Seminar

TYC@imperial: Cuprate High Temperature Superconductivity – The Quest for the Mechanism

Dr Dennis m Newns

IBM· Thomas J Watson research centre

Tuesday 18th December 2018
Time: 12.00pm
Venue: Lecture theatre G20, Royal School of Mines, Imperial College London
Contact: Ms Hafiza Bibi
Tel: 020 7594 7252

Abstract: TheHigh Temperature Superconductors (HTS), with transition temperatures Tc up to 160 K, were at first investigated as a novel class of Quantum Liquid. However HTS, converted to the normal state by a large magnetic field, are found at low temperatures to be good metals. The pairing interaction must contain a strong component of electron-phonon coupling, as evidenced by a clear (but anomalous) isotope shift. The logarithmic van Hove singularity in the density of states will act to enhance the coupling.  The d-wave nature of the order parameter suggests the interaction is on a bond,not on a site. The Cu-O-Cu perovskite bond is unstable in the bond-transverse mode which strongly interacts with the electron system. Based on this interaction, termed the “Fluctuating Bond Model”, we show how the phase diagram, with d-wave superconductivity, and the distortion leading to the pseudogap phenomenon, can be reproduced theoretically.

1.      D.M. Newns and C.C. Tsuei, Nature Physics 3, 184 (2007).

2.      Jenhao Hsiao, Glenn J. Martyna and Dennis M. Newns, Phys. Rev. Lett. 114, 107001 (2015); R. A. Nistor et al., Phys. Rev. B 83, 144503 (2011).

3.      Dennis M. Newns, Glenn J. Martyna, and Chang C. Tsuei, Spin (World Scientific) 07, 1750006 (2017).

Cuprate High Temperature superconductors show an unusual combination of d-wave superconductivity and an associated pseudogap phase transition, which leads to local breaking of C4àC2 symmetry. We argue [1-3] that the underlying phenomena arise from a combination of electron-electron and electron-phonon coupling, resulting in a local soft oxygen vibrational mode which underlies the pseudogap symmetry-breaking and mediates the d-wave superconductivity. Experimental evidence showing a strong but anomalous isotope shift [1-3], and a close association between planar oxygen degree of freedom and the C4àC2 symmetry breaking supports the picture. A theory based on electronic coupling to anharmonic oxygens explains the main features of the phase diagram.

4.      D.M. Newns and C.C. Tsuei, Nature Physics 3, 184 (2007).

5.      Jenhao Hsiao, Glenn J. Martyna and Dennis M. Newns, Phys. Rev. Lett. 114, 107001 (2015).

6.      “Cuprate High Temperature Superconductors and the Vision for Room Temperature Superconductivity”, Dennis M. Newns, Glenn J. Martyna, and Chang C. Tsuei, Spin, in press.

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