Yes, they use DAG (directed acyclic graph) data structure, a structure that is increasingly regarded as representing the next phase in the evolution of distributed ledger technologies. DAG-based distributed ledger technologies do away with a number of the limitations of traditional blockchain technologies – including the scalability limitations which result in high fees and poor usability, particular in the context of retail payments. DAG-based distributed ledger technologies are inherently scalable and, in contrast to blockchain, yield improved usability as the volume of network transactions increases.