Superconductivity, the property of zero electrical resistance and expulsion of magnetic fields, typically involves the formation of Cooper pairs—bound states of electrons with opposite momenta and spins. Conventionally, the superconducting order parameter, which reflects the density and phase of these Cooper pairs, remains uniform throughout the material. However, CPDM states represent a remarkable deviation: their superconducting order parameter varies periodically in real space. Intriguingly, this modulation occurs without globally breaking the translational symmetry of the system, marking a novel quantum phase that intertwines subtlety with complexity.

Moiré superlattices, formed by overlaying two crystalline layers with slightly mismatched lattice constants or orientations, have emerged as a dynamic platform for manipulating electron interactions and band structures. These synthetic lattices craft new periodic potentials, enabling phenomena unobserved in the constituent materials alone. While prior research has extensively demonstrated correlated insulating states, unconventional superconductivity, and topological phases within moiré heterostructures like twisted bilayer graphene and transition metal dichalcogenides, Wang et al.’s work pioneers their use in sculpting CPDM states through precise lattice engineering.

The researchers constructed an epitaxial bilayer heterostructure by stacking a single quintuple layer (1QL) of the topological insulator Sb2Te3 atop a six-unit-cell-thick (6UC) antiferromagnetic FeTe film. This stacking juxtaposes two distinct tellurium lattices: the hexagonal symmetry of Sb2Te3 resting on the square lattice of FeTe. The resulting lattice mismatch naturally generates a moiré superlattice, whose periodicity subtly modulates the electronic environment of the bilayer. This engineered superlattice becomes the scaffold upon which Cooper-pair densities spatially organize.

By applying advanced scanning tunnelling microscopy and spectroscopy (STM/S), the team achieved atomic-scale visualization and measurement of the superconducting gaps across the 1QL Sb2Te3/6UC FeTe bilayer. They observed that the two distinct superconducting gaps—arising from different electronic states—undergo periodic modulations synchronized with the moiré pattern. This modulation directly evidences the spatial variation in Cooper-pair density, signaling the unambiguous presence of CPDM states tethered to the moiré periodicity.

The hallmark of this study lies in the use of Josephson STM spectroscopy, a technique sensitively probing the Cooper-pair tunneling amplitude in real space. Leveraging this method, Wang and colleagues visualized the spatial oscillations of the superconducting order parameter with unprecedented clarity. The wavelength of the CPDM states closely matched the moiré superlattice periodicity, confirming that the engineered structural modulation orchestrates the emergence of spatially patterned superconductivity. This connection between real-space lattice interference and superconducting order parameter modulation is a milestone in our ability to tailor quantum phases.

Beyond observation, the team demonstrated tunability by substituting Sb2Te3 with Bi2Te3, another topological insulator with slightly different lattice parameters. This substitution altered both the magnitude and periodicity of the CPDM states, showcasing an effective knob to engineer and control superconducting modulations. Such tunability opens avenues for designing bespoke superconducting devices where spatial variation of Cooper pairs can be manipulated for desired quantum functionalities, including quantum computing platforms and novel sensors.

The epitaxial approach outlined here is particularly notable due to the challenge of interfacing materials with fundamentally different crystal symmetries—hexagonal versus square lattices—while maintaining high crystalline quality and clean interfaces. Successfully synthesizing such heterostructures exemplifies the precision of current material growth techniques like molecular beam epitaxy (MBE). By harnessing these synthetic superlattices, researchers gain a versatile toolkit for probing emergent phenomena at the confluence of topology, magnetism, and superconductivity.

Collectively, this work builds upon a growing corpus of studies leveraging moiré physics to uncover exotic quantum phases. Previous landmark results in magic-angle twisted bilayer graphene have revealed flat bands that dramatically enhance electronic correlations, spurring superconductivity and insulating states. Meanwhile, investigations into transition metal dichalcogenide heterostructures have mapped out intricate phase diagrams of correlated insulators, superconductors, and quantum anomalous Hall states. Wang et al.’s findings add CPDM states to the roster of emergent phases accessible via moiré engineering, broadening the landscape of designer quantum materials.

At the theoretical level, the study also touches upon the significance of symmetry and electronic nematicity—where rotational symmetry is spontaneously broken—in stabilizing CPDM states. The interplay between glide symmetry breaking and nematic superconductivity, as discussed in complementary theoretical works, provides a robust framework for understanding how modulated pairing fields arise without destroying translational invariance. This nuanced symmetry interplay hints at richer classes of superconducting order parameters awaiting exploration.

Pragmatically, these findings portend advancements in quantum electronics where spatial control over superconducting properties could translate into devices with tailored Josephson junction arrays, localized topological excitations, or engineered quantum bits (qubits). The direct visualization capability of Josephson STM further enables feedback-driven optimization of heterostructure design, accelerating the translation from fundamental discovery to application.

In conclusion, the realization of moiré-engineered CPDM states in epitaxial Sb2Te3/FeTe bilayers marks a significant leap forward in quantum materials science. By melding the tunability of moiré superlattices with the richness of topological insulators and magnetic substrates, Wang et al. have established a platform where Cooper-pair densities can be patterned at will. This advance sets the stage for future explorations into novel superconducting phases and opens fresh horizons in the quest to harness quantum coherence for technology.

Subject of Research: Moiré superlattice-induced Cooper-pair density modulation (CPDM) states in epitaxially grown topological insulator/antiferromagnetic bilayer heterostructures.

