The Ground-state Inter-plane Superconducting Coherence Length of La1.875_{1.875}Sr0.125_{0.125}CuO4_4 Measured by a "Xiometer"

A long excitation coil piercing a superconducting (SC) ring is used to generate ever increasing persistent current in the ring, until the current destroys the order parameter. Given that the penetration depth $\lambda$ is known, this experiment measures, hypothetically, the coherence length $\xi$, hence the name "Xiometer". We examine various aspects of this theoretically driven hypothesis by testing niobium rings with different dimensions, and by comparing the results to the known values of $\xi$. We then apply the method to two La$_{1.875}$Sr$_{0.125}$CuO$_4$ rings at $T \rightarrow 0$. In one, the current flows in the CuO$_2$ planes hence it is set by $\xi_{ab}$. In the other, the current must cross planes and is determined by $\xi_{c}$. We find that $\xi_{c}=1.3 \pm 0.1$~nm, and $\xi_{ab}<2.3~$nm indicating that at low temperatures the Cooper pairs are three dimensional.Comment: 6 pages with 7 figure

Lack of static lattice distortion in Tb2Ti2O7Tb_2 Ti_2 O_7

We investigated the possibility of temperature dependent lattice distortions in the pyrochlore compound Tb$_{2}$Ti$_{2}$O$_{7}$ by measuring the internal magnetic field distribution, using muon spin resonance, and comparing it to the susceptibility. The measurements are done at temperatures as low as 70 mK and external fields up to 6 kG. We find that the evolution of the width of the field distribution can be explained by spin susceptibility only, thus ruling out a temperature dependent hyperfine coupling. We conclude that lattice deformations are absent in Tb$_{2}$Ti$_{2}$O$_{7}$.Comment: 8 pages, 5 figures, accepted for publication in J. Phys. Condens. Matter. (Proceedings of Highly Frustrated Magnetism 2006); Corrections of various typo