Spectroscopic Evidence for Competing Order-Induced Pseudogap Phenomena and Unconventional Low-Energy Excitations in High-T c Cuprate Superconductors

Abstract

The low-energy excitations of cuprate superconductors exhibit various characteristics that differ from those of simple Bogoliubov quasiparticles for pure d x 2 -y 2-wave superconductors. Here we report experimental studies of spatially resolved quasiparticle tunnelling spectra of hole-and electron-type cuprate superconductors that manifest direct evidences for the presence of competing orders (COs) in the cuprates. In contrast to conventional type-II superconductors that exhibit enhanced local density of states (LDOS) peaking at zero energy near the centre of field-induced vortices, the vortex-state LDOS of YBa 2 Cu 3 O 7-δ (Y-123) and La 0.1 Sr 0.9 CuO 2 (La-112) remains suppressed inside the vortex core, with pseudogap (PG)-like features at an energy larger (smaller) than the superconducting (SC) gap Δ SC in Y-123 (La-112). Energy histograms of the SC and PG features reveal steady spectral shifts from SC to PG with increasing magnetic field H. These findings may be explained by coexisting COs and SC: For hole-type cuprates with PG above T c , the primary CO gap (V CO ) is larger than Δ SC and the corresponding COs are charge/pair-density waves with wave-vectors parallel to (π,0)/(0,π). For electron-type cuprates without PG above T c , V CO is smaller than Δ SC and the CO wave-vector is along (π,π). This CO scenario may be extended to the ARPES data to consistently account for the presence (absence) of Fermi arcs in hole-(electron)-type cuprates. Fourier transformation of the vortex-state LDOS in Y-123 further reveals multiple sets of energyindependent wave-vectors due to field-enhanced pairand spin-density waves. These results imply important interplay of SC with low-energy collective excitations.

Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-DopedBa(Fe1−xCox)2As2

“…Overall, we attribute q 1 , q 2 , and q 3 to the QPI scattering wave vectors because they are not only slightly energy dependent but also doping dependent, and so they cannot be simply attributed to Bragg diffractions of the lattices. The relatively weak energy dependence of the QPI wave vectors is the result of small and nearly isotropic Fermi pockets in the iron arsenides, which differs from the highly energy-dependent QPI wave vectors in the cuprate superconductors [36][37][38][39].…”

Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganiteLa0.7Ca0.3MnO3Hughes1, Beyer2, Yeh3 2010Phys. Rev. BSelf Cite6020View full textAdd to dashboardCite

“…Hence, the physical origin for the occurrence of PG phenomena appears to be fundamentally different for these two strongly correlated perovskite oxides, which also suggests that the appearance of PG alone in the cuprates is unlikely a sufficient condition for the occurrence of high-temperature superconductivity. 27,28 …”

Comparative studies of the scanning tunneling spectra in cuprate and iron-arsenide superconductors

“…For scanning tunneling spectroscopic studies, the surface of the cuprates was prepared by chemical etching [14][15][16][17], and samples were kept either in high-purity helium gas or under high vacuum at all times. This surface preparation technique for the structurally highly three-dimensional Y-123 and La-112 cuprates has the advantage of terminating the sample top surface at the metallic CuO 2 plane according to the XPS studies [14], thus yielding reproducible spectra with atomic resolution achievable in the constant-bias conductance maps [15][16][17].…”

“…For scanning tunneling spectroscopic studies, the surface of the cuprates was prepared by chemical etching [14][15][16][17], and samples were kept either in high-purity helium gas or under high vacuum at all times. This surface preparation technique for the structurally highly three-dimensional Y-123 and La-112 cuprates has the advantage of terminating the sample top surface at the metallic CuO 2 plane according to the XPS studies [14], thus yielding reproducible spectra with atomic resolution achievable in the constant-bias conductance maps [15][16][17]. In the case of surface preparation for iron arsenides [18], we performed mechanical cleavage of the single crystals in pure argon atmosphere at room temperature, well above the tetragonal-to-orthorhombic structural phase transition to minimize the commonly observed surface reconstruction for samples cleaved at cryogenic temperatures.…”