Novel field induced quantum phase transition of the kagome lattice antiferromagnet

Sakai, Toru; Nakano, Hiroki*

The kagome-lattice antiferromagnets have attracted a lot of interest in the field of the low-temperature physics. It exhibits some exotic field-induced phenomena, like a magnetization plateau, jump etc. Our previous large-scale yumerical exact diagonalization study on the S=1/2 kagome-lattice antiferromagnet revealed that a novel field-induced phenomenon, "the magnetization ramp", occurs at 1/3 of the saturation magnetization. It is characterized by different critical exponents between the lower-field and higher-field sides of the magnetization curve. In order to clarify unconventional properties around the 1/3 magnetization, we considered some extended lattice models; a distorted kagome lattice and distorted triangular lattice etc. Our numerical exact diagonalization study also indicates that the ground state of the kagome-lattice antiferromagnet is gapless quantum spin liquid.