Physicists uncover a breakthrough material in bosonic matter

By overlapping lattices of tungsten diselenide and tungsten disulfide in a twisted configuration known as a moiré pattern, they created a highly ordered crystal of bosonic particles called excitons, resulting in a new state of matter termed a “bosonic correlated insulator.”

What sets bosons apart from fermions is their distinct behavior. While fermions avoid occupying the same energy level, bosons readily share the same energy level, giving rise to their peculiar characteristics.

According to Professor Chenhao Jin, a condensed matter physicist at UCSB, “Bosons can occupy the same energy level; fermions don’t like to stay together. Together, these behaviors construct the universe as we know it.”

The key to understanding these distinctive behaviors lies in the quantum mechanical traits of fermions and bosons. Fermions possess half-integer spins (e.g., 1/2 or 3/2), while bosons exhibit whole integer spins (1, 2, etc.). In the case of excitons, negatively charged electrons (fermions) bind to positively charged “holes” (also fermions), resulting in their collective spins combining to form a whole integer, thus creating a bosonic particle.

To observe and identify excitons within the material, the researchers employed a ” pump-probe spectroscopy technique.” They layered the two lattices and subjected them to intense light; the researchers stimulated the creation and interaction of excitons. This method provided a favorable environment for the excitons to manifest and allowed for investigating their behavior.

Remarkably, as the density of excitons increased, they became immobile due to strong interactions, resulting in a highly ordered crystalline state and an insulating effect. The correlation between these bosonic particles at a specific density compelled them to organize into a symmetric solid and charge-neutral insulator. This discovery marks the first time such a material has been created in a real-world matter system rather than a synthetic one.

Richen Xiong, a graduate student researcher in Jin’s group and the lead author of the study published in Science, emphasized their findings’ significance: “What happened here is that we discovered the correlation that drove the bosons into a highly ordered state. We’ve created a platform to study bosons in real materials, which was previously lacking.”

Paving the way for exploring novel bosonic materials

By harnessing the moiré platform and pump-probe spectroscopy, this breakthrough could pave the way for developing and exploring novel bosonic materials. Jin highlights the potential implications: “There are many-body phases with fermions that result in superconductivity. There are also many-body counterparts with bosons that are also exotic phases. So we’ve created a platform to study bosons and open up new possibilities for understanding condensed matter physics.”

This groundbreaking discovery not only unravels the mysteries of bosonic materials but also provides insights into the peculiar properties observed in various substances. The researchers aim to delve deeper into the rich behaviors exhibited by these materials and uncover ways to harness them more reliably.