Abstract
Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi2Sr2CaCu2O8+δ (Bi-2212) from the underdoped to overdoped regimes. The different doping dependences of the electron–boson coupling strengths enable us to identify them as phonons and spin fluctuations: electron–phonon coupling (λe−ph) peaks at optimal doping, while electron–spin fluctuation coupling (λe−sf) decreases monotonically with doping. This observation is consistent with two facts: (i) superconductivity is in close proximity with antiferromagnetism at low dopings and (ii) a pronounced lattice renormalization effect at larger dopings.
Highlights
The family of the bi-layer cuprate Bi-2212 has been the most intensively studied class of high-Tc superconductors in recent years, due to their (a) extreme cleavability, (b) containing only CuO2 planes and not chains and (c) the possibility of growing samples with a larger range of Tc variations
For the short time delays presented in our work, and since the same amount of incident laser power was absorbed by all the samples, we make the reasonable assumption that the measured reflectivity of the sample is proportional to the electronic temperature, i.e. Te/Te = η R/R, with η being doping independent
The contribution of our work, besides working on a different class of cuprate superconductors, is that we have obtained the doping dependence of the different electron–boson coupling constants from the UD to the OD regimes
Summary
The family of the bi-layer cuprate Bi-2212 has been the most intensively studied class of high-Tc superconductors in recent years, due to their (a) extreme cleavability, (b) containing only CuO2 planes and not chains and (c) the possibility of growing samples with a larger range of Tc variations. In the optimally doped (OPT) sample, Ca has been doped with Y to obtain the highest Tc of 95 K. The more OD samples have been doped with Pb to obtain lower values of Tc. The values of p were obtained from the Tc values using the parabolic law [32] Tc/Tcmax = 1 − 82.6( p − 0.16), where Tcmax = 95 K. An 80 MHz Ti:sapphire laser produces 45 fs pulses at ≈800 nm (1.55 eV) as a source of both pump and probe pulses. The reflected probe beam was focused onto an avalanche photodiode detector. Probe reflection is specular from the mirror-like sample surfaces, and the same fraction of the incident laser power is absorbed by the sample, i.e. To avoid any competing relaxation processes from emergent low temperature states (e.g. superconducting, pseudogap, antiferromagnetic or stripe order), all data were taken at room temperature [23], and up to a pump–probe delay of 7 ps
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
