Magnetic-field effect on the quasiparticle excitation observed by the tunneling spectroscopy in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystal*

In the $d$-wave superconductor, due to the existence of nodes of the pairing gap, the field-dependence of the quasiparticle density of state has been predicted to be essentially different from the behavior in the $s$-wave case [1]. Here we report the planar junction tunneling spectra at different magnetic fields in the high-$T_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ to study how the field modifies the quasiparticle excitation. [1] G. E. Volovik, JETP Lett. \textbf{58}, 469 (1993).