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arXiv:2608.02501

Superconducting dome due to the Fano-Feshbach shape resonance in artificial high-Tc superlattices

Gaetano Campi, Andrea Alimenti, Danielle Villa, G. Alexander Smith, Fedor F. Balakirev, Luis Balicas, Andrea Perali, S. Caprara, Gennady Logvenov, Antonio Bianconi

Published Aug 3, 2026• 0 citations
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Abstract

In this work we provide compelling experimental validation of the Bianconi Perali Valletta (BPV) theory predicting a superconducting dome based on a quantum material design of Artificial High TC Superlattices (AHTS) made with a selected nanoscale heterostructure geometry. These AHTS are SNSN superlattices of quantum wells of period d, composed of first units, superconducting doped Mott insulator layers with Rashba spin orbit coupling (S) of thickness L, intercalated by second units, normal metal spacers (N). In these superlattices, grown by molecular beam epitaxy (MBE), the experimental superconducting dome is obtained by material quantum design changing the chemical potential via the quantum geometrical factor L/d which tunes the Fano-Feshbach shape resonance in the pair transfer between superconducting gaps in the BCS regime and different gaps in the BEC-BCS crossover. Here we present a systematic magneto-transport study of AHTS artificial superlattices across the full doping range of the superconducting dome, from the deeply underdoped to the overdoped regime, using pulsed magnetic fields up to 72 T. By varying the L/d ratio, we tune the effective hole concentration delta=0.45(1-L/d) and map the evolution of the resistive transitions, the upper critical magnetic field and the Ginzburg-Landau coherence length

