最近发现的具有高转变温度$T_c \sim 40$ K的铁基金属超导体AFe $_2$ Se $_2$（A = K，Rb，Cs）中的配对对称性是目前激烈争论的主题。根据光电发射，这些系统仅包含电子袋，并且与大多数铁基超导体不同，铁基超导体中存在电子袋和空穴袋。对于AFe $_2$ Se $_2$，d波和s波配对对称性都已经被提出，但是d波间隙通常具有节点，而实验清楚地指向无节点行为，并且常规的s波间隙与$T_c$以下的中子共振的观察不一致。我们认为，目前的理论在这样的系统中的配对是不完整的，必须包括不仅口袋内的配对冷凝物，但也属于不同的电子口袋的费米子口袋间的冷凝物。我们分析了口袋内和口袋间配对之间的相互作用，这取决于电子口袋的椭圆率和它们的杂交强度，并表明杂交使系统进入一个新的$s^{+-}$状态，在该状态下，杂交口袋之间的间隙改变符号。这种状态具有完整的能隙，同时支持自旋共振，与数据一致。在$s^{+-}$态的边界附近，我们发现了一个人们长期认为的破坏时间反演对称性的$s+id$态。
英文摘要：
Pairing symmetry in recently discovered Fe-based metallic superconductors AFe$_2$Se$_2$ (A = K, Rb, Cs) with high transition temperature $T_c \sim 40$ K is currently a subject of intensive debates. These systems contain only electron pockets, according to photoemission, and differ from the majority of Fe-based superconductors in which both electron and hole pockets are present. Both d-wave and s-wave pairing symmetries have been proposed for AFe$_2$Se$_2$, but a d-wave gap generally has nodes, while experiments clearly point to no-nodal behavior, and a conventional s-wave gap is inconsistent with the observation of the neutron resonance below $T_c$. We argue that current theories of pairing in such systems are incomplete and must include not only intra-pocket pairing condensate but also inter-pocket condensate made of fermions belonging to different electron pockets. We analyze the interplay between intra-pocket and inter-pocket pairing depending on the ellipticity of electron pockets and the strength of their hybridization and show that hybridization brings the system into a new $s^{+-}$ state, in which the gap changes sign between hybridized pockets. This state has the full gap and at the same time supports spin resonance, in agreement with the data. Near the boundary of $s^{+-}$ state we found a long-thought $s+id$ state which breaks time-reversal symmetry.
Simultaneous emergence of superconductivity, inter-pocket scattering and nematic fluctuation in potassium-coated FeSe superconductor
超导性起源于电子配对。因此，费米面上的配对沟道和配对胶是理解超导体的两个关键问题。最近，在电子掺杂的FeSe超导体中发现了超过40 K的高温超导性，包括K $_x$ Fe $_{2-y}$ Se $_2$、Li $_{0.8}$ Fe $_{0.2}$ OHFeSe和单层FeSe薄膜。然而，它们的配对机制仍然存在争议。本文研究了包钾FeSe单晶电子结构的系统演化。通过在样品表面上原位蒸发钾来精确控制掺杂水平。我们发现当费米面的Lifshitz跃迁使两个电子袋之间的袋间散射打开时，超导性就出现了。在相同的掺杂浓度下，电子有序度显著降低，在较宽的掺杂范围内，电子有序度仍有较大的涨落。我们的研究结果表明，在电子掺杂的FeSe超导体的超导电性，袋间散射，和涨落之间的潜在的相关性。
Persistent Fermi Pockets and Robust Electron Pairing in Lightly Doped CuO$_2$ Planes of Cuprate Superconductors
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究研究所）；Technical Institute of Physics and Chemistry, Chinese Academy of Sciences（中国科学院理化技术研究所）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）
Coexistence of High Temperature Superconductivity and Antiferromagnetic Order in a Cuprate with Multiple Hole Fermi Pockets
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Max Planck Institute for Solid State Research（马克斯·普朗克固相研究所）；Technical Institute of Physics and Chemistry, Chinese Academy of Sciences（中国科学院化学物理研究所）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）
Orbital-Selective Diagonal-Gap Test of Pairing in La$_3$Ni$_2$O$_7$
Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；School of Physics, Beijing Institute of Technology（北京理工大学物理学院）；Department of Physics, Xiamen University（厦门大学物理系）；School of Physics, Hangzhou Normal University（杭州师范大学物理学院）
Reproduction of Experimental Gap Structure in LiFeAs based on the Orbital-Spin Fluctuation Theory: $s_{++}$-wave, $s_\pm$-wave, and hole-$s_\pm$-wave states
Magnetic Correlations and Pairing Tendencies of the Hybrid Stacking Nickelate Superlattice La$_7$Ni$_5$O$_{17}$ (La$_3$Ni$_2$O$_7$/La$_4$Ni$_3$O$_{10}$) under Pressure
Anomalous spectral weight transfer in the nematic state of iron-selenide superconductor
在铁基超导体中，向列相与高温超导性密切相关。它的机制与超导的配对机制密切相关，但仍存在争议。因此，对电子态如何在双相中重建的全面表征至关重要。然而，大多数实验只关注带色散的重建。电子态的另一个重要特征--谱权至今还没有得到详细的研究。本文利用角分辨光电子能谱和原位去孪晶技术研究了FeSe $_{0.9}$ S $_{0.1}$的电子转移过程。在布里渊区拐角处有两个相互垂直重叠的椭圆形电子袋。我们发现，在冷却时，一个电子口袋失去光谱重量和消失，而另一个电子口袋获得光谱重量和变得明显。结果表明，电子态的对称性破缺不仅表现为各向异性的能带色散，还表现为谱权的带选择性调制。我们的观察完成了我们对电子态的理解，并对理论模型提出了强有力的约束。它进一步为理解铁硒化物超导体的能隙各向异性和轨道选择配对提供了重要线索。
Possibility of Unconventional Pairing Due to Coulomb Interaction in Fe-Based Pnictide Superconductors: Perturbative Analysis of Multi-Band Hubbard Models
Detecting pairing symmetry of bilayer nickelates using electronic Raman scattering
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Facultad de Ciencias Exactas, Ingeniería y Agrimensura and Instituto de Física Rosario (UNR-CONICET)（罗萨里奥大学精确科学、工程与测量学院及罗萨里奥物理研究所）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Institute for Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences（中国科学院大学 Kavli 理论科学研究院）；New Cornerstone Science Laboratory（新基石科学实验室）
The evolution of pairing correlation with $3d_{z^{2}}$ electron filling in a bilayer two-orbital model for La$_3$Ni$_2$O$_7$
Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院人工结构与量子控制教育部重点实验室）；State Key Laboratory of Quantum Functional Materials, School of Physical Science and Technology, ShanghaiTech University（上海科技大学物理科学与技术学院量子功能材料国家重点实验室）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学李政道研究所）；Hefei National Laboratory（合肥国家实验室）
