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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

848
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
848
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

918
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
918
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

603
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.
603
Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

1.6K
All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not...
1.6K
Atomic Nuclei: Nuclear Magnetic Moment00:59

Atomic Nuclei: Nuclear Magnetic Moment

1.0K
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
1.0K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.2K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
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Cooling and Heating Nuclear Spins by Strongly Localized Electrons.

D S Smirnov1, K V Kavokin2,3

  • 1Ioffe Institute, 194021 Saint Petersburg, Russia.

Physical Review Letters
|February 6, 2025
PubMed
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Nuclear spin temperature theory is extended for localized electrons. Efficient cooling requires strong magnetic fields, and heating times vary significantly with field strength.

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Area of Science:

  • Condensed matter physics
  • Quantum dot research
  • Spin dynamics

Background:

  • Nuclear spin temperature is key for dynamic nuclear spin polarization in semiconductors.
  • The central spin model is often used for quantum dot nuclear spin dynamics.
  • Existing models struggle with strongly localized electrons due to long spin correlation times.

Purpose of the Study:

  • To develop a microscopic theory for nuclear spin thermodynamics in systems with long electron spin correlation times.
  • To bridge the gap between traditional nuclear spin temperature theory and models for localized electrons.
  • To provide a more accurate description of nuclear spin dynamics in quantum dots.

Main Methods:

  • Developed a microscopic theory for nuclear spin thermodynamics.
  • Analyzed systems with long electron spin correlation times.
  • Investigated the role of external magnetic fields.

Main Results:

  • The theory successfully describes nuclear spin thermodynamics for systems with long electron spin correlation times.
  • Efficient nuclear spin cooling by localized electrons necessitates external magnetic fields significantly stronger than nuclear spin-spin interaction fields.
  • The time scale for nuclear spin heating by unpolarized electrons can vary by orders of magnitude based on the applied magnetic field.

Conclusions:

  • The new theory offers a more comprehensive understanding of nuclear spin dynamics in quantum dots.
  • External magnetic field strength is a critical parameter for controlling nuclear spin cooling and heating.
  • Findings have implications for quantum information processing and spintronics in semiconductor nanostructures.