What algorithm is Alephium?

Could you please elaborate on the nature of Alephium's algorithm? As an avid follower of the cryptocurrency space, I'm curious to understand the unique features and advantages of the algorithmic design behind Alephium. Is it a Proof-of-Work (PoW) protocol, or does it employ a different consensus mechanism? How does it differentiate itself from other popular blockchains like Bitcoin or Ethereum in terms of its algorithmic approach? I'm particularly interested in knowing if Alephium's algorithm contributes to its scalability, security, or energy efficiency.