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Related Concept Videos

Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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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.
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Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

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Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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 one, the...
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NMR Spectroscopy: Spin–Spin Coupling01:08

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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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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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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.
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Related Experiment Video

Updated: May 3, 2026

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon
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Anisotropy-driven spin relaxation in germanium.

Pengke Li1, Jing Li2, Lan Qing3

  • 1Department of Physics and Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA and Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627, USA.

Physical Review Letters
|February 4, 2014
PubMed
Summary
This summary is machine-generated.

Researchers discovered a new spin depolarization mechanism in germanium (Ge) devices. This finding allows for precise measurement of spin lifetimes, revealing exceptionally long spin coherence times at low temperatures.

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Area of Science:

  • Solid State Physics
  • Materials Science
  • Quantum Information Science

Background:

  • Spin transport in semiconductors is crucial for spintronics.
  • Understanding spin depolarization mechanisms is key to preserving spin information.
  • Germanium (Ge) is a promising material for spintronic applications.

Purpose of the Study:

  • To investigate spin depolarization mechanisms in germanium.
  • To develop a method for extracting spin lifetime without spin precession.
  • To measure long spin lifetimes in germanium devices.

Main Methods:

  • Spin-transport measurements on long-distance germanium devices.
  • Application of a magnetic field longitudinal to the initial spin orientation.
  • Analysis of electron-phonon scattering and intervalley scattering effects.

Main Results:

  • A novel spin depolarization mechanism involving g-factor anisotropy and intervalley scattering was identified.
  • Spin lifetime was extracted solely from spin-valve measurements, independent of spin precession.
  • Spin lifetimes in germanium reached several hundreds of nanoseconds at low temperatures, exceeding previous experimental results.

Conclusions:

  • The discovered mechanism provides new insights into spin dynamics in germanium.
  • The developed method enables accurate determination of spin lifetimes under electric-field-induced carrier heating.
  • The exceptionally long spin lifetimes in germanium pave the way for advanced spintronic devices.