Realistic many-body theory of Kondo insulators: Renormalizations and fluctuations in Ce$_3$Bi$_4$Pt$_3$

Abstract

Our theoretical understanding of heavy-fermion compounds mainly derives from iconic models, such as those due to Kondo or Anderson. While providing invaluable qualitative insight, detailed comparisons to experiments are encumbered by the materials' complexity, including the spin-orbit coupling, crystal fields, and ligand hybridizations. Here, we study the paradigmatic Kondo insulator Ce3Bi4Pt3 with a first principles dynamical mean-field method that includes these complications. We find that salient signatures of many-body effects in this material-large effective masses, the insulator-to-metal crossover, the concomitant emergence of Curie-Weiss behaviour and notable transfers of optical spectral weight-are captured quantitatively. With this validation, we elucidate the fabric of the many-body state. In particular, we extent the phenomenology of the Kondo crossover to time-scales of fluctuations: We evidence that spin and charge degrees of freedom each realize two regimes in which fluctuations adhere to vastly different decay laws. We find these regimes to be separated by a common temperature T max χ , linked to the onset of Kondo screening. Interestingly, below (above) T max χ , valence fluctuations become faster (slower) than the dynamical screening of the local moments. Overall, however, spin and charge fluctuations occur on comparable time-scales of O(0.5 − 12 fs), placing them on the brink of detection for modern time-resolved probes.

Resistivity saturation in Kondo insulators

“…with the Kondo scenario [16,17]. While a topological bulk state has been envisaged [18], experiments argue against surface-dominated transport [6].…”

Prototypical many-body signatures in transport properties of semiconductors

“…(32)(33), fulfill Eq. (46). In this sense, the saturation of both σ xx and σ B xy dictates the Nernst coefficient to vanish linearly for T → 0.…”

“…1. For instance, other marcasite compounds (FeAs 2 , RuSb 2 [17,[23][24][25], CrSb 2 [26]), silicides (FeSi [27][28][29], RuSi [30][31][32]), Heusler systems (e.g., Fe 2 VAl [33][34][35][36][37]), other intermetallic compounds [38] (e.g., FeGa 3 , RuGa 3 [18,39,40]), as well as Kondo insulators (e.g., Ce 3 Bi 4 Pt 3 [22,[41][42][43][44][45][46])-strongly suggesting that our scenario based on carriers with finite lifetimes is prototypical for a wide array of different systems.…”

Characteristic Timescales of the Local Moment Dynamics in Hund’s Metals

“…While the dynamics of the magnetic moments is particularly intriguing in the Hund's metal materials considered here, the same procedure is directly applicable to all many-electron systems and to fluctuations of different kinds [2]. A precise quantification of the characteristic time scales may provide new keys to connect the findings of equilibrium and out-of-equilibrium spectroscopies, as well as crucial information on the applicability of adiabatic spin dynamics approaches [25].…”

“…Their proper description is indeed a key to understanding many-electron systems beyond the conventional band-theory framework. The formation of sizable local moments and their screening-processes is central to: The Kondo physics [1,2], Mott-Hubbard [3][4][5] or Mott-Hund's [6][7][8][9][10] metal-insulator transitions, quantum-criticality of heavy fermion systems [11,12], magnetic and spectroscopic properties of Ni and Fe [13][14][15] and of unconventional superconductors [16].…”