A quantum twisting microscope (QTM) enables energy- and momentum-resolved measurements of quantum phases through tunneling spectroscopy in twistable van der Waals heterostructures. Here, we improve its resolution and extend its range to higher energies and twist angles by integrating hexagonal boron nitride as a tunneling dielectric. This advance reveals previously inaccessible dispersion features in tunneling between two monolayer graphene sheets, consistent with a logarithmic correction to the linear Dirac spectrum arising from electron-electron interactions, with a fine-structure constant alpha approximate to 0.32 +/- 0.01. Remarkably, these extremely subtle corrections are resolved even at room temperature. Our results highlight the exceptional sensitivity of the QTM, where interferometric interlayer tunneling amplifies small band-structure modifications. They further show that strong electron-electron interactions persist in symmetric, nonordered graphene states and demonstrate the QTM's capability to probe spectral functions and excitations of correlated ground states across twisted and untwisted two-dimensional systems.

While extensively studied in normal metals, semimetals, and semiconductors, the superconducting (SC) proximity effect remains elusive in the emerging field of flat-band systems. In this study, we probe proximity-induced superconductivity in Josephson junctions (JJs) formed between superconducting NbTiN electrodes and twisted bilayer graphene (TBG) weak links. Here, the TBG acts as a highly tunable topological flat-band system, which, due to its twist-angle-dependent bandwidth, allows us to probe the SC proximity effect at the crossover from the dispersive to the flat-band limit. Contrary to our original expectations, we find that the induced superconductivity remains strong even in the flat-band limit and gives rise to broad, dome-shaped SC regions, in the filling-dependent phase diagram. In addition, we find that, unlike in conventional JJs, the critical current Ic strongly deviates from a scaling with the normal state conductance GN. We attribute these findings to the onset of strong electron interactions, which can give rise to an excess critical current. By also studying the dependence of Ic on the filling and twist angle across multiple samples, we further uncover the importance of quantum geometric terms as well as multiband pairing mechanisms in describing the induced superconductivity in the TBG flat bands as their bandwidth decreases. To the best of our knowledge, our results present the first detailed study of the SC proximity effect in the flat-band limit and shed new light on the mechanisms that drive the formation of SC domes in flat-band systems.

We analyze the properties of flat-band superconductor junctions that behave differently from ordinary junctions containing only metals with Fermi surfaces. In particular, we show how in the tunneling limit the critical Josephson current between flat-band superconductors is inversely proportional to the pair potential, how the quantum geometric contribution to the supercurrent appears even in the normal state of a flat-band weak link, and how Andreev reflection is strongly affected by the presence of bound states. Our results are relevant for analyzing the superconducting properties of junctions involving electronic systems with flat bands.

Triggered by advances in atomic-layer exfoliation and growth techniques, along with the identification of a wide range of extraordinary physical properties in self-standing films consisting of one or a few atomic layers, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and other van der Waals (vdW) crystals now constitute a broad research field expanding in multiple directions through the combination of layer stacking and twisting, nanofabrication, surface-science methods, and integration into nanostructured environments. Photonics encompasses a multidisciplinary subset of those directions, where 2D materials contribute remarkable nonlinearities, long-lived and ultraconfined polaritons, strong excitons, topological and chiral effects, susceptibility to external stimuli, accessibility, robustness, and a completely new range of photonic materials based on layer stacking, gating, and the formation of moire patterns. These properties are being leveraged to develop applications in electro-optical modulation, light emission and detection, imaging and metasurfaces, integrated optics, sensing, and quantum physics across a broad spectral range extending from the far-infrared to the ultraviolet, as well as enabling hybridization with spin and momentum textures of electronic band structures and magnetic degrees of freedom. The rapid expansion of photonics with 2D materials as a dynamic research arena is yielding breakthroughs, which this Roadmap summarizes while identifying challenges and opportunities for future goals and how to meet them through a wide collection of topical sections prepared by leading practitioners.

"We investigate in detail the v=+1 displacement-field-tuned interacting phase diagram of L=3,4,5,6,7 layer rhombohedral graphene aligned to hBN (RLG/hBN). Our calculations account for the 3D nature of the Coulomb interaction, the inequivalent stacking orientations xi=0,1, the effects of the filled valence bands, and the choice of ""interaction scheme"" for specifying the many-body Hamiltonian. We show that the latter has a dramatic impact on the Hartree-Fock phase boundaries and the properties of the phases, including for pentalayers (R5G/hBN) with large displacement field D, where recent experiments observed a Chern insulator at v=+1 and fractional Chern insulators for v<1. In this large D regime, the low-energy conduction bands are polarized away from the aligned hBN layer, making them well described by the folded bands of moir & eacute,.less rhombohedral graphene at the noninteracting level. Despite this, the filled valence bands develop moir & eacute,.-periodic charge density variations, which can generate an effective moir & eacute,. potential, thereby explicitly breaking the approximate continuous translation symmetry in the conduction bands and leading to contrasting electronic topology in the ground state for the two stacking arrangements. Within time-dependent Hartree-Fock theory, we further characterize the strength of the moir & eacute,. pinning potential in the Chern insulator phase by computing the low-energy q=0 collective mode spectrum, where we identify competing gapped pseudophonon and valley magnon excitations. Our results emphasize the importance of careful examination of both the single-particle and interaction model for a proper understanding of the correlated phases in RLG/hBN."

