Lecture Harold Y. Hwang
|26 augustus 2010||FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Prof. Dr. Harold Y. Hwang|
Department of Advanced Materials, University of Tokyo, Chiba, JapanJapan Science and Technology Agency, Saitama, Japan
|Title:||Low-Dimensional Superconductivity in SrTiO3 Heterostructures|
|Date:||Thu Aug 26, 2010|
|Telephone:||+31 50 363 8394|
SrTiO3 is the lowest density known bulk superconductor . In addition, it is a dielectric material which is well-known for its very large low-temperature dielectric constant, arising due to the proximity of a ferroelectric instability . With recent advances in complex oxide heteroepitaxy, these physical properties provide a unique opportunity to apply concepts of band structure engineering to this superconducting semiconductor.
At the conducting LaAlO3/SrTiO3 interface, the superconducting state can be back-gate modulated to induce a 2D superconductor-insulator transition . Using magnetotransport studies in the normal state, we find that the mobility variation is five times as large as the change in sheet carrier density . These results indicate that the relative disorder strength increases across the superconductor-insulator transition, which can be understood to be driven by localization as in previous examples of ultra-thin quenched amorphous superconductors such as Bi .
Using heterostructures of Nb:SrTiO3 embedded in undoped SrTiO3, we have studied the crossover from 3D to 2D superconductivity as the thickness of the doped layer is decreased. A notable feature is that the mobility increases in the 2D limit to over 6 times the highest bulk value at comparable doping, in analogy to d -doping in semiconductors. As a result, in the thinnest samples, suppression of superconductivity by magnetic field leads to the onset of 2D Shubnikov-de Haas oscillations . This aspect suggests that a new regime of 2D superconducting phase transitions can be experimentally accessed approaching the clean limit.
This work was done in collaboration with Y. Kozuka, C. Bell, M. Kim, S. Harashima, Y. Hikita, and B. G. Kim.
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|Laatst gewijzigd:||22 oktober 2012 14:30|