Related Experiment Video
Updated: Oct 19, 2025
10:36
Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials
Published on: January 21, 2016
10.7K
Andreev Reflections in NbN/Graphene Junctions under Large Magnetic Fields.
Da Wang1,2, Evan J Telford1, Avishai Benyamini1,2
1Department of Physics, Columbia University, New York, New York 10027, United States.
Nano Letters
|September 27, 2021
Summary
We explored hybrid superconductor/graphene junctions to study quantum phenomena. Our research demonstrates tunable Andreev reflections and magnetic field effects on superconductivity in graphene, advancing condensed matter physics.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Phenomena
Background:
- Hybrid superconductor/graphene (SC/g) junctions are key for studying Cooper pairs and quantum Hall (QH) edge modes.
- Experimental challenges include sensitivity to disorder and the need for high magnetic fields to form QH states.
Purpose of the Study:
- Investigate correlations between Cooper pairs and QH edge modes in SC/g junctions.
- Fabricate and characterize low-resistance SC/g interfaces stable in high magnetic fields.
- Explore the role of graphene's band structure and magnetic fields on Andreev reflections.
Main Methods:
- Fabrication of low-resistance SC/g interfaces (NbN/graphene) with barrier strength Z ≈ 0.4.
- Application of magnetic fields (parallel and perpendicular) to tune SC/g junction properties.
- Measurement of 2-probe conductance and analysis of Andreev reflection spectra.
Main Results:
- SC/g junctions remained superconducting above 18 T.
- Graphene's Dirac band structure influences zero-field Andreev reflections.
- Parallel magnetic fields dynamically tuned the Andreev reflection spectrum.
- Perpendicular magnetic fields caused oscillatory suppression of conductance in the ν = 4 Landau level due to reduced Andreev process efficiency.
Conclusions:
- Demonstrated the tunability of Andreev reflections in SC/g junctions using magnetic fields.
- Confirmed the impact of graphene's electronic structure on quantum transport phenomena.
- Provided experimental evidence consistent with theoretical predictions for SC/g hybrid systems.
Related Concept Videos
01:27π Electron Effects on Chemical Shift: Overview
1.2K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.2K
01:28Magnetic Field Due To A Thin Straight Wire
5.1K
Consider an infinitely long straight wire carrying a current I. The magnetic field at point P at a distance a from the origin can be calculated using the Biot-Savart law.
5.1K
01:28Magnetostatic Boundary Conditions
1.2K
An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
1.2K
01:23Magnetic Field due to Moving Charges
9.5K
A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
9.5K
01:26Divergence and Curl of Magnetic Field
3.3K
The magnetic field due to a volume current distribution given by the Biot–Savart Law can be expressed as follows:
3.3K
01:23Atomic Nuclei: Nuclear Relaxation Processes
775
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.
775