Linking the pseudogap in the cuprates with local symmetry breaking: A commentary

Abstract

In the last 2 decades, increasingly precise measurements have established that the cuprate high-temperature superconductors exhibit numerous ordering tendencies. In addition to the “big 2”—Neel antiferromagnetism (AF) and d -wave superconductivity (SC)—a variety of other orders have been observed, especially in the enigmatic “pseudogap” regime of the phase diagram. The term pseudogap denotes a suppression of the density of states between a doping-dependent crossover temperature, T * ( p ) , and the (lower) SC transition temperature, T c ( p ) . Thus, for doping less than p * ≈ 0.19 [above which T * ( p ) vanishes], the pseudogap is the “normal state” out of which SC emerges.\n\nMukhopadhyay et al. (1), in PNAS, venture a bold proposition as to the origin of the pseudogap on the basis of a careful examination of high-resolution scanning tunneling spectroscopy on Bi2Sr2CaCu2O8+x (Bi-2212). They focus on 2 distinct forms of order: charge density wave (CDW), the breaking of lattice translation symmetry; and nematicity, the breaking of lattice rotational symmetry. Both of these have been identified in well-defined regimes of the phase diagrams of all hole-doped cuprates. By measuring tunneling conductance over a large field of view, performing a Fourier transform, and analyzing data from distinct regions of momentum space, Mukhopadhyay et al. identify energies Δ * , E m a x D , and E m a x N characterizing the pseudogap, CDW, and nematicity, respectively. Measured on samples whose doping spans the pseudogap regime, these energies are, within experimental error, identical.\n\nOn the basis of this result, Mukhopadhyay et al. (1) argue that the pseudogap is a consequence of a tendency toward a unidirectional density wave that, if long-range–ordered, would break both translation and rotation symmetry. In the presence of disorder, translation symmetry breaking cannot … \n\n[↵][1]2To whom correspondence may be addressed. Email: samuel.lederer{at}gmail.com.\n\n [1]: #xref-corresp-1-1