DOI
10.48550/arxiv.2608.02501

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In this work we provide compelling experimental validation of the Bianconi Perali Valletta (BPV) theory predicting a superconducting dome based on a quantum material design of Artificial High TC Superlattices (AHTS) made with a selected nanoscale heterostructure geometry. These AHTS are SNSN superlattices of quantum wells of period d, composed of first units, superconducting doped Mott insulator layers with Rashba spin orbit coupling (S) of thickness L, intercalated by second units, normal metal spacers (N). In these superlattices, grown by molecular beam epitaxy (MBE), the experimental superconducting dome is obtained by material quantum design changing the chemical potential via the quantum geometrical factor L/d which tunes the Fano-Feshbach shape resonance in the pair transfer between superconducting gaps in the BCS regime and different gaps in the BEC-BCS crossover. Here we present a systematic magneto-transport study of AHTS artificial superlattices across the full doping range of the superconducting dome, from the deeply underdoped to the overdoped regime, using pulsed magnetic fields up to 72 T. By varying the L/d ratio, we tune the effective hole concentration delta=0.45(1-L/d) and map the evolution of the resistive transitions, the upper critical magnetic field and the Ginzburg-Landau coherence length
It is known that cuprate artificial high Tc superlattices (AHTS) with period d, composed of quantum wells confining interface space charge in stoichiometric Mott insulator layers (S), with thickness L, at the interface with overdoped normal metallic cuprate layers (N) show a superconducting dome by tuning the geometric L over d ratio of the SNSN superlattice with the top predicted by quantum material design engineering quantum size effects. Here we report high-field magneto transport measurements up to 41 Tesla of AHTS across the entire superconducting dome. The results show the universal upward-concave behavior of the temperature dependent upper critical magnetic field in low Tc samples at rising edge and drop edge of the dome providing strong evidence consistent with two-band superconductivity for two-band superconductivity in agreement with multigap theory used for quantum design of the SNSN superlattices. The measured superconducting coherence length demonstrates that atomic-scale engineering controls not only the critical temperature but also the intrinsic pair size at Fano-Feshbach resonances physics paving the way toward next generation quantum devices and shedding light on unconventional superconductivity.
The multigap superconductivity modulated by quantum confinement effects in a superlattice of quantum wells is presented. Our theoretical BCS approach captures the low-energy physics of a shape resonance in the superconducting gaps when the chemical potential is tuned near a Lifshitz transition. We focus on the case of weak Cooper-pairing coupling channels and strong pair exchange interaction driven by repulsive Coulomb interaction that allows to use the BCS theory in the weak-coupling regime neglecting retardation effects like in quantum condensates of ultracold gases. The calculated matrix element effects in the pairing interaction are shown to yield a complex physics near the particular quantum critical points due to Lifshitz transitions in multigap superconductivity. Strong deviations of the ratio 2Δ/Tc2Δ/T_c2Δ/Tc​ from the standard BCS value as a function of the position of the chemical potential relative to the Lifshitz transition point measured by the Lifshitz parameter are found. The response of the condensate phase to the tuning of the Lifshitz parameter is compared with the response of ultracold gases in the BCS-BEC crossover tuned by an external magnetic field. The results provide the description of the condensates in this regime where matrix element effects play a key role.
In multiband superconductivity, the case where the single electron hopping between different Fermi surface spots of different symmetry is forbidden by selection rules is recently attracting a large interest. The focus is addressed to superconductivity made of multiple condensates with different symmetry where the chemical potential crosses a 2.5 Lifshitz transition. This can now be investigated experimentally by fine-tuning of the chemical potential in the range of tens meV around a band edge using gate voltage control. We discuss here the case of a superconducting two-dimensional electron gas (2DEG), at the interface between two insulating oxides confined within a slab of 5 nanometers thickness, where the electronic structure is made of subbands generated by quantum size effects. We obtain shape resonances in the superconducting gaps, characterisc gaps to T c ratios and the BCS-BEC crossover in the upper subband for different pairing strength in the shallow Fermi surface, pointing toward the best configurations for enhanced superconductivity in 2DEG.
Motivated by the presence of an extremely small electron pocket in the electronic band structure of infinite-layer (IL) nickelate superconductors, we systematically explore the superconducting (SC) properties of a two-dimensional Hubbard model influenced by an additional conduction band with small occupancy (dry Fermi sea). Our dynamic cluster quantum Monte Carlo calculations demonstrated the unusual impact of this additional dry metallic layer, which shifts the SC dome of the correlated Hubbard layer towards the overdoped regime, namely the ddd-wave SC can be enhanced (suppressed) in the overdoped (underdoped) regime. Simultaneously, the pseudogap (PG) crossover line shifts to the same higher doping regime as well. Our analysis revealed the interplay of the effective pairing interaction, pair-field susceptibility, and antiferromagnetic spin fluctuation in the underlying non-monotonic physics. We postulate on the physical picture of SC dome shift in terms of the Kondo-type electron-hole binding in the case of a dry additional conduction band. Our investigation provided valuable new insights on tuning the SC properties via external dry bands.
We generalize the condition under which a quantum material exhibiting a pseudogap phase is a precursor to a superconducting (SC) dome. The result reveals the non-analytic T* as a function of doping. A well-known example is the high-Tc cuprates. Essentially, the SC dome is generated under two conditions: (1) that the pseudogap T* is a decreasing function of doping, due to the decrease in size of extended pairing of doped holes with doping, and most importantly, (2) that the rate of configurational-ordering parameter is an increasing function of doping as a result of the decrease in extended length of the disordered pairs. The theory behind these hinges on a novel strong entanglement and confinement hole pairing (ECHP) mechanism that unravels the microscopic features of the entire phase diagram of both electron and hole-doped high-Tc cuprates, recently discussed in the by Buot et al. The ECHP configurational ordering (CO) at the underdoped and overdoped regions qualitatively agrees with spin texture experiments, and strongly suggests that strange metal phase can only occur in the overdoped region, in agreement with experiments.
Resonant interactions associated with the emergence of a bound state constitute one of the cornerstones of modern many-body physics, ranging from Kondo physics, BEC-BCS crossover, to tunable interactions at Feshbach resonances in ultracold atoms or 2D semiconductors. Here we present a Feshbach perspective on the origin of strong pairing in Fermi-Hubbard type models. We perform a theoretical analysis of interactions between charge carriers in doped Mott insulators, modeled by a near-resonant two-channel scattering problem, and find strong evidence for Feshbach-type interactions in the dx2−y2d_{x^2-y^2}dx2−y2​ channel that can support strong pairing, consistent with the established phenomenology of cuprates. Existing experimental and numerical results on hole-doped cuprates lead us to conjecture the existence of a light, long-lived, low-energy excited state of two holes with bipolaron character in these systems, which enables near-resonant interactions and can thus provide a microscopic foundation for theories of high-temperature superconductivity involving strong attraction, as assumed e.g. in BEC-BCS crossover scenarios. To put our theory to a direct test we suggest to use coincidence angle-resolved photoemission spectroscopy (cARPES), pair-tunneling measurements or less direct pump-probe experiments. The emergent Feshbach resonance we propose could also underlie superconductivity in other doped antiferromagnetic Mott insulators, as recently proposed for bilayer nickelates, highlighting its potential as a unifying strong-coupling pairing mechanism rooted in quantum magnetism.