Pengcheng Dai - US grants

This project addresses the dominant new scientific theme of our time, the fundamental and practical importance of understanding complex, self-organizing behavior exhibited in transition metal oxides (TMOs). The objective of this research program is to explore and understand the microscopic origins of various phases in the TMOs using neutron scattering as a primary tool. Specially, the project will focus on high-transition temperature (high-Tc) superconductors and colossal magneto-resistance (CMR) manganese-oxides. For high-Tc superconductors, the project will investigate the nature of the interplay between magnetism and superconductivity. For CMR manganese-oxides, the project will focus on understanding how the microscopic spin/lattice dynamics determine the bulk magnetic and transport properties of these materials. Neutron scattering experiments, the core part of this research program, will be performed mostly at the newly upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the TMOs.

Physics in the new millennium will take us into the world of emergent complexity from simple and basic laws. This project addresses the fundamental physical processes that give rise to novel collective phenomena. The materials known to exhibit these collective phenomena are the strongly correlated electron transition metal oxides (TMOs). The understanding of these phenomena will not only enhance our knowledge of basic science, but also gives us the ability to design materials with novel and predictable properties. This project will use neutron scattering to investigate two families of the TMOs, the high-transition-temperature copper-oxide superconductors and colossal magneto-resistance manganese-oxides. The objective of the program is to explore and understand the microscopic origins of various phases in the TMOs using neutron as a probe. Neutron scattering experiments will be performed mostly at the newly upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the TMOs.

***NON-TECHNICAL ABSTRACT***
Understanding how complex behavior emerges from simple and basic laws is one of the areas of current interest in Condensed Matter Physics. This individual investigator project addresses the fundamental physical processes that give rise to novel phenomena, such as high-transition temperature superconductivity and colossal magnetoresistance (where a material displays a very large change in its electrical resistance when exposed to a magnetic field), resulting from the collective behavior of electrons. Materials in the family known as transition metal oxides (TMOs) exhibit these collective phenomena. Understanding these phenomena will not only enhance our knowledge of basic science, but also gives us the ability to design materials with novel and predictable properties. The objective of the program is to explore and understand the microscopic origins of various phases in the TMOs using neutrons as a probe. Neutron scattering experiments will be performed mostly at the upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) and on the new spallation neutron source at ORNL. The project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at ORNL. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the TMOs.


***TECHNICAL ABSTRACT***
This individual investigator project will establish an experimental program integrating neutron scattering experiments with lab based materials efforts. The aim of the project is to further our understanding of the phase transition from a Mott insulator to a metallic/superconducting state in transition metal oxides (TMOs). The objective of this research program is to explore and understand the microscopic origins of various phases in the TMOs using neutron scattering as a primary tool. The project will focus on electron-doped high-Tc superconductors and colossal magneto-resistance (CMR) manganese-oxides. The program has two components: advanced synthesis with initial materials characterization and neutron scattering. Neutron scattering, the core part of this research program, will be used to study the exotic spin and lattice dynamical properties of the highly correlated electron materials. Most experiments will be performed at the newly upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). However, other world-class facilities in the U.S. and Europe will be utilized when similar capabilities are unavailable at HFIR. Students will be trained in state-of-the art materials synthesis and neutron scattering techniques.

NONTECHNICAL ABSTRACT

This NSF project addresses the fundamental physical processes that give rise to novel collective phenomena and self-assembled nano-structures. The materials known to exhibit these collective phenomena are the strongly correlated electron transition metal oxides (TMOs). The understanding of these phenomena will not only enhance our knowledge of basic science, but also gives us the ability to design materials with novel and predictable properties. Specifically, the experimental program integrates neutron scattering experiments with lab based materials efforts, aimed at the fundamental understanding of the spin and lattice excitations in TMOs such as electron-doped high-transition-temperature (high-Tc) superconductors and layered manganese oxides. The objective of the program is to explore and understand the microscopic origins of various phases in the TMOs using neutron as a probe. Neutron scattering experiments will be performed mostly at the newly upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory. However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the TMOs.


TECHNICAL ABSTRACT

This NSF project addresses the dominant new scientific theme of our time, the fundamental and practical importance of understanding complex, self-organizing behavior exhibited in transition metal oxides (TMOs). The objective of this research program is to explore and understand the microscopic origins of various phases in the TMOs using neutron scattering as a primary tool. Specially, the project will focus on electron-doped high-transition temperature (high-Tc) superconductors and layered colossal magneto-resistance (CMR) manganese-oxides. For high-Tc superconductors, the project will investigate the nature of the interplay between magnetism and superconductivity. For CMR manganese-oxides, the project will focus on understanding how the microscopic spin/lattice dynamics determine the bulk magnetic and transport properties of these materials. Neutron scattering experiments, the core part of this research program, will be performed mostly at the newly upgraded high-flux isotope reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the TMOs.

This PIRE project forms an international consortium of leading superconductivity researchers from the U.S., Japan, Canada, UK, and China to investigate novel superconductors to clarify superconducting mechanisms and properties and develop novel superconducting materials. In conventional electrical systems heat is generated by friction as electrons collide with atoms and impurities in the wire, a property that is ideal for appliances such as toasters or irons but not for most other electrical applications. Superconductivity can be thought of as "frictionless" electricity whereby electrons glide unimpeded between atoms, thus vastly improving the conductor's energy efficiency. To date this has only been achieved at extremely low temperatures; the challenge is to harness this phenomenon at or near room temperature and at high electrical currents. This project will fill gaps in our current understanding of superconductivity, reconcile current theories, and advance the development of better materials for fast-performing devices and cost-saving electric motors, generators, and power transmission lines.

The project links leading materials experimentalists and eminent theorists in a study of FeAs, CuO, CeCoIn5, and URu2Si2 superconductors using powerful experimental probing techniques including neutron scattering, muon spin relaxation, X-ray scattering, Raman spectroscopy, and scanning tunneling microscopy. These advanced methods allow elucidation of the phase diagrams of these important new materials of which some significant aspects are currently unknown. The PIRE team will explore the parameters affecting the highest temperature at which a certain material is superconducting and ways of increasing that temperature so that superconductivity will not require such expensive refrigeration. Some anomalies in the superfluid density and specific heat discontinuities, inconsistent with the standard theory of superconductivity, will also be investigated both experimentally and theoretically.

International collaboration is essential for this work because it will provide U.S. scientists and students with access to critical world-class accelerator-based facilities available in the UK and Canada but not in the U.S., to high quality specimens fabricated in China and Japan, and to first-rate scientific expertise from all countries. Combining and comparing the results of multiple probes on the same high-quality specimens will significantly improve the accuracy of data. Face to face collaboration of theorists and experimentalists focused on key concepts will facilitate the translation of mathematical theory into realistic and effective models and materials. The project places great emphasis on training students and early career scientists. Students and postdoctoral researchers will undertake 3-6 month research visits to work on superconducting mechanisms at foreign sites, where they will also receive language and cultural training. The project will actively recruit minority students into the sciences via workshops for high-school students and teachers from disadvantaged schools in New York and via an outreach program on superconductivity and scanning tunneling microscopy. High school and undergraduate students will gain valuable beam-time experience through the project, and female students, who are as a group underrepresented in the physical sciences, will be provided valuable mentoring from four female leading scientists on the team. The PIRE team will also develop a contemporary, internet-based set of solid state physics lectures and a text book on introductory solid state physics that reflect current knowledge in condensed matter physics and related experimental techniques.

The project will strengthen and internationalize materials research programs at the U.S. institutions and engage more U.S. students in international research collaborations. It will place Columbia University and its students and faculty at the core of a research and education partnership with extensive research collaborations, teaching cooperation, and frequent reciprocal research visits for participating faculty and students. Impacts extend beyond the PI and his institution, including providing U.S. students with research opportunities at two Department of Energy U.S. National Laboratories (Oak Ridge and Los Alamos) and training of early career scientists at the UK's ISIS and Canada's TRIUMF facilities, both of which will build the core workforce for new probing facilities currently under construction in the U.S. and Japan. This PIRE project will build upon an existing Inter American materials science network (CIAM) and forge a foundation for long-term research and educational collaborations among scientists and institutions in the five participating nations, all advancing the state-of-the-art in superconductivity and its applications.

Participating U.S. institutions include Columbia University (NY), University of Tennessee at Knoxville, and the Department of Energy's Oak Ridge (TN) and Los Alamos (NM) National Laboratories. Foreign institutions include Institute of Physics - Chinese Academy of Sciences, University of Bristol (UK), the UK Science and Technology Facilities Council's ISIS facility, McMaster University (Canada), TRIUMF Canada's National Laboratory for Particle and Nuclear Physics, Tokyo University (Japan), Osaka University (Japan), Tohoku University (Japan), and the National Institute of Advanced Industrial Science and Technology (AIST) (Japan).

This award is co-funded by the Office of International Science and Engineering and the Division of Materials Research.

Technical Abstract

The objective of this research program is to explore and understand the microscopic origin of high-transition-temperature (high-Tc) superconductivity in iron and copper based superconductors using neutron scattering as a primary tool. Specially, the project will focus on electron-doped iron and copper based high-Tc superconductors. We will investigate the nature of the interplay between magnetism and superconductivity. Neutron scattering experiments, the core part of this research program, will be performed mostly at the high-flux isotope reactor (HFIR) and Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL). However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR and SNS. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of these high-Tc superconductors.

