Light Doping Creates High-Temperature Superconductivity

Scientists are exploring novel pathways to achieve high-temperature superconductivity, and new research from Lei Geng at the Department of Physics, University of Fribourg, Switzerland, and Aaram J. Kim from the Department of Physics and Chemistry, DGIST, Daegu 42988, Korea, working with colleagues at Aaram J., details a promising mechanism within the photodoped Hubbard model. Their study, utilising advanced dynamical mean-field theory, reveals a remarkably high effective critical temperature for ηη-pairing superconductivity induced by light. This finding is significant because it demonstrates a route towards controllable high-temperature superconductivity in a non-equilibrium, strongly correlated system, offering a fundamentally different approach from conventional equilibrium-based superconductivity observed in materials like cuprates. The researchers further identified clear spectroscopic signatures, such as a superconducting gap in the momentum-resolved spectral function and optical conductivity, which could be experimentally verified. Can light be used to create superconductivity at relatively warm temperatures — calculations suggest it can, revealing a pathway to this effect by ‘doping’ materials with photons. This offers a completely different approach to achieving superconductivity, moving beyond conventional methods reliant on extremely cold conditions, and scientists are now reporting a pathway to achieving superconductivity, the lossless flow of electricity. Through a method that bypasses the limitations of conventional materials and temperatures. For decades, the pursuit of room-temperature superconductivity has remained a central, yet elusive, goal in physics due to its potential for revolutionary technological advances. Recent investigations detail a process where shining light onto a specific material induces a superconducting state, creating what is termed η-pairing superconductivity. Unlike traditional superconductors which rely on low temperatures and specific material compositions, this light-induced state emerges within a strongly correlated material, a system where electron interactions play a dominant role. Exhibits a remarkably high effective critical temperature. Accurate simulations of these complex systems demand considerable computational power, hindering detailed assessments of how and when η-pairing superconductivity can be reliably achieved.

Scientists have employed a sophisticated theoretical technique, steady-state dynamical mean-field theory, to model this behaviour in the photodoped Mott insulatingHubbard model By utilising advanced computational methods, they have mapped out the conditions under which this unconventional superconductivity arises, and identified clear spectroscopic signatures that could be detected in experiments. This photoinduced state is fundamentally different from equilibrium-based superconductivity, relying on the creation and control of doublon, holon pairs, electron-hole pairs generated by the incident light. Once created, these pairs are relatively stable. For the formation of long-lived superconducting states even at relatively low levels of light exposure. Calculations reveal that effective transition temperatures remain above room temperature even with a photodoping concentration of approximately 0.1. At the heart of this effort lies the Hubbard model, a simplified representation of interacting electrons in a solid. To solve this model, the team used dynamical mean-field theory — this transforms the complex many-body problem into a more manageable single-impurity problem. Here, this impurity problem was then solved using a newly developed, high-order strong-coupling impurity solver. Accurate calculations of the material’s electronic properties. The resulting spectral functions and optical conductivity reveal a clear superconducting gap, a key indicator of the η-pairing state. Provide a pathway for experimental verification of these findings. Real-frequency DMFT and third-order solvers reveal strong correlations and nonequilibrium superconductivity Steady-state dynamical mean-field theory (DMFT) underpinned this effort. Investigation of superconductivity emerging in the photodoped Mott insulating Hubbard model. The method maps the complex interactions within the material onto an effective impurity problem, simplifying calculations while retaining essential physics. By solving this impurity model directly on the real-frequency axis, researchers avoided the inaccuracies inherent in analytic continuation methods commonly used in DMFT. The chosen approach enabled The effort of nonequilibrium steady states, essential for modelling photodoping where the system is not in thermal equilibrium. High-order strong-coupling impurity solvers were employed to accurately capture the strong correlations present in the material. Specifically, a newly developed third-order solver, quantics tensor cross interpolation (QTCI), proved vital for obtaining high-resolution spectral functions. Unlike lower-order schemes like the non-crossing approximation (NCA) or one-crossing