Spin density wave and pseudogap in HTSC cuprates

The evidence for the spin density wave (SDW) nature of the pseudogap in HTSC cuprates is presented from resistive and direct gap measurements (ARPES, tunneling experiments, etc.). Its d-wave symmetry mimics the symmetry of the order parameter measured in the SC state. The magnetic phase $H-T$ diagram for HTSC cuprates is formed. The possible influence of an additional (SDW) order parameter on the vortex structure in the applied magnetic field is analysed. The behavior is discussed in terms of itinerant electron systems with interplay between superconductivity and magnetism.