Non-Technical Abstract

This NSF project addresses the fundamental physical processes that give rise to novel collective phenomena such as high-transition temperature superconductivity. The materials known to exhibit these collective phenomena are the strongly correlated electron materials. The understanding of these phenomena will not only enhance our knowledge of basic science, but also gives us the ability to design materials with novel and predictable properties. Specifically, the experimental program integrates neutron scattering experiments with lab based materials efforts, aimed at the fundamental understanding of the spin and lattice excitations in electron-doped high-transition-temperature (high-Tc) superconductors based on iron and copper. The objective of the program is to explore and understand the microscopic origins of various phases of iron and copper high-Tc superconductors using neutron as a probe. Neutron scattering experiments will be performed mostly at the high-flux isotope reactor (HFIR) and Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory. However, the project will also utilize other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR and SNS. The impact of this research program will include the training of the next generation of neutron scatters and elucidating the nature of the exotic properties of the correlated electron materials.

Non-technical Summary

The ability to understand and predict the behavior of solids is key to accelerating the discovery of new materials and their rapid deployment into new technologies. This combined computational modeling and neutron scattering characterization project focuses on a class of systems known as strongly correlated electron systems, which offer particularly exciting prospects for applications due to their complex emergent behavior and exotic physical properties. We will use computational and neutron scattering methods to study magnetic properties of these materials. Our goal is to understand the magnetic and superconducting properties of certain families of these materials, which will allow us to design future materials with desired and optimized properties.

Technical Summary

Quantum Monte Carlo and random phase approximation calculations, in conjunction with resonant inelastic x-ray scattering measurements will be used to study magnetic excitations in the cuprate and iron-based high-temperature superconductors, two of the most prominent and fascinating members of the class of strongly correlated electron systems. Our primary goal is to understand the interplay between magnetism and superconductivity in these systems, focusing on the pairing mechanism, which poses one of the most important and challenging problems in condensed matter physics. The impact of this research program will be two-fold: First, the link we will develop between neutron scattering experiments and insights gained from high-end simulations will establish a new modus operandi that will greatly conserve beam time and enhance the effectiveness of computing cycles. Second, this project will provide funding primarily for training of graduate students. They will be under the supervision of both PIs and therefore have the opportunity to learn both theoretical and experimental aspects of the study of correlated materials. This kind of training will benefit tremendously their future career prospects, providing a skill set that makes them highly competitive in the future job market.

NON-TECHNICAL SUMMARY
This DMREF project aims to make breakthroughs in understanding and designing novel superconductors, magnetic semiconductors, and other magnetic materials. The research can lead to development of materials with higher transition temperatures suitable for applications to electronic devices with novel functionalities. To achieve this goal, collaborative research will be performed by five Principal Investigators (PIs) specializing in a variety of techniques and methods, including neutron scattering (Dai) and muon spin relaxation (Uemura) as advanced magnetic probes, synthesis and charge transport of nano-scale systems (Ni and Kim), and theory and computational material design (Kotliar). The team members will unite their forces and expertise to characterize high-quality specimens with multiple experimental probes, to explore electric field-effect doping of charge carriers using nano-scale devices, to interpret the results using advanced computational models, and to design and synthesize new materials. As demonstrated in recent discoveries of ferromagnetic semiconductors that have crystal structures identical to those of Fe-based high-Tc superconductors, encounters and coherent collaboration between experts from different research communities will lead to unanticipated breakthroughs. Since 2011, the PIs from Columbia and Rice have organized live/video lecture courses for entry-level graduate students "Frontiers of Condensed Matter Physics" seeking broader impact, and have accumulated about 100 video lectures of leading scientists describing modern studies of solid state physics. The present project will allow adding a new series to this course involving faculty members from Columbia, Rice, Harvard, Rutgers, and UCLA and connecting their classrooms with a web-based technology for simultaneous broadcast.

TECHNICAL SUMMARY
Condensation and pairing mechanisms of high-Tc cuprate and iron-based superconductors have not yet been established. However, there are growing signatures pointing toward the important role played by magnetic interactions. With multi-probe experimental researchers using neutrons, muons, transport, and scanning tunneling microscopy (STM), supplemented by quantitative comparison to advanced computation, the present DMREF project will shed new light on the quest for understanding unconventional superconductors. In conjunction with the predictive powers of advanced computational methods, a better understanding of the physical mechanisms at work will contribute to the ability to design materials with higher transition temperatures. Carrier doping using electric field effects will provide a new route to search for novel superconductors, less sensitive to disorder effects associated with conventional doping with chemical substitutions. Transport results on Fermi-level tuning via electrolyte gate voltage will be directly compared to advanced theoretical computations on electronic structures. Additionally, the formation of interfaces of unconventional superconductors and their magnetic derivatives, and engineering of phase changes via charge-doping with field-effect gating, will result in devices with novel functionality, leading to an as yet unexplored interdisciplinary research front. This project will provide a unique collaborative experience involving leading researchers, graduate students, and postdocs with multiple research fields and techniques that will make important contributions to the development of the future leaders of modern physics research.