Article Title: Moiré engineering of Cooper-pair density modulation states.

Article References:
Wang, Z., Xia, B., Paolini, S. et al. Moiré engineering of Cooper-pair density modulation states. Nature (2026). https://doi.org/10.1038/s41586-026-10325-w

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10325-w

Keywords: Cooper-pair density modulation, moiré superlattice, topological insulator, Sb2Te3, FeTe, Josephson STM, superconductivity, epitaxial heterostructure, quantum materials, nematic superconductivity, glide symmetry breaking, real-space imaging

Moiré materials have captivated the condensed matter physics community over the past several years due to their extraordinary ability to engender novel electronic phenomena through the delicate control of atomic registry and stacking angles. By assembling sheets of semiconducting transition metal dichalcogenides (TMDs), such as WSe₂ and MoSe₂, researchers create moiré superlattices with twist angles that determine the material’s emergent optical and electronic properties. These moiré patterns can host strongly correlated insulating states, generalized Wigner crystals, and exotic excitonic and polaronic effects, all reliant on the precise interlayer coupling dictated by atomic registry.

However, prior to this advance, the understanding of how these moiré configurations could be altered dynamically on ultrashort timescales remained elusive. Conventional wisdom suggested that lattice deformations induced by photoexcitation typically lead to incoherent lattice heating and disordering, not coherent modulation of twist angles. This new work overturns that notion by directly observing a coherent twist–untwist oscillation within the moiré superlattice of twisted WSe₂/MoSe₂ heterobilayers, with twist angles initially set at 2° and 57°.

Utilizing state-of-the-art ultrafast electron diffraction techniques with femtosecond temporal resolution, the team captured the time-resolved evolution of the moiré diffraction peaks following above-band-gap optical excitation. Rather than fading monotonically due to thermal disordering, the intensity of the moiré superlattice diffraction features first increased sharply within 1 picosecond, indicative of an enhanced periodic lattice distortion, before gradually diminishing several picoseconds later. This nontrivial behavior signals that an unusual phonon mode associated with lattice twisting is coherently excited.

Detailed kinetic diffraction analysis corroborated by advanced simulations revealed the underlying lattice dynamics—a sub-terahertz frequency oscillation corresponding to a twist-angle modulation of approximately 0.6°, a profound magnitude considering the atomic scale. This twist–untwist motion can be understood as the transient mechanical response of the bilayer heterostructure, where optically generated charge transfer enhances interlayer attraction, effectively pulling the two layers into a slightly altered atomic registry.

This photoinduced lattice motion fundamentally changes the native moiré potential landscape. Since excitons, polarons, and correlated electron behaviors in TMD heterobilayers are sensitively dependent on this periodic potential, the ability to drive and control twist angle oscillations could provide a revolutionary handle for manipulating quantum states of matter dynamically, all on ultrafast timescales previously inaccessible.

The implications are enormous. The rise of controlled moiré dynamics paves the way for engineering tunable quantum phases, where transient manipulations of interlayer twist may switch correlated insulating states on and off or modulate topological properties with a mere optical pulse. Such capabilities would position moiré materials as a new platform for coherent quantum devices, with ultrafast optical control replacing mechanical or static methods.

Furthermore, the discovery highlights the critical importance of coupling electronic and structural degrees of freedom in layered quantum materials. Here, charge redistribution via photoexcitation profoundly modifies interlayer forces and, consequently, lattice geometry. This electron-phonon interplay is a crucial piece of the puzzle in understanding emergent moiré phenomena and could inspire similar studies in other van der Waals heterostructures.

From an experimental standpoint, the use of femtosecond electron diffraction represents a tour de force, directly visualizing atomic-scale lattice motions with unprecedented time resolution. By resolving not only the magnitude but also the direction and frequency of moiré phonons, researchers have opened a window into the transient structural dynamics that underpin optoelectronic functionalities.

Looking forward, one can envision integrating such ultrafast control schemes with other moiré-enabled quantum devices. Combining optical pulses with electrical gating or magnetic field tuning could lead to versatile, multifunctional quantum systems where interactions and topological attributes are modulated on the fly, yielding unprecedented device architectures.

The study also raises intriguing theoretical questions about the stability and nonlinear response of moiré superlattices under strong nonequilibrium perturbations. As photoinduced twist angles oscillate beyond equilibrium regimes, the potential energy landscape may access new metastable configurations, hinting at photoinduced phase transitions or dynamically stabilized states yet to be discovered.

This breakthrough synergizes the rapid advances in ultrafast laser techniques, quantum materials synthesis, and electron microscopy to map dynamic atomic-scale phenomena, promising to propel the field of quantum materials engineering into a new era where static constraints give way to ultrafast tunability.

In essence, the demonstration of photoinduced twist and untwist in moiré superlattices is a vivid testament to the ingenuity of modern materials science. It heralds a future where light can sculpt the quantum landscape in layered materials at will, with profound consequences for next-generation quantum technologies and fundamental condensed matter physics alike.

Subject of Research: Ultrafast dynamics and photoinduced structural modulation in two-dimensional moiré superlattices of twisted WSe₂/MoSe₂ heterobilayers.

Article Title: Photoinduced twist and untwist of moiré superlattices.

Article References:
Duncan, C.J.R., Johnson, A.C., Maity, I. et al. Photoinduced twist and untwist of moiré superlattices. Nature (2025). https://doi.org/10.1038/s41586-025-09707-3

DOI: https://doi.org/10.1038/s41586-025-09707-3