Abstract
The light-matter interaction can be utilized to qualitatively alter physical properties of materials. Recent theoretical and experimental studies have explored this possibility of controlling matter by light based on driving many-body systems via strong classical electromagnetic radiation, leading to a time-dependent Hamiltonian for electronic or lattice degrees of freedom. To avoid inevitable heating, pump-probe setups with ultrashort laser pulses have so far been used to study transient light-induced modifications in materials. Here, we pursue yet another direction of controlling quantum matter by modifying quantum fluctuations of its electromagnetic environment. In contrast to earlier proposals on light-enhanced electron-electron interactions, we consider a dipolar quantum many-body system embedded in a cavity composed of metal mirrors and formulate a theoretical framework to manipulate its equilibrium properties on the basis of quantum light-matter interaction. We analyze hybridization of different types of the fundamental excitations, including dipolar phonons, cavity photons, and plasmons in metal mirrors, arising from the cavity confinement in the regime of strong light-matter interaction. This hybridization qualitatively alters the nature of the collective excitations and can be used to selectively control energy-level structures in a wide range of platforms. Most notably, in quantum paraelectrics, we show that the cavity-induced softening of infrared optical phonons enhances the ferroelectric phase in comparison with the bulk materials. Our findings suggest an intriguing possibility of inducing a superradiant-type transition via the light-matter coupling without external pumping. We also discuss possible applications of the cavity-induced modifications in collective excitations to molecular materials and excitonic devices.
- Received 30 March 2020
- Revised 7 August 2020
- Accepted 15 September 2020
DOI:https://doi.org/10.1103/PhysRevX.10.041027
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.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Light-matter interactions lie at the heart of many technologies such as light-emitting devices, lasers, and photovoltaic cells. Over the past decade, it has been shown that such interactions can be used to alter material properties, which could lead to novel device functionalities. However, progress toward this goal has been restricted to systems interacting with classical light fields, where a strong external drive is essential. Here, we show another way to control the phase of matter without any external drive but with the quantum nature of light.
We consider quantum materials whose atomic dipole moments are naturally on the verge of spontaneous polarization. We show that the dramatic enhancement of light-matter interactions, which is obtained by confining electromagnetic fields to volumes much smaller than their free-space wavelengths, induces a quantum phase transition. Since this phase accompanies the spontaneous formation of polarized dipoles, one can view the transition as a cavity-enhanced superradiant transition—a changeover from a state with relatively few emitters to one with significantly enhanced emission.
The possibility of cavity-mediated transitions has long been under debate since work by Dicke in 1954. In contrast to all the existing realizations of the Dicke-type superradiant transitions in atomic gases, our work reveals that, in real materials with a macroscopic number of excitation modes, the superradiant transition can be induced by vacuum quantum fluctuations of light in the absence of external drives.
Our work opens the door to harness the quantum nature of light to control matter and should be relevant to many light-matter hybrid systems.
