Physicists at Rutgers University have identified a quantum state that fits into none of the four familiar categories of solid, liquid, gas, or plasma. Reported in Science Advances, the discovery emerged not from a single material, but from the boundary where two exotic ones meet.
Eu₂Ir₂O₇ was combined with Dy₂Ti₂O₇. While Eu₂Ir₂O₇ is a Weyl semimetal in which electrons conduct through Weyl fermions, an exotic form of particle-like electronic excitation, Dy₂Ti₂O₇ is a magnetic insulator referred to as spin ice, in which magnetic moments order similarly to how hydrogen atoms form ice.
The two compounds are magnetic pyrochlores and have been extensively researched independently but not yet together before this study done by first author Tsung-Chi Wu, whose doctorate he obtained from Rutgers in June.
At extremely low temperatures and high magnetic fields, the researchers recorded a sixfold pattern in the material’s electrical conductivity, which was weakest along six specific directions.
They attribute this to Kondo coupling, in which the shifting magnetic state of the spin ice alters how electrons scatter within the Weyl semimetal’s surface, known as Fermi-arc states.
As the magnetic field increased further, that sixfold pattern collapsed into a twofold one, a phenomenon called rotational symmetry breaking, pointing to a many-body state driven by interactions among large numbers of particles rather than individual ones.
Creating the atoms-thick heterostructure required a purpose-built instrument, the Q-DiP, or quantum phenomena discovery platform, developed after four years of prior experimentation by Chakhalian’s team.
Most of the latest measurements were carried out at the National High Magnetic Field Laboratory in Tallahassee, Florida, where ultra-low temperatures and intense magnetic fields made the observations possible.
Jedediah Pixley’s theory group, including postdoctoral researcher Yueqing Chang, spent more than two years modelling the results to explain what the experimental data showed.
The findings suggest interfaces between dissimilar materials can host physics not present in either material alone, a principle researchers say could inform new approaches to controlling electronic and magnetic behaviour.
Wu said the team plans to continue exploring heterostructures built from other combinations of quantum materials, calling the current findings “just the beginning” of a broader research direction at Rutgers.
