Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites
Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites
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DOI：
10.1038/nature04273
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发表时间：
2005-11-24
期刊：
影响因子：
64.8
通讯作者：
Shen, ZX
中科院分区：
文献类型：
--
作者：
Mannella, N;Yang, WL;Shen, ZX
铜氧化物高温超导体的一个特征是在动量空间中沿着沿着节（对角线）和反节（平行于Cu-O键）方向的电子激发之间的二分法，通常被认为与超导态的“d波”对称性有关。在超导状态下的角分辨光电子能谱测量揭示了具有d-波隙结构的准粒子谱，该结构沿着波腹方向呈现最大值，沿着波节方向消失（1）。随后的测量表明，在低掺杂水平下，即使在高温金属状态下，这种带隙结构仍然存在，尽管超导状态的节点在有限的“费米弧”中展开（2）。这就是所谓的赝能隙相，人们认为它与超导态密切相关，要么将其归因于波动的超导性（3），要么调用d波超导体的天然竞争者（4，5）。在这里，我们报告的实验证据表明，一个非常相似的赝能隙状态与一个pseudogap-antinodal二分字符存在于一个系统，是显着不同的超导体：铁磁金属基态的巨磁阻双层锰氧化物La1.2Sr1.8Mn2O7。因此，我们的研究结果对铜氧化物中的赝能隙态和超导-反结二分法是超导态标志的假设提出了质疑。
A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the 'd-wave' symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction(1). Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite 'Fermi arcs'(2). This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity(3) or by invoking orders which are natural competitors of d-wave superconductors(4,5). Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.