Development of Chiral Charge Density Wave Devices

Drexel University, Philadelphia PA

Investigators

Abstract

The goal of this proposal is to extend our fundamental understanding of the properties of chiral charge density wave materials and utilize its properties in new opto-electronic devices. Manipulation of chiral charge domains will be transformative to the condensed matter physics and it will open the doors to devices based on collective electron excitations. The main advantage of using collective charge systems for electronics is lower power dissipation, high density of information storage and high speed. The fundamental studies will involve both macroscopic electronic and optical properties characterization and atomic scale investigations of the chiral charge density wave properties in carefully engineered two-dimensional materials and devices. The program will provide students and young researchers with necessary tools to carry out modern fundamental research in the fields of materials science, condensed matter physics and optoelectronic device engineering. Since the designed research activities are highly interdisciplinary, the students will be stimulated to take classes across disciplines, such as nanoscience, electron and scanning probe microscopy and nanofabrication. The plan is to broaden participation and appreciation of students through (a) incorporating elements of the research in existing nanoscience, nano-electronics and solid-state physics courses at both the undergraduate and graduate level; (b) train students to use state of the art fabrication and characterization tools and (c) expose the students to research enterprise and collaborative research across different organizations. This work should lead to training a PhD student and several undergraduate students. Outreach to local area high schools through senior thesis work experience and science research clubs as well as College' s open houses are part of the overreaching strategy to prepare high school students to pursue science and engineering degrees. Chirality breaks down the spatial inversion symmetry and results in unexpected new electronic properties, in particular in systems with reduced dimensionality. In many cases the electronic chirality is facilitated by the specific structure of the system in which it emerges, either on atomic scale or on mesoscopic scale. Recently, it was discovered that one of the well-studied macroscopically correlated electronic state, the charge density wave, also exhibits chiral properties. This proposal explores the opportunity to use the nanometer-size domains of opposite chirality that are separated with domain walls as basic elements for memory and logic units. In this proposal we will expand the fundamental understanding of the dynamic nature of the coupling of the chiral CDW with femtosecond optical perturbations and nanosecond current pulses. The dynamics of the excited metastable states through which the system traverses before coming back to equilibrium could include unconventional order such as ferroelectricity, CDW or superconductivity. The origin of these phenomena is in the existence of various types of symmetry breaking (inversion symmetry in TiSe2) that gives rise to degenerate ground states. The opportunity exists to exploit these metastable states in low power electronic devices. We will also optimize the growth of TiSe2 thin films in order to enable efficient device fabrication. The effect on strain and doping on chiral CDW thermodynamics will be explored.