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Quantum oscillations and the Fermi surface in an underdoped high-T_c superconductor

机译：欠掺杂高T_c超导体中的量子振荡和费米表面

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Despite twenty years of research, the phase diagram of high-transition-temperature superconductors remains enigmatic. A central issue is the origin of the differences in the physical properties of these copper oxides doped to opposite sides of the superconducting region. In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface. The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected 'Fermi arcs'. The fundamental question, then, is whether under-doped copper oxides have a Fermi surface, and if so, whether it is topologically different from that seen in the overdoped regime. Here we report the observation of quantum oscillations in the electrical resistance of the oxygen-ordered copper oxide YBa_2Cu_3O_(6.5), establishing the existence of a well-defined Fermi surface in the ground state of underdoped copper oxides, once superconductivity is suppressed by a magnetic field. The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime. Two possible interpretations are discussed: either a small pocket is part of the band structure specific to YBa_2Cu_3O_(6.5) or small pockets arise from a topological change at a critical point in the phase diagram. Our understanding of high-transition-temperature (high-T_c) superconductors will depend critically on which of these two interpretations proves to be correct.
机译：尽管进行了二十多年的研究，但高转变温度超导体的相图仍然是个谜。中心问题是掺杂到超导区域相对侧的这些铜氧化物的物理性质差异的根源。在过量掺杂状态下，该材料表现为具有较大费米表面的合理常规金属。然而，掺杂不足的状态是高度异常的，并且似乎没有相干的费米表面，而只是不连续的“费米弧”。那么，根本的问题是，掺杂不足的氧化铜是否具有费米表面，如果存在，则其拓扑结构是否与掺杂过量的拓扑结构不同。在这里，我们报告观察到氧有序氧化铜YBa_2Cu_3O_（6.5）的电阻中发生了量子振荡，一旦通过磁性抑制了超导性，就建立了在掺杂不足的氧化铜基态下存在清晰定义的费米表面的存在。领域。低的振荡频率揭示了费米表面由小凹穴构成，与过掺杂状态的大圆柱体特性相反。讨论了两种可能的解释：要么小凹穴是YBa_2Cu_3O_（6.5）特有的能带结构的一部分，要么是小凹穴是由相图中关键点的拓扑变化引起的。我们对高转变温度（high-T_c）超导体的理解将主要取决于这两种解释中的哪一种被证明是正确的。

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