  We report measurements of the specific heat and magnetization of single
crystal samples of the spin-1/2 kagome compound ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$
(herbertsmithite), a promising quantum spin-liquid candidate, in high magnetic
fields and at low temperatures. The magnetization was measured up to $\mu_{0}H$
= 55 T at $T$ = 0.4 K, showing a saturation of the weakly interacting impurity
moments in fields above $\sim10$ T. The specific heat was measured down to $T <
0.4$ K in magnetic fields up to 18 T, revealing $T$-linear and $T$-squared
contributions. The $T$-linear contribution is surprisingly large and indicates
the presence of gapless excitations in large applied fields. These results
further highlight the unusual excitation spectrum of the spin liquid ground
state of herbertsmithite.
