Journal Article

Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid

McKeown Walker, S., Mesot, J., Meevasana, W., King, P. D. C., Baumberger, F., Tamai, A., Varykhalov, A., Moritz, B., Riccò, S., Radovic, M., Bruno, F. Y., Shi, M., Hlawenka, P., Devereaux, T. P., Diebold, U., de la Torre, A., Sánchez-Barriga, J., Hoesch, M., Wang, Y., Wang, Z., Ristic, Z., Plumb, N. C., Kim, T. K.

2016

Overview

The transition from a polaronic to a metallic state as the carrier density increases in strontium titanate overlaps with the onset and peak of the bulk superconducting behaviour. Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides 1 , 2 , 3 , 4 . Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO 3 (001) surface 5 , 6 , 7 to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO 3 /SrTiO 3 interface 8 , 9 , 10 , 11 , 12 , 13 , our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO 3 -based 2DELs.

• Publisher: Nature Publishing Group UK
• Subject: 639/301 / 639/301/119/544 / 639/766/119/995 / Biomaterials / Condensed Matter Physics / letter / Materials Science / Nanotechnology / Optical and Electronic Materials