Ground state and excitation properties of the quantum kagom\'{e} system   ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ investigated by local probes
  We characterize the ground state and excitation spectrum of the $S=1/2$, nominally pure and perfect kagom\'{e} system ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ using the following measurements: magnetization, muon spin rotation frequency shift $K$, transverse relaxation time $T_{2}^{\ast}$, and zero field relaxation, and Cl nuclear spin-lattice relaxation $T_{1}$. We found no sign of singlet formation, no long range order or spin freezing, and no sign of spin-Peierls transition even at temperatures as low as 60 mK. The density of states has $E^{1/4}$ energy dependence with a negligible gap to excitation. 
Oren Ofer, and Amit Keren, Emily A. Nytko, Matthew P. Shores, Bart M.   Bartlett, and Daniel G. Nocera, Chris Baines and Ale...