Isotope effect on the E_(2g) phonon and mesoscopic phase separation near the electronic topological transition in Mg_(1-x)Al_xB_2

摘要

We report boron isotope effect on the E_(2g) phonon mode by micro-Raman spectroscopy on the ternary Mg_(1-x)Al_xB_2 system, synthesized with pure isotopes ~(10)B and ~(11)B. The isotope coefficient on the E_(2g) mode frequency is nearly 0.5 in the wide range of Al, with a tendency to decrease at MgB_2 (x=0). The intraband electron-phonon (e-ph) coupling relative to the sigma band has been extracted from the E_(2g) line-shape parameters. By tuning the Fermi energy near the electronic topological transition (ETT), where the sigma Fermi surface changes from two-dimensional to three-dimensional topology (in range 0