%0 Journal Article
%A Orenstein, Gal
%A Krapivin, Viktor
%A Huang, Yijing
%A Zhang, Zhuquan
%A de la Peña Muñoz, Gilberto
%A Duncan, Ryan A.
%A Nguyen, Quynh
%A Stanton, Jade
%A Teitelbaum, Samuel
%A Yavas, Hasan
%A Sato, Takahiro
%A Hoffmann, Matthias C.
%A Kramer, Patrick
%A Zhang, Jiahao
%A Cavalleri, Andrea
%A Comin, Riccardo
%A Dean, Mark P. M.
%A Disa, Ankit S.
%A Först, Michael
%A Johnson, Steven L.
%A Mitrano, Matteo
%A Rappe, Andrew M.
%A Reis, David A.
%A Zhu, Diling
%A Nelson, Keith A.
%A Trigo, Mariano
%T Observation of polarization density waves in SrTiO<sub>3</sub>
%J Nature physics
%V 21
%N 6
%@ 1745-2473
%C Basingstoke
%I Nature Publishing Group
%M PUBDB-2025-02006
%P 961 - 965
%D 2025
%Z Waiting for fulltext 
%X The nature of the incipient ferroelectric transition in SrTiO<sub>3</sub> has been a long-standing puzzle in condensed matter physics. One explanation involves the competition between ferroelectricity and an instability characterized by the mesoscopic modulation of the polarization. These polarization density waves, which should intensify near the quantum critical point, break local inversion symmetry and are difficult to characterize with conventional X-ray scattering methods. Here we probe inversion symmetry breaking at finite momenta and visualize the instability of the polarization at the nanometre scale in SrTiO<sub>3</sub> by combining a femtosecond X-ray free-electron laser with terahertz coherent control methods. We found polar-acoustic collective modes that are soft, particularly at the tens of nanometre scale. These precursor collective excitations provide evidence for the conjectured mesoscopic-modulated phase in SrTiO<sub>3</sub>.  
%F PUB:(DE-HGF)16
%9 Journal Article
%R 10.1038/s41567-025-02874-0
%U https://bib-pubdb1.desy.de/record/631494