Speaker
Description
The La2-x-yNdy=0.4Srx=0.125CuO4 (Nd-LSCO) system is one of three 214 families of quasi-two dimensional cuprate superconductors which has been tuned to 1/8 hole doping. At this doping, the three dimensional superconducting transition temperature, Tc, is strongly suppressed compared to hole doping concentrations near x=0.125 in Nd-LSCO. A similar “1/8 anomaly” describes the superconducting phase diagram in La2-xBax=0.125CuO4 (LBCO) while that in La2-xSrx=0.125CuO4 (LSCO) is only minimally suppressed compared to hole doping concentrations near x=0.125. This has allowed us to grow a series of single crystals of the form La2-x-yNdySrx=0.125CuO4 where the Nd concentration is varied from y=0 (LSCO) to y=0.4 (0.4 Nd-LSCO) such that the superconducting Tc varies by almost a factor of 10, all at the same hole doping (x=0.125). We have carried out a series of time-of-flight neutron spectroscopic measurements on the ARCS spectrometer at SNS, Oak Ridge National Laboratory, which map out four-dimensional (Q and ω) phonon and spin excitations as a function of temperatures for large single crystal samples of 0.4 Nd-LSCO, 0.2 Nd-LSCO and LSCO. This presentation will mostly focus on the systematics of the variation in the phonons below ~ 40 meV in these materials. The most striking result is the clear emergence of sharp phonon mode near the (π,π) position in the basal plane reciprocal space and 19 meV, which correlates strongly with Tc, being strong for La2-xSrx=0.125CuO4 (LSCO) with Tc ~ 27 K, but weak for La2-yNdy=0.4Srx=0.125CuO4 (0.4 Nd-LSCO) where Tc ~ 3 K.
| Keyword-1 | Cuprate Superconductor |
|---|---|
| Keyword-2 | Phonon |