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Magnetic Fields

Magnetic Fields

A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...

Metal-Semiconductor Junctions

Metal-Semiconductor Junctions

The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The semiconductor's...

Magnetostatic Boundary Conditions

Magnetostatic Boundary Conditions

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...

Imperfections in Crystal Structure: Stoichiometric Point Defects

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...

Potential Due to a Magnetized Object

Potential Due to a Magnetized Object

Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...

Diamagnetism

Diamagnetism

Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets.

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Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform

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Published on: August 2, 2019

Magnetic impurity formation in quantum point contacts.

Tomaz Rejec¹, Yigal Meir

¹Department of Physics, Ben Gurion University, Beer Sheva 84105, Israel. tomaz.rejec@ijs.si

|August 25, 2006

Summary

A magnetic impurity forms in quantum point contacts, explaining the puzzling 0.7G(0) conductance anomaly. This finding impacts quantum dots and qubits, crucial for quantum computing advancements.

Area of Science:

Condensed Matter Physics
Quantum Information Science

Background:

Quantum point contacts (QPCs) are fundamental to quantum devices like quantum dots and qubits.
The '0.7 anomaly' in QPC conductance has been a long-standing mystery.

Purpose of the Study:

To investigate the origin of the 0.7 anomaly in quantum point contact conductance.
To determine the conditions under which magnetic impurities form in QPCs.

Main Methods:

Extensive numerical density-functional calculations were performed.
The formation of electronic states with spin-1/2 magnetic moments was analyzed.

Main Results:

A spin-1/2 magnetic moment (impurity) forms in the QPC channel under general conditions.

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Impurities also form at high magnetic fields and specific field values, and during the opening of the second transverse mode.

Conclusions:

The study explains the source of the 0.7 anomaly in QPCs.
Results have implications for spin-filling in quantum dots and dephasing in semiconductor qubits.