Visualizing pair formation in $Bi_2Sr_2CaCu_2O_{8+x}$

Unlike traditional superconductors, the density of states (DOS) of the high-Tc superconductor $Bi_2Sr_2CaCu_2O_{8+x}$ shows large nanoscale variations that have been detected using scanning tunneling microscopy (STM) [1,2]. Such variations are seen in the low temperature superconducting gap [1] and in features associated with the coupling of pairs to boson modes [2]. In order to understand these variations in the spectra, we perform atomic resolution STM measurements of $Bi_2Sr_2CaCu_2O_{8+x}$ as a function of temperature [3]. Using newly developed experimental techniques, we measure the evolution of the DOS from low temperature $(T<T^*)$. Such measurements show that the pairing gap nucleates in nanoscale regions at temperatures between Tc and T*. By normalizing the low temperature DOS $(T<