Cascade of Magnetic-Field-Induced Quantum Phase Transitions in a Spin-12Triangular-Lattice Antiferromagnet

Abstract

We report magnetocaloric and magnetic-torque evidence that in Cs2CuBr4--a geometrically frustrated Heisenberg S=1/2 triangular-lattice antiferromagnet--quantum fluctuations stabilize a series of spin states at simple increasing fractions of the saturation magnetization Ms. Only the first of these states--at M=1/3Ms--has been theoretically predicted. We discuss how the higher fraction quantum states might arise and propose model spin arrangements. We argue that the first-order nature of the transitions into those states is due to strong lowering of the energies by quantum fluctuations, with implications for the general character of quantum phase transitions in geometrically frustrated systems.

Ground states of spin-12triangular antiferromagnets in a magnetic field

“…54 Our study indicates that few such transitions should be expected in the pure J − J model. Likely additional DM interactions (beyond the one given in Eq.…”

The Magnetization Process of the Spin-One Triangular-Lattice Heisenberg Antiferromagnet

“…One spectacular feature of this model system for a strongly frustrated magnet is the unconventional magnetization process of the triangular-lattice Heisenberg antiferromagnet. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] While for the classical isotropic Heisenberg model at zero temperature the magnetization M increases linearly with the applied magnetic field H, thermal or quantum fluctuations induce a plateau at 1/3 of the saturation magnetization M sat (''order from disorder'' phenomenon). For the extreme quantum case, i.e., spin quantum number s ¼ 1=2, this plateau at T ¼ 0 has been widely discussed.…”

Magnetization Process and Collective Excitations in theS=1/2Triangular-Lattice Heisenberg AntiferromagnetBa3CoSb2Susuki1, Kurita2, Tanaka3 et al. 2013Phys. Rev. Lett.217272641View full textAdd to dashboardCite

“…This is mainly due to the experimental difficulty in growing the model material, let alone in observing the M s /3 plateau purely driven by quantum fluctuations. In fact, most of the TLHAFs ever studied, such as Cs 2 CuBr 4 , [15,16] have a distorted triangular lattice, which induces an antisymmetric Dzyaloshinsky-Moriya (DM) interaction.It is believed that the spin state in the lower-field range above the higher edge field of the M s /3 plateau is the 2 : 1 canted coplanar state that is a continuous variant of the up-up-down state [7][8][9][10][11]. However, whether the 2 : 1 canted coplanar state is stable up to the saturation or a new quantum spin state emerges in higher-field range is still unclear [17].…”

“…This is mainly due to the experimental difficulty in growing the model material, let alone in observing the M s /3 plateau purely driven by quantum fluctuations. In fact, most of the TLHAFs ever studied, such as Cs 2 CuBr 4 , [15,16] have a distorted triangular lattice, which induces an antisymmetric Dzyaloshinsky-Moriya (DM) interaction.…”