Revisiting Coulomb diamond signatures in quantum Hall interferometers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-03-31 |
| Journal | Physical review. B./Physical review. B |
| Authors | Nicolas Moreau, SĂ©bastien Faniel, Frederico Martins, L. Desplanque, X. Wallart |
| Institutions | Université de Lille, Centre National de la Recherche Scientifique |
| Citations | 2 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Nanoscale Quantum Hall Interferometers
Section titled âTechnical Documentation & Analysis: Nanoscale Quantum Hall InterferometersâExecutive Summary
Section titled âExecutive SummaryâThis research details the spectroscopic analysis of a nanometer-sized Quantum Hall Interferometer (QHI) spontaneously formed within a semiconductor Quantum Point Contact (QPC) structure. The findings challenge conventional interpretations of quantum transport regimes and highlight the critical need for highly coherent, nanoscale platformsâa domain where 6CCVDâs diamond materials offer significant advantages.
- Core Achievement: Observation of a continuous transition between Aharonov-Bohm (AB, checkerboard) and Coulomb-Dominated (CD, diamond) patterns in QHI spectroscopy.
- Novel Interpretation: The transition is successfully modeled using a simple Fabry-PĂ©rot (FP) framework, demonstrating that both patterns can exist in a fully coherent AB regime, explained solely by varying reflection/transmission probabilities, not Coulomb charging effects.
- Nanoscale Coherence: The QHI operates coherently despite its extremely small size (diameter â 250 nm, area < 0.05 ”m2) at T â 100 mK.
- Methodology: Scanning Gate Microscopy (SGM) and DC bias spectroscopy were used to map the differential resistance (Rxx) as a function of magnetic field (B) and gate voltage (Vtip).
- Implication for Quantum Technology: The work confirms the feasibility of realizing robust, nanoscale QHIs, paving the way for advanced integrated quantum circuits and fundamental physics tests (e.g., anyonic braiding), applications ideally suited for diamond platforms.
- Material Requirement: The success relies on a specific potential landscape that avoids localized states, emphasizing the need for ultra-high material purity and precise fabrication control.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental setup and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Base Temperature (T) | â 100 | mK | Dilution refrigerator operating condition |
| Magnetic Field (B) Range | 5.0 to 8.5 | T | Range for Quantum Hall regime analysis |
| Bulk Electron Density (Ns) | 5.7 x 1015 | m-2 | Property of the InGaAs/InAlAs 2DEG |
| Electron Mobility (”) | 5.3 x 104 | cm2/Vs | Property of the InGaAs/InAlAs 2DEG |
| QPC Constriction Width | â 350 | nm | Defined by wet etching and EBL |
| QHI Diameter (Fitted) | â 250 | nm | Derived from AB oscillation fitting |
| QHI Area (A) | < 0.05 | ”m2 | Extremely small interferometer size |
| Scanning Gate Tip Distance (dtip) | â 60 | nm | Distance above the 2DEG plane |
| QHEC Velocity (v) | 0.5 x 105 | m/s | Parameter used in Fabry-PĂ©rot model fit |
| Resistance Plateau (v*=3) | 2.2 | kΩ | Observed at filling factor v=4 |
| Resistance Plateau (v*=2) | 4.3 | kΩ | Observed at filling factor v=3 |
| Extracted Energy Scale (Vsd) | â 0.2 | mV | Consistent energy scale for both diamond and checkerboard patterns |
Key Methodologies
Section titled âKey MethodologiesâThe experiment combined advanced semiconductor fabrication with ultra-low temperature, high-field transport measurements and local probing techniques.
- Material Growth & Structure: A 15 nm thick In0.7Ga0.3As/In0.52Al0.48As quantum well was grown by Molecular Beam Epitaxy (MBE) on an InP substrate, hosting a 2DEG 25 nm below the surface.
- Device Patterning: Electron Beam Lithography (EBL) and wet etching were used to define the Hall bar and the QPC geometry, creating a constriction width of approximately 350 nm.
- Ohmic Contacts: Ge/Au contacts were used to establish electrical connection to the 2DEG.
