Manifestations of fine features of the density of states in the transport properties of $\mathrm{K}{\mathrm{Os}}_2{\mathrm{O}}_6$

We performed high-pressure transport measurements on high-quality single crystals of $\mathrm{K}{\mathrm{Os}}_2{\mathrm{O}}_6$, a $\beta$-pyrochlore superconductor. While the resistivity at high temperatures might approach saturation, there is no sign of saturation at low temperatures, down to the superconducting phase. The anomalous resistivity is accompanied by a nonmetallic behavior in the thermoelectric power (TEP) up to temperatures of at least $700\mathrm{K}$, which also exhibits a broad hump with a maximum at $60\mathrm{K}$. The pressure influences mostly the low-energy electronic excitations. A simple band model based on enhanced density of states in a narrow window around the Fermi energy $\left(E_F\right)$ explains the main features of this unconventional behavior in the transport coefficients and its evolution under pressure.

Figure 1

(Color online) The wide-range temperature dependencies of resistivity (left) and thermoelectric power (right) at ambient pressure.

Figure 2

(Color online) The temperature dependence of resistivity for various pressures. The lowest curve is the ambient pressure resistivity. As pressure is applied, the resistivity increases. The inset shows the pressure dependence of the relative change of the resistivity with respect to its value at ambient pressure for various temperatures.

Figure 3

(Color online) The temperature dependence of the thermoelectric power is shown at different pressures. This transport coefficient decreases in the absolute value as pressure is applied.

Figure 4

The ambient pressure resistivity (top) and TEP (bottom) fitted by the model depicted in the top panel inset. In the DOS model, the dashed vertical line sets the position of the band filling at $T=0$, the values of the DOS in different regions are indicated by $g_w$ and $g_n$, and ${\sigma }_w$ and ${\sigma }_n$ are the respective conductivity parameters. The origin of the energy scale is set to the center of the enhanced part of the DOS.