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arXiv 1102.1806cond-mat.supr-concond-mat.str-el
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铜氧化物超导相和赝能隙相电子结构的光谱成像研究STM

Electronic Structure of the Cuprate Superconducting and Pseudogap Phases from Spectroscopic Imaging STM

A R Schmidt, K Fujita, E -A Kim, M J Lawler, H Eisaki, S Uchida, D-H Lee, J C Davis

摘要:

我们调查使用光谱成像STM探测欠掺杂铜氧化物的电子结构。在d波超导(dSC)和赝能隙(PG)相中观察到两种不同的电子态。第一类由色散Bogoliubov准粒子激发的均匀d波超导体,存在低于一个较低的能量标度E= Delta 0。我们发现离域Cooper对的Bogoliubov准粒子干涉特征被限制在一个k空间弧上,该弧终止于连接k= \pm(pi/a0,0)到k= \pm(pi/a0)的直线附近.该弧随着孔密度的减小而连续收缩,使得如果它表示由k= \pm(pi/a0,0)和k= \pm(0,pi/a0)之间的线在后面界定的孔袋的前侧,则可以满足Luttinger定理。在这两个阶段中,对于|E| <Delta 0状态,检测到的唯一对称性破缺是d波超导体的对称性破缺。第二类状态发生在接近赝能隙能级E= Delta 1的位置。在这里,非色散电子结构打破了每个晶胞内电子结构的预期90 °旋转对称性,至少低至180 °旋转对称性。这种Q=0的电子对称性破缺首先被检测为每个晶胞内两个氧位点处的电子不等价性,通过使用C2对称性的测量。无公度的非色散电导调制,局部打破旋转和平移对称性,共存于此内的单位细胞的电子对称性破缺在E= Delta 1。它们的特征波矢Q由Bogoliubov准粒子干涉终止的k空间点决定,因此随着掺杂而连续变化。发现在dSC和PG相中共存于E~ Δ 1处的不同的电子对称性破缺态(Q=0和有限Q)是不可区分的。

英文摘要:

We survey the use of spectroscopic imaging STM to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E=Delta0. We find that the Bogoliubov quasiparticle interference signatures of delocalized Cooper pairing are restricted to a k-space arc which terminates near the lines connecting k=\pm(pi/a0,0) to k=\pm(pi/a0). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket which is bounded behind by the lines between k=\pm(pi/a0,0) and k=\pm(0,pi/a0). In both phases the only broken symmetries detected for the |E|<Delta0 states are those of a d-wave superconductor. The second class of states occurs proximate to the pseudogap energy scale E=Delta1. Here the non-dispersive electronic structure breaks the expected 90o-rotational symmetry of electronic structure within each unit cell, at least down to 180o-rotational symmetry. This Q=0 electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C2) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E=Delta1. Their characteristic wavevector Q is determined by the k-space points where Bogoliubov quasiparticle interference terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (Q=0 and finite Q) coexisting at E~Delta1 are found to be indistinguishable in the dSC and PG phases.

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