Biography
Nicholas Plumb completed his PhD in 2011 at the University of Colorado, where he performed spectroscopic studies of cuprate high-Tc superconductors and helped to develop the technique of laser-based angle-resolved photoemission spectroscopy (laser-ARPES). He came to PSI as a postdoc, working at the SIS beamline of SLS, where he focused on combining synchrotron-based ARPES with in situ thin film growth in order to study novel oxide materials, interfaces, and surfaces. He became a staff scientist at PSI in 2013 and has held a permanent staff position since 2017.
Institutional Responsibilities
Dr. Plumb conducts research within the Spectroscopy of Quantum Materials group. He is also contributing to the design and realization of the new QUEST beamline for ARPES in SLS 2.0.
Scientific Research
Dr. Plumb's research centers around using ARPES to investigate strongly correlated electrons in quantum materials. Much of this work is focused on understanding the interactions that underlie unconventional/high-Tc superconductivity, and in probing its attendant phenomena, such as density waves and ``pseudogap'' behavior. His work frequently leverages the unique capabilities of the SIS beamline (soon to be QUEST) for in situ investigations of oxide thin films.
Selected Publications
For an extensive overview we kindly refer you to our publication repository DORA.
Persistence of small polarons into the superconducting doping range of Ba1−xKxBiO3, M. Naamneh, E. C. O’Quinn, E. Paris, D. McNally, Y. Tseng, W. R. Pudełko, D. J. Gawryluk, J. Shamblin, B. Cohen-Stead, M. Shi, M. Radovic, M. K. Lang, T. Schmitt, S. Johnston, and N. C. Plumb, Physical Review Research 7, 043082 (2025).
Ba1-xKxBiO3 (BKBO) is an intriguing superconductor that displays many unconventional traits and has an unusually high maximum transition temperature of over 30 K. There is longstanding interest in the nature of the interactions that underpin its superconducting phase. In this work, we combined resonant inelastic x-ray and neutron total scattering techniques with advanced modeling to study the local lattice distortions, electronic structure, and electron-phonon (e-ph) coupling in BKBO as a function of K doping. The results showed that structural distortions and strong e-ph coupling associated with so-called bipolarons of the BaBiO3 parent compound persist into the superconducting doping range. This allows for the possibility that BKBO could host a novel bipolaronic superconductor phase.
Probing enhanced superconductivity in van der Waals polytypes of VxTaS2, W. R. Pudelko, H. Liu, F. Petocchi, H. Li, E. B. Guedes, J. Küspert, K. von Arx, Q. Wang, R. C. Wagner, C. M. Polley, M. Leandersson, J. Osiecki, B. Thiagarajan, M. Radović, P. Werner, A. Schilling, J. Chang, and N. C. Plumb, Physical Review Materials 8, 104802 (2024).
Layered transition metal dichalcogenides stabilize in multiple structural forms with profoundly distinct and exotic electronic phases. Interfacing different layer types is a promising route to manipulate these compounds' properties, not only as a means to engineer quantum devices but also as a route to explore fundamental physics in complex matter. We used ARPES to investigate a strong layering-dependent enhancement of superconductivity in TaS2, in which the superconducting transition temperature, Tc, of its "2H" structural phase is nearly tripled when insulating "1T" layers are inserted into the system. Our experiments on these mixed 2H/1T phases observed the suppression of the charge density wave in the 2H layers, alongside a strongly momentum-anisotropic increase in electron-phonon coupling near the Fermi level. Both phenomena help to account for the increased Tc in mixed 2H/1T layer structures.
Strong- to weak-coupling superconductivity in high-Tc bismuthates: Revisiting the phase diagram via μSR, T. Shang, D. J. Gawryluk, M. Naamneh, Z. Salman, Z. Guguchia, M. Medarde, M. Shi, N. C. Plumb, and T. Shiroka, Physical Review B 101, 014508 (2020).
Understanding how perovskite bismuth oxides (bismuthates) can superconduct at temperatures over 30 Kelvin is a longstanding problem that may give insights into other high-Tc superconductors, as well as a more general view of strong electron-phonon interactions. With partners in the NUM department of PSI, we extended the phase diagram of Ba1-xKxBiO3 to exceptionally high K doping, and established a crossover from strong- to weak-coupling superconductivity as the hole doping exceeds the point at which optimal Tc occurs.
Angle-resolved photoemission spectroscopy studies of metallic surface and interface states of oxide insulators, N. C. Plumb and M. Radović, Journal of Physics: Condensed Matter 29, 433005 (2017).
Low-dimensional metallic states in oxide systems hold enormous promise for novel electronic and spintronic devices, and they can also serve as platforms for fundamental research into the exotic phenomenology of oxides. This Topical Review article surveys recent progress in using ARPES to discover and understand metallic states that can be realized on the surfaces of bulk-insulating oxide materials, or at interfaces between them.
Evolution of the SrTiO3 surface electronic state as a function of LaAlO3 overlayer thickness, N. C. Plumb, M. Kobayashi, M. Salluzzo, E. Razzoli, C. E. Matt, V. N. Strocov, K. J. Zhou, M. Shi, J. Mesot, T. Schmitt, L. Patthey, and M. Radović,. Applied Surface Science 412, 271-278 (2017).
The discovery of a confined metallic state formed at the interface between insulating LaAlO3 and SrTiO3 spurred significant interest–both in its fundamental origins and properties, as well as its potential uses in novel devices. Later revelations by ARPES that a metallic state could also be formed on the surface of bare SrTiO3 brought even more possibilities for creating and manipulating such systems, along with a number of new questions. We combined ARPES, resonant inelastic x-ray scattering (RIXS), and PLD film growth to investigate how the SrTiO3 surface state evolves as LaAlO3 is grown on top of it. Overall our study found a striking connection in the band structures of the bare and buried metallic states, but we also observed a new structural order at the interface when LaAlO3 exceeds a critical thickness.
Momentum-resolved electronic structure of the high-Tc superconductor parent compound BaBiO3, N. C. Plumb, D. J. Gawryluk, Y. Wang, Z. Ristić, J. Park, B. Q. Lv, Z. Wang, C. E. Matt, N. Xu, T. Shang, K. Conder, J. Mesot, S. Johnston, M. Shi, and M. Radović, Physical Review Letters 117, 037002 (2016).
BaBiO3 is an insulating parent compound of bismuthate superconductors. The insulating phase is long known to occur alongside long-range ordered "breathing" distortions of its BiO6 octahedra, but the electronic configuration associated with this structure has drawn considerable debate. By performing in situ ARPES on freshly grown thin films, we determined that BaBiO3's unusual electronic phase is best described as a “bond-disproportionated insulator,” where charges pair within molecular-like orbital combinations of the oxygen atoms. This model that has strong implications for the nature and strength of the electron-phonon coupling–and thus the superconductivity–in bismuthates.