Graphene’s Nonlinear Electron Flow Creates Analog Spacetime and Acoustic Horizons

The quest to understand gravity and the universe often leads researchers to unexpected places, and a new study demonstrates how materials can mimic the behaviour of spacetime itself. Surajit Das from the University of Science and Technology of China, Surojit Dalui from Shanghai University, and Hrishit Banerjee from the University of Dundee, along with colleagues, reveal how nonlinear interactions within a special class of materials called topological materials create dynamic environments that resemble the curved spacetime around black holes. Unlike previous work focusing on simplified scenarios, this research develops a complete mathematical description of these interactions, showing how they generate evolving acoustic horizons and even predict the emission of heat, similar to Hawking radiation. This breakthrough suggests topological materials offer a powerful, experimentally viable platform for investigating complex gravitational phenomena and could ultimately bridge the gap between condensed matter physics and our understanding of the cosmos.

Emergent spacetime analogs in condensed matter systems have opened a fascinating window into simulating aspects of gravitational physics in controlled laboratory environments. This approach allows researchers to investigate phenomena that are otherwise inaccessible due to the extreme conditions or scales involved in astrophysical observations. Therefore, a need exists for more sophisticated analog systems that can accurately replicate a wider range of gravitational phenomena and provide new insights into fundamental physics. This work develops a comprehensive nonlinear analog gravity framework, aiming to address these limitations and provide a platform for exploring complex gravitational effects in a laboratory setting.

Condensed Matter Analogues of Black Hole Physics

Researchers are exploring the creation of “analog black holes” and “analog Hawking radiation” within condensed matter systems, using materials with properties that mimic the behavior of spacetime around black holes. This allows them to investigate quantum gravity and black hole physics without directly observing astrophysical black holes. Concepts from quantum mechanics, such as Berry phase and Berry curvature, describe the geometric phase acquired by a quantum system and act as an effective gravitational field for quasi-particles, collective excitations within the material. Topological insulators and Dirac materials, with their unique electronic properties and massless quasi-particles behaving like particles moving at the speed of light, are ideal for creating these analogs.

Researchers manipulate materials to create an effective spacetime metric that mimics the curvature of spacetime around a black hole, controlling the speed of quasi-particles and forming an event horizon, a boundary beyond which nothing can escape. Researchers employ Density Functional Theory (DFT) and VASP to model materials and predict their properties. They perform numerical simulations to model the behavior of quasi-particles and calculate the Hawking radiation, emphasizing the role of Berry curvature in creating the effective gravitational field and event horizon. The primary goal is to identify or design materials that exhibit the necessary properties to create an effective spacetime metric with an event horizon, and to simulate or experimentally observe the emission of Hawking radiation from the analog black hole. They aim to understand how Berry curvature contributes to the formation of the event horizon and the emission of Hawking radiation, testing theoretical predictions about Hawking radiation and quantum gravity in a laboratory setting.

Acoustic Spacetime Simulation in Graphene

Researchers have demonstrated a novel framework for simulating aspects of gravitational physics within condensed matter systems, specifically using topological materials like graphene. This work moves beyond previous studies by developing a comprehensive, nonlinear model that accurately captures the complex behavior of fluid-like electron flows influenced by the material’s unique electronic properties, including Berry curvature. The team’s approach generates an “acoustic metric” within the material, allowing them to model phenomena typically associated with gravity. The core of this research lies in the creation of a fully nonlinear wave equation that governs how density and velocity fields change within the material, dynamically forming acoustic horizons, analogous to the event horizons of black holes.

Importantly, these calculated temperatures, reaching tens of microkelvins, fall well within the reach of current experimental detection techniques, opening the door to direct observation of these effects. This new framework differs significantly from earlier approaches that relied on linear approximations, which often oversimplify the complex interactions within these materials. By retaining all nonlinear contributions, the model accurately captures rich dynamics, including oscillating horizons and frequency-dependent causal structures, offering a more realistic simulation of gravitational phenomena. The researchers observed unique behaviors, such as horizon recession under specific perturbations, which have no direct counterpart in classical black hole physics, highlighting the potential for discovering new physics through these analog systems. The implications of this work extend beyond simply simulating black holes; it establishes topological materials as versatile platforms for probing a wide range of gravitational phenomena, including horizon formation and analog Hawking radiation. This research paves the way for exploring nonlinear emergent spacetime in a broad class of materials, offering a novel avenue for investigating the mysteries of the universe

Graphene Simulates Gravity and Hawking Radiation

This work establishes a comprehensive nonlinear framework for simulating aspects of gravity using electrons in topological materials, notably graphene. Researchers developed a mathematical model describing how disturbances propagate through these materials, demonstrating the formation of evolving acoustic horizons, boundaries beyond which signals cannot escape, and quantifying the resulting analog Hawking temperatures. These temperatures, reaching tens of micro-kelvin under realistic conditions, are within the range of current experimental capabilities, offering a promising avenue for laboratory investigation of phenomena typically associated with black holes. The study extends beyond previous research by incorporating the impact of Berry curvature and by formulating a fully nonlinear wave equation.

This allows for a more accurate representation of complex gravitational effects, including dynamic horizons and frequency-dependent signal propagation. While acknowledging the complexity of fully replicating gravitational systems, the authors highlight the potential of topological materials as versatile platforms for exploring fundamental concepts in gravitational physics. Future research could focus on experimentally verifying these predictions and extending the framework to investigate other nonlinear spacetime phenomena