Evidence for Quantum Critical Behavior in the Optimally Doped Cuprate Bi ₂ Sr ₂ CaCu ₂ O _8+δ

Abstract

The photoemission line shapes of the optimally doped cuprate Bi(2)Sr(2)CaCu(2)O(8+delta) were studied in the direction of a node in the superconducting order parameter by means of very high resolution photoemission spectroscopy. The peak width or inverse lifetime of the excitation displays a linear temperature dependence, independent of binding energy, for small energies, and a linear energy dependence, independent of temperature, for large binding energies. This behavior is unaffected by the superconducting transition, which is an indication that the nodal states play no role in the superconductivity. Temperature-dependent scaling suggests that the system displays quantum critical behavior.

Electronic excitations: density-functional versus many-body Green’s-function approaches

“…Photoelectron spectra with high spatial resolution are at the basis of photoelectron microscopy, where a 20-nm resolution can be obtained (Nolting et al, 2000). The determination of the Fermi surface of very complex materials such as cuprate superconductors (Zhou et al, 1999), the study of a Fermi gap opening in complex structures (Cepek et al, 2001), and the measurement of the energy dependence of the linewidth associated with photoemission peaks near the Fermi energy (Valla et al, 1999a(Valla et al, , 1999b are now possible because of the improved spectral resolution.…”

Spectral properties and isotope effect in strongly interacting systems: Mott-Hubbard insulator versus polaronic semiconductor

“…It should be noted that the slope of the dispersion of such high energy features deviates significantly from the unrenormalized Fermi velocity v F . For this reason, in strongly correlated electron systems, some care should be taken when extracting the function ReΣ(ω) from experimental data under the assumption that v F tends asymptotically to its unrenormalized value at sufficiently high energy, as is customary in the field [29] (see also ref. [30]).…”

Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

“…It has emerged at the front and center of the physics of strongly correlated electron systems known to host competing quantum orders, and is witnessed by a proliferation of reports on heavy Fermions (2)(3)(4)(5), itinerant (quantum) magnets (6), and hightransition-temperature (high-T c ) superconductors (7), with quantum matter tuned (at times arguably) through a transition by pressure, magnetic field, or doping-arguably because one has to rely on long shadows cast by quantum criticality far above zero temperature (8), for, obviously, T ϭ 0 K cannot ever be attained.…”

“…This has led to new theoretical concepts, some related [e.g., phenomenology of ''marginal Fermi liquid'' (10)] and some unrelated [e.g., ''strange metal'' state (11)] to quantum criticality. In most considerations of cuprates near quantum critical points (QCPs) the tuning parameter is charge doping (1,10); and although there is some experimental support (7,12) for a doping-driven QCP, it is still to be broadly confirmed. Thus, it is of primary import to probe experimentally how the n-FL state transforms into the conventional FL state, and whether and how charge or spin degrees of freedom are involved.…”