Low Temperature Two Fluid State in SmB6

Abstract

Comprehensive study using DC transport, specific heat, magnetization, and two-coil mutual inductance measurements unveils an understanding of three temperature regimes in SmB${}_6$: (i) $T\ge T^{\ast }$ ($\sim 66$K), (ii) $T_g$ ($\sim 40$ K) $\le T<T^{\ast }$, and (iii) $T<T_g$. Onset of Kondo breakdown below $T^{\ast }$ releases disorder-driven magnetic fluctuations, which splits the bulk ($\sim 116$K) and surface Kondo temperature ($T_k^s\approx 7$ K). Below $T_g$, as magnetic fluctuations subside, surface Kondo screening revives, stabilizing the topological surface state and generating an in-gap feature ($\sim 2.2$ meV) across which Dirac-like carriers are excited. Nyquist impedance analysis reveals a crossover from purely capacitive to capacitive-inductive behavior, signalling a disorder-driven two-fluid phase of heavy quasiparticles and light, high-mobility carriers below $T_g$. We identify a characteristic length scale, $L_{\hat{I}{½}_0}(T)$, associated with the high-mobility phase, exhibiting an almost divergent trend below $T_k^s$. These findings underscore the complex nature of the surface conducting state in SmB${}_6$.