Scientists revealed previously unobserved and unexpected FQH states in monolayer graphene that raise new questions regarding the interaction between electrons in these states.
In the 14 years since its discovery, graphene has amazed scientists around the world with both the ground-breaking physics and technological potential it displays. Recently, scientists from Penn State University added to graphene's gallery of impressive scientific achievements and constructed a map that will aid future exploration of this material. This work is emblematic of the large number of university-based materials research efforts that use the MagLab to explore the frontiers of science.
Decades ago a mechanism was proposed that described a quantum phase transition to an insulating ground state from a semi-metal (excitonic insulator, or EI) using very similar mechanics to those found in the BCS description of superconductivity. The discovery of this transition to an EI in InAs/GaSb quantum wells is striking not only for the long-sought experimental realization of important physics, but also the presence of recently proposed topological behavior.
Physicists prove a 30-year-old theory — the even-denominator fractional quantum Hall state — and establish bilayer graphene as a promising platform that could lead to quantum computation.
Two independent research teams observed same behavior in double bilayer graphene.
Discovering previously unobserved quantum states nested inside the quantum Hall effect in a single-layer form of carbon known as graphene, researchers have found evidence of a new state of matter that challenges scientists' understanding of collective electron behavior.
New kind of quantum Hall state observed in graphene superlattices.
Studies of the magnetotransport of strongly interacting 2D holes in high mobility, gated, GaAs quantum wells have been carried out a very low temperatures to search for possible anisotropy in the field-induced re-entrant insulating phase. The latter phase was observed in the resistivity at a magnetic field that depended on hole density but that was independent of current direction. This shows that the re-entrant insulating phase is not due to a proposed anisotropic stripe order, but is instead caused by Wigner crystallization.
The work by Chen et. al. explores the quantum hall effect (QHE) that develops in BiSbTeSe2 at low temperatures and high magnetic fields. BiSbTeSe2 is a topological insulator, meaning it is a bulk insulating material that at low temperatures develops a quantum mechanical state that allows conduction of electrons at the surface similar to a metal. The observation of the QHE in BiSbTeSe2 is further confirmation of the theory governing these unique materials.
New physics has had to be invoked to explain the existence of exotic quantum Hall states such as the n =5/2 and 7/2 states. Recent progress in fabrication of high-quality low-density samples allows one to probe these states in a new regime where the electron-electron interactions are strong. The results reveal the existence of anisotropic transport for n = 7/2 in a high-quality very dilute 2D electron system. The new behavior is attributed to a large Landau level mixing effect that perturbs the pairing stability of composite fermions in the dilute limit.