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Laser-driven ferroelectricity in $\mathrm{SrTiO_{3}}$ via quantum fluctuation quenching

Francesco Libbi, Lorenzo Monacelli, Boris Kozinsky

Abstract

Similar to other perovskites in its family, $\mathrm{SrTiO_{3}}$ exhibits a significant softening of the ferroelectric mode with decreasing temperature, a behavior that typically heralds the onset of a ferroelectric transition. However, this material remains paraelectric down to 0K due to quantum fluctuations that prevent stabilization of the ferroelectric minimum. This work shows that in the strong out-of-equilibrium regime induced by resonant mid-IR pulses, quantum fluctuations can be suppressed, inducing a ferroelectric transition in $\mathrm{SrTiO_{3}}$ that is otherwise impossible at equilibrium. The appearance of a metastable state, that is distinct from the conventional ground state, is the first demonstration of how it is possible to leverage and control quantum fluctuations with pulsed light to qualitatively alter the free energy landscape of a quantum system. We predict the conditions and system parameters under which the induced non-equilibrium state can be long-lived and metastable. In providing a quantitative description, based on first principles machine learned potential energy surface, we explain recent experimental observations of light-induced ferroelectric transition in this material. Our results indicate a general nonequilibrium route to light-induced ferroelectric order in oxide perovskites near a ferroelectric instability.

Laser-driven ferroelectricity in $\mathrm{SrTiO_{3}}$ via quantum fluctuation quenching

Abstract

Similar to other perovskites in its family, exhibits a significant softening of the ferroelectric mode with decreasing temperature, a behavior that typically heralds the onset of a ferroelectric transition. However, this material remains paraelectric down to 0K due to quantum fluctuations that prevent stabilization of the ferroelectric minimum. This work shows that in the strong out-of-equilibrium regime induced by resonant mid-IR pulses, quantum fluctuations can be suppressed, inducing a ferroelectric transition in that is otherwise impossible at equilibrium. The appearance of a metastable state, that is distinct from the conventional ground state, is the first demonstration of how it is possible to leverage and control quantum fluctuations with pulsed light to qualitatively alter the free energy landscape of a quantum system. We predict the conditions and system parameters under which the induced non-equilibrium state can be long-lived and metastable. In providing a quantitative description, based on first principles machine learned potential energy surface, we explain recent experimental observations of light-induced ferroelectric transition in this material. Our results indicate a general nonequilibrium route to light-induced ferroelectric order in oxide perovskites near a ferroelectric instability.

Paper Structure

This paper contains 1 section, 4 equations, 3 figures.

Table of Contents

  1. Methods

Figures (3)

  • Figure 1: a Schematic representation of the STO unit cell irradiated with a laser pulse. b Displacement of the FE, AFD, and IR modes as a function of time. c Logarithmic plot of the FE displacement and fluctuations. d FE and AFD fluctuations as a function of time. e Nonequilibrium potential energy surface of the FE mode, computed as described in Sec. V of the SI, shown at several time instants during the dynamics. f Signed logarithmic representation of the force components acting on the FE mode. The analysis shows that the quantum force provides the dominant driving contribution to the ferroelectric transition.
  • Figure 2: a Schematic representation of the FE transition mechanism. b Electric-field dependence of the FE transition. c Temperature dependence of the FE transition for $E = 2000$ kV/cm. d Temperature dependence of the FE transition for $E = 8000$ kV/cm. e Schematic representation of the double-well PES of STO. f Schematic representation of the FES shapes corresponding to regions I, II, and III in panel e.
  • Figure 3: a Map showing the FE-mode frequency and the stability of STO as a function of the potential-energy parameters $(V_0, x_0)$. b Time evolution of the FE-mode displacement and fluctuations calculated for the parameter set corresponding to point B. c Time evolution of the FE-mode potential energy surface during the dynamics at point B, reflecting the increase in lattice fluctuations.