Based on specific heat and magnetoresistance measurements, we report that a “heavy” electronic state exists below $T$ ≈ 20 K in KNi${}_2$Se${}_2$, with an increased carrier mobility and enhanced effective electronic band mass, $m^{*}$ = 6$m_{\mathrm{b}}$ to 18$m_{\mathrm{b}}$. This heavy state evolves into superconductivity at $T_{\mathrm{c}}$ = 0.80(1) K. These properties resemble that of a many-body heavy-fermion state, which derives from the hybridization between localized magnetic states and conduction electrons. Yet, no evidence for localized magnetism or magnetic order is found in KNi${}_2$Se${}_2$ from magnetization measurements or neutron diffraction. Instead, neutron pair-distribution-function analysis reveals the presence of local charge-density-wave distortions that disappear on cooling, an effect opposite to what is typically observed, suggesting that the low-temperature electronic state of KNi${}_2$Se${}_2$ arises from cooperative Coulomb interactions and proximity to, but avoidance of, charge order.

• Received 16 July 2012

DOI:https://doi.org/10.1103/PhysRevB.86.054512