Two-Channel Kondo Effect in Glasslike ThAsSe

We present low-temperature heat and charge transport as well as caloric properties of a ThAsSe single crystal. An extra $-A{T}^{1/2}$ term in the electrical resistivity, independent of magnetic fields as high as 14 T, provides evidence for an unusual scattering of conduction electrons. Additionally, both the thermal conductivity and the specific heat show a glass-type temperature dependence which signifies the presence of tunneling states. These observations apparently point to an experimental realization of a two-channel Kondo effect derived from structural two-level systems.

Figure 1

Low-temperature thermal properties of the ThAsSe single crystal. (a) Total thermal conductivity (circles) and estimated electronic contribution ${\kappa }_{\mathrm{el}}^{\mathrm{WF}}$ (dotted line) as a function of temperature. The solid line is a fit to the data as described in the text. For comparison, $\kappa (T)$ of the noncrystalline insulator ${\mathrm{As}}_2{\mathrm{S}}_3$ is also shown [24]. (b) Specific heat in a double-logarithmic plot (circles). Crosses are the previous $C(T)$ data for a sample composed of several pieces [18]. The dotted line shows the $\gamma T+\beta T^3$ dependence with $\gamma =0.3\mathrm{mJ}/{\mathrm{K}}^2\mathrm{mol}$, the Sommerfeld coefficient of the electronic specific heat, and $\beta =3\times 1944/{\Theta }_{\mathrm{D}}^3$ in units of $\mathrm{J}/{\mathrm{K}}^4\mathrm{mol}$. The parameters $\gamma$ and $\beta$ were determined from the fit in the temperature range 1.7–5 K. The solid line indicates the presence of an additional linear-in-$T$ term due to TLS.

Figure 2

Low-temperature electrical resistivity of ThAsSe as $\Delta \rho /{\rho }_{1\mathrm{K}}$ vs $T^{1/2}$ in varying magnetic fields applied along the $c$ axis. For clarity, the different curves in $B>0$ were shifted subsequently by 0.1%. Circles display the $B=1\mathrm{T}$ data and the dashed line represents a $-A{T}^{1/2}$ behavior with $A=0.38\mu \Omega \mathrm{cm}/{\mathrm{K}}^{1/2}$, independent of field at $B\ge 1\mathrm{T}$. Arrows indicate the upper limit of the square-root temperature dependence of the resistivity.

Figure 3

(a) Magnetic field dependence of the electrical resistivity for ThAsSe at temperatures where a $-A{T}^{1/2}$ term is observed (see Fig. 2). (b) Magnetoresistivity at higher temperatures. (c) The normalized resistivity for ThAsSe with very different resistivity ratios $RR={\rho }_{4\mathrm{K}}/{\rho }_{300\mathrm{K}}$ (see text for details).