Dragana Popovic - US grants

9510355 Popovic During the grant period several problems in quantum insulators will be explored on small Si metal-oxide-semiconductor field-effect transistors fabricated at IBM. Issues that will be studied include: (1) Kondo impurity vs Coulomb blockade in disordered hopping and tunneling systems, (2) statistics of localized states and noise in correlated insulators, (3) lineshape of resonance peaks in correlated insulators, (4) direct measurement of resonant tunneling and hopping conduction via two different paths, (5) Hall effects and magnetic field driven metal-insulator transitions in Kondo systems, (6) length scales associated with quantum interference in correlated insulators. The experiments will comprise linear and non-linear transport meassurements in zero magnetic field and in non-zero field. Equilibrium and shot noise experiments will be analyzed in terms of recent theoretical developments about noise and the response of correlated systems to shed new light on the problem of correlated electron transport in quantum insulators. %%% During the period of this award, recently discovered behavior in very short transistors that cannot be understood in terms of the conventional physics of electronic devices will be explored through a variety of experiments. The research will be centered on electronic quantum transport (discrete moverment of electrons) in submicron-size silicon transistors (one micron = 40 millionths of an inch). One focus of this effort will be nonlinear effects (the quality which gives any transistor the ability to amplify), which are also significant for a wide variety of applications. This research project will be a university-industry collaboration among three institutions: the measurements will be performed at the City College of CUNY and the University of North Carolina at Chapel Hill, and the transistors will be fabricated at t he IBM T. J. Watson Research Center. ***

This project from a female assistant scientist at Florida State University and the Natioanl High Magnetic Field Laboratory will focus on the study of low-temperature transport in Si metal-oxide-semiconductor field-effect transistors (MOSFETs). The two-dimensional electron system in Si MOSFETs exhibits a metal-insulator transition that is still unexplained. The experiments will lead to a deeper characterization of the insulator, the metal, and the transition. The project will include measurements of long-time relaxation of electronic states in the insulating phase, studies of the role of the spin degrees of freedom in the metallic behavior, studies of the effects of the variation in the screening length on all different regimes, and the effects of different types of disorder. The experiments will be carried out in both large and mesoscopic
MOSFETs. The studies will be compared to the proposed theoretical models. The results of this research are
expected to further stimulate and constrain theories of the metal-insulator transition, and greatly improve
understanding of highly correlated systems in general. Graduate students involved in the project will receive
training in a variety of experimental techniques. This training will prepare them for a wide range of careers
in the areas of science and technology.
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Many of the novel materials with potentially great technological importance, find themselves close to the metal-insulator transition. In all of the relevant examples, ranging from the long-known doped semiconductors to recently discovered high temperature superconductors, the metallic state is created by
chemically doping an otherwise insulating material. Understanding the nature of the metal-insulator
transition thus represents an important issue for materials science and technology. It also presents a fundamental problem in condensed matter physics. This project from a female assistant scientist at Florida State University and the Natioanl High Magnetic Field Laboratory will focus on the study of the metal-insulator transition in a two-dimensional electron system. The measurements will lead to a deeper characterization of the insulator, the metal, and the transition, and they will provide an experimental test of the numerous competing theories. The results of this research are expected to further stimulate and constrain theories of the metal-insulator transition. Graduate students involved in the project will receive training in a variety of experimental techniques. This training will prepare them for a wide range of careers in the areas of science and technology.
***

This award will provide partial support for the International Society for Optical Engineering (SPIE) International Symposium on Fluctuations and Noise, to be held at Maspalomas, Gran Canaria Island, Spain, May 26-28, 2004. The Conference Chairwoman is Professor Dragana Popovic, Florida State University. This is only the second conference of its type, which addresses the study of materials by noise and stochastic techniques. Areas of interest include noise as a probe of glass transitions and glassy states, noise in metal-insulator transitions, shot noise as a probe of conduction mechanisms, and noise in domain dynamics, Barkhausen noise. A session on soft materials will also be included. The European venue ensures strong participation by European scientists who have been leaders in this emerging research field. The NSF support will assist the attendance of approximately 10 graduate students, postdocs, or junior faculty. Participation in the Conference will expose these young scientists to unique information and techniques that allow the dynamics of materials, particularly strongly correlated electron materials to be characterized.

