Related Experiment Video
Updated: Aug 11, 2026
11:42
Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities
Published on: July 24, 2015
Electron-hole coupling and the charge density wave transition in TiSe2
1Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.
Physical Review Letters
|June 13, 2002
Summary
Angle-resolved photoemission reveals titanium diselenide (TiSe2) undergoes a charge density wave transition driven by electron-hole coupling and an indirect Jahn-Teller effect, not Fermi surface topology. This transition alters the material's band structure and indirect band gap.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Solid-State Physics
Background:
- Titanium diselenide (TiSe2) exhibits a (2x2x2) charge density wave (CDW) transition.
- The precise mechanism driving this CDW transition in TiSe2 has been a subject of ongoing research.
- Previous hypotheses often centered on Fermi surface topology as the primary driver.
Purpose of the Study:
- To elucidate the fundamental nature of the charge density wave transition in TiSe2.
- To investigate the role of band structure modifications in the CDW transition.
- To determine the key physical mechanisms responsible for the observed transition.
Main Methods:
- Utilized angle-resolved photoemission spectroscopy (ARPES) to probe the electronic band structure of TiSe2.
- Analyzed the band structure in both the normal and charge density wave phases.
- Examined changes in the electronic band gap and its location within the Brillouin zone.
Main Results:
- Observed a very small indirect band gap in the normal phase of TiSe2.
- Documented the transformation into a larger indirect band gap at a different Brillouin zone location upon transition.
- Demonstrated that Fermi surface topology plays an insignificant role in this specific transition.
Conclusions:
- The (2x2x2) charge density wave transition in TiSe2 is primarily driven by strong electron-hole coupling.
- A novel indirect Jahn-Teller effect is identified as a crucial factor in initiating the transition.
- The findings challenge previous assumptions and highlight a new mechanism for CDW formation in layered materials.
Related Concept Videos
02:54Trends in Lattice Energy: Ion Size and Charge
An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure of the strength of this attraction. The lattice energy (ΔHlattice) of an ionic compound is defined as the energy required to separate one mole of the solid into its component gaseous ions. For the ionic solid sodium chloride, the lattice energy is the enthalpy change of the process:
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
02:58Crystal 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...
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...
02:46Crystal 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,...
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,...
01:20Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
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...
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...
01:30The Electrical Double Layer
In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...