CAREER: FRACTAL ELECTRONIC TEXTURES IN QUANTUM CRITICAL SOLIDS

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Non-technical Abstract: For over a century, the understanding and description of critical phenomena posed a significant challenge. More recently, the hallmarks of criticality have been found in solids where quantum fluctuations play a central role. In such solids, fractal organization was proposed, with self-similar structures and patterns akin to those displayed by snowflakes or rugged shorelines. Imaging these electronic fractals is challenging because of the need to explore multiple length scales spanning the nanometer to millimeter range. In this study we use a recently-developed X-ray nanoscope of very high accuracy. The goal is to reveal the unifying traits of quantum critical matter. In a broader context, the understanding and control of quantum phases of matter, such as superconductivity, is a stepping stone toward the development of future quantum technologies, quantum computing, efficient energy transport, and powerful medical scanners. On the educational front, this project aims to engage undergraduate and graduate students in basic and advanced X-ray science. Activities include field trips to national facilities and the development of new academic tools and modules. These initiatives serve a broad base of participants, including college students and middle/high school teachers, with a focus on underrepresented groups. Technical Abstract: Quantum solids exhibit collective phases of matter that cannot be found in ordinary metals or semiconductors, engendering technologically-relevant properties such as high-temperature superconductivity, colossal magnetoresistance, and magnetoelectricity. Some of these phenomena appear near a quantum critical point, where electrons tend to organize into self-similar patterns that look the same at all length scales. The resulting fractal geometries are a hallmark of quantum criticality and unfold in the form of inhomogeneous electronic textures with spatially-modulated spin and charge distributions. Imaging these textures is a pressing experimental challenge, which requires probing a broad range of length scales. While these electronic orders often escape detection by conventional diffraction, they can be measured using resonant X-ray scattering. The recent development of a resonant X-ray nanoprobe (with a spatial resolution better than 100 nm) offers a unique tool to visualize the nanoscale texture of electronic orders and reveal emergent charge/spin fractal patterns in quantum critical solids. Three known quantum critical systems are investigated: cuprates, nickelates, and chalcogenides, whose electronic phases can be tuned by doping, pressure/strain, and composition, respectively. The primary goal of this research is to disclose the fractal nature of the electronic fabric in systems manifesting distinct forms of electronic orders in the quantum critical regime. This project is executed in close collaboration with light source facilities, and fulfils a crucial educational mission geared toward the training of students and teachers in the field of X-ray science, using in-house and large-scale facilities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.