Periodic Reporting for period 1 - ACCESS (Engineering Spin-Splitting in Atomically Thin 2D Non-Centrosymmetric Crystals)
Berichtszeitraum: 2024-01-01 bis 2025-12-31
ACCESS explored how ultra‑thin materials only a few atoms thick can be engineered to behave in entirely new electrical ways by deliberately breaking their natural symmetries. By twisting, stacking, or electrically tuning materials like bilayer graphene and WTe2, the project created nonlinear electrical responses—effects that could enable future low‑power electronics, ultra‑sensitive sensors, and advanced energy‑harvesting technologies. At the same time, ACCESS supported the professional growth of the researcher through international collaboration, mentoring, and research training. Together, the project’s scientific and career‑development goals were achieved, leading to new discoveries and ongoing collaborations in this rapidly advancing field.
The information and communication technology (ICT) sector consumes approximately 10% of global electricity, which is expected to further increase sharply in the coming decade. At the same time, the back-bone of ICT, the computing processors, and memory devices are hitting the physical limits of transistor miniaturization, where further scaling leads to prohibitive heat loss. To build faster, more efficient electronic devices, ACCESS focuses on atomically thin van der Waals (vdW) materials. By deliberately breaking their symmetry—through twisting, stacking, or electrical tuning—we induce a novel nonlinear electrical response. These effects open the door to ultra-low-power switches and integrated energy-harvesting capabilities. Furthermore, these same symmetry-breaking conditions enhance charge-to-spin conversion, a cornerstone of spintronics. These positions vdW materials as a key platform for merging energy-efficient charge-based logic with advanced spin-based functionality.
ACCESS aims to unlock new ways of controlling the flow of electricity in atomically thin vdW materials by stacking and twisting them with extreme precision. By engineering these delicate structures, we seek to reveal how their internal symmetries, electric polarization, and unique “moiré” patterns influence the way electrons move and interact. ACCESS will develop advanced fabrication methods to build complex stacks of two-dimensional materials, use electric fields to break or manipulate their natural symmetries, and explore how these changes give rise to unusual electrical responses that do not occur in ordinary materials. Ultimately, the goal is to understand how twisting, symmetry, and polarization can be harnessed to create new forms of electronic behavior, paving the way for future low-energy technologies, smarter sensors, and devices that use the strange rules of quantum physics to perform tasks that today’s electronics cannot. In addition to these scientific objectives, ACCESS also focuses on strengthening the researcher’s transferable skills, preparing him to become an independent scientist. The scientific excellence and interdisciplinary natures of the host organizations also provide the researcher with a unique opportunity to work with world leaders in the relevant fields, helping the researcher to build his research career in Europe.
The information and communication technology (ICT) sector consumes approximately 10% of global electricity, which is expected to further increase sharply in the coming decade. At the same time, the back-bone of ICT, the computing processors, and memory devices are hitting the physical limits of transistor miniaturization, where further scaling leads to prohibitive heat loss. To build faster, more efficient electronic devices, ACCESS focuses on atomically thin van der Waals (vdW) materials. By deliberately breaking their symmetry—through twisting, stacking, or electrical tuning—we induce a novel nonlinear electrical response. These effects open the door to ultra-low-power switches and integrated energy-harvesting capabilities. Furthermore, these same symmetry-breaking conditions enhance charge-to-spin conversion, a cornerstone of spintronics. These positions vdW materials as a key platform for merging energy-efficient charge-based logic with advanced spin-based functionality.
ACCESS aims to unlock new ways of controlling the flow of electricity in atomically thin vdW materials by stacking and twisting them with extreme precision. By engineering these delicate structures, we seek to reveal how their internal symmetries, electric polarization, and unique “moiré” patterns influence the way electrons move and interact. ACCESS will develop advanced fabrication methods to build complex stacks of two-dimensional materials, use electric fields to break or manipulate their natural symmetries, and explore how these changes give rise to unusual electrical responses that do not occur in ordinary materials. Ultimately, the goal is to understand how twisting, symmetry, and polarization can be harnessed to create new forms of electronic behavior, paving the way for future low-energy technologies, smarter sensors, and devices that use the strange rules of quantum physics to perform tasks that today’s electronics cannot. In addition to these scientific objectives, ACCESS also focuses on strengthening the researcher’s transferable skills, preparing him to become an independent scientist. The scientific excellence and interdisciplinary natures of the host organizations also provide the researcher with a unique opportunity to work with world leaders in the relevant fields, helping the researcher to build his research career in Europe.
