Pseudogap and pairing: shot noise reveals the pseudogap as pairing energy in a cuprate superconductor
by
TDLI Meeting Room N499Dr. Jiasen Niu, University of Munich
In the cuprate high-temperature superconductors, the pseudogap phase connects the Mott insulator and superconductivity phases. Despite extensive research, the origin of the pseudogap remains elusive. A key question, debated for decades, is whether the pseudogap is associated with electron pairing, or if it corresponds to a local ordered state. Shot noise experiments, which can directly detect electron pairing, have the potential to resolve this long-standing debate. In my talk, I will present two distinct experimental approaches we used and the corresponding results.
Firstly, I will present unambiguous evidence supporting the pairing scenario using local shot-noise spectroscopy measurements in 
[1]. Our data demonstrates that the pseudogap energy ΔPG is associated with electron pairing, with pairing energies reaching above 70 meV. Our finding excludes the possibility of the pseudogap arising solely from local orders, and instead indicates a clear relation between the pseudogap phase and Cooper pair formation. These results suggest that the limiting factor for higher Tc in cuprates is not the pairing strength, but rather the phase coherence. Our work resolves a long-standing controversy in the field of high-temperature superconductivity and may reignite the hope to increase Tc in high-temperature superconductors by increasing phase coherence.
At the second part, I will discuss shot-noise measurements on mesoscopic superconducting devices of Nb, NbN, and YBa2Cu3O7 [2]. In contrast to previously published work [3], we find that shot noise does not reflect pairing in typical superconducting mesoscopic tunneling devices. This is in agreement with theoretical expectations.
[1] J. Niu, M. Larrazabal, et. al., arXiv: 2409.15928.
[2] J. Niu, et. al., Phys. Rev. Lett. 132, 076001 (2024)
[3] P. Zhou, et. al., Nature 572, 493 (2019).
Dr. Jiasen Niu obtained his bachelor's degree from Jilin University in 2014, and PhD from Peking University in 2020. He then began his postdoctoral research at Leiden University under the supervision of Milan Allan. In 2024, he moved to the University of Munich (LMU) to continue his postdoctoral work with Milan.
Dr. Niu's current research focuses on investigating electron correlation in high-temperature superconductors with shot noise measurement. He is particularly interested in understanding quantum phenomena through unconventional methods, especially noise measurement. His research interests include the development of advanced scanning and transport techniques, as well as the study of quantum materials and the quantum Hall effect.
Tencent Meeting link: https://meeting.tencent.com/dm/r1Z0EmLy3j4A Meeting ID: 109 865 274, no password
