[seminar] SEMINAR na IF-u u PETAK, 27. 05. 2011.

[Ivica Zivkovic]

*Doping, Strains, Disorder and Electric Field Effect on*

*Superconductivity in Ultra-Thin La_2- _/x/ Sr_/x/ CuO_4 Films*

*Prof. Davor Pavuna*

*Physics of Complex Matter, Station 3, *

*EPFL, CH-1015 Lausanne, Switzerland*


/*E-mail: */_/*davor.pavuna at epfl.ch*/_


*I briefly review main results of our systematic experiments on strained 
thin films of LSCO-214 grown by laser ablation [1-3], and then discuss 
recent method to smoothly tune the carrier concentration of MBE grown 
LSCO monolayer by means of an applied electric field [4,5]. Thin film 
devices were made in an electrical double layer transistor configuration 
utilizing an ionic liquid as gate electrolyte. Very large fields and 
induced changes in surface carrier density enable shifts in the critical 
temperature by up to 30 K. As reported elsewhere in more detail [4], 
dozens of reproducible resistance vs temperature and carrier density 
curves were recorded and have shown to collapse onto a single function 
as predicted for a two-dimensional superconductor-insulator transition. 
The observed critical resistance is precisely the quantum resistance for 
pairs, /R/_Q  = /h//(2/e/)^2  = 6.45 k?, suggestive of a phase 
transition driven by quantum phase fluctuations, and Cooper pair 
(de)localization. The implications of these results and the ongoing 
field effect studies on other materials will also be discussed [5].*


*1. D. Pavuna et al., Journal of Physics 108, 012040 (2008) and 
references therein*

*2. C. Cancellieri et al., Phys. Rev. B76, 174520 (2007); EPFL Thesis 
no. 4120 (2008)*

*3. D. Ariosa et al. Appl. Phys. Lett. 92, 092506 (2008) and references 
therein*

*4. A. T. Bollinger, G. Dubuis, J. Yoon, D. Pavuna, J. Misewich, I. 
Bozovic, Nature 472, 458 (2011)*

*5. G. Dubuis, A. T. Bollinger, D. Pavuna, I. Bozovic, unpublished (2011) *

_*http://www.ph2.uni-koeln.de/379.html?&L=1* 
<http://www.ph2.uni-koeln.de/379.html?&L=1>_


*Voditelji seminara IF-a: Vlasta Horvatić & Ivica Živković*



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