A new high-temperature quantum spin liquid with polaron spins

摘要

The existence of a quantum spin liquid (QSL) in which quantum fluctuations ofspins are sufficiently strong to preclude spin ordering down to zerotemperature was originally proposed theoretically more than 40 years ago, butits experimental realisation turned out to be very elusive. Here we report onan almost ideal spin liquid state that appears to be realized by atomic-clusterspins on the triangular lattice of a charge-density wave (CDW) state of1T-TaS$_2$. In this system, the charge excitations have a well-defined gap of$\sim 0.3$ eV, while nuclear magnetic quadrupole resonance and muon spinrelaxation experiments reveal that the spins show gapless quantum spin liquiddynamics and no long range magnetic order down to 70~mK. Canonical $T^{2}$power-law temperature dependence of the spin relaxation dynamics characteristicof a QSL is observed from 200~K to $T_f= 55$ K. Below this temperature weobserve a new gapless state with reduced density of spin excitations and highdegree of local disorder signifying new quantum spin order emerging from theQSL.