When two monolayer materials are stacked with a relative twist, an effective moire translation symmetry emerges, leading to fundamentally different properties in the resulting heterostructure. As such, moire materials have recently provided highly tunable platforms for exploring strongly correlated systems(1,2). However, previous studies have focused almost exclusively on monolayers with triangular lattices and low-energy states near the G (refs. 3,4) or K (refs. 5-9) points of the Brillouin zone (BZ). Here we introduce a new class of moire systems based on monolayers with triangular lattices but low-energy states at the M points of the BZ. These M-point moire materials feature three time-reversal-preserving valleys related by threefold rotational symmetry. We propose twisted bilayers of exfoliable 1T-SnSe2 and 1T-ZrS2 as realizations of this new class. Using extensive ab initio simulations, we identify twist angles that yield flat conduction bands, provide accurate continuum models, analyse their topology and charge density and explore the platform's rich physics. Notably, the M-point moire Hamiltonians exhibit emergent momentum-space non-symmorphic symmetries and a kagome plane-wave lattice structure. This represents, to our knowledge, the first experimentally viable realization of projective representations of crystalline space groups in a non-magnetic system. With interactions, these systems act as six-flavour Hubbard simulators with Mott physics. Moreover, the presence of a momentum-space non-symmorphic in-plane mirror symmetry renders some of the M-point moire Hamiltonians quasi-one-dimensional in each valley, suggesting the possibility of realizing Luttinger-liquid physics.

Recent studies have suggested that the strongly correlated flat bands of magic-angle twisted bilayer graphene may host coexisting light and heavy carriers. Although transport and spectroscopic measurements have hinted at this behaviour, distinct signatures of incoherent heavy carriers have not been reported. Here we provide evidence of this by performing thermoelectric transport measurements of magic-angle twisted bilayer graphene using the photo-thermoelectric effect in gate-defined p-n junctions. At low temperatures, we observe sign-preserving, filling-dependent oscillations of the Seebeck coefficient at non-zero integer fillings of the moir & eacute,. superlattice. This suggests the preponderance of one carrier type even when the Fermi level is tuned through the charge neutrality point of the correlated states. At higher temperatures, the thermoelectric response provides evidence of strong electron correlations in the unordered, normal state. Our observations are explained by the interplay between light, long-lived electron states and heavy, short-lived hole excitations near the Fermi level of the symmetry-broken ground states. These findings are in qualitative agreement with the topological heavy fermion model.

The moire superconductor magic-angle twisted bilayer graphene (MATBG) shows exceptional properties, with an electron (hole) ensemble of only similar to 10(11) carriers per square centimeter, which is five orders of magnitude lower than traditional superconductors (SCs). This results in an ultralow electronic heat capacity and a large kinetic inductance of this truly two-dimensional SC, providing record-breaking parameters for quantum sensing applications, specifically thermal sensing and single-photon detection. To fully exploit these unique superconducting properties for quantum sensing, here, we demonstrate a proof-of-principle experiment to detect single near-infrared photons by voltage biasing an MATBG device near its superconducting phase transition. We observe complete destruction of the SC state upon absorption of a single infrared photon even in a 16-square micrometer device, showcasing exceptional sensitivity. Our work offers insights into the MATBG-photon interaction and demonstrates pathways to use moire superconductors as an exciting platform for revolutionary quantum devices and sensors.

"The experimental discovery of fractional Chern insulators (FCIs) in rhombohedral pentalayer graphene twisted on hexagonal boron nitride (hBN) has preceded theoretical prediction. Supported by large-scale first -principles relaxation calculations at the experimental twist angle of 0.77 degrees, we obtain an accurate continuum model of n = 3, 4, 5, 6, 7 layer rhombohedral graphene-hBN moiré systems. Focusing on the pentalayer case, we analytically explain the robust |C| = 0, 5 Chern numbers seen in the low -energy single -particle bands and their flattening with displacement field, making use of a minimal two -flavor continuum Hamiltonian derived from the full model. We then predict nonzero valley Chern numbers at the nu = -4, 0 insulators observed in experiment. Our analysis makes clear the importance of displacement field and the moiré potential in producing localized ""heavy fermion"" charge density in the top valence band, in addition to the nearly free conduction band. Lastly, we study doubly aligned devices as additional platforms for moiré FCIs with higher Chern number bands."

We propose minimal transport experiments in the coherent regime that can probe the chirality of twisted moire structures. We show that only with a third contact and in the presence of an in-plane magnetic field (or another time-reversal symmetry breaking effect) a chiral system may display nonreciprocal transport in the linear regime. We then propose to use the third lead as a voltage probe and show that opposite enantiomers give rise to different voltage drops on the third lead. Additionally, in the scenario of layer-discriminating contacts, the third lead can serve as a current probe capable of detecting different handedness even in the absence of a magnetic field. In a complementary configuration, applying opposite voltages on the two layers of the third lead gives rise to a chiral (super)current in the absence of a source-drain voltage whose direction is determined by its chirality.

