Doped ladders under magnetic field studied by Density-Matrix Renormalization Group
Jeudi 18/01/2007, 11:00
Petit Amphi, LPS Bât. 510, Orsay
The effect of a parallel magnetic field on superconducting two-leg
ladders is investigated numerically. The magnetization curve displays an
irrational plateau at a magnetization equal to the hole density.
Remarkably, its stability is fundamentally connected to the existence of
a well-known magnetic resonant mode. Once the zero-field spin gap is
suppressed by the field, pairs acquire a finite momentum characteristic
of a Fulde-Ferrell-Larkin-Ovchinnikov phase. In addition, $S^z=0$ triplet
superconducting correlations coexist with singlet ones above the
irrational plateau. This provides a simple mechanism in which the Pauli
limit is exceeded as suggested by recent experiments.