insikt - Solid State Physics - # Electronic Structure and Phase Transitions in Group-5 Transition Metal Ditellurides

Electronic Properties and Phase Transitions in Group-5 Transition Metal Ditellurides MTe2 (M = V, Nb, Ta)

Q: How do the electronic properties of these materials change under external perturbations such as pressure, strain, or doping, and how can these be used to tune their functional properties?

The electronic properties of group-5 transition metal ditellurides (MTe2, where M = V, Nb, Ta) are significantly influenced by external perturbations such as pressure, strain, and doping. These perturbations can induce phase transitions, modify electronic band structures, and alter the stability of various crystal phases. Pressure: Applying pressure can lead to lattice collapse or structural phase transitions. For instance, NbTe2 undergoes a lattice-collapse phase transition at approximately 20 GPa, which is accompanied by Nb dimerization. This transition can enhance superconductivity, as seen in TaTe2, which exhibits multiple superconducting phases under pressure. The application of pressure can also modify the Fermi surface topology, potentially leading to new quantum phenomena. Strain: Strain can induce anisotropic changes in the electronic structure, particularly in materials with quasi-one-dimensional characteristics like the ribbon-chain structures in MTe2. Strain can enhance or suppress the formation of flat bands, which are crucial for electronic properties such as conductivity and superconductivity. The ability to tune the strain allows for the manipulation of the electronic states and can lead to the emergence of new phases or enhance existing properties. Doping: Doping with different elements (e.g., Ti in VTe2) can suppress or stabilize certain phases, such as the 1T-1T” transition in VTe2. Doping alters the charge carrier concentration, which can lead to significant changes in the Fermi surface and the associated electronic properties. For example, Ti doping can shift the transition temperature and modify the electronic band structure, impacting the material's conductivity and potential for superconductivity. These external perturbations provide a powerful means to tune the functional properties of MTe2 materials, enabling the exploration of novel quantum phenomena and applications in electronic devices.

Q: What are the potential mechanisms behind the kink-like band reconstruction observed in TaTe2, and how do they relate to the structural and electronic fluctuations in this material?

The kink-like band reconstruction observed in TaTe2 is a complex phenomenon that can be attributed to several interrelated mechanisms: Orbital-dependent interactions: The kink-like structure is primarily associated with the dXY-derived bands at the Brillouin zone boundary. The transformation from a linear band to a kink-like structure indicates a significant change in the electronic interactions, likely due to the coupling between different orbital states (dXY, dYZ, dZX) as the material transitions from the ribbon-chain to the butterfly-like-cluster phase. Structural fluctuations: The transition from the ribbon-chain to the butterfly-like-cluster phase involves substantial atomic displacements and the formation of butterfly-like clusters. These structural changes can lead to variations in the electronic environment, affecting the band structure and resulting in the observed kink-like features. The temperature-dependent structural fluctuations may also contribute to the energy scale of the kink, as the electronic states adapt to the new local bonding configurations. Charge density variations: The splitting of core-level spectra, such as the Ta 4f core-level spectra, indicates variations in electron density among inequivalent Ta sites. This charge density variation can influence the electronic states and contribute to the kink-like band reconstruction. The observed energy shifts in the core-level spectra suggest that the chemical potential is also affected by these fluctuations, further influencing the electronic structure. Overall, the kink-like band reconstruction in TaTe2 is a manifestation of the interplay between electronic and structural fluctuations, highlighting the importance of local bonding and orbital interactions in determining the material's electronic properties.

Q: Given the importance of local molecular-like bonding in organizing the complex electronic structures, are there other classes of inorganic materials where similar concepts could be applied to understand their emergent phenomena?

