Chapter

Spectroscopic Imaging STM Studies of Electronic Structure in Both the Superconducting and Pseudogap Phases of Underdoped Cuprates

K Fujita, A.R Schmidt, E.-A Kim, M.J Lawler, H Eisaki, S Uchida and J.C Davis

in Conductor-Insulator Quantum Phase Transitions

Published in print June 2012 | ISBN: 9780199592593
Published online September 2012 | e-ISBN: 9780191741050 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199592593.003.0016
Spectroscopic Imaging STM Studies of Electronic Structure in Both the Superconducting and Pseudogap Phases of Underdoped Cuprates

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A motivation for the development of atomically resolved spectroscopic imaging STM (SI-STM) has been to study the broken symmetries in the electronic structure of cuprate high temperature superconductors. Both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates exhibit two distinct classes of electronic states when studied using SI-STM. The class consists of the dispersive Bogoliubov quasiparticles of a homogeneous d-wave superconductor. These signature are detected below a lower energy scale |E| = D0 and only upon a momentum space (k-space) arc which terminates near the lines connecting k = ±(p/a0, 0) to k = ±(0̣,p/a0). This ‘nodal’ arc shrinks continuously with decreasing hole density. In both the dSC and PG phases, the only broken symmetries detected in the |E|≤D0 states are those of a d-wave superconductor. The second class of states occurs at energies near the pseudogap energy scale |E|~̣D1 can be associated with the ‘antinodal’ states near k = ±(p/a0,0) and k = ±(0̣,p/a0). These states break the expected 90º-rotational (C4) symmetry of electronic structure within CuO2 unit cells, at least down to 180º-rotational (C2) symmetry (nematic) but in a spatially disordered fashion. This intra-unit-cell C4 symmetry breaking coexists at |E|~̣D1 with incommensurate conductance modulations locally breaking both rotational and translational symmetries (smectic). Empirically, the characteristic wavevector Q of the latter is determined by the k-space points where Bogoliubov quasiparticle interference terminates and therefore evolves continuously with doping. The properties of these two classes of |E|~̣D1 states are indistinguishable in the dSC and PG phases. To explain these two regimes of k-space that are distinguished by the symmetries of their electronic states and their energy scales |E|~D1 and |E|≤D0, and to understand their relationship to the electronic phase diagram and the mechanism of high-Tc superconductivity, represent key challenges for cuprate studies.

Keywords: cuprate superconductivity; spectroscopic imaging STM; pseudogap states; broken spatial symmetry; electronic structure

Chapter.  13851 words.  Illustrated.

Subjects: Mathematical and Statistical Physics

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