-Boulder physicists use ultrafast lasers to create first tabletop X-ray device
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Laser mastery narrows down sources of superconductivity
(Date:6/27/2016)... PHILADELPHIA , June 27, 2016  Liquid ... today announced the funding of a Sponsored Research ... study circulating tumor cells (CTCs) from cancer patients.  ... changes in CTC levels correlate with clinical outcomes ... therapies. These data will then be employed to ...
(Date:6/24/2016)... June 24, 2016 Epic Sciences unveiled ... cancers susceptible to PARP inhibitors by targeting homologous ... (CTCs). The new test has already been incorporated ... multiple cancer types. Over 230 clinical ... response pathways, including PARP, ATM, ATR, DNA-PK and ...
(Date:6/23/2016)... ... June 23, 2016 , ... Mosio, a leader in clinical ... Patient Recruitment and Retention Tips.” Partnering with experienced clinical research professionals, Mosio revisits ... tips, tools, and strategies for clinical researchers. , “The landscape of how patients ...
(Date:6/23/2016)... TORONTO , June 23, 2016 /PRNewswire/ - ... Ontario biotechnology company, Propellon ... the development and commercialization of a portfolio of ... cancers. Epigenetic targets such as WDR5 represent an ... contribute significantly in precision medicine for cancer patients. ...
Breaking Biology Technology:
(Date:6/3/2016)... Das DOTM (Department ... hat ein 44 Millionen $-Projekt ... einschließlich Personalisierung, Registrierung und IT-Infrastruktur, an Decatur ... Implementierung von Identitätsmanagementlösungen. Zahlreiche renommierte internationale Anbieter ... aber Decatur wurde als konformste und innovativste ...
(Date:5/24/2016)... May 24, 2016 Ampronix facilitates superior patient care by providing unparalleled technology ... LCD display is the latest premium product recently added to the range of products ... ... ... 3d Imaging- LCD Medical Display- Ampronix News ...
(Date:5/3/2016)... May 3, 2016  Neurotechnology, a provider of ... MegaMatcher Automated Biometric Identification System (ABIS) , a ... projects. MegaMatcher ABIS can process multiple complex biometric ... combination of fingerprint, face or iris biometrics. It ... and MegaMatcher Accelerator , which have ...
Breaking Biology News(10 mins):