****NON-TECHNICAL ABSTRACT****
In many materials with potentially great technological importance, such as high temperature superconductors, the electrically conducting state is created by chemically doping an otherwise insulating material. Therefore by varying a parameter, one is able to change a material from one that conducts electricity to one that does not (an insulator) and vice versa. Understanding the nature of this conductor-insulator transition represents an important issue for materials science and technology. It also presents a fundamental problem in condensed matter physics. Furthermore, many studies have shown striking similarities in the behavior of systems close to a conductor-insulator transition and those of various glassy materials, the understanding of which also presents one of the deepest and most interesting problems in physics. Glassy behavior is exhibited by many different types of materials, including window glasses, metals doped with magnetic impurities, polymers, gels, etc., all of which have a wide range of current and potential applications. This award supports a project that will address the problem of complex, glassy behavior near the conductor-insulator transition by performing electrical transport and noise measurements on semiconductor devices and high temperature superconductor materials. The anticipated results are expected to provide a fundamental insight into these problems, and may be of relevance for future applications. The project will give graduate and undergraduate students an excellent preparation for careers in academia, industry, and government.

****TECHNICAL ABSTRACT****
This award supports a project that will tackle two of the grand scientific challenges in condensed matter physics: i) How do complex phenomena emerge from simple ingredients? and ii) What happens far from equilibrium and why? In particular, many strongly correlated electronic materials exhibit complex, inhomogeneous behavior near the transition from an insulating into a conducting state. The out-of-equilibrium dynamics may very well be the smoking gun manifestation of this emerging complexity. This project will address the problem of complexity near the conductor-insulator transition by carrying out a comprehensive, comparative study of charge dynamics in two types of materials: two-dimensional systems in semiconductor heterostructures and lightly doped cuprates. The experiments will involve transport combined with low-frequency dynamical response measurements. The carefully designed comparative study will make it possible to separate out the more universal behavior from the material specific one, and thus identify the main ingredients necessary for the development of successful theoretical models. This project will support the education and training of graduate and undergraduate students, who will acquire valuable technical and analytical skills for a wide range of careers in the areas of science and technology in academic, industrial or government settings. The PI and graduate students will also engage in a variety of outreach activities, such as the Annual Open House at the National High Magnetic Field Laboratory.

The Colleges of Engineering and Departments of Chemistry at five large state universities in Florida will join together to form the Alliance for the Advancement of Florida's Academic Women in Chemistry and Engineering (AAFAWCE). The University of South Florida is the lead institution with four partners: Florida State University, Florida Agricultural and Mechanical University (FAMU), University of Florida, and Florida International University (FIU). The project will modify and adapt successful programs developed by previous ADVANCE projects focusing on the Colleges of Engineering and Departments of Chemistry at the partner institutions. The project will implement strategies for; 1) recruiting women in academic searches based on work developed at the University of Wisconsin, Madison; 2) transforming careers via leadership COACh workshops developed at the University of Oregon; and 3) advising and mentoring academic women at the assistant and associate levels based on work developed by the University of Texas-El Paso. In addition, the project will adapt and implement a faculty climate survey within all of the participating departments which was first developed by the Women in Science and Engineering Leadership Institute (WESLI) at the University of Wisconsin, Madison. The survey will be used to identify issues for faculty related to recruitment, mentoring, and the tenure process.

Intellectual Merit: The project will adapt previously developed strategies to a state-wide consortium of universities in Florida. The collaboration between the five institutions is important given the low numbers of female faculty in engineering and chemistry within these institutions. Faculty in each of the participating campuses' engineering and chemistry programs will participate in recruitment workshops along side department chairs, deans and other administrators. Faculty will have an opportunity to participate in the COACh workshop on advancing one's career and engage in a mentoring and advising program.

Broader Impacts: The project provides opportunities for female faculty at all ranks to engage in activities with others in their discipline areas from other Florida campuses as well as on their own campus. The collaboration includes two Minority-Serving Institutions; FAMU which is a Historically Black University and FIU which is a Hispanic-Serving Institution. This network will provide support for the faculty as they progress in their academic careers. The project will post videos of the workshops and other materials on the Global Educational Outreach web portal. In addition, the project team expects to publish a monograph with chapters by the project team on the objectives and activities of the program as well as by the participants in the alliance activities.
Intellectual Merit: The project will adapt previously developed strategies to a state-wide consortium of universities in Florida. The collaboration between the five institutions is important given the low numbers of female faculty in engineering and chemistry within these institutions. Faculty in each of the participating campuses' engineering and chemistry programs will participate in recruitment workshops along side department chairs, deans and other administrators. Faculty will have an opportunity to participate in the COACh workshop on advancing one's career and engage in a mentoring and advising program.

