Spontaneous Spin Ordering of a Dirac Spin Liquid in a Magnetic Field

The Dirac spin liquid was proposed to be the ground state of the spin-1/2 kagome antiferromagnets. In a magnetic field B, we show that the state with Fermi pocket is unstable to the Landau level (LL) state. The LL state breaks the spin rotation around the axis of the magnetic field. We find that the LL state has an in-plane 120 degrees q=0 magnetization M which scales with the external field M similar to B-alpha, where alpha is a universal number of the Dirac spin liquid. We discuss the related experimental implications which can be used to detect the possible Dirac spin liquid phase in herbertsmithite ZnCu3(OH)(6)Cl-2.