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A polarised X-ray absorption study is made on an underdoped YBCO substantially detwinned single crystal to study the anomalous temperature dependence of itinerant holes, charge aggregation and pair formation along the E∥b and E∥a directions. The measurements were made at the O K and Cu L3 edges varying the temperature from 10 K to room temperature (∼300 K) using a liquid helium cryostat. In earlier reports on the YBCO reported observing the charge aggregation and the Cooper pair formation taking place only once each at temperatures T∗ and T∗∗, both greater than Tc we observe these phenomena repeating themselves at two more temperatures, still in the normal state though. We have observed much smaller magnitude of the fluctuations of the itinerant holes in the ‘a’-direction as compared to ‘b’-direction in our experiment. Our results at T

Here we report use of angle scanning photoemission spectroscopy using polarized synchrotron light to explore the Fermi surface topology of Bi 2 Sr 2 CaCu 2 O 8± δ superconductors. The measurements were made in different experimental geometry to take care of the polarization dependence of photoemission transition probability (matrix element effect) and discriminate the true features along the high symmetry directions. We find an asymmetric suppression of spectral weight around M(π,0) point indicating coupling of the itinerant carriers with an incommensurate charge density wave (ICDW) i.e. stripes, involving modulation of the orbital momentum.

Penetration depth λ ( T ) has been derived from the measurements of temperature-dependent complex conductivity on Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212) superconducting system using a single-coil inductance method. Temperature dependence of λ ( T ) in the vicinity of the superconducting transition temperature has been used to explore the fluctuations of the superconducting order parameter. Doping dependence of these fluctuations reveals that the fluctuation region in the underdoped system is far greater than in the optimally doped system. We find a linear doping dependence of the fluctuation region below T c , suggesting that superfluid density might be the only parameter to control these fluctuations.

We have studied momentum distribution of photoemission intensity around the Fermi surface of Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212) high T c superconductor by angle-resolved photoemission. The line shape of the energy distribution curves show a spectral function A ( k , ω ) expected for a non-Fermi liquid behaviour. The Fermi surface contour in the `even symmetry' reveals the suppression of spectral weight due to coupling with joint incommensurate charge density wave (ICDW) at q (−0.4 π ,0.4 π ) in the diagonal direction and the spin density wave (SDW) at G ( π , π ). Additional spectral weight is found at (0.6 π ,0.6 π ) due to scattering of electrons with SDW at optimum doping as revealed by constant energy contour in `odd symmetry'.

The structure of HgBa 2 CuO 4+δ is studied as function of temperature by neutron diffraction and Cu-Kedge EXAFS on the same powder sample with Tc=97K. Both techniques reveal the presence of an anomalous behaviour of the Cu O in-plane bond length starting at ≈140K.