Condensed matter physicists have long been fascinated by fractionalization, a phenomenon in which a collective state of electrons carries a charge that is a fraction of the electron charge, even in the absence of a magnetic field. This observation, although the electron itself remains indivisible, points to the intriguing possibility of strong interaction among electrons leading to non-trivial effects. Beyond the intellectual interest it presents, fractionalization could also have significant implications for new technological applications such as quantum computing. In a recent study published in Physical Review Letters, the Kim Group proposes a novel theory for achieving fractionalization without the need for a magnetic field. This article explores the groundbreaking research and its potential implications.
Traditionally, physicists have achieved fractionalization by employing magnetic fields to suppress kinetic energy, thereby enhancing interaction effects and observing the fractional quantum Hall effect in two-dimensional systems. However, this approach is limited by the requirement of specialized laboratories equipped with strong magnetic fields, prompting scientists to seek alternative strategies for achieving fractionalization. In this regard, the Kim Group breaks new ground by leveraging the geometric properties of twisted bilayer graphene (TBG) lattice to predict new effects. Unlike previous studies that primarily focused on magnetic systems, the Group’s approach introduces geometric insights to study charge distribution, utilizing the unique characteristics of electron wave functions in TBG.
One defining aspect of electrons in twisted bilayer graphene is that their wave functions cannot be confined to a single lattice site, but rather are spread across multiple moiré lattice sites. Moreover, the wavefunction’s distribution forms an anisotropic, three-leaf clover shape. Exploiting these properties, the researchers propose the existence of fractional correlated insulator phases characterized by the following key properties:
In these novel phases, excitations (or particles) carry fractional electric charges, a highly unusual and distinctive feature of fractionalization. This fractionalization challenges the conventional notion that the electron charge is indivisible, opening up new possibilities for exploring the fundamental nature of charge transport and manipulation.
Another intriguing aspect of the proposed fractionalization in TBG systems is the concept of “fractonic” excitations. Unlike conventional particles, these excitations can only move in specific directions, leading to intriguing possibilities for controlling and manipulating their behavior. Additionally, the researchers have identified an emergent symmetry that plays a crucial role in unifying the behavior of fractional excitations in these phases. This emergent symmetry introduces a new theoretical framework for understanding the dynamics of fractonic particles and their collective behavior.
The research conducted by the Kim Group illuminates a previously unexplored realm of physics by providing the first physical setting for investigating emergent symmetries and fractonic dynamics. The study’s findings offer immense potential for advancing our understanding of new theoretical concepts and for developing novel technological applications. While the current work represents just the tip of the iceberg, the researchers are actively collaborating with experimental colleagues to confirm their predictions and further explore the possibilities presented by fractionalization in condensed matter systems.
The quest for observing fractionalization in condensed matter systems without the need for a magnetic field has taken a significant leap forward with the research conducted by the Kim Group. By harnessing the unique geometric properties of twisted bilayer graphene, the researchers have proposed the existence of fractional correlated insulator phases characterized by fractonic excitations and emergent symmetries. These novel findings not only deepen our understanding of fundamental physics but also open up exciting avenues for technological advancements in fields such as quantum computing. The future looks promising as scientists continue to push the boundaries of condensed matter physics and uncover the mysteries of fractionalization.