Probing Fractional Statistics and Correlated States in Cleaved-Edge Devices

Duke University, Durham NC

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** The behavior of systems composed of electrons interacting with other electrons can change dramatically when confined to spatial dimensions less than the familiar three dimensions in which we live. For example, in a two-dimensional world, placing the interacting electrons in a very strong magnetic field creates unusual matter, which contains new entities with a fraction of the electron charge. Moreover these new entities, called "quasi-particles," behave neither as particles of light (photons) nor as electrons. Photons are bosons, and bosons like to aggregate, making it possible to build lasers. However, electrons like to avoid each other; leading to the known quantum-mechanical behaviors of solids such as conductors, semiconductors, and insulators. The new quasi-particles are neither bosons nor fermions, and obey a new type of quantum statistical behavior called fractional statistics. Using specially created semiconductor devices this project will probe the electrical conduction properties of these unique systems. A related topic will be the study of new states of matter with a new type of ordering, very different from familiar ordering such as the alignment of spins, responsible for the magnetism in iron. Understanding these new behaviors may enable us to design new types of superconductors, and pave the way to more robust quantum computers, which are much less sensitive to environmental interference. Additionally very narrow one-dimensional superconducting wires will be investigated to ascertain their robustness, providing a better understanding of their potential application as interconnects in ultra dense circuitry. Graduate and undergraduate students working on these projects will be trained in state-of-the-art semiconductor processing, and on ultra sensitive electrical measurements, to prepare them for careers in academia or industry. At the same time, the outreach component will introduce K-12 students to important concepts such as charge, current, spins, superconductivity, and statistics of particles. **** TECHNICAL ABSTRACT**** This program seeks to elucidate unusual properties of correlated electronic systems in reduced dimensions. Such systems are created in special devices on the cleaved-edge of semiconductor crystals. The emergence of new properties, such as fractional statistics of fractionally-charged quasi-particles, and unusual underlying quantum orders of correlated states, will be investigated. In the two-dimensional fractional quantum Hall states, measuring the temporal correlation of the noise in the electrical currents injected into different collectors from a single coherent source is expected to yield evidence indicative of fractional statistics, intermediate between the familiar bosonic and fermionic statistic in three-dimensional systems for photons and electrons, respectively. Alternatively, studying the magnetic field period of the Aharonov-Bohm quantum interference modulation could reveal unusual topological quantum orders in the wave functions of the Pfaffian fractional quantum Hall states. Uncovering such properties helps bring a greater understanding of a new type of superconductivity termed "anyon superconductivity," and may enable future realization of topological quantum computation, a scheme largely free from decoherence effects. Additionally, very narrow one-dimensional superconducting wires will be investigated to probe the existence of new quantum phase transitions. Investigating the behaviors of ultra narrow superconducting wires will provide a better understanding for their potential application as interconnects in ultra dense circuitry. Graduate students and undergraduate students will be trained in state-of-the-art semiconductor processing and ultra sensitive electrical measurements. The training received will prepare them for careers in academia or industry. At the same time, the outreach component will introduce pre-college students to modern concepts such as quantum mechanics and statistics of particles.