# Laboratoire de Physique ThéoriqueToulouse - UMR 5152

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## Exceeding the Pauli limit

par - 20 septembre 2006

Superconducting doped ladders under a magnetic field parallel to their plane reveal interesting novel phases and phenomena, including irrational magnetization plateaus and exceeding of the Pauli limit, as was shown recently by members of the Laboratory in collaboration with Steve White (UC Irvine).

The magnetization curve displays two plateaus, one with and one with , where is the hole density. These plateaus are typical effects of strong interactions between electrons and mostly found in low-dimensional strongly-correlated systems. In this particular case, the magnetization plateau with has a value controlled by doping and thus is irrational contrary to undoped systems for which rational values only are expected. This plateau phenomenologically originates from an energetic stabilization of holes with polarized electrons.

Furthermore, the superconducting critical field of the system is found to be much larger than the Pauli limit . Such a surprising exceeding of this limit can be explained by the existence of a wide Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase. Lastly, non-polarized triplet correlations emerge at high magnetic field : a signature of the modification of the magnetic fluctuations which occur under magnetic field.

The corresponding paper, Zeeman Effect in Superconducting Two-Leg Ladders : Irrational Magnetization Plateaus and Exceeding the Pauli Limit has been published in Physical Review Letters 97, 087207 (2006). The corresponding author in the laboratory is Guillaume Roux