# Presentation: 487692

## Rare earth substitutions in the heavy-fermion superconductor CeCoIn5M. Brian Maple, University of California, San Diego, DMR 0335173

- Single crystal of Ce0.1Yb0.9CoIn5.  The crystal was grown by under-graduate students in our lab using a technique known as the flux-growth method.  By using a low melting point material as a flux, the melting point of the material comprising the single crystals is reduced, and single crystals form within the melt.

- Characteristic temperatures of the (Ce,R)CoIn5 materials.  The superconducting transition tem-perature Tc and heavy fermion coherence temperature Tcoh are suppressed by the addition of R ions, whether or not they are magnetic.  Pr, Gd, Dy, Er, and Yb are magnetic, whereas Y and Lu are not.

- In the intermetallic compound CeCoIn5, strong interactions between the electrons cause them to behave at low temperature as if their masses have ballooned by a factor of several hundred, forming heavy fermions. Further, at temper-atures below 2.3 K, the electrons participate in an unconventional form of superconductivity. Typical superconductivity is easily destroyed by small amounts of magnetic impurities, but is less sensitive to nonmagnetic impurities.  However, we find that adding magnetic rare earth (R) ions to CeCoIn5 has the *same* effect on its superconducting state as adding nonmagnetic rare earth ions.  The formation of the heavy fermion state in CeCoIn5 is also comparably affected by both types of impurities.  These results indicate that an exotic physical mechanism, likely magnetic in nature, is responsible for superconductivity in CeCoIn5.
***Nature Physics – in press***

**Notes:**
The heavy fermion compound CeCoIn5, in which  the conduction electrons behave as if they had a mass of several hundred times the free electron mass, exhibits an unconventional type of superconductivity.  To develop a better understanding of the superconductivity, we have measured the electrical resistivity (T) of CeCoIn5 into which various rare earth (R) elements, some of which (e.g., Pr, Gd, Dy, Er) carry a magnetic moment and some of which (e.g., Y, Lu) do not, have been substituted for Ce.  Both the coherence temperature Tcoh below which the heavy fermion state forms, and the critical temperature Tc, below which the superconductivity occurs, are suppressed with residual resistivity o of the R substituent (a measure of the rate at which electrons are scattered by the R substituent ions) in the same way for all R elements, irrespective of whether they carry a magnetic moment (see figure at upper right).  This behavior is in marked contrast to that of conventional superconductors whose Tc’s are strongly suppressed by impurities that carry magnetic moments which break up the superconducting electron pairs (Cooper pairs).  These results indicate that a different pairing mechanism, probably of magnetic origin, is responsible for the unconventional superconductivity of CeCoIn5.   Better understanding of unconventional superconductors like CeCoIn5 may provide insight into the behavior of technologically important superconductors like the high Tc cuprates.

## Rare earth substitutions in the heavy-fermion superconductor CeCoIn5M. Brian Maple, University of California, San Diego, DMR 0335173

**Education**
- Individuals at different stages of their careers (a post-doc, a graduate student, five undergraduates – including two who participated in the research experience for undergraduate [REU] program) have been involved in this ongoing research. Johnpierre Paglione, the post-doc, recently accepted a faculty position as Assistant Professor of Physics at the University of Maryland, the graduate student, Todd Sayles, continues to work on the project (currently completing the investigation of the effects of Yb doping), several of the undergraduate students have gone on to graduate school, while several others are still with us in the lab.

**Outreach**
- Our lab has a strong commitment to increasing awareness and understanding of the importance of experimental physics to a variety of communities. We currently administer an advanced physics lab (Phys 133) at the University of California, San Diego, where students are required to plan and carry out a research project, and then present the results to their peers in the class. Additionally, each year we perform regularly scheduled demonstrations at nearby elementary schools displaying some of the interesting aspects of low temperature physics (including the effect of liquid nitrogen when it is in contact with different materials.)

- To the left are two of the undergraduates working in our lab.  Kevin Huang (far left) is preparing samples for growth, while Xiao Zhang is removing a sample from the furnace.  To the right are students at Toler Elementary  School (San Diego) experi-menting on the effects of liquid nitrogen  on a variety of materials.