Session 22bB

Transport and Optical Study of the Competition between Stripe and Superconducting Orders in La-214 Cuprates

Shin-ichi Uchida

Graduate School of Frontier Sciences, University of Tokyo, Tokyo 113-8656, Japan

We have investigated the Hall coefficient (R_H) and the c-axis optical spectrum of La_2-x-yNd_ySr_xCuO₄ by applying various perturbations to this system, magnetic field, Zn-impurity doping, changing the Nd content, and applying pressures. The suppression of R_H and the reduction of the c-axis Josephson plasma frequency are most remarkable phenomena observable when the stripe order overwhelms the superconducting order. It is found that pressure which exert the in-plane strain most effectively control the competition between these two orders.

Superconductivity Induced Transfer of Spectral Weight in Bi₂Sr₂CaCu₂O_8+d

Dirk van der Marel^a, Hajo J. A. Molegraaf^a, Cristian-Nicolae Presura^a, Peter H. Kes^b, Ming Li^b

^aMaterials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands

^bKamerlingh Onnes Laboratory, Leiden University, P.O.Box 9504, 2300 RA Leiden, The Netherlands

Optical data are reported of a spectral weight transfer over a broad frequency range of Bi₂Sr₂CaCu₂O_8+d when this material becomes superconducting. Using spectroscopic ellipsometry, we observe the removal of a small amount of spectral weight in a broad frequency band from 10⁴cm^-1 to at least 2*10⁴cm^-1, due to the onset of superconductivity. We observe a blue-shift of the ab-plane plasma frequency when the material becomes superconducting, indicating that the spectral weight is transferred to the infrared range. Our observations are in agreement with models where superconductivity is accompanied by a decrease of the in-plane kinetic energy of the charge carriers.

Phase diagram of cuprates derived from the Nernst effect

N. P. Ong^a, Yayu Wang^a, Z. A. Xu^b, T. Kakeshita^c, S. Uchida^c, D. A. Bonn^d, R. Liang^d, W.N. Hardy^d

^aDepartment of Physics, Princeton University, Princeton, New Jersey 08544, U.S.A.

^bDepartment of Physics, Zhejiang University, Hangzhou, China

^cSchool of Frontier Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan

^dDepartment of Physics and Astronomy, University of British Columbia, BC V6T 1Z1, Canada

Measurements of the Nernst signal in the vortex-liquid state of several cuprates families reveal that vorticity extends to very high fields (30 T) even close to the zero-field critical temperature T_c0. The upper critical field H_c2, derived from the vortex line-entropy, does not end at T_c0, but at a much higher temperature. These results imply that T_c0 corresponds to a loss in phase rigidity rather than a vanishing of the pairing amplitude.