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We present neutron inelastic scattering measurements of the full three-dimensional spin-wave dispersion in the multiferroic material BiFeO3, for temperatures from 5 to 700 K. Despite the presence of strong electromagnetic coupling, the magnetic excitations behave as conventional magnons over all parts of the Brillouin zone. At low temperature the spin waves are well-defined coherent modes, described by a classical model for a G-type antiferromagnet. A softening of the spin-wave velocity and broadening in energy is already present at room temperature, which is well below the Neel temperature TN ~ 640 K, and increases on heating. In addition, a strong hybridization of the Fe 3d and 0 2p states is found to modify significantly the distribution of the spin-wave spectral weight, which implies that the spins are not restricted to the Fe atomic sites as previously believed. [ABSTRACT FROM AUTHOR]

High-temperature superconductors exhibit a wide variety of novel excitations. If contacted with a topological insulator, the lifting of spin rotation symmetry in the surface states can lead to the emergence of unconventional superconductivity and novel particles. In pursuit of this possibility, we fabricated high critical-temperature (Tc∼85K) superconductor/topological insulator (Bi2Sr2CaCu2O8+δ/Bi2Te2Se) junctions. Below 75 K, a zero-bias conductance peak (ZBCP) emerges in the differential conductance spectra of this junction. The magnitude of the ZBCP is suppressed at the same rate for magnetic fields applied parallel or perpendicular to the junction. Furthermore, it can still be observed and does not split up to at least 8.5 T. The temperature and magnetic field dependence of the excitation we observe appears to fall outside the known paradigms for a ZBCP. [ABSTRACT FROM AUTHOR]