Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy
D. A. Tenne,1*
A. Bruchhausen,2
N. D. Lanzillotti-Kimura,2
A. Fainstein,2
R. S. Katiyar,3
A. Cantarero,4
A. Soukiassian,5
V. Vaithyanathan,5
J. H. Haeni,5
W. Tian,5
D. G. Schlom,5
K. J. Choi,6
D. M. Kim,6
C. B. Eom,6
H. P. Sun,7
X. Q. Pan,7
Y. L. Li,5,8
L. Q. Chen,5
Q. X. Jia,8
S. M. Nakhmanson,9
K. M. Rabe,9
X. X. Xi1,5
We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature (Tc) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (with Tc as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by 
500 kelvin by varying the thicknesses of the BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.
1 Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.
2 Centro Atómico Bariloche y Instituto Balseiro, Comisión Nacional de Energía Atómica, 8400 San Carlos de Bariloche, Argentina.
3 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico 00931–3343, USA.
4 Materials Science Institute, University of Valencia, Post Office Box 22085, E-46071 Valencia, Spain.
5 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
6 Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706, USA.
7 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
8 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
9 Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854–8019, USA.
* To whom correspondence should be addressed: Department of Physics, Boise State University, 1910 University Drive, Boise, ID 83725–1570, USA. E-mail: dmitritenne{at}boisestate.edu
