  We present thermodynamic studies of a new spin-1/2 antiferromagnet containing
undistorted kagome lattices---barlowite Cu$_{4}$(OH)$_{6}$FBr. Magnetic
susceptibility gives $\theta_{CW}$ = $-$136 K, while long-range order does not
happen until $T_{N}$ = 15 K with a weak ferromagnetic moment $\mu$ $<$
0.1$\mu_{B}$/Cu. A 60 T magnetic field induces a moment less than
0.5$\mu_{B}$/Cu at $T$ = 0.6 K. Specific-heat measurements have observed
multiple phase transitions at $T \ll$ $\mid$$\theta_{CW}$$\mid$. The magnetic
entropy of these transitions is merely 18% of $k_{B}$ln2 per Cu spin. These
observations suggest that nontrivial spin textures are realized in barlowite
with magnetic frustration. Comparing with the leading spin-liquid candidate
herbertsmithite, the superior interkagome environment of barlowite sheds light
on new spin-liquid compounds with minimum disorder. The robust perfect geometry
of the kagome lattice makes charge doping promising.

Strongly Correlated Electrons