Optically-induced Faraday-Goldstone Waves Demonstrate Ultrafast Light-Matter Interactions and Emergent Spatiotemporal Order

The interplay between light and matter frequently gives rise to unexpected phenomena, and researchers now demonstrate that ordered solids exhibit wave-like behaviour when excited by light pulses, akin to Faraday waves typically seen in fluids. Daniel Kaplan from Rutgers University, Pavel A. Volkov from the University of Connecticut, and Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter and the University of Oxford, alongside Premala Chandra from Rutgers University and The Flatiron Institute, reveal that these newly observed ‘Faraday-Goldstone waves’ persist far longer than the initial light pulse. The team develops a theoretical framework explaining how light triggers a coupling between different modes within the material, creating a dynamic, oscillating order that is surprisingly resilient to thermal noise. This discovery establishes a new method for creating periodic structures within materials using ultrafast light, potentially opening avenues for advanced materials design and manipulation.

Light Drives Novel Faraday Wave Patterns

Researchers investigate the emergence of Faraday waves, patterns formed at a fluid interface vibrating due to external forces, when induced by light instead of mechanical vibrations. This study reveals a new mechanism for exciting these waves, involving the interplay between optical force and the fluid’s restoring force, leading to standing waves. The team demonstrates that optically-induced Faraday waves exhibit distinct characteristics compared to those generated by traditional mechanical vibrations, particularly in their frequency dependence and spatial structure. The approach utilizes a theoretical framework combining hydrodynamic equations with the equations governing light propagation and absorption within the fluid.

This framework allows calculation of the optical force acting on the fluid surface and its subsequent influence on the fluid’s dynamic response. Researchers then analyse the stability of the fluid interface to determine the conditions under which Faraday waves emerge and their corresponding properties. The analysis predicts that the frequency of the optically-induced Faraday waves depends on both the optical properties of the fluid and the intensity of the incident light, offering a pathway for external control. The team also predicts the existence of Goldstone modes, gapless waves arising from the breaking of continuous symmetry, within the Faraday wave spectrum, representing a novel phenomenon in wave dynamics.

The findings provide a theoretical foundation for manipulating fluid surfaces with light, potentially enabling applications in microfluidics, optical sensing, and surface patterning. The team presents a theory of ultrafast light-matter interactions within a symmetry-broken state, where dynamic coupling between the Higgs (amplitude) and Goldstone (phase) modes drives an emergent spatiotemporal order. Calculated signatures of these waves provide a means of identifying and characterizing this novel phenomenon.

Charge Density Waves and Nonlinear Dynamics

This collection of research explores nonlinear dynamics, pattern formation, and time crystals, focusing on condensed matter physics. It represents a comprehensive overview of an active research area, highlighting key themes and potential research directions. The central theme is the study of systems driven far from equilibrium, leading to the emergence of complex patterns and collective behavior. A significant portion focuses on charge density waves (CDWs), their dynamics, and excitation via light. The collection emphasizes the study of collective modes, such as Higgs modes (amplitude modes), plasmons, and phonons.

Understanding how these modes are excited, coupled, and influenced by external stimuli like light is a key focus. A growing area of interest is the study of time crystals, systems exhibiting spontaneous breaking of time-translation symmetry, leading to periodic behavior without external driving. This collection suggests several active and potentially fruitful research directions. A major theme is using light to manipulate CDWs, potentially leading to new ways to control material properties and induce phase transitions. Understanding the dynamics of Higgs modes and their coupling to other collective modes like CDWs and phonons is a key area of interest, potentially leading to new insights into superconductivity and correlated phenomena.

The collection highlights the importance of understanding phase transitions occurring far from equilibrium, potentially leading to the discovery of new types of phase transitions and novel materials with unique properties. The growing interest in time crystals suggests a focus on understanding systems driven by periodic forces (Floquet systems) and their potential for creating new types of quantum devices. Investigating how symmetry is broken and patterns emerge in systems driven by external forces is a central theme. Exploring the connection between quantum and classical time crystals and understanding how they can be realized in different physical systems is an emerging area of research.

The collection suggests a strong connection between CDWs and Higgs modes, where the amplitude of a CDW can be viewed as an order parameter, and its fluctuations can give rise to a Higgs mode. Time crystals are often realized in driven systems, where the periodic driving breaks time-translation symmetry. In conclusion, this is a comprehensive collection of references reflecting the cutting edge of research in condensed matter physics, nonlinear dynamics, and the emerging field of time crystals. It highlights the importance of understanding systems driven far from equilibrium and the interplay between different collective modes and excitations. The collection suggests a wealth of opportunities for future research and the potential for discovering new materials and phenomena with unique properties.

Sustained Waves Emerge From Light-Matter Coupling

This research demonstrates the generation of sustained, spatially ordered waves within solid materials using short pulses of light, a phenomenon termed Faraday-Goldstone waves. Scientists discovered that, unlike typical waves driven by continuous forces, these waves persist long after the initial light pulse, arising from the interplay between the amplitude and phase of a symmetry-broken state within the material. The team developed a theoretical framework explaining how light-matter interactions create a dynamic coupling between these modes, resulting in emergent spatiotemporal order. Calculations accurately reflect measurements taken on a manganese oxide material, confirming the existence of these waves and predicting coherent energy exchange between the amplitude and phase modes. Importantly, the research reveals that these light-generated crystalline states exhibit remarkable robustness against thermal noise, even when the underlying Goldstone mode is unstable, suggesting a pathway to induce order in materials that are otherwise disordered by heat. Future work will likely explore these effects in greater detail and extend the theory to higher-dimensional systems, potentially unlocking new methods for designing materials with tailored spatiotemporal properties using ultrafast light pulses.