Low Temperature Two Fluid State in SmB6

TL;DR

This study uncovers a complex, temperature-dependent two-fluid electronic state in SmB6, revealing surface Kondo revival, magnetic fluctuations, and a crossover from capacitive to inductive behavior, advancing understanding of its topological surface states.

Contribution

It provides a detailed experimental characterization of the temperature regimes and electronic phases in SmB6, highlighting the interplay between Kondo breakdown, magnetic fluctuations, and surface state stabilization.

Findings

Identification of three temperature regimes with distinct electronic behaviors.

Observation of a surface Kondo revival below 40 K.

Detection of a crossover from capacitive to inductive impedance behavior.

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) $T \geq T^{*}$ ($\sim66$K), (ii) $T_g$ ($\sim40$ K) $\leq T < T^{*}$, and (iii) $T < T_g$. Onset of Kondo breakdown below $T^{*}$ releases disorder-driven magnetic fluctuations, which splits the bulk ($\sim116$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 ($\sim2.2$ 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, $L_{\nu_0}(T)$, 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$_6$.