Two-dimensional (2D) ferroelectric semiconductors offer unique opportunities for ultrathin non-volatile memory and neuromorphic devices, yet the role of stacking order in intrinsic ferroelectric systems remains largely unexplored. Here we report the stacking-controlled growth of large-area 2D β'- and α-In2Se3 with distinct 2H and 3R configurations through chemical vapour deposition by regulating selenium kinetics and strain relaxation. By combining atomic-resolution microscopy, non-linear optical characterization and first-principles calculations, we uncover a strong correlation between stacking order and ferroelectric behaviour: β'-In2Se3 undergoes an antiferroelectric-to-paraelectric transition when switching from 2H to 3R stacking, whereas in α-In2Se3, in-plane ferroelectric polarization vanishes during the 3R-to-2H transition. We further achieve the controlled synthesis of 2H/3R ferroelectric homojunctions and directly visualize polarization-dependent interfacial potential barriers using differential phase-contrast scanning transmission electron microscopy. The engineered homojunctions exhibit switchable band alignment and tunable carrier transport, yielding memristors with significantly reduced switching voltages and an on/off ratio of ∼2.6 × 10[4], approximately one order of magnitude higher than devices based on single-stacking α-In2Se3. These findings establish stacking order as a powerful structural parameter for tailoring ferroelectricity in 2D materials and introduce stacking-engineered polymorphic heterogeneity as a versatile platform for high-performance ferroelectric electronics and memory technologies.

Chemical ligation of polymer segments is an essential approach to extend the length of synthetic polymers. Ligating individual polymer chains at the molecular level remains a formidable challenge owing to the entropically disfavoured collision probability between reactive end groups, and the need to overcome the activation barrier. Here we report a pathway to chemical ligation of synthetic polymers via folding-driven supramolecular polymerization followed by dynamic covalent polycondensation. Our strategy, which does not require thermal activation, uses hydrogen bonds that induce conformational folding to rigidify the polymer backbone while providing sticky ends for supramolecular pre-organization. This promotes base-catalysed covalent exchange between terminal groups (in our case, thiolate-disulfide groups). We obtain mechanistic insight in the ligation process by engineering side-chain units that determine conformational foldability and intermolecular H-bonding pre-organization. The resulting extended helical polymers fold into hierarchical globular architectures in solution and exhibit thermo-responsive macromolecular entanglements in bulk films. The combination of noncovalent assembly and dynamic covalent polymerization offers a supramolecular pathway for non-thermal and controllable polycondensation of dynamic polymers with secondary structures.

Piezoelectric nanomechanical resonators operating at gigahertz frequencies are a promising platform for quantum information processing and precision sensing, but phonon lifetimes have been limited to the microsecond range, widely attributed to the higher intrinsic loss of piezoelectric materials. Here we show that this limitation is not fundamental. Using a fabrication process informed by recent studies of defect-mediated loss in lithium niobate, we combine the chemical restoration of ion-milled surfaces with a shadow-mask metallization process to produce lithium niobate phononic crystal resonators with inferred internal phonon lifetimes of up to 21 ms at 3.6 GHz, corresponding to quality factors exceeding 4 × 10[8] (f × Qi > 10[18]) at millikelvin temperatures. By systematically varying the electrode-to-resonator spacing, we demonstrate that the measured lifetime is set by external coupling between the device and measurement circuit rather than material loss. This establishes that lithium niobate, once fabrication-induced surface damage is removed, achieves an intrinsic quality comparable with the best mechanical materials while remaining an intrinsically piezoelectric platform with strong electromechanical coupling.

Rhombohedral multilayer graphene offers a tunable platform for correlated electron physics, featuring field-effect control of magnetic, superconducting and topological phases. The promise of these materials has been held back by the limited abundance of rhombohedral stacking in natural graphite, which constrains both sample yield and useful area. Here we introduce cryogenic shock exfoliation to produce large-area rhombohedral graphene flakes. This exfoliation, combined with a low-pressure van der Waals assembly technique that preserves stacking order, enables highly uniform devices exceeding 1,300 μm[2] in area with fabrication yields of ∼90%. Using scanning nanoSQUID-on-tip imaging, we demonstrate uniform spin magnetism over the full central 10 × 10 μm[2] area of our devices. Transverse magnetic focusing reveals a disorder mean free path exceeding 200 μm at low temperatures. Within the flat surface bands of rhombohedral multilayer graphene, we observe a size-driven crossover from Poiseuille to porous electron flow in the intermediate-temperature regime of strong electron-electron hydrodynamics, providing a further signature of ultrahigh device quality. Our approach overcomes a key materials bottleneck in the fabrication of mesoscopic rhombohedral graphene devices, paving the way for incorporating strongly correlated phases into two-dimensional nanoelectronics.

Layer stacking in two-dimensional materials can strongly impact electronic phases. In graphene, for instance, the metastable rhombohedral stacking arrangement hosts correlated and topological electronic phases, which are absent in conventional Bernal stacking. Here we use the sliding-induced first-order structural phase transition between Bernal and rhombohedral tetralayer graphene driven by gate voltages to manipulate the magnetic phase of the sample. Through transport measurement on marginally twisted double-bilayer graphene samples, we observe bistable switching between a Bernal-dominant state and a rhombohedral-Bernal mixed state across a wide space of the gate-voltage phase diagram. The structural phase transition induces a non-volatile switching between a non-magnetic and a ferromagnetic phase. We characterize the latter phase via low-temperature electric transport measurements and observe an anomalous Hall effect. The sign reversal of the anomalous Hall signal under opposite displacement fields suggests that the Hall signal may originate from domain boundaries between Bernal and rhombohedral regions. Our experiments showcase how gating-induced sliding phase transitions of two-dimensional materials can provide on-demand toggle switching between complex phases and offer insights on the effect of stacking domain boundaries on the global response of the system.

Heat dissipation limits the performance of nanoscale electronic and quantum devices, yet the fundamental limits of phonon-mediated heat transport at the atomic scale remains unknown. By contrast, atomic-scale electron transport has been extensively studied over the past decades using electronic break-junction platforms. Here we show a custom-fabricated, picowatt-resolution scanning thermal probe that uses thermal feedback to create phononic break junctions at the ultimate atomic scale. We report the formation of atomic junctions of amorphous silicon dioxide (a-SiO2)-an archetypal glass-capturing, in real time, the transition from a bulk diffusive heat insulator to a ballistic efficient heat conductor as the tip is withdrawn from a nano-contact to an atomic contact. Remarkably, atomically thin glass junctions support phononic thermal conductance up to 40% of the quantum limit at room temperature, approximately an order of magnitude higher than the phonon thermal conductance of crystalline gold. These results, in conjunction with our atomic simulations, demonstrate that intrinsic structural disorder, which strongly affects macroscopic thermal properties, does not fundamentally constrain heat flow at the atomic limit. Instead, we find that it is the Debye frequency that dictates the phononic thermal conductance. We expect our approach to offer an experimental platform to study heat flow via wave-like coherent phonons and enable the engineering of high-performance thermal phononic devices, such as a thermal diode and transistor.