Electron pairing in the pseudogap state revealed by shot noise in copper oxide junctions
Electron pairing in the pseudogap state revealed by shot noise in copper oxide junctions
复制标题
DOI：
10.1038/s41586-019-1486-7
复制
发表时间：
2019-08
期刊：
影响因子：
64.8
通讯作者：
Panpan Zhou;Liyang Chen;Yue Liu;I. Sochnikov;A. Bollinger;Myung‐Geun Han;Yimei Zhu;Xi He;I. Božović;D. Natelson
中科院分区：
文献类型：
--
作者：
Panpan Zhou;Liyang Chen;Yue Liu;I. Sochnikov;A. Bollinger;Myung‐Geun Han;Yimei Zhu;Xi He;I. Božović;D. Natelson
在寻求理解铜氧化物的高温超导性的过程中，争论一直集中在赝能隙上，赝能隙是在高于体临界温度的“正常”状态下费米表面部分开放的部分能隙。赝能隙被归因于先驱超导性，预成型对的存在和竞争秩序，如电荷密度波。直接确定载流子的电荷随温度和偏压的变化可以帮助解决这些问题。在这里，我们报告的测量隧道电流的散粒噪声在高品质的La 2 − xSrxCuO 4/La 2CuO 4/La 2 − xSrxCuO 4（LSCO/LCO/LSCO）异质结构制造使用原子层的分子束外延在几个掺杂水平。数据描绘了偏置电压-温度空间中的三个不同区域。在超导能隙区域之外，散粒噪声与单个电荷载流子的独立隧穿定量一致。在超导间隙的深处，散粒噪声大大增强，让人想起多次Andreev反射。在临界温度以上，并延伸到比超导间隙大得多的偏置，有一个很宽的区域，其中噪声大大超过了单电荷隧穿的理论预期，表明电荷载流子的配对。这些对是可检测到的温度和偏置的赝能隙区域深处。这些对的存在限制了赝能隙和对称性破缺态的当前模型，而相位波动限制了超导性的范围。
In the quest to understand high-temperature superconductivity in copper oxides, debate has been focused on the pseudogap—a partial energy gap that opens over portions of the Fermi surface in the ‘normal’ state above the bulk critical temperature. The pseudogap has been attributed to precursor superconductivity, to the existence of preformed pairs and to competing orders such as charge-density waves, , –. A direct determination of the charge of carriers as a function of temperature and bias could help resolve among these alternatives. Here we report measurements of the shot noise of tunnelling current in high-quality La2−xSrxCuO4/La2CuO4/La2−xSrxCuO4(LSCO/LCO/LSCO) heterostructures fabricated using atomic layer-by-layer molecular beam epitaxy at several doping levels. The data delineate three distinct regions in the bias voltage–temperature space. Well outside the superconducting gap region, the shot noise agrees quantitatively with independent tunnelling of individual charge carriers. Deep within the superconducting gap, shot noise is greatly enhanced, reminiscent of multiple Andreev reflections, –. Above the critical temperature and extending to biases much larger than the superconducting gap, there is a broad region in which the noise substantially exceeds theoretical expectations for single-charge tunnelling, indicating pairing of charge carriers. These pairs are detectable deep into the pseudogap region of temperature and bias. The presence of these pairs constrains current models of the pseudogap and broken symmetry states, while phase fluctuations limit the domain of superconductivity.