The dodecaboride LuB12 with cage-glass state and rattling modes has been studied to clarify the nature of the large amplitude vibrations of Lu ions. Discovered anisotropy of charge transport in conjunction with distortions of the conventional fcc symmetry of the crystal lattice may be attributed to coherent motion of Lu ions along singular direction in the lattice. Arguments are presented in favor of cooperative dynamic Jahn-Teller effect in the boron sublattice to be the reason of the rattling mode, lattice distortion and formation of the filamentary structure of the conductive channels. PACS numbers: 61.66.Fn, 72.15.Gd:
The model strongly correlated electron system Ho 0.8 Lu 0.2 B 12 which demonstrates a cooperative Jahn-Teller instability of the boron sub-lattice in combination with rattling modes of Ho(Lu) ions, dynamic charge stripes and unusual antiferromagnetic (AF) ground state has been studied in detail at low temperatures by magnetoresistance (Δρ/ρ), magnetization and heat capacity measurements. Based on received results it turns out that the angular H-φ-T magnetic phase diagrams of this non-equilibrium AF metal can be reconstructed in the form of a "Maltese cross". The dramatic AF ground state symmetry lowering of this dodecaboride with fcc crystal structure can be attributed to the redistribution of conduction electrons which leave the RKKY oscillations of the electron spin density to participate in the dynamic charge stripes providing with extraordinary changes in the indirect exchange interaction between magnetic moments of Ho 3+ ions and resulting in the emergence of a number of various magnetic phases. It is also shown that the two main contributions to magnetoresistance in the complex AF phase, the (i) positive linear on magnetic field and the (ii) negative quadratic -Δρ/ρ~H 2 component can be separated and analyzed quantitatively, correspondingly, in terms of charge carrier scattering on spin density wave (5d) component of the magnetic structure and on local 4f-5d spin fluctuations of holmium sites. PACS: 72.15.Qm, 72.15.Gd I. INTRODUCTION. The complexity of strongly correlated electron systems (SCES) is a subject of active debates, and numerous investigations have been carried out to clarify its nature [see e.g. [1-2]).In recent years it was demonstrated that at least some of SCES are spatially inhomogeneous materials and that their electronic complexity arises from charge, spin, lattice and orbital degrees of freedom which act simultaneously, leading to giant responses at small perturbations [1-5].Moreover, when several metallic and insulating phases compete, it creates the potential for novel behavior and practical applications, and well-known examples of it are the Mn oxides called manganites [1,[6][7][8][9][10][11][12], high temperature superconducting cuprates [1][2][3][4][13][14][15][16], iron-based pnictides and chalcogenides [4][5][17][18][19][20], etc. Among the widely discussed issues in these materials are very complicated phase diagrams with various magnetic phases and ground states in combination with diverse mechanisms responsible for their competition and stabilization [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. According to conclusions of ref. 7, the ground states diversity and mixed-phase tendencies have two origins: (i) electronic phase separation between phases with different densities that leads to nanometer scale coexisting clusters, and (ii) disorder-induced phase separation with
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