Ginzburg-Landau functional for nearly antiferromagnetic perfect and disordered Kondo lattices

Abstract

Interplay between Kondo effect and trends to antiferromagnetic and spin glass ordering in perfect and disordered bipartite Kondo lattices is considered. Ginzburg-Landau equation is derived from the microscopic effective action written in three mode representation (Kondo screening, antiferromagnetic correlations and spin liquid correlations). The problem of local constraint is resolved by means of Popov-Fedotov representation for localized spin operators. It is shown that the Kondo screening enhances the trend to a spin liquid crossover and suppresses antiferromagnetic ordering in perfect Kondo lattices and spin glass ordering in doped Kondo lattices. The modified Doniach's diagram is constructed, and possibilities of going beyond the mean field approximation are discussed.

An unusual interplay among disorder, Kondo-effect and spin-glass behavior in the Kondo lattices, Ce2Au1−xCoxSi3

“…It is intriguing to note that the disorder-induced spin-glass behavior is realised only at the weak coupling limit, but not close to QCP, in contrast to the hitherto observed, predicted or assumed behavior. [1][2][3][4][5] Absence of this disorder effect at QCP is surprising, particularly considering that a stoichiometric end of the solid solution is by itself a spin-glass. It is therefore a real theoretical challenge to understand this unusual interplay among the disorder, spin-glass ordering and the Kondo effect.…”

“…This made this topic of research more fascinating and new theoretical ideas have been initiated in the recent literature under the assumption that such disorder effects are operative only at QCP. [3][4][5] In this Letter, we bring out a counter-example, viz., the recently discovered 6,7 solid solution, Ce 2 Au 1−x Co x Si 3 , in which spin-glass behavior in fact is observed only when one approaches the weak coupling limit, that is, as one moves towards larger unit-cell volume. In otherwords, this glassy behavior surprisingly gets suppressed with increasing chemically-induced disorder as one approaches QCP, as though increasing Kondo interaction strength plays an unusual role of favoring long-range magnetic order at the expense of spin-glass behavior.…”

Kondo lattice without Nozières exhaustion effect

“…by means of the Hubbard-Stratonovich scheme [15] in terms of the fields [9,16] [17]. These two fields resolve Doniach's dichotomy, because the long-range AFM order is absent in 1D.…”

“…According to a scenario offered in [8,9], in the critical region |I| ∼ T K of Doniach's phase diagram, where the magnetic correlations are nearly suppressed by the on-site Kondo coupling, the spin liquid phase enters the game. This phase is characterized by the energy scale…”

“…In order to describe the Doniach-like phase diagram we adopt the method of [9]. Namely, we derive an effective action functional by integrating out all "fast" fermionic degrees of freedom with the energies ∼ D 0 , where 2D 0 is the conduction bandwidth.…”