- Measurement Environment: Transport measurements were conducted in a dilution refrigerator at a base temperature of T â 100 mK, with a magnetic field (B) applied perpendicular to the 2DEG plane.
- Scanning Gate Microscopy (SGM): An Atomic Force Microscope (AFM) with a metallic tip, biased at voltage Vtip, was scanned at a distance of â 60 nm above the surface to locally modulate the electrostatic potential and QHI characteristics.
- DC Bias Spectroscopy: Differential resistance Rxx was measured as a function of DC source-drain voltage (Vsd) and either the magnetic field (B) or the tip voltage (Vtip) to generate the characteristic checkerboard and diamond maps.
- Modeling: A theoretical Fabry-PĂ©rot (FP) model was developed (Appendix B) to simulate the conductance (G) through the QHI, relying on tunable reflection (R) and transmission (T) probabilities to reproduce the experimental Rxx maps.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research demonstrates the feasibility of highly coherent, nanoscale quantum interferometry. While this study utilized a semiconductor 2DEG, the next generation of integrated quantum devicesâespecially those requiring extreme stability, high-field operation, and integration with quantum emittersâwill benefit immensely from diamond platforms. 6CCVD is uniquely positioned to supply the necessary materials and fabrication support to advance this research into the diamond domain.
| Research Requirement/Challenge | 6CCVD Solution & Capability | Technical Advantage for Quantum Applications |
|---|---|---|
| Applicable Materials | High Purity Single Crystal Diamond (SCD) | Essential for integrated quantum circuits (e.g., NV or SiV centers) requiring ultra-low defect density and superior thermal management. SCD offers the highest stability for coherent quantum systems. |
| Heavy Boron-Doped Diamond (BDD/PCD) | Provides a robust, conductive platform (analogous to the 2DEG) for creating complex gate architectures and electrodes necessary for QPC/QHI operation in extreme environments (high B fields). | |
| Precise Nanoscale Fabrication | Ultra-Smooth Polishing (Ra < 1 nm for SCD) | The paper relies on EBL to define 350 nm features. 6CCVDâs SCD substrates feature Ra < 1 nm, crucial for high-fidelity lithography and minimizing surface scattering that could degrade coherence. |
| Custom Device Dimensions | Plates/Wafers up to 125 mm (PCD) | We offer custom dimensions and thicknesses (SCD/PCD: 0.1 ”m to 500 ”m; Substrates up to 10 mm) to meet specific experimental or scaling requirements for integrated quantum circuits. |
| Integrated Gate Electrodes | In-House Custom Metalization | We provide internal deposition services for critical metals (Au, Pt, Pd, Ti, W, Cu) required for ohmic contacts, side gates, and scanning gate electrodes used in QHI experiments. |
| Complex QHI Design & Modeling | Expert Engineering Support | 6CCVDâs in-house PhD team can assist researchers in selecting optimal diamond material properties (e.g., doping concentration, crystal orientation, surface termination) for similar Nanoscale Quantum Interferometry projects. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Coulomb diamonds are the archetypal signatures of Coulomb blockade, a\nwell-known charging effect mainly observed in nanometer-sized âelectronic\nislandsâ tunnel-coupled with charge reservoirs. Here, we identify apparent\nCoulomb diamond features in the scanning gate spectroscopy of a quantum point\ncontact carved out of a semiconductor heterostructure, in the quantum Hall\nregime. Varying the scanning gate parameters and the magnetic field, the\ndiamonds are found to smoothly evolve to checkerboard patterns. To explain this\nsurprising behavior, we put forward a model which relies on the presence of a\nnanometer-sized Fabry-P\âerot quantum Hall interferometer at the center of the\nconstriction with tunable tunneling paths coupling the central part of the\ninterferometer to the quantum Hall channels running along the device edges.\nBoth types of signatures, diamonds and checkerboards, and the observed\ntransition, are reproduced by simply varying the interferometer size and the\ntransmission probabilities at the tunneling paths. The new proposed\ninterpretation of diamond phenomenology will likely lead to revisit previous\ndata, and opens the way towards engineering more complex interferometric\ndevices with nanoscale dimensions.\n