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Hardening of the soft phonon in bulk SrTiO3 interfaced with LaAlO3 and SrRuO3

A. Nucara ; M. Ortolani ; L. Baldassarre ; W. S. Mohamed ; U. Schade ; Pier Paolo Aurino (Institutionen för mikroteknologi och nanovetenskap, Kvantkomponentfysik) ; Alexei Kalaboukhov (Institutionen för mikroteknologi och nanovetenskap, Kvantkomponentfysik) ; Dag Winkler (Institutionen för mikroteknologi och nanovetenskap, Kvantkomponentfysik) ; A. Khare ; F. Miletto Granozio ; P. Calvani
Physical Review B: covering condensed matter and materials physics (2469-9950). Vol. 93 (2016), 22, p. Art. no. 224103.
[Artikel, refereegranskad vetenskaplig]

The low-temperature softening of the TO1 phonon of SrTiO3 (STO), which determines its incipient ferroelectricity, is known to be partially hindered either in the bulk under strong electric fields, or in thin STO films. Here we show, by terahertz (THz) reflectivity measurements, that a similar effect is produced in bulk STO and at zero static field by ultrathin metallic films on its surface, like a 10-nm-thick film of SrRuO3 (SRO), or the two-dimensional electron system (2DES) present at the interface with LaAlO3. In SRO/STO, the observed hardening is well explained by the depolarizing action of the SRO free electrons which follow adiabatically the ion motion. In LAO/STO, a weaker TO1 hardening could be detected by patterning the 2DES in the form of microstripes and using a polarized THz field parallel (E-) or orthogonal (E-) to the stripes. At 10 K, when TO1 is excited together with the free electrons by E-, its absorbance is harder by about 7 cm-1 than that measured when TO1 is coupled to the plasmon-polariton confined within the stripes, being excited by E-.

Denna post skapades 2016-07-07. Senast ändrad 2017-09-14.
CPL Pubid: 239125


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