NON TECHNICAL ABSTRACT

This award from the Condensed Matter Physics program of the Division of Materials Research supports a project addressing the fundamental physical processes that give rise to novel phenomena such as high-transition temperature superconductivity. Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. Understanding of superconductivity and related properties will not only enhance our knowledge of basic science, but also gives us the ability to design materials with novel and predictable properties. The investigators conduct neutron scattering experiments performed mostly at the high-flux isotope reactor (HFIR) and Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory. The project also utilizes other world-class facilities in the U.S. and Europe when similar capabilities are unavailable at HFIR and SNS. The impact of this research program will include the training of the next generation of neutron scattering experts and elucidating the nature of the special properties of the correlated electron materials.

TECHNICAL ABSTRACT

This award from the Condensed Matter Physics program of the Division of Materials Research supports an experimental program integrating neutron scattering experiments with laboratory-based materials efforts, aimed at the fundamental understanding of spin excitations and their relationship with superconductivity in iron-based high-transition-temperature (high-Tc) superconductors. The objective of the project is to explore and understand the microscopic origins of various phases in iron-based superconductors, specifically the iron arsenide superconductors BaFe2-xNixAs2, (B, K) Fe2A2, and BaFe2As2-xPx. The program has two components: initial materials characterization and neutron scattering. Single crystals of these materials are grown at the William Marsh Rice University where the initial characterization of will be performed. Neutron scattering, the core part of this research program, will be used to study the spin dynamical properties of these materials. Experiments will be performed at the High-Flux Isotope Reactor and the Spallation Neutron Source at Oak Ridge National Laboratory and the NIST Center for Neutron Research in Maryland. In addition, other world-class neutron scattering facilities in Europe will also be utilized when similar capabilities are unavailable in the US. The impact of this research program will include the training of the next generation of neutron scattering experts and elucidating the nature of the special properties of the correlated electron materials.

Advances in information technology, energy, and many other fields rely upon the development and characterization of materials with desirable mechanical, electrical, magnetic, and thermal properties. Investigators who first synthesize high-quality, bulk single crystals of novel materials are in an optimal position to conduct definitive studies of their fundamental properties. Moreover, these investigators are also well positioned to facilitate further development of these materials toward applications in advanced technologies. This project develops a high-pressure laser floating zone furnace, not commercially available, capable of growing single crystals of novel materials that cannot be grown any other way. The high-pressure laser floating zone furnace will be a part of Rice’s Shared Equipment Authority and therefore have a broad user base from Rice University and the extended research community in and around Houston, Texas. In addition to training undergraduate and graduate students in the art of growing single crystals using the furnace, the successful execution of this project will open areas of research currently not possible for faculty and students. These activities will broaden the avenues of research in solid-state science and will provide new opportunities for discoveries of novel phenomena in single crystals of quantum materials.<br/><br/>Conventional laser floating zone furnaces are powerful tools used to grow high-quality single crystals of oxides, intermetallics, carbides, and silicides, as long as the melting temperature is below ~2,800°C, but the growth chamber is limited up to 300 bar gas pressure. Growing single crystals of more complex materials, however, requires special capabilities, particularly the use of high pressure in the growth chamber. This is because the boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas around it. Increasing the gas pressure to 1000 bar inside the chamber will dramatically enhance the opportunities to stabilize the melt, and therefore allowing growth of single crystals not possible with conventional laser floating zone furnace. Recently, the investigator at the University of California, Santa Barbara (UCSB), developed a novel design for a high-pressure laser floating zone furnace for operational pressures up to 1000 bars of gas pressure. The objective of this project is to continue this innovation through the design and construction of a next-generation high-pressure laser floating zone furnace at Rice University; it will be the first of its kind in Texas and the southern U.S. and will represent a continued advance in high-pressure floating zone technology for advanced crystal growth. With the development of an improved high-pressure laser floating zone furnace under 1000 bars of gas pressure, the investigators will be able to obtain entire new phase parameter regimes and grow single crystals not possible with a commercial instrument. The proposed furnace will be operated and maintained by Rice University’s Shared Equipment Authority, where it will be easily accessible not only to Rice researchers but also to researchers throughout Texas and the southern U.S., thereby significantly broadening the capacity to advance research in materials synthesis.<br/><br/>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.