approximation (OCA), QTCI accurately resolves the complex electronic structure arising from photodoping. Meanwhile, the Hubbard model itself is defined by a Hamiltonian incorporating nearest-neighbour hopping, on-site interaction, and chemical potential, providing a framework for describing electron behaviour. Across symmetry-adapted calculations, the DMFT equations were formulated using Nambu bases, accommodating both conventional and η-pairing superconducting states. A small pairing seed field was introduced to stabilise solutions exhibiting broken symmetry, and the effective transition temperature was extracted from the anomalous expectation value using a mean-field square-root scaling. Here, the simulation of photodoped states was achieved by shifting effective Fermi levels for photocarriers. In turn, the two-dimensional Hubbard model was primarily investigated with a hopping parameter of 0.35 eV, although results from a three-dimensional model are also presented. High-temperature η-pairing confirmed via spectroscopic evidence of a superconducting gap Calculations reveal effective critical temperatures reaching 1400 K for photoinduced superconductivity in the doped Mott insulator. These temperatures, obtained using steady-state dynamical mean-field theory, surpass those observed in equilibrium d-wave superconductors. Analysis of the two- and three-dimensional Hubbard model demonstrates this η-pairing state persists even at relatively low doping levels. At a doping concentration of approximately 0.1, the effective transition temperature remains above room temperature, suggesting potential for practical applications. Determining the existence of a clear superconducting gap with spectroscopic signatures remained a challenge until this effort. Spectral functions and optical conductivity measurements display distinct evidence of this gap, providing experimentally accessible confirmation of η pairing. Meanwhile, the momentum-resolved spectral function clearly shows the opening of a gap at the Fermi level, a hallmark of superconductivity. High-resolution spectral functions were obtained without requiring analytic continuation, due to the use of third-order strong-coupling impurity solvers. At the same time, at higher doping levels, the effective transition temperature initially decreases, but remains substantial across the investigated range. Comparison with previous theoretical results showed a marked difference. Unlike d-wave superconductivity calculations using dynamical cluster approximation, the η-pairing state exhibits a markedly higher transition temperature. Outcomes also contrast with those from attractive Hubbard models solved with network cluster approximation and orbital cancellation approximation. Previous studies confirmed η-pairing superconductivity in one-dimensional systems at zero temperature by employing density-matrix renormalization group and exact diagonalization methods. However, these methods faced limitations when applied to quasi-two- or three-dimensional materials, prompting the use of DMFT in this project. Light-induced superconductivity in Mott insulators offers novel pathway beyond cryogenic limitations To achieve substantial superconductivity without extreme cooling now appears a little less fanciful — scientists have demonstrated a pathway to high-temperature superconductivity, not through materials discovery. But by artificially engineering conditions within existing materials using light, and they’ve modelled how ‘shining’ light onto a Mott insulator, a material normally resistant to electrical flow. Can induce a superconducting state with a surprisingly high effective critical temperature. The challenge has been to move beyond superconductivity requiring liquid helium or nitrogen — this effort offers a fundamentally different approach, sidestepping the need for exotic materials. Instead, it focuses on manipulating the electronic structure of known compounds, and the method relies on creating a ‘non-equilibrium’ state, meaning the system is driven away from its natural, lowest-energy configuration. Maintaining that state requires continuous illumination. The implications for materials science are considerable. This effort identifies clear spectroscopic signatures, patterns in how the material absorbs and emits light — that could be used to confirm the existence of this photo-induced superconductivity in experiments. Sustaining this effect and scaling it up remain significant hurdles, and the project is largely theoretical, employing advanced computational techniques to model the behaviour of electrons within the material. Experimental verification is vital, and future work will likely focus on identifying materials where this light-induced effect is most pronounced and long-lasting. This approach opens up a new design space, and could eventually lead to controllable, albeit power-dependent, superconducting devices with applications ranging from lossless power transmission to ultra-sensitive sensors. 👉 More information 🗞 High-temperature ηη-pairing superconductivity in the photodoped Hubbard model 🧠 ArXiv: https://arxiv.org/abs/2602.17238 Tags: