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Magnetic Order

Magnetism and Phase Diagram of a High-Transition-Temperature Superconductor M. Greven, Stanford University, DMR-0405655.

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Magnetic Order

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  1. Magnetism and Phase Diagram of a High-Transition-Temperature SuperconductorM. Greven, Stanford University, DMR-0405655 Using neutron scattering, we measured the distance (/a) over which the magnetic moments (or spins) “talk” to each other in the electron-doped high transition-temperature (Tc) superconductor Nd2-xCexCuO4 (NCCO). By plotting this magnetic length on a graph of temperature vs. chemical composition x, we were able to construct the most complete magnetic phase diagram so far of any electron-doped high-Tc superconductor. One surprise was that, unlike previous thought, the magnetically ordered state (red hashes) and the superconducting state (blue hashes) may not overlap. We also found that there is a clear relationship between the electronic anomaly known as the “pseudogap” and the measured magnetic length. E.M. Motoyama et al., Nature (in review). See also: xxx.lanl.gov/abs/cond-mat/0609286. Pseudogap Line Magnetic Order Superconductivity Phase diagram of magnetic correlation length as a function of temperature and chemical composition (x) in NCCO. The red hashed area is the antiferromagnetically ordered phase, and the blue hashed area is the superconducting phase. The color map indicates the magnetic correlation length.

  2. Magnetism and Phase Diagram of a High-Transition-Temperature SuperconductorM. Greven, Stanford University, DMR-0405655 Education: This research comprises a significant portion of the graduate thesis work by Eugene Motoyama, who holds an NSF Graduate Fellowship. One other graduate student (Guichuan Yu) and an undergraduate student (Inna Vishik) also benefited from the NSF grant. Inna Vishik was on of this year’s APS Apker Award finalists in honor of her significant undergraduate research. She also won NSF and Stanford Graduate Fellowships. Impact: This research has led to significant new insights into the relationship between magnetism and superconductivity in a well-known complex oxide material. This success was enabled by advanced crystal growth methods and by the use of neutron scattering techniques. It lays the foundation for future experimental work involving the Spallation Neutron Source, and it allows tests of non-trivial theoretical ideas. Quite generally, a deeper understanding of complex oxide materials will likely have a significant positive future impact on technology. Crystal growth of NCCO in an image furnace at Stanford University.

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