Broader Impacts: The project provides opportunities for female faculty at all ranks to engage in activities with others in their discipline areas from other Florida campuses as well as on their own campus. The collaboration includes two Minority-Serving Institutions; FAMU which is a Historically Black University and FIU which is a Hispanic-Serving Institution. This network will provide support for the faculty as they progress in their academic careers. The project will post videos of the workshops and other materials on the Global Educational Outreach web portal. In addition, the project team expects to publish a monograph with chapters by the project team on the objectives and activities of the program as well as by the participants in the alliance activities.

****Technical Abstract****
One of the central issues in condensed matter physics is understanding the nature of the ground states in strongly correlated materials, the transitions between those states, and the associated dynamics. This project will seek to answer those questions by conducting a series of linear, non-linear and time-resolved transport measurements on two model experimental systems: two-dimensional electron system in semiconductor heterostructures and underdoped copper oxides. The knowledge gained from those studies will be essential to the development of condensed matter subfields of strongly correlated materials and out-of-equilibrium phenomena. This project will support the education and training of graduate and undergraduate students, who will acquire valuable technical and analytical skills for a wide range of careers in the areas of science and technology in academic, industrial or government settings. The PI and graduate students will also engage in a variety of outreach activities, such as the Annual Open House at the National High Magnetic Field Laboratory.

****Non-Technical Abstract****
In many novel materials with potentially great technological importance, such as high-temperature superconductors, the state that conducts electricity (a "conductor") is created by chemically doping an otherwise insulating material. Such materials, therefore, find themselves close to the conductor-insulator transition. Understanding the nature of this transition thus represents an important issue for materials science and technology. It also presents a fundamental problem in condensed matter physics. This project will address the problem of complex behavior near the conductor-insulator transition by performing electrical transport measurements on semiconductor devices and high temperature superconductor materials. The results anticipated from these experiments are expected to provide fundamental insights into these problems, and may be of relevance for future applications. The project will give graduate and undergraduate students an excellent preparation for careers in academia, industry, and government.

Non-Technical Abstract:
Electronic properties of many new materials with potentially great technological importance are dominated by interactions among charge carriers. Those correlations give rise to a variety of phenomena of current interest in condensed matter physics, including the emergence of novel states of matter. These effects are most pronounced near transitions between different phases - conductor to insulator, or superconductor to normal - that can be tuned by an external parameter, like magnetic or electric field. The underlying quantum nature of those transitions contributes to the complexity of the observed behaviors. This research addresses fundamental questions about the nature and the dynamics of several charge-ordered states in the presence of other, competing phases, especially in the vicinity of quantum phase transitions. Most of the experiments involve measurements of charge transport, including various time-dependent protocols, using either electric or extremely high magnetic fields to tune through the phase transitions in two-dimensional crystals and high-temperature superconductor materials. A key component of the project is education and training of a diverse group of young researchers for future careers in academia, national laboratories, and industry. It also incorporates various activities to broaden the participation of underrepresented groups in the areas of science, technology, engineering, and mathematics.


Technical Abstract:
Many unusual properties of strongly correlated materials have been attributed to the proximity of quantum critical points, where different types of orders compete and coexist, and may even give rise to novel phases. The role of collective fluctuations near quantum critical points is thus increasingly recognized as one of the key questions in the physics of strongly correlated systems. Even though fluctuations of various charge-ordered states have been of particular interest, e.g. to clarify their relationship with high-temperature superconductivity in cuprates, there have been few studies of charge, as opposed to spin, dynamics. The aim of the project is to bridge this gap by using time-resolved charge transport measurements on very long time scales, proven to be powerful probes of out-of-equilibrium or glassy charge dynamics, quantum critical points, and novel, intermediate phases. The research is designed to provide answers to several fundamental questions in condensed matter physics concerning the interplay of charge correlations and disorder, their relationship to high-temperature superconductivity, and the nature of various ground states and quantum critical points, such as the two-dimensional metal-insulator transition and the magnetic-field-tuned superconducting transition in cuprates. This knowledge is essential to the development of condensed matter subfields of strongly correlated materials and out-of-equilibrium phenomena.