Evidence of one-dimensional magnetic heat transport in the triangular-lattice antiferromagnet ${\mathrm{Cs}}_2{\mathrm{CuCl}}_4$

We report on low-temperature heat-transport properties of the spin-1/2 triangular-lattice antiferromagnet ${\mathrm{Cs}}_2{\mathrm{CuCl}}_4$. Broad maxima in the thermal conductivity along the three principal axes, observed at about 5 K, are interpreted in terms of the Debye model, including the phonon umklapp scattering. For thermal transport along the $b$ axis, we found a pronounced field-dependent anomaly, close to the transition into the three-dimensional long-range-ordered state. No such anomalies were found for the transport along the $a$ and $c$ directions. We argue that this anisotropic behavior is related to an additional heat-transport channel through magnetic excitations, that can best propagate along the direction of the largest exchange interaction. In addition, peculiarities of the heat transport of ${\mathrm{Cs}}_2{\mathrm{CuCl}}_4$ in magnetic fields up to the saturation field and above are discussed.

Figure 1

Schematic view of exchange paths in ${\mathrm{Cs}}_2{\mathrm{CuCl}}_4$ with the exchange coupling $J$ along the $b$ axis (chain direction) and $J^{\prime }$ along the zigzag bonds in the $bc$ plane.

Figure 2

Temperature dependence of the thermal conductivity ${\kappa }_b$ (a), ${\kappa }_a$ (b), and ${\kappa }_c$ (c) along the $b, a$, and $c$ axes, respectively, in selected magnetic fields. Lines are guides to the eye.

Figure 3

Field dependence of the thermal conductivity ${\kappa }_b$ (a), ${\kappa }_a$ (b), and ${\kappa }_c$ (c) at selected temperatures. The magnetic field was applied along the heat-transport directions. Lines are guides to the eye.

Figure 4

Phase diagram of ${\mathrm{Cs}}_2{\mathrm{CuCl}}_4$ for magnetic field applied along the $b$ direction. Data from our thermal-transport measurements are shown by red solid circles, while specific-heat and susceptibility data from [11] are denoted by open circles. The crosses correspond to the thermal conductivity maxima in the fully spin-polarized phase above $H_{\mathrm{sat}}$ (Fig. 3). Lines are guides to the eye.

Figure 5

Temperature dependencies of the thermal conductivity ${\kappa }_b$ along the $b$ axis (rough experimental data; blue symbols), nonmagnetic background ${\kappa }_b^{nm}$ as the result of the power-law fit (magenta line), magnetic contribution to the thermal conductivity ${\kappa }_b^m$ as the result of the subtraction ${\kappa }_b^{nm}$ from ${\kappa }_b$ (red symbols), and rescaled thermal conductivity ${\kappa }_a/2$ along the $a$ direction (green symbols).