A Hidden Quantum Paraelectric Phase in SrTiO3 Induced by Terahertz Field

TL;DR

This study demonstrates ultrafast terahertz-induced re-entrant phase transitions in SrTiO3, revealing a hidden quantum paraelectric phase and elucidating the underlying nonlinear light-phonon interaction mechanisms.

Contribution

It uncovers a new hidden quantum paraelectric phase in SrTiO3 induced by intense terahertz fields and explains the complex phase behavior with first-principles calculations.

Findings

Re-entrant phase transition observed at high terahertz fields

Identification of a hidden quantum paraelectric phase

Distinct lattice dynamics in the hidden phase

Abstract

Coherent manipulation of lattice vibrations using ultrafast light pulses enables access to nonequilibrium 'hidden' phases with designed functionalities in quantum materials. However, expanding the understanding of nonlinear light-phonon interaction mechanisms remains crucial for developing new strategies. Here, we report re-entrant ultrafast phase transitions in SrTiO3 driven by intense terahertz excitation. As the terahertz field increases, the system transitions from the quantum paraelectric (QPE) ground state to an intermediate ferroelectric phase, and then unexpectedly reverts to a QPE state above ~500 kV/cm. The latter hidden QPE phase exhibits distinct lattice dynamics compared to the initial phases, highlighting activated antiferrodistortive phonon modes. Aided by first-principles dynamical calculations, we identify the mechanism for these complex behaviors as a superposition of multiple coherently excited eigenstates of the polar soft mode. Our results reveal a previously uncharted quantum facet of SrTiO3 and open pathways for harnessing high-order excitations to engineer quantum materials in the ultrafast regime.