THE NOVEL PROPERTIES OF A VORTEX STATE IN D-WAVE SUPERCONDUCTIVITY

The vortex state of d-wave superconductivity in high-T-c cuprates exhi bits a number of properties unexpected for conventional s-wave superco nductivity. First of all, in a magnetic field parallel to the c-axis, a square lattice tilted by 45 degrees from the a-axis is the most stab le for T less than or equal to 0.88 T-c; this has been observed by usi ng a small-angle neutron scattering experiment and STM imaging in YBCO monocrystals. Second, as seen in recent torque magnetometry on an YBC O monocrystal, when a magnetic field is in the a-b plane, the upper cr itical field exhibits a fourfold symmetry. Furthermore, the sine-wave- like Fulde-Ferrell-Larkin-Ovchinikov state is expected to appear at lo w temperatures.