Quest for Fractionalization in Condensed Matter Physics
Many condensed matter physicists harbor a dream of witnessing fractionalization. In this phenomenon, a collective state of electrons carries a charge that is a fraction of the electron charge without a magnetic field.
The Concept of Fractionalization
Eun-Ah Kim, a professor of physics at the College of Arts and Sciences (A&S), clarifies that fractionalization does not involve splitting the electron into pieces.
Instead, it consists of a group of electrons behaving as if they carry a charge deficit that is merely a fraction of an electron’s charge. This observation represents a pinnacle of non-trivial effects stemming from solid electron interactions.
Kim emphasizes that achieving states with fractional charge is not solely a matter of intellectual curiosity. It holds significant potential for innovative technological applications, particularly in quantum computing.
A Theoretical Breakthrough
Researchers in the Kim Group have proposed a way to achieve fractionalization without a magnetic field. Their findings are elucidated in the “Fractionalization in Fractional Correlated Insulating States at n ± 1/3 Filled Twisted Bilayer Graphene” paper published in Physical Review Letters.
The lead author of this research is Dan Mao, a Bethe/Wilkins/Kavli Institute at Cornell (KIC) postdoctoral fellow in the Laboratory of Atomic and Solid State Physics (LASSP), with co-authors including Kim and doctoral student Kevin Zhang.
Magnetic Fields and the Quest for Fractionalization
In prior investigations, physicists attained fractionalization by utilizing magnetic fields to suppress kinetic energy, amplifying interaction effects, and achieving the celebrated fractional quantum Hall effect in two-dimensional systems.
However, the limited availability of strong magnetic fields in specialized laboratories has prompted the search for alternative strategies to realize fractionalization without relying on magnetic fields.
Leveraging Geometric Insights in Twisted Bilayer Graphene
The Kim Group has taken an innovative approach by leveraging geometric insights within a twisted bilayer graphene (TBG) lattice to predict new effects.
While geometric thinking is common in studies of magnetic systems, it has yet to be previously applied to the study of charge distribution due to the typically isotropic nature of electron wave functions centered at lattice sites.
In twisted bilayer graphene, electrons exhibit unique characteristics. Their wave functions are not confined to a single lattice site but are spread across multiple moiré lattice sites, assuming an anisotropic, three-leaf clover shape.
Characterizing Fractional Correlated Insulator Phases
The researchers propose the existence of fractional correlated insulator phases within moiré graphene systems, marked by the following fundamental properties:
- Excitations carry fractional electric charges, a hallmark of fractionalization.
- Some fractional excitations exhibit “fractonic” behavior, limited to specific movement directions.
- An emergent symmetry, crucial for unifying the behavior of fractional excitations in these phases, has been identified.
Future Endeavors
Kim says this discovery sets the stage for exploring novel theoretical concepts related to emergent symmetries and fractional dynamics within a physical context. Collaborating with experimental colleagues to validate these predictions, the researchers report promising preliminary results.
Kim concludes that this research represents just the beginning of a journey into uncharted territory. With a tangible framework for studying emerging theoretical concepts, exploring measurable properties, such as emergent symmetries and fractional dynamics, is poised to expand our understanding of the quantum world.
Read the original article on PHYS.
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