Abstract
We report STM/STS measurements at 8 K in underdoped Bi2Sr2CaCu2O8+δ crystals (Tc = 76 K and hole-doping level p ∼ 0.12) whose energy spectra around the Fermi level are characterized by a two-gap structure consisting of spatially inhomogeneous pseudogap (PG) and comparatively homogeneous superconducting gap (SCG). Two electronic superstructures, checkerboard modulation (CBM) and Cu-O-Cu bond-centered modulation (BCM), are observed with mapping spectral weights at low energies within the SCG and the ratio of spectral weights at ±ΔPG (PG energy), respectively. On the basis of the present findings, we suggest that the lower-energy scale CBM is an intrinsic property of Cu-O planes and can coexist with the BCM whose characteristic energy is ∼ΔPG in identical regions in real space.
Highlights
In high-Tc cuprates, it has been demonstrated by many spectroscopic techniques such as ARPES and STM/STS that the electronic states around the Fermi level exhibit distinct features in different momentum and/or energy regions [1–3]
Such a subgap structure in STS spectra can be explained in terms of the superconductivity, because if the density of states near the Fermi level is completely suppressed in the vicinity of the antinodal point with the marked development of PG and no pairing gap opens up there, leading to a reduction of the effective pairing gap size
We performed STM/STS measurements at 8 K in UD Bi2212 crystals with Tc = 76 K and p ∼ 0.12 to examine the characteristic energy of checkerboard modulation (CBM) and its mutual relationship with the bond-centered modulation (BCM) whose characteristic energy is of the order of the spatially inhomogeneous PG
Summary
In high-Tc cuprates, it has been demonstrated by many spectroscopic techniques such as ARPES and STM/STS that the electronic states around the Fermi level exhibit distinct features in different momentum and/or energy regions [1–3]. In the antinodal region, consisting of incoherent electronic states, a pseudogap (PG) develops below around temperature T ∗ higher than Tc , and another energy gap, which has been considered to be due to pairing, develops successively below around temperature Tpair [4, 5]. It has been revealed in STM/STS experiments on highTc cuprates Bi2 Sr2 CaCu2 O8+δ (Bi2212), Ca2−x Nax CuO2 Cl2 (Na-CCOC) and so on that the antinodal PG is very sensitive to disorders and tends to be spatially inhomogeneous in nanometer scale, the pairing gap, whose amplitude is hereafter referred to as Δ0 , is comparatively homogeneous [3].
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