Understanding electron-phonon interactions is fundamentally important and has crucial implications for device applications. However, in twisted bilayer graphene near the magic angle, this understanding is currently lacking. Here, we study electron-phonon coupling using time- and frequency-resolved photovoltage measurements as direct and complementary probes of phonon-mediated hot-electron cooling. We find a remarkable speedup in cooling of twisted bilayer graphene near the magic angle: The cooling time is a few picoseconds from room temperature down to 5 kelvin, whereas in pristine bilayer graphene, cooling to phonons becomes much slower for lower temperatures. Our experimental and theoretical analysis indicates that this ultrafast cooling is a combined effect of superlattice formation with low-energy moiré,. phonons, spatially compressed electronic Wannier orbitals, and a reduced superlattice Brillouin zone. This enables efficient electron-phonon Umklapp scattering that overcomes electron-phonon momentum mismatch. These results establish twist angle as an effective way to control energy relaxation and electronic heat flow.

The discovery of magic angle twisted bilayer graphene (MATBG), in which two sheets of monolayer graphene are precisely stacked at a specific angle, has opened up a plethora of grand new opportunities in the field of topology, superconductivity, strange metal, and other strongly correlated effects. This review will focus on the various forms of quantum phases in MATBG revealed through quantum transport measurements. The goal is to highlight the uniqueness and current understanding of the various phases, especially how electronic interaction plays a role in them, as well as open questions in regard to the phase diagram.

Detecting light at the single-photon level is one of the pillars of emergent photonic technologies. This is realized through state-of-the-art superconducting detectors that offer efficient, broadband and fast response. However, the use of low TC superconducting thin films limits their operation temperature to approximately 4 K and below. Here, we demonstrate proof-of-concept nanodetectors based on exfoliated, two-dimensional cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8-delta )that exhibit single-photon sensitivity at telecom wavelength at a record temperature of T = 20 K. These non-optimized devices exhibit a slow (similar to ms) reset time and a low detection efficiency (-10(-4)). We realize the elusive prospect of single-photon sensitivity on a high-TC nanodetector thanks to a novel approach, combining van der Waals fabrication techniques and a non-invasive nanopatterning based on light ion irradiation. This result paves the way for broader application of single-photon technologies, relaxing the cryogenic constraints for single-photon detection at telecom wavelength.

Detecting light at the single-photon level is one of the pillars of emergent photonic technologies. This is realized through state-of-the-art superconducting detectors that offer efficient, broadband and fast response. However, the use of low TC superconducting thin films limits their operation temperature to approximately 4 K and below. Here, we demonstrate proof-of-concept nanodetectors based on exfoliated, two-dimensional cuprate superconductor Bi2Sr2CaCu2O8-delta that exhibit single-photon sensitivity at telecom wavelength at a record temperature of T = 20 K. These non-optimized devices exhibit a slow (similar to ms) reset time and a low detection efficiency (-10(-4)). We realize the elusive prospect of single-photon sensitivity on a high-TC nanodetector thanks to a novel approach, combining van der Waals fabrication techniques and a non-invasive nanopatterning based on light ion irradiation. This result paves the way for broader application of single-photon technologies, relaxing the cryogenic constraints for single-photon detection at telecom wavelength.

We report on observation of the infrared photoresistance of twisted bilayer graphene (tBLG) under continuous quantum cascade laser illumination at a frequency of 57.1 THz. The photoresistance shows an intricate sign-alternating behavior under variations of temperature and back gate voltage, and exhibits giant resonance-like enhancements at certain gate voltages. The structure of the photoresponse correlates with weaker features in the dark dc resistance reflecting the complex band structure of tBLG. It is shown that the observed photoresistance is well captured by a bolometric model describing the electron and hole gas heating, which implies an ultrafast thermalization of the photoexcited electron-hole pairs in the whole range of studied temperatures and back gate voltages. We establish that photoresistance can serve a highly sensitive probe of the temperature variations of electronic transport in tBLG.

Magic-angle twisted trilayer graphene (MATTG) hosts flat electronic bands, and exhibits correlated quantum phases with electrical tunability. In this work, we demonstrate a spectroscopy technique that allows for dissociation of intertwined bands and quantification of the energy gaps and Chern numbers C of the correlated states in MATTG by driving band crossings between Dirac cone Landau levels and energy gaps in the flat bands. We uncover hard correlated gaps with C = 0 at integer moiré unit cell fillings of v = 2 and 3 and reveal charge density wave states originating from van Hove singularities at fractional fillings v = 5/3 and 11/3. In addition, we demonstrate displacement-field-driven first-order phase transitions at charge neutrality and v = 2, which are consistent with a theoretical strong-coupling analysis, implying C(2)Tsymmetry breaking. Overall, these properties establish a diverse electrically tunable phase diagram of MATTG and provide an avenue for investigating other related systems hosting both steep and flat bands.