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Videos de Conceptos Relacionados

Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Types Of Superconductors01:28

Types Of Superconductors

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A superconductor is a substance that offers zero resistance to the electric current when it drops below a critical temperature. Zero resistance is not the only interesting phenomenon as materials reach their transition temperatures. A second effect is the exclusion of magnetic fields. This is known as the Meissner effect. A light, permanent magnet placed over a superconducting sample will levitate in a stable position above the superconductor. High-speed trains that levitate on strong...
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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.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
918
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

854
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

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Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
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Superconductor01:24

Superconductor

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A substance that reaches superconductivity, a state in which magnetic fields cannot penetrate, and there is no electrical resistance, is referred to as a superconductor. In 1911, Heike Kamerlingh Onnes of Leiden University, a Dutch physicist, observed a relation between the temperature and the resistance of the element mercury. The mercury sample was then cooled in liquid helium to study the linear dependence of resistance on temperature. It was observed that, as the temperature decreased, the...
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Superconductividad programable por torsión en grafeno de dos capas acoplado a órbita de espín

Yiran Zhang1,2,3, Gal Shavit4,5,6, Huiyang Ma7,8

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Área de la Ciencia:

  • Física de la materia condensada
  • Ciencias de los materiales
  • Los materiales cuánticos

Sus antecedentes:

  • El ángulo de torsión en los materiales de van der Waals es clave para las bandas planas de moiré.
  • El control de ángulo de giro también puede estabilizar estados correlacionados a través de la ruptura de simetría.
  • Las superredes Moiré no son la única plataforma para efectos de ángulo de giro.

Objetivo del estudio:

  • Para demostrar el ajuste de torsión "sin moiré" de la superconductividad y las órdenes correlacionadas.
  • Para investigar el impacto del acoplamiento de espín-órbita de Ising (SOC) en el diagrama de fase del grafeno.
  • Para explorar nuevos estados superconductores en las heteroestructuras de van der Waals.

Principales métodos:

  • Se ha demostrado experimentalmente el ajuste de torsión en el grafeno de doble capa de Bernal proximizado por deselenuro de tungsteno.
  • Se varió sistemáticamente la alineación entre el grafeno y el deselenuro de tungsteno.
  • Se analizaron las propiedades superconductoras y las transiciones de fase en diferentes SOC de Ising.

Principales resultados:

  • El inicio de la superconductividad se desplazó a campos de desplazamiento más altos con un aumento de la SOC de Ising.
  • La temperatura crítica de la superconductividad aumentó hasta 0,5 K.
  • Se observó una transición de fase nemática y una mayor resistencia a los campos magnéticos en el límite de SOC de Ising.
  • Identificamos dos regiones superconductoras adicionales, una con un coeficiente de violación del límite de Pauli superior a 40.

Conclusiones:

  • La ingeniería de torsión "Moiréless" ofrece un método poderoso para controlar los estados correlacionados en las heteroestructuras de van der Waals.
  • El SOC de Ising altera significativamente el diagrama de fase superconductor del grafeno de dos capas.
  • Los hallazgos proporcionan información sobre los superconductores de grafeno ultralimpios y los nuevos fenómenos cuánticos.