Abstract
Dynamical perturbations modify the states of classical systems in surprising ways and give rise to important applications in science and technology. For example, Floquet engineering exploits the possibility of band formation in the frequency domain when a strong, periodic variation is imposed on parameters such as spring constants. We describe here Kapitza engineering, where a drive field oscillating at a frequency much higher than the characteristic frequencies for the linear response of a system changes the potential energy surface so much that maxima found at equilibrium become local minima, in precise analogy to the celebrated Kapitza pendulum where the unstable inverted configuration, with the mass above rather than below the fulcrum, actually becomes stable. Our starting point is a quantum field theory of the Ginzburg-Devonshire type, suitable for many condensed matter systems, including particularly ferroelectrics and quantum paralectrics. We show that an off-resonance oscillatory electric field generated by a laser-driven terahertz source can induce ferroelectric order in the quantum-critical limit. Heating effects are estimated to be manageable using pulsed radiation; “hidden” radiation-induced order can persist to low temperatures without further pumping due to stabilization by strain. We estimate the Ginzburg-Devonshire free-energy coefficients in using density-functional theory and the stochastic self-consistent harmonic approximation accelerated by a machine-learned force field. Although we find that is not an optimal choice for Kapitza stabilization, we show that scanning for further candidate materials can be performed at the computationally convenient density-functional theory level. We suggest second harmonic generation, soft-mode spectroscopy, and x-ray diffraction experiments to characterize the induced order.
- Received 25 August 2022
- Revised 21 February 2024
- Accepted 18 March 2024
DOI:https://doi.org/10.1103/PhysRevX.14.021016
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Driving an anharmonic oscillator at a frequency much higher than its natural frequency can stabilize the oscillator at otherwise unstable equilibrium points. This “Kapitza effect” has been used to stabilize a range of systems, from Bose-Einstein condensates to Josephson junctions. Here, we apply the concept of Kapitza engineering to the realm of quantum critical points. Specifically, we explore the potential use of this technique to stabilize the ferroelectric phase in certain materials using the electric field of a laser pulse: The rapid shaking of atoms by light provides enough modulation to induce steady ferroelectric order.
In this study, we use first-principles calculations to identify potential candidate materials for Kapitza engineering. We also predict the necessary orientation of an optical electric field to induce the desired effects, depending on the polarization of light and the direction of the induced ferroelectric moment. To detect the induced ferroelectric order, we suggest using low-frequency electrical measurements of displacement current, optical measurements of second harmonic generation, and x-ray diffraction measurements to analyze the resulting strain.
These findings provide a road map for achieving Kapitza stabilization in quantum materials near critical points. Although this study focuses on ferroelectrics, the principles extend to other quantum-critical phenomena like magnetism and superconductivity. This work introduces an overlooked method to manage emerging orders without direct resonance drive, offering a promising avenue for dynamic control of quantum matter. It aims to inspire experimental validation and potential application of this approach.
