(received ; accepted) PACS. 63.20Kr – Phonon-electron and phonon-phonon interactions. PACS. 75.30Et – Exchange and superexchange interactions. PACS. 78.30−j – Infrared and Raman spectra. Abstract. – We show that the asymmetric crystal environment of the V site in the ladder compound NaV2O5 leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the c...

The magnetic excitations of a double-exchange ~DE! model are usually discussed in terms of an equivalent ferromagnetic Heisenberg model. We argue that this equivalence is valid only at a quasiclassical level—both quantum and thermal corrections to the magnetic properties of a DE model differ from any effective Heisenberg model because its spin excitations interact only indirectly, through the e...

In the presence of Hubbard interaction, graphene zigzag nanoribbons have spontaneous edge magnetism with anti-parallel configuration, whose amplitude can be tuned by a transversal electric field. As field increases or decreases across critical value, edges are demagnetized re-magnetized, respectively. A magnetic at each determines orientation re-magnetization. Thus, combination slowly varying a...

We consider ferromagnetism in spatially randomly located magnetic moments, as in a diluted magnetic semiconductor, coupled via the carrier-mediated indirect exchange RKKY interaction. We obtain, via Monte Carlo calculations, the magnetic phase diagram as a function of the impurity moment density n(i) and the relative carrier concentration n(c)/n(i). As evidenced by the diverging correlation len...

Cooper pairing instability in a Fermi liquid is well understood by the BCS theory, but pairing mechanism for doped Mott insulators still remains elusive. Previously it has been shown by density matrix renormalization group (DMRG) method that a single doped hole is always self-localized due to the quantum destructive interference of the phase string signs hidden in the t-J ladders. Here we repor...

We describe the ferromagnetism in the manganese pyrochlores, such as Tl2Mn2O7 and Sc2Mn2O7 , in terms of the interplay between superexchange, Zener double exchange, and indirect exchange, the first being antiferromagnetic ~AF! while the last two are ferromagnetic. The tendency towards the antiferroalignment of the localized Mn spins is significantly weakened due to ~i! the presence of spin frus...

J.-S. Zhou,1,* J. A. Alonso,2 V. Pomjakushin,3 J. B. Goodenough,1 Y. Ren,4 J.-Q. Yan,5 and J.-G. Cheng1 1Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, USA 2Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain 3Laboratory for Neutron Scattering, Paul Scherrer Institut, ETH Zurich, CH-5232 Villigen PSI, Switzerland 4Advanced Photo...

The lowest eigenenergies of few, strongly interacting electrons in a one–dimensional ring are studied in presence of an impurity barrier. The persistent current I , periodic in an Aharonov–Bohm flux penetrating the ring, is strongly influenced by the electron spin. The impurity does not remove discontinuities in I at zero temperature. The total electron spin of the ground state oscillates with ...

Multiferroics, where two or more ferroic order parameters coexist, is one of the hottest fields in condensed matter physics and materials science. To search multiferroics, currently most researches are focused on frustrated magnets, which usually have complicated magnetic structure and low magnetic ordering temperature. Here, we argue that actually simple interatomic magnetic exchange interacti...