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Register a new userMuon Spin Rotation Measurements of Heterogeneous Field Response in Overdoped La2-xSrxCuO4
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Transverse-field muon spin rotation measurements of overdoped La2-xSrxCuO4 reveal a large broadening of the local magnetic field distribution in response to applied field, persisting to high temperatures. The field-response is approximately Curie-Weiss like in temperature and is largest for the highest doping investigated. Such behaviour is contrary to the canonical Fermi-liquid picture commonly associated with the overdoped cuprates and implies extensive heterogeneity in this region of the phase diagram. A possible explanation for the result lies in regions of staggered magnetization about dopant cations, analogous to what is argued to exist in underdoped systems.
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We have measured the temperature dependence and magnitude of the superfluid density $rho_{rm s}(T)$ via the magnetic field penetration depth $lambda(T)$ in PuCoGa$_5$ (nominal critical temperature $T_{c0} = 18.5$ K) using the muon spin rotation technique in order to investigate the symmetry of the order parameter, and to study the effects of aging on the superconducting properties of a radioactive material. The same single crystals were measured after 25 days ($T_c = 18.25$ K) and 400 days ($T_c = 15.0$ K) of aging at room temperature. The temperature dependence of the superfluid density is well described in both materials by a model using d-wave gap symmetry. The magnitude of the muon spin relaxation rate $sigma$ in the aged sample, $sigmapropto 1/lambda^2proptorho_s/m^*$, where $m^*$ is the effective mass, is reduced by about 70% compared to fresh sample. This indicates that the scattering from self-irradiation induced defects is not in the limit of the conventional Abrikosov-Gorkov pair-breaking theory, but rather in the limit of short coherence length (about 2 nm in PuCoGa$_5$) superconductivity.
Using the transverse field muon spin relaxation technique we measure the temperature dependence of the magnetic field penetration depth $lambda$, in the Na$_{x}$CoO$_{2}cdot y$H$_{2}$O system. We find that $lambda,$ which is determined by superfluid density $n_{s}$ and the effective mass $m^{ast}$, is very small and on the edge of the TF-$mu$SR sensitivity. Nevertheless, the results indicate that the order parameter in this system has nodes and that it obeys the Uemura relation. By comparing $lambda$ with the normal state electron density we conclude that $m^{ast}$ of the superconductivity carrier is 70 times larger than the mass of bare electrons.
Relationship between the superconducting gap and the pseudogap has been the subject of controversies. In order to clarify this issue, we have studied the superconducting gap and pseudogap of the high-Tc superconductor La2-xSrxCuO4 (x=0.10, 0.14) by angle-resolved photoemission spectroscopy (ARPES). Through the analysis of the ARPES spectra above and below Tc, we have identified a superconducting coherence peak even in the anti-nodal region on top of the pseudogap of a larger energy scale. The superconducting peak energy nearly follows the pure d-wave form. The d-wave order parameter Delta_0 [defined by Delta(k)=Delta_0(cos(kxa)-cos(kya)) ] for x=0.10 and 0.14 are nearly the same, Delta_0 ~ 12-14 meV, leading to strong coupling 2Delta_0/kB Tc ~ 10. The present result indicates that the pseudogap and the superconducting gap are distinct phenomena and can be described by the two-gap scenario.
We have investigated the doping and temperature dependences of the pseudogap/superconducting gap in the single-layer cuprate La$_{2-x}$Sr$_x$CuO$_4$ by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around ($pi$,0) of magnitude $Delta^*$ and the gap around the node characterized by the d-wave order parameter $Delta_0$, like the double-layer cuprate Bi2212. In comparison with Bi2212 having higher $T_c$s, $Delta_0$ is smaller, while $Delta^*$ and $T^*$ are similar. This result suggests that $Delta^*$ and $T^*$ are approximately material-independent properties of a single CuO$_2$ plane, in contrast the material-dependent $Delta_0$, representing the pairing strength.
Using angle-resolved photoemission spectroscopy it is revealed that in the vicinity of optimal doping the electronic structure of La2-xSrxCuO4 cuprate undergoes an electronic reconstruction associated with a wave vector q_a=(pi, 0). The reconstructed Fermi surface and folded band are distinct to the shadow bands observed in BSCCO cuprates and in underdoped La2-xSrxCuO4 with x <= 0.12, which shift the primary band along the zone diagonal direction. Furthermore the folded bands appear only with q_a=(pi, 0) vector, but not with q_b= (0, pi). We demonstrate that the absence of q_b reconstruction is not due to the matrix-element effects in the photoemission process, which indicates the four-fold symmetry is broken in the system.
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