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#### Specific Heat Study of 1D and 2D Excitations in the Layered Frustrated
Quantum Antiferromagnets Cs_{2}CuCl_{4-x}Br_{x}

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##### Citation

Tutsch, U., Tsyplyatyev, O., Kuhnt, M., Postulka, L., Wolf, B., Cong, P. T., et al. (2019).
Specific Heat Study of 1D and 2D Excitations in the Layered Frustrated Quantum Antiferromagnets Cs_{2}CuCl_{4-x}Br_{x}.* Physical Review Letters,* *123*(14): 147202, pp. 1-6. doi:10.1103/PhysRevLett.123.147202.

Cite as: http://hdl.handle.net/21.11116/0000-0005-1B85-7

##### Abstract

We report an experimental and theoretical study of the low-temperature specific heat C and magnetic susceptibility chi of the layered anisotropic triangular-lattice spin-1/2 Heisenberg antiferromagnets Cs2CuCl4-xBrx with x= 0, 1, 2, and 4. We find that the ratio J'/J of the exchange couplings ranges from 0.32 approximate to 0.78, implying a change (crossover or quantum phase transition) in the materials' magnetic properties from one-dimensional (1D) behavior for J'/J < 0.6 to two-dimensional (2D) behavior for J'/J approximate to 0.78. For J'/J < 0.6, realized for x= 0, 1, and 4, we find a magnetic contribution to the low-temperature specific heat, C-m proportional to T, consistent with spinon excitations in 1D spin-1/2 Heisenberg antiferromagnets. Remarkably, for x = 2, where J'/J approximate to 0.78 implies a 2D magnetic character, we also observe C-m( )proportional to T. This finding, which contrasts the prediction of C-m proportional to T-2 made by standard spin-wave theories, shows that Fermi-like statistics also plays a significant role for the magnetic excitations in spin-1/2 frustrated 2D antiferromagnets.