Beyond solid gas and liquid: Scientists have discovered a new state of matter where two exotic substances meet

Physicists at Rutgers University have discovered a quantum state that does not fit into solid, liquid, gas or plasma states. According to a report published in the journal Science Advances, this discovery did not emerge from a single substance but from the boundary where two unusual compounds meet.

The study involved combining Eu₂Ir₂O₇ with Dy₂Ti₂O₇. Eu₂Ir₂O₇ acts as a Weyl semi-metal, where electrical conduction occurs through Weyl fermions, an exotic type of particle-like electronic excitation, while Dy₂Ti₂O₇ acts as a magnetic insulator known as spin ice, where magnetic moments arrange themselves in a pattern similar to how hydrogen atoms form ice.

Both compounds are magnetic pyrochlores and have been extensively studied on their own; However, they had not been examined together until this study, conducted by first author Tsung-Chi Wu, who completed his PhD at Rutgers University in June.

The researchers recorded a hexagonal pattern in the material’s electrical conductivity at extremely low temperatures and high magnetic fields, with the weakening effect along six specific directions. They consider this phenomenon Kondo coupling, noting that the transition of the magnetic state of the spin ice changes how electrons scatter within the surface of the Weyl semimetal, which are also known as Fermi arc states.

As the magnetic field advances further, this hexagonal pattern also collapses into a double pattern, so-called rotational symmetry breaking, indicating a many-body state driven by interactions between larger numbers of particles than single particles.

Building the atom-thick heterostructure required a specially designed tool, the Q-DiP (Quantum Phenomena Detection Platform), which Chakalian’s team developed four years after previous experiments. The bulk of the recent measurements were made at the National High Magnetic Field Laboratory in Tallahassee, Florida, where extremely low temperatures and strong magnetic fields enabled the observations.

Meanwhile, Jedediah Pixley’s theoretical group, which included postdoctoral researcher Yueqing Zhang, spent more than two years developing models to interpret the experimental results. The results suggest that interfaces between different materials can give rise to physics not observed in any of the materials individually, a principle that researchers believe could pave the way for new ways to control electronic and magnetic properties.