High Temperature Superconductors

High temperature superconducting cuprates have been the subject of intense research for the past 20 years, e.g. ever since their discovery.  However, the mechanism of their superconductivity remains one of the mysteries of modern condensed matter physics. The difficulty in understanding these systems arises essentially from the fact that the problem consists of many puzzle pieces representing the many degrees of freedom – lattice, charge, spin etc. – that are intricately intertwined with each other. 




Naturally, there are numerous on-going controversies, experimental and theoretical, surrounding these cuprates. rties of these systems through angle resolved photoemission spectroscopy (ARPES) in order to answer the most important questions in this field.  Because of the anisotropic nature of the superconducting order parameter, uniquely momentum-dependent angle resolved photoemission spectroscopy (ARPES) has been an essential tool.  According to the nobelist P. W. Anderson, ARPES “has been the most useful spectroscopy for the high-Tc superconductors, playing the key role which tunneling played for conventional superconductors.”  

1. Unambiguously single out the role of the lattice in high temperature superconductivity by measurements on isotope-substituted samples and also by studying the role of the lattice strain.  This direct approach is pioneered in this group and our results are revealing unusual and striking ways that the lattice degrees of freedom influence the valence electrons.  When this piece of the puzzle, i.e. the lattice piece, is properly understood, the picture of high temperature superconductivity is expected to become much clearer.
2. Understand the role of the spin degrees of freedom through spin-resolved photoemission experiments.  This study will provide the first high resolution spin-ARPES study of these materials and allow to investigate proposition as the Zhang Rice singlet picture.
3. Search for competing orders in ARPES.
4. Draw a comparison between real momentum probes such as scanning tunneling measurements and ARPES.

For more information see Cond-mat/0505333

Selected Publications (please see publications for a more complete list)

Universal high energy anomaly in the electron spectrum of high temperature superconductors by angle-resolved photoemission spectrascopy

J. Graf, G.-H. Gweon, K. McElroy, S.Y. Zhou, C. Jozwiak, E. Rotenberg, A. Bill, T. Sasagawa, H. Eisaki, S. Uchida, H. Takagi, D.-H. Lee, and A. Lanzara

Submitted to Phys. Rev. Lett (2006), cond-mat/0607319

Non-Migdal-Eliashberg electron-lattice interaction in optimally doped Bi2Sr2CaCu2O8+x

G.-H. Gweon, S. Y. Zhou, M. C. Watson, T. Sasagawa, H. Takagi, and A. Lanzara

Submitted to Phys. Rev. Lett.  (2005)

Elastic scattering susceptibility of the high-temperature superconductor Bi₂Sr₂CaCu₂O_8+d:  A comparison between real and momentum space spectroscopy

K. McElroy, G.-H. Gweon, S. Y. Zhou, J. Graf, S. I. Uchida, H. Eisaki, H. Takagi, T. Sasagawa, D.-H. Lee, A. Lanzara

Phys. Rev. Lett 96, 067005 (2005)

An unusual isotope effect in a high-transition-temperature superconductor
G.-H. Gweon, T. Sasagawa, S.Y. Zhou, J. Graf, H. Takagi, D.-H. Lee, A. Lanzara
Nature 430, 187-190 (2004)

Strong Influence of Phonons on the Electron Dynamics of Bi₂Sr₂CaCu₂O_8+d
G.-H. Gweon, S.Y. Zhou, A. Lanzara
J Phys Chem Solids 65, 1397-1401 (2004)

Evidence for Ubiquitous Electron-Phonon Coupling in High Temperature Superconductors.
A.Lanzara, P. V. Bogdanov, X. J. Zhou, S. A. Kellar, D. L. Feng, E. D. Lu, T. Yoshida, H. Eisaki, A. Fujimori, K. Kishio, J. -I.  Shimoyama, T. Noda, S. Uchida, Z. Hussain and Z. X. Shen
Nature 412, 510-514 (2001)