The in- and out-of-plane magnetisation of highly underdoped YBa₂Cu₃O_6+x single crystals

Abstract Previously we have shown how measurements of static magnetic susceptibility χ c (T) YBa 2 Cu 3 O 6+x single crystals for fields applied along the -axis, and ab in ab-plane , can give useful information about their thermodynamic properties which are still being hotly debated. SQUID magnetometry above superconducting (s/c) transition temperature T is used larger crystals, while piezolever torque gives (T)-χ tiny crystals. Here present new data more heavily under-doped with hole concentrations per CuO plane, p =0.058 to 0.073. We again find that T-dependent anisotropy well arises from pseudogap g-factor anisotropy, at lower there Gaussian s/c fluctuations a strong cut-off. This possibly different region where neutron scattering studies evidence competition between incommensurate short-range order superconductivity. studied three values x, measuring immediately after fixing x by quenching on copper block allowing sufficient time room Cu-O chains order. Thus, report pairs underdoped (UD) ranging 13 36 K, namely UD13 UD20, UD15 UD30, UD23 UD36. As found previously polycrystalline samples, ordering increases substantially reduces Curie term. These isotropic, contrast Pauli-like planes g factor this allows us make powerful novel analysis. At higher T, (T)- varies as + bT term pseudogap. deviations behaviour analysed terms 2D or 3D obtain in-plane coherence lengths upper critical T→0.