Scanning multi-modality microscopy of moiré quantum matter

Informazioni relative al progetto

MoireMultiProbe

ID dell’accordo di sovvenzione: 101089714

DOI

10.3030/101089714

Data della firma CE 31 Maggio 2023

Data di avvio 1 Giugno 2023

Data di completamento 31 Maggio 2028

Finanziato da

• European Research Council (ERC)

Costo totale

€ 3 018 750,00

Contributo UE

€ 3 018 750,00

Coordinato da

WEIZMANN INSTITUTE OF SCIENCE
Israel

Periodic Reporting for period 1 - MoireMultiProbe (Scanning multi-modality microscopy of moiré quantum matter)

Periodo di rendicontazione: 2023-06-01 al 2025-11-30

Sintesi del contesto e degli obiettivi generali del progetto

The MoiréMultiProbe project addresses a central challenge in quantum materials science: how to probe and understand the complex electronic phenomena emerging in moiré and van der Waals (vdW) materials at the nanoscale. These systems—formed by stacking graphene and other two-dimensional (2D) atomic layers with small twist angles—host a rich variety of strongly correlated and topological states, including superconductivity, orbital ferromagnetism, Chern insulators, and strongly correlated quantum phases. These phenomena are highly tunable via electrostatic gating, twist angle engineering, and displacement fields, making moiré systems ideal platforms for exploring quantum matter.

However, experimental access to these phenomena is hindered by the microscopic size of the devices and buried nature of the active layers, which render conventional spectroscopic and transport techniques insufficient. To meet this challenge, the project set out two main objectives:

(1) the development of a revolutionary multi-modality scanning probe platform based on superconducting quantum interference device on a tip (SQUID-on-tip) capable of imaging thermal, magnetic, electronic, and transport properties with ultrahigh spatial resolution at cryogenic temperatures; and

(2) the use of this platform to gain unprecedented microscopic insight into correlated and topological states in moiré systems.

These advances are expected to significantly impact condensed matter physics by enabling direct imaging of subtle phenomena such as orbital magnetism, local dissipation, and symmetry broken states. In the longer term, the results can support future applications in nanoscale quantum sensing, device miniaturization, and integrated cryogenic electronics.

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

The project has achieved major milestones in both instrumentation and scientific discovery:

• Cryogenic Multi-Modality Microscope: A custom-built scanning SQUID-on-tip microscope operating in a dilution refrigerator was designed and constructed, offering a combination of magnetic, thermal, current, electrostatic, and noise imaging modalities. Operating at temperatures down to 10 mK and in vector magnetic fields up to 9 T, this system delivers µK-scale thermal sensitivity and nanometre resolution. It supports both vacuum and superfluid helium environments, enabling the first-ever nanoscale thermal imaging at mK temperatures.

• Thermodynamic Quantum Oscillations: The team demonstrated de Haas–van Alphen (dHvA) imaging in moiré graphene structures, revealing large thermodynamic magnetization oscillations in weak fields and reconstructing miniband structures with unprecedented precision. These measurements revealed multiple overlapping Fermi surfaces and coherent magnetic breakdown—a signature of exotic band mixing and topological transitions.

• Pseudomagnetic Fields from Strain: By analyzing spatial variations in quantum oscillations, the project mapped strain-induced pseudomagnetic fields as low as 1 mT. These were traced to naturally occurring twist-angle gradients, revealing strain landscapes that had previously been inaccessible.

• Imaging Broken Symmetry Phases: In alternating-twist trilayer graphene, scanning measurements showed spontaneous breaking of threefold rotational symmetry and direct evidence of nematic semimetal ground states. At finite doping, a transition to a spin- and valley-polarized insulating state was observed, consistent with Stoner ferromagnetism.

• Cryogenic Ettingshausen Cooling: Using thermal imaging in WTe2 semimetals, the team observed magneto-thermoelectric cooling and mapped the Ettingshausen effect with nanometre resolution. Remarkably, absolute cooling (below the bath temperature) was achieved at 4 K—marking the first such demonstration in a mesoscopic device. The spatial temperature profiles showed a rich interplay between sample geometry, recombination length, and magnetic field.

• Device Fabrication: The project developed full in-house capability for preparing twisted and untwisted moiré devices. These include rhombohedral graphene, double bilayer graphene, and heterostructures designed for simultaneous access to multiple experimental observables.

Overall, these achievements represent a leap forward in both experimental instrumentation and fundamental understanding of quantum moiré matter.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

MoiréMultiProbe has delivered multiple breakthroughs that extend well beyond the state of the art in both instrumentation and scientific discovery:

• Multi-Modality Imaging at mK temperatures: The project established a new standard for cryogenic scanning microscopy, integrating various distinct modalities—including local thermometry, magnetometry, current imaging, and fluctuation dynamics—into a single system. The achieved sensitivity levels (e.g. ~1 µK thermal resolution, single-electron magnetic moment detection) set global benchmarks for cryogenic nano-imaging.

• Direct Mapping of Moiré Band Topology: The ability to resolve quantum oscillations in thermodynamic properties allowed for detailed band structure reconstruction. The observation of magnetic breakdown and violations of the Onsager rule signify the onset of hybridization and topological mixing across bands, a phenomenon not accessible by standard transport or global techniques.

• Probing Strain-Driven Quantum States: The demonstration of mT-scale pseudomagnetic fields arising from intrinsic strain establishes a powerful new framework for analyzing symmetry breaking in 2D systems. It links local geometry to global band topology, enabling strain engineering as a viable route to control quantum phases.

• Microscale Thermoelectric Cooling: The imaging of Ettingshausen cooling at 4 K—along with a quantitative understanding of the mechanisms—represents a key step toward on-chip cryogenic refrigeration and integrated thermal control in quantum devices.

• Path to Future Applications: The project's outcomes identify several future avenues, including:

o Further development of electronic thermometry to study non-equilibrium dynamics.
o Integration with spectroscopic techniques.
o Application to other quantum materials beyond graphene, including twisted transition metal dichalcogenides and magnetic/topological insulators.
o Device-level implementation of nanoscale thermal management based on thermoelectric effects.

Together, these innovations provide new tools and insights for probing the quantum landscape of strongly correlated systems, offering pathways to both fundamental understanding and technological exploitation.