Magnetothermal evidence of a partial gap at the Fermi surface of ${\text{UPt}}_2{\text{Si}}_2$

Motivated by the observation of a giant Nernst effect in ${\text{URu}}_2{\text{Si}}_2$, the thermoelectric response of the related system ${\text{UPt}}_2{\text{Si}}_2$ was investigated using thermal and electric transport properties such as the Nernst and Seebeck effects, thermal conductivity, Hall effect, and electrical resistivity. Unlike ${\text{URu}}_2{\text{Si}}_2$, ${\text{UPt}}_2{\text{Si}}_2$ is neither superconducting nor exhibits a “hidden-order” state. Nevertheless a pronounced Nernst effect anomaly is found to coincide with the onset of the antiferromagnetic order in ${\text{UPt}}_2{\text{Si}}_2$. Although the absolute values are substantially lower, its appearance and characteristics can favorably be compared to the giant Nernst effect in ${\text{URu}}_2{\text{Si}}_2$, indicating the common feature of a partial Fermi surface gap.

Figure 1

(Color online) Upper panel: thermal conductivity along the $a$ axis of ${\text{UPt}}_2{\text{Si}}_2$ for magnetic fields applied along $c$. The inset shows the off-diagonal component ${\kappa }_{xy}$, which is of the order of 1% of ${\kappa }_{xx}$. The open symbols give an upper-limit estimation of the electronic contribution to the thermal conductivity as calculated by the Wiedemann-Franz law. Lower panel: Resistivity along the $a$ axis in 0 and 14 T along $c$. The inset shows the temperature dependence of the Hall coefficient of ${\text{UPt}}_2{\text{Si}}_2$ in 14 T with its pronounced increase below $T_N$.

Figure 2

(Color online) Thermopower of ${\text{UPt}}_2{\text{Si}}_2$ for magnetic fields of 0, 8, and 14 T ($\nabla T\parallel a$, $H\parallel c$).

Figure 3

(Color online) Upper panel: Temperature dependence of the Nernst signal of ${\text{UPt}}_2{\text{Si}}_2$ in various magnetic fields. Lower panel: Comparison of the temperature dependent thermal Hall contribution to the measured Nernst signal, in $H=14\text{T}$ ($\nabla T\parallel a$, $H\parallel c$).

Figure 4

(Color online) Upper panel: The Nernst signal of ${\text{URu}}_2{\text{Si}}_2$ compared to the product of its thermopower and Hall coefficient at $H=12\text{T}$. Data are taken from (Ref. 7) with a $T_{\text{Order}}=T_{\text{HO}}=17.5\text{K}$. The lower panel depicts the scaling behavior for ${\text{UPt}}_2{\text{Si}}_2$ as expected from calculations for a generic antiferromagnet due to the opening of a superzone gap (Ref. 23). The maximum positions of roughly $0.5\cdot T_{\text{Order}}$ well agree with the theoretical expectations. Here, $T_{\text{Order}}=T_N=31.5\text{K}$.