The cerium based ‘115’ materials, CeMIn 5 (M = Co, Rh, Ir), are highly unconventional metals that can display superconductivity, magnetism, or, as we found, a coexistence of both. There are several ways to explore the many degrees of freedom of these systems, including: alloying, dilution of the active cerium ion with a non- magnetic analog, and the suppression of super- conductivity with magnetic fields. We found in an alloying study of antiferromagnetic CeRhIn 5 and CeCoIn 5 that the antiferromagnetic character of CeRhIn 5 is retained throughout much of the alloy composition range, with the antiferromagnetism completely suppressed when the alloy is 75% CeCoIn 5. However, the most surprising aspect is the coexistence of the normally competing phases of antiferromagnetism and superconductivity, an indication of the highly novel character of these fascinating materials. A second study we are currently pursuing shows a suppression of superconductivity as cerium is replaced with one of its non-magnetic analogs, yttrium. This behavior was further characterized by studying the effects of magnetic field on the super- conducting behavior. These materials are incredibly fascinating, with their exotic superconductivity, ‘tunable’ ground states, and unconventional metallic behavior. Aside from these, the ‘115’s’ may give us glimpses into the unconventional behavior of the high-T c cuprate superconductors. Exotic Superconductivity and Magnetism in Cerium Based ‘115’ Materials M. Brian Maple, University of California San Diego - DMR a bc a - The two distinct electronic phases, antiferromagnetism (AFM) and superconductivity (SC), of the CeRh 1-x Co x In 5 system, including the region of the coexistence (SC/AFM). b - Suppression of T c in Ce 1-x Y x CoIn 5 with increasing yttrium concentration, x. c - Suppression of T c, in Ce 1– x Y x CoIn 5 for x = 0.1, 0.2, and 0.25, with varying field. Physical Review B 65, (2001) Physical Review B 72, (2005)

Exotic Superconductivity and Magnetism in Cerium Based ‘115’ Materials M. Brian Maple, University of California San Diego - DMR Societal Impact: There is currently great interest, both academically and technologically, in the high-T c cuprates, which become superconducting at temperatures above liquid nitrogen temperatures. This would allow, the low cost, production and transmission of electrical energy, as well as future technologies, such as magnetically levitated trains or magnetic rail to launch space craft. The 115’s display characteristics which are similar to the high–T c superconductors, including possible unconvention- al superconductivity and non-Fermi liquid be- havior. Additionally the new phases of matter seen in the ‘115’s’ are important to our further understanding of the behavior of materials at low temperatures. Single crystal of CeCoIn 5 on 1mm scale paper for reference. Tetragonal crystal structure of CeCoIn 5. Education: Three undergraduate REU students (Yvonne Edwards, Matthew Mottley, and Zackary Dupré) contributed to these projects. Yvonne is currently a graduate student at Stanford University, Matthew is planning on attending medical school, while Zackary is completing his final year as an undergraduate with plans to attend graduate school the following year. Several graduate students, Vivian Zapf (currently a Post Doctoral Research Physicist at Los Alamos National Lab), Jason Jeffries, and Todd Sayles (both of whom are continuing their graduate education in the Maple lab), and a NSERC postdoctoral fellow, Johnpierre Paglione, have been involved with these studies,