Formation of ultracold weakly bound dimers of bosonic 23Na39 K

We create weakly bound bosonic 23Na39K molecules in a mixture of ultracold Na23 and K39. The creation is done in the vicinity of a so far undetected Feshbach resonance at about 196 G which we identify in this work by atom-loss spectroscopy. We investigate the involved molecular state by performing destructive radio-frequency binding-energy measurements. For the constructive molecule creation we use radio-frequency pulses with which we assemble up to 6000 molecules. We analyze the molecule creation efficiency as a function of the radio-frequency pulse duration and the atom number ratio between Na23 and K39. We find an overall optimal efficiency of 6% referring to the K39 atom number. The measured lifetime of the molecules in the bath of trapped atoms is about 0.3 ms.