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Crystal Field Theory - Octahedral Complexes

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...

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Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...

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Color in Coordination Complexes
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Valence Bond Theory

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VSEPR Theory and the Effect of Lone Pairs

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Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals

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Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...

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Related Experiment Video

Updated: Jul 25, 2025

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Published on: October 5, 2013

Smectic pair-density-wave order in EuRbFe₄As₄.

He Zhao¹, Raymond Blackwell¹, Morgan Thinel^2,3

¹Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA.

|June 28, 2023

Summary

This summary is machine-generated.

Researchers discovered a novel zero-field pair density wave (PDW) state in the EuRbFe4As4 superconductor. This state exhibits unique superconducting gap modulations, independent of other ordered states, offering new insights into unconventional superconductivity.

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Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

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Published on: May 10, 2021

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

Published on: October 9, 2012

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Last Updated: Jul 25, 2025

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Published on: October 5, 2013

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

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Published on: May 10, 2021

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

Published on: October 9, 2012

Area of Science:

Condensed Matter Physics
Superconductivity Research
Materials Science

Background:

A pair density wave (PDW) is a superconducting state breaking translational symmetry.
Previous PDW evidence was limited to high magnetic fields or coexisting with other orders.
A zero-field PDW, independent of other states, remained elusive.

Purpose of the Study:

To investigate the existence of a primary, zero-field pair density wave (PDW) state.
To characterize the nature of superconductivity in the iron pnictide EuRbFe4As4.
To determine the relationship between PDW, magnetism, and other electronic orders.

Main Methods:

Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM) was employed.
Bulk measurements were conducted to corroborate SI-STM findings.
Temperature and magnetic field variations were used to probe the PDW state.

Main Results:

A zero-field PDW state was identified in EuRbFe4As4.
Long-range, unidirectional modulations of the superconducting gap were observed.
The PDW state coexists with magnetism (Tm ≈ 15 K) and superconductivity (Tc ≈ 37 K).
The PDW state disappears above Tm, with translational and rotational symmetry recovered.

Conclusions:

EuRbFe4As4 hosts a primary, zero-field PDW state, independent of other density-wave orders.
The PDW state in this material exhibits smectic order.
This discovery advances the understanding of unconventional superconducting states.