%0 Book Section %1 statphys23_0866 %A Bertussi, P.R. %A Malvezzi, A.L. %A Paiva, T. %A Rappaport, T.G. %A Santos, R.R. Dos %B Abstract Book of the XXIII IUPAP International Conference on Statistical Physics %C Genova, Italy %D 2007 %E Pietronero, Luciano %E Loreto, Vittorio %E Zapperi, Stefano %K borocarbides coexistence fermions heavy magnetism magnetism-superconductivity statphys23 superconductivity topic-8 %T Coexistence of magnetism and superconductivity: a microscopic model %U http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=866 %X In recent years, coexistence between magnetic order and superconductivity has been detected in a variety of materials such as some heavy fermions and borocarbides. For the latter class of materials, in particular, local moments originating from 4f electrons may become magnetically ordered, while itinerant electrons can form Cooper pairs. We propose a simple model to describe these systems, which incorporates these two tendencies by considering an effective attraction, $U$, whenever two band electrons occupy the same site, and a Kondo coupling, $J$, between the spins of the band electrons (s) and the local moments (S). DMRG studies of this model in one dimension, allow us to discuss magnetic correlation functions ($ ss $, $SS$, and $sS$, the latter measuring the condensation of Kondo singlets), pairing correlations, and charge correlations, as well as their respective structure factors, for wide ranges of $U$ and $J$ and for a filling factor 1/3. We have found numerical evidence of distinct magnetic orderings for the local moments coexisting with superconductivity of band spins, the latter without magnetic ordering. Based on these results, a zero-temperature phase diagram is proposed. For large values of $U$, there is a single transition, as a function of $J/U$, between a state with coexistence superconducting and spin-density wave (SDW) and a spiral ferromagnetic one. For intermediate values of $U$, an incommensurate SDW (ISDW) coexists with superconductivity at small $J/U$; as the latter increases, first superconductivity disappears, while the ISDW phase remains, and then it changes to a spiral ferromagnetic.

@incollection{statphys23_0866, abstract = {In recent years, coexistence between magnetic order and superconductivity has been detected in a variety of materials such as some heavy fermions and borocarbides. For the latter class of materials, in particular, local moments originating from 4f electrons may become magnetically ordered, while itinerant electrons can form Cooper pairs. We propose a simple model to describe these systems, which incorporates these two tendencies by considering an effective attraction, $U$, whenever two band electrons occupy the same site, and a Kondo coupling, $J$, between the spins of the band electrons ({\bf s}) and the local moments ({\bf S}). DMRG studies of this model in one dimension, allow us to discuss magnetic correlation functions ($ \langle{\bf s}\cdot {\bf s} \rangle $, $\langle {\bf S}\cdot {\bf S}\rangle $, and $\langle {\bf s}\cdot {\bf S}\rangle $, the latter measuring the condensation of Kondo singlets), pairing correlations, and charge correlations, as well as their respective structure factors, for wide ranges of $U$ and $J$ and for a filling factor 1/3. We have found numerical evidence of distinct magnetic orderings for the local moments coexisting with superconductivity of band spins, the latter without magnetic ordering. Based on these results, a zero-temperature phase diagram is proposed. For large values of $U$, there is a single transition, as a function of $J/U$, between a state with coexistence [superconducting and spin-density wave (SDW)] and a spiral ferromagnetic one. For intermediate values of $U$, an incommensurate SDW (ISDW) coexists with superconductivity at small $J/U$; as the latter increases, first superconductivity disappears, while the ISDW phase remains, and then it changes to a spiral ferromagnetic.}, added-at = {2007-06-20T10:16:09.000+0200}, address = {Genova, Italy}, author = {Bertussi, P.R. and Malvezzi, A.L. and Paiva, T. and Rappaport, T.G. and Santos, R.R. Dos}, biburl = {https://www.bibsonomy.org/bibtex/2c801055427224b16d224ddd8c75273e2/statphys23}, booktitle = {Abstract Book of the XXIII IUPAP International Conference on Statistical Physics}, editor = {Pietronero, Luciano and Loreto, Vittorio and Zapperi, Stefano}, interhash = {3a20a0a4bb6631d0ac173c7d0fb6fa73}, intrahash = {c801055427224b16d224ddd8c75273e2}, keywords = {borocarbides coexistence fermions heavy magnetism magnetism-superconductivity statphys23 superconductivity topic-8}, month = {9-13 July}, timestamp = {2007-06-20T10:16:31.000+0200}, title = {Coexistence of magnetism and superconductivity: a microscopic model}, url = {http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=866}, year = 2007 }