| AVS 57th International Symposium & Exhibition | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM+MI-MoA |
| Session: | Semiconducting and Highly Correlated Oxides |
| Presenter: | H.Y. Hwang, University of Tokyo, Japan |
| Correspondent: | Click to Email |
SrTiO3 is the lowest density known bulk superconductor [1]. 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 [2]. 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 [3]. 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 [4]. 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 [5].
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 delta-doping in semiconductors. This aspect suggests that a new regime of 2D superconducting phase transitions can be accessed approaching the clean limit, in contrast to the dirty limit seen at the back-gated LaAlO3/SrTiO3 interface [6].
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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[2] K. A. Mueller and H. Burkard, Phys. Rev. B 19 (1979) 3593.
[3] A. D. Caviglia et al., Nature 456 (2008) 624.
[4] C. Bell et al., Phys. Rev. Lett. 103 (2009) 226802.
[5] A. M. Goldman and N. Markovic, Physics Today 226 (1998) 39.
[6] Y. Kozuka et al., Nature 462 (2009) 487.