ACCESS demonstrated the emergence of second-order nonlinear electrical transport (NET) in dual-gated field-effect transistors of WTe2, bilayer graphene (BLG), and twisted double bilayer graphene (tDBLG) moiré superlattices. In the case of BLG, ACCESS showed that, NET enables detection of Lifshitz transitions through robust sign changes in the nonlinear conductivity. By performing temperature dependent scaling law analysis, ACCESS showed that both extrinsic scattering and intrinsic Berry-curvature-dipole effects shape the nonlinear response, with strain enhancing the intrinsic contribution. High nonlinear conductivity in BLG, exceeding 30 µm V⁻¹ Ω⁻¹, establishes BLG as a platform for exploitable rectification and energy-harvesting devices.
ACCESS demonstrated the control of NET in the bilayer and tetralayer thick WTe2 crystals by controlling the sliding ferroelectricity in them. Additionally, synaptic functionality was demonstrated in pure carbon for the first time in this project. Strained moiré superlattices of tDBLG naturally exhibit hysteresis, plasticity, and multi-level memory without requiring any polar components or extrinsic elements such as charge traps. Interfacial strain from twist angle disorder was identified as the driving force, showing that such disorder can enable new functionality.
ACCESS also highlights that this electronic plasticity coexists with a strong NET response, enabling synaptic memory devices based on nonlinear effects. ACCESS’s dual gated tDBLG FET devices demonstrate multi-level non-volatile memory with high retention, endurance, and low-power operation (0.5–0.8 pJ per event), comparable to state-of-the-art first-order synaptic devices.
Additionally, ACCESS carefully studied the second-order NET in low angle twisted tDBLG moiré superlattices by tuning Fermi energy across several superlattice bands. NET was established as a sensitive probe of Fermi surface reconstructions in these moiré superlattices, exhibiting sign reversals at van Hove singularities (vHS). The second-order nonlinear conductivity demonstrates local maxima near these vHSs. Record-high nonlinear conductivity reaching ~70 µm V⁻¹ Ω⁻¹ near mid-band vHSs—an order of magnitude larger than previously observed—opens pathways for gate-tunable low-power rectifiers, and nonlinear mixers.
ACCESS demonstrated the control of NET in the bilayer and tetralayer thick WTe2 crystals by controlling the sliding ferroelectricity in them. Additionally, synaptic functionality was demonstrated in pure carbon for the first time in this project. Strained moiré superlattices of tDBLG naturally exhibit hysteresis, plasticity, and multi-level memory without requiring any polar components or extrinsic elements such as charge traps. Interfacial strain from twist angle disorder was identified as the driving force, showing that such disorder can enable new functionality.
ACCESS also highlights that this electronic plasticity coexists with a strong NET response, enabling synaptic memory devices based on nonlinear effects. ACCESS’s dual gated tDBLG FET devices demonstrate multi-level non-volatile memory with high retention, endurance, and low-power operation (0.5–0.8 pJ per event), comparable to state-of-the-art first-order synaptic devices.
Additionally, ACCESS carefully studied the second-order NET in low angle twisted tDBLG moiré superlattices by tuning Fermi energy across several superlattice bands. NET was established as a sensitive probe of Fermi surface reconstructions in these moiré superlattices, exhibiting sign reversals at van Hove singularities (vHS). The second-order nonlinear conductivity demonstrates local maxima near these vHSs. Record-high nonlinear conductivity reaching ~70 µm V⁻¹ Ω⁻¹ near mid-band vHSs—an order of magnitude larger than previously observed—opens pathways for gate-tunable low-power rectifiers, and nonlinear mixers.
ACCESS has delivered several breakthroughs that advance the state of the art in 2D materials and nonlinear electronics. It established second-order nonlinear electrical transport as a powerful probe of Fermi-surface topology and Lifshitz transitions in bilayer graphene and moiré superlattices, achieving record-high nonlinear conductivities and demonstrating that intrinsic Berry-curvature effects and extrinsic scattering can be disentangled and tuned. ACCESS also introduced a new concept in neuromorphic hardware: synaptic functionality and electronic plasticity emerging naturally in strained moiré structures of pure carbon—requiring no oxides, interfaces, or trap engineering—and coexisting with strong nonlinear transport to enable low-power, reconfigurable, multi-level memory devices. These advances open routes to scalable 2D-material-based rectifiers, THz detectors, and neuromorphic elements compatible with energy-efficient future electronics. To translate these achievements into possible technologies, further work is needed on large-area material growth, device integration, reliability testing, and pathways to industrial adoption—including demonstration projects, investment access, and supportive standards for emerging 2D electronic and neuromorphic platforms.