“…Moreover, since the ability of these anisotropies to affect the VL structure decreases with increasing vortex separation, one commonly finds a hexagonal VL at low fields which undergoes a transition to a square symmetry as the field is increased. Materials where such a field-driven hexagonal to square VL transition have been observed includes members of the nickelborocarbide superconductors [14][15][16][17][18][19][20][21][22], V 3 Si [23,24], LSCO [25], CeCoIn 5 [26,27], YBCO [4,28], and NCCO [29]. Notable exceptions to this are BSCCO [30,31], and more recently HgBa 2 CuO 4+δ [32].…”