Quantum noise experiments reveal unusual liquidlike form of charge transport in “strange metals
In a groundbreaking study published in the journal Science, physicists at Rice University have discovered compelling evidence of exotic charge transport in a quantum material known as a “strange metal.” The research provides new insights into the nature of electricity flow in these materials, challenging conventional theories of quantized charge transport. By measuring quantum charge fluctuations, known as “shot noise,” the study reveals that charge in strange metals moves in a highly unusual liquidlike form, suggesting the presence of complex collective charge movement.
Exploring Quantum Critical Materials:
The experiments were conducted on nanoscale wires made of a quantum critical material with a precise composition of ytterbium, rhodium, and silicon (YbRh2Si2). This material has been extensively studied by solid-state physicist Silke Paschen at the Vienna University of Technology. Quantum critical materials exhibit unique temperature-dependent behaviors that differ significantly from those observed in normal metals like silver or gold. The high degree of quantum entanglement in these materials gives rise to their intriguing properties.
Challenging the Quasiparticle Picture:
In normal metals, charge is carried by quasiparticles, which are the result of countless interactions between electrons. However, theoretical studies have suggested that strange metals may not rely on quasiparticles for charge transport. The shot noise experiments conducted by Rice University researchers provided the first direct empirical evidence to test this idea. Shot noise measurements reveal the granularity of charge as it flows through a material, and the results showed that the noise in strange metals is significantly suppressed compared to ordinary wires.
Performing shot noise experiments on YbRh2Si2 crystals presented significant technical challenges. The experiments required samples of nanoscopic dimensions, which meant growing extremely thin yet perfectly crystalline films. After nearly a decade of hard work, Paschen and her collaborators at TU Wien successfully achieved this feat. The lead author of the study, Liyang Chen, then fashioned wires from these thin films that were about 5,000 times narrower than a human hair, ensuring the preservation of the material’s unique properties.
Theoretical Perspectives and Future Implications:
Rice University’s lead theorist, Qimiao Si, collaborated with Paschen and Douglas Natelson of Rice University to design the experiments. Si’s theory of quantum criticality, published in 2001, provided the framework for interpreting the results. Si’s calculations ruled out the existence of quasiparticles in strange metals, further supporting the experimental findings. The study’s authors believe that the low shot noise observed in YbRh2Si2 opens up new avenues for understanding the entanglement of charge carriers and other agents of quantum criticality. The broader question remains: could similar behavior be observed in other compounds that exhibit strange metal behavior?
The discovery of exotic charge transport in strange metals represents a significant breakthrough in the field of quantum materials. The suppressed shot noise observed in YbRh2Si2 provides compelling evidence that the traditional quasiparticle picture may not fully explain charge transport in these materials. The findings challenge our understanding of how charge moves collectively and calls for a reevaluation of the vocabulary used to describe these phenomena. As researchers continue to explore the nature of strange metals, the hope is to uncover the underlying principles that govern their unique behavior, which may have implications for a wide range of physical systems.