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Lecture Harold Y. Hwang


26 August 2010 FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen
Speaker: Prof. Dr. Harold Y. Hwang

Department of Advanced Materials, University of Tokyo, Chiba, Japan

Japan Science and Technology Agency, Saitama, Japan
Title: Low-Dimensional Superconductivity in SrTiO3 Heterostructures
Date: Thu Aug 26, 2010
Start: 15.00
Location: FWN-Building 5111.0080
Host: Tamalika Banerjee
Telephone: +31 50 363 8394


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 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 [6]. 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.


[1] J. F. Schooley et al., Phys. Rev. Lett. 12 (1964) 474.

[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.

Last modified:22 October 2012 2.30 p.m.