Breakthrough Discovery: Graphene's Electrons Form Nearly Perfect Quantum Fluid

Researchers at the Indian Institute of Science (IISc) have observed electrons in graphene behaving as a nearly perfect quantum fluid, challenging the long-standing Wiedemann-Franz law and opening new avenues for quantum research.

By creating ultra-clean graphene samples, the IISc team discovered a decoupling of heat and charge transport, particularly near the "Dirac point," where electrons exhibited ultra-low viscosity akin to quark-gluon plasma. This finding not only advances our understanding of quantum materials but also provides a platform for studying complex phenomena like black holes and quantum entanglement in laboratory settings.

Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, has garnered immense interest due to its exceptional electrical, thermal, and mechanical properties. Its electrons behave as massless Dirac fermions, leading to unique quantum behaviors.

In certain conditions, electrons in materials can exhibit collective behaviors characteristic of quantum fluids. These fluids are governed by quantum mechanics and can display properties like superfluidity and ultra-low viscosity. The quark-gluon plasma, a state of matter believed to have existed shortly after the Big Bang, is an example of such a nearly perfect quantum fluid.

The Wiedemann-Franz law states that the ratio of thermal conductivity to electrical conductivity in metals is proportional to temperature, implying a constant Lorenz number. This law holds for conventional metals where heat and charge are carried by the same particles—electrons.

However, in systems where electron interactions are strong, such as in the Dirac fluid regime of graphene, this law can break down. Studies have shown that in graphene, especially near the charge neutrality point (Dirac point), the Lorenz number deviates from the expected value, indicating a decoupling of heat and charge transport. This violation suggests that thermal and electrical conductivities are influenced by different scattering mechanisms and interactions in such regimes.

The IISc research team achieved this discovery by creating ultra-clean graphene samples, minimizing impurities that could obscure intrinsic electronic behaviors. By cooling these samples to temperatures where quantum effects dominate, they observed electrons forming a nearly perfect quantum fluid. Notably, near the Dirac point, the electrons exhibited ultra-low viscosity, a hallmark of such fluids.

This behavior mirrors that of the quark-gluon plasma, where quarks and gluons move with minimal resistance. The similarity suggests that graphene can serve as a tabletop model for studying complex quantum phenomena, including aspects of high-energy physics and cosmology.

The IISc's findings have profound implications:

• Fundamental Physics: Understanding the behavior of electrons in graphene as a quantum fluid can shed light on other strongly correlated systems and deepen our comprehension of quantum mechanics.
• Technological Applications: Insights into the decoupling of heat and charge transport can inform the design of advanced electronic devices, potentially leading to more efficient thermal management and novel functionalities.
• Cosmology and High-Energy Physics: The parallels between graphene's electron behavior and quark-gluon plasma open avenues for simulating and studying early universe conditions and black hole physics in laboratory settings.

Previous studies have indicated the potential for graphene to exhibit hydrodynamic behaviors and violate the Wiedemann-Franz law. For instance, research published in 2016 observed the Dirac fluid in graphene and its deviation from the Wiedemann-Franz law. The IISc's recent discovery builds upon these findings by providing more direct evidence of ultra-low viscosity and the formation of a nearly perfect quantum fluid, marking a significant advancement in the field.

The IISc's groundbreaking discovery of electrons in graphene behaving as a nearly perfect quantum fluid not only challenges existing physical laws but also opens new frontiers in both fundamental physics and technological applications. This research underscores the versatility of graphene as a platform for exploring complex quantum phenomena and its potential to bridge gaps between condensed matter physics and cosmology.