In recent years, a phenomenon called the quantum Hall effect has emerged as a platform for hosting exotic features called quasiparticles, with properties that could lead to exciting applications in areas like quantum computing. When a strong magnetic field is applied to a 2D material or gas, the electrons at the interface, unlike the ones within the bulk, are free to move along the edges in what are called edge modes or channels—somewhat similar to highway lanes. This edge movement, which is the essence of the quantum Hall effect, can lead to many interesting properties depending on the material and conditions.
For conventional electrons, the current flows only in one direction dictated by the magnetic field ('downstream'). However, physicists have predicted that some materials can have counter-propagating channels where some quasiparticles can also travel in the opposite ('upstream') direction. Although these upstream channels are of great interest to scientists because they can host a variety of new kinds of quasiparticles, they have been extremely difficult to identify because they do not carry any electrical current.
In a new study, researchers from the Indian Institute of Science (IISc) and international collaborators provide "smoking gun" evidence for the presence of upstream modes along which certain neutral quasiparticles move in two-layered graphene. To detect these modes or channels, the team used a novel method employing electrical noise—fluctuations in the output signal caused by heat dissipation.
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