Competition between the pseudogap and superconductivity in the high-Tc copper oxides

Abstract

A pairing gap and coherence are the two hallmarks of superconductivity. In a classical BCS superconductor they are established simultaneously at T c . In the cuprates, however, an energy gap (pseudogap) extends above T c [1, 2, 3,4,5,6,7,8]. The origin of this gap is one of the central issues in high temperature superconductivity. Recent experimental evidence demonstrates that the pseudogap and the superconducting gap are associated with different energy scales [9,10,11,12,13,14]. It is however not clear whether they coexist independently or compete [9,12,14,15]. In order to understand the physics of cuprates and improve their superconducting properties it is vital to determine whether the pseudogap is friend or foe of high temperature supercondctivity [16]. Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that the pseudogap and high temperature superconductivity represent two competing orders. We find that there is a direct correlation between a loss in the low energy spectral weight due to the pseudogap and a decrease of the coherent fraction of paired electrons. Therefore, the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing in the region of momentum space where the superconducting gap is largest. This leads to a very unusual state in the underdoped cuprates, where only part of the Fermi surface develops coherence.Coherence in the superconducting state of the cuprates manifests itself by the appearance of a narrow peak in the ARPES lineshape [17], while the pseudogap [2, 3,4,12] depletes the low energy spectral weight below the pseudogap energy. The simplicity of the Bi 2 Sr 2 CuO 6+δ (Bi2201) spectra, as measured by ARPES, permits us to perform a straight forward quantitative analysis of the two features because the energy distribution curves (EDCs) in this single layer material lack the large renormalization effects (e.g. peak-hump-dip structure) and bilayer splitting that are present [6,7] in double layered Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212). This feature, however, means the spectral changes associated with the superconducting transition in Bi2201 are much more difficult to observe [18]. By acquiring very high resolution and stable ARPES data with high statistics, we are able to study the temperature and momentum dependence of the spectral weight near the chemical potential, with unprecedented accuracy. Experimental and sample preparation details are provided in the Supplementary Information. In Fig. 1 we examine the temperature dependence of the spectral lineshape in overdoped Bi2201 (T c =29K). Above the pseudogap temperature (T * ) (∼110K for this sample), the symmetrized EDCs [4] (see Supplementary Information) show a peak centered at the chemical potential -consistent with the metallic state of the sample. Upon cooling below T * , the low energy spectral weight decreases (within ∼20 meV), leading to a characteristic dip and very broad spectral peaks that signify the opening of an energy gap, as shown in Fig. 1(d). The loss...

Dynamic competition between spin-density wave order and superconductivity in underdoped Ba1−xKxFe2As2

“…Traditionally, there have been two main interpretations of the PG phase: (i) a precursor state of SC, (ii) a competing phase to SC. While several recent reports favour the scenario of competition [1][2][3][4] , the elusive nature of the PG complicates the interpretations. Here, we demonstrate clearly with spectroscopic evidence the competition between SC and a well-characterized long-range density wave, which is intriguingly similar to a recent study in cuprates showing a similar suppression of the PG spectral features associated with the onset of SC (M. Hashimoto et al submitted).…”

“…In the cuprates, one of the biggest puzzles is the nature of the pseudogap (PG) phase, which envelops a large portion of the superconducting dome in the phase diagram. Recently, a large amount of experimental evidence suggests a competition between the PG and SC [1][2][3][4] . However, the controversial nature of the PG phase itself complicates a direct study of this competition.…”

Gaps and kinks in the electronic structure of the superconductor2H-NbSe2from angle-resolved photoemission at 1 K

“…23 In the absence of realistic selfenergy models for coexisting SC and CDW ground states, this simple criterion appears to be the most effective and transparent one, although it may be hampered by background and matrix-element effects. To keep both effects to a minimum, we consider only a small energy window (E F ±40 meV), normalize the symmetrized spectra to the intensity of the background, and determine only relative changes of the integrated spectral weight along segments of the Fermi contours on which the matrix element shows a weak k dependence (see Fig.…”

“…The quantitative analysis is presented in Figs. 4(e)-4(l) which compare the Fermi-angle dependence of the position of the inflection point of the leading edge, the gap value determined by self-energy fitting, and the spectral weight of the SC coherent peak emerging at the gap edge. 14,16,17,23 As to the reliability of the data analysis scheme detailed in Sec. II, three aspects are worth noting: (i) There is an almost perfect correlation between the fitted gap values and leading-edge shifts on all four Fermi-surface sheets We are thus led to conclude that the spectral gap on the K-H sheets has two competing components: a SC gap and a CDW gap.…”

Non-conventional superconducting fluctuations in Ba(Fe1−xRhx)2As2 iron-based superconductors

“…19 This theory successfully described the behavior of several materials, 13,17,20 and it is in agreement with scanning SQUID microscopy results, 4 as well as Nernst effect, 2,19 and ARPES. 21 After 2008, much attention was devoted to the iron-based superconductors. Among all the families, the 122 is one of the most promising for applications, as it is characterized by reduced thermal fluctuations, owing to a small Ginzburg number, G i ∼ 1.5 × 10 −5 .…”