Yes, the concept of local molecular-like bonding is applicable to various classes of inorganic materials, particularly those exhibiting complex electronic structures and emergent phenomena. Some notable examples include: Transition Metal Oxides: Many transition metal oxides, such as cuprates and manganites, exhibit rich electronic phenomena, including high-temperature superconductivity and colossal magnetoresistance. The local bonding characteristics, such as dimerization and orbital ordering, play a crucial role in determining their electronic properties and phase transitions. Spinels and Perovskites: In materials like spinel oxides (e.g., LiMn2O4) and perovskites (e.g., LaMnO3), local bonding configurations and orbital hybridization significantly influence their magnetic and electronic properties. The interplay between local bonding and long-range order can lead to phenomena such as charge ordering and orbital ordering. Layered Materials: Other layered materials, such as transition metal dichalcogenides (TMDs) and black phosphorus, also exhibit local bonding characteristics that affect their electronic properties. The formation of flat bands and the emergence of topological states in these materials can be understood through the lens of local molecular-like bonding. Metal-Organic Frameworks (MOFs): In MOFs, the coordination of metal ions with organic ligands can lead to complex electronic structures and emergent properties, such as gas adsorption and catalysis. The local bonding interactions within these frameworks can be crucial for tuning their functional properties. In summary, the principles of local molecular-like bonding can be extended to a wide range of inorganic materials, providing a framework for understanding their complex electronic structures and the emergent phenomena that arise from them.

Centrala begrepp

The group-5 transition metal ditellurides MTe2 (M = V, Nb, Ta) exhibit complex superperiodic crystal structures and electronic band structures, including the formation of flat bands, quasi-one-dimensional Fermi surfaces, and nontrivial topological properties. These electronic properties are closely tied to the local molecular-like orbital bonding patterns in the materials.

Sammanfattning

This review article systematically examines the electronic properties of group-5 transition metal ditellurides MTe2 (M = V, Nb, Ta) based on recent angle-resolved photoemission spectroscopy (ARPES) studies and first-principles calculations. The key findings are:

The 1T-1T" phase transition in (V,Ti)Te2 is accompanied by the formation of flat bands and quasi-one-dimensional Fermi surfaces due to the trimerization of dYZ/dZX orbitals. This transition also significantly impacts the topological surface states.
The 1T" ribbon-chain phase is common in MTe2 (M = V, Nb, Ta) at room temperature, but the phase stability relative to the 1T phase varies with the metal M. This is attributed to the energy gain from the flat band formation, which depends on the d-orbital bandwidth.
TaTe2 undergoes a further transition from the ribbon-chain 1T" to a butterfly-like-cluster phase at low temperature. This transition leads to various electronic modifications, including core-level splitting, chemical potential shift, band folding, and kink-like band reconstruction.
The electronic properties of these materials are closely tied to the local molecular-like orbital bonding patterns, highlighting the importance of understanding the real-space chemical bonding in organizing the complex electronic structures.

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arxiv.org

Statistik

The lattice parameters of the 1T" ribbon-chain phase show a ~9% contraction of the M-M bond distance compared to the undistorted 1T phase.
The energy splitting of the Ta 4f7/2 core-level spectra across the ribbon-chain to butterfly-like-cluster transition in TaTe2 is up to ~0.31 eV.
The chemical potential in TaTe2 shifts by up to ~45 meV upon cooling through the phase transition.

Citat

"Molecular-like orbital bonding, analogues of dimers, polymers or clusters in organic molecules, is becoming one of the key concept for organizing complex inorganic compounds with versatile physical properties."
"The importance of Te-Te hybridization and M-Te charge transfer has been argued in tellurides (MTe2), which may make the picture of M-M and/or Te-Te local bonding more plausible as compared to sulfides and selenides."
"The orbital-dependent modification on the Fermi surface can be illustrated as the superposition of the three virtual one-dimensional Fermi surfaces derived from the t2g σ-bonding states."

Viktiga insikter från

Electronic Landscape of Group-5 Transition Metal Ditellurides $M$Te$_2$ ($M$ = V, Nb, Ta): Multiple Crystal Phases with Local Bonds and Flat Bands

by Natsuki Mits... på arxiv.org 09-30-2024

https://arxiv.org/pdf/2408.00915.pdf

Electronic Landscape of Group-5 Transition Metal Ditellurides $M$Te$_2$ ($M$ = V, Nb, Ta): Multiple Crystal Phases with Local Bonds and Flat Bands

Djupare frågor

How do the electronic properties of these materials change under external perturbations such as pressure, strain, or doping, and how can these be used to tune their functional properties?

The electronic properties of group-5 transition metal ditellurides (MTe2, where M = V, Nb, Ta) are significantly influenced by external perturbations such as pressure, strain, and doping. These perturbations can induce phase transitions, modify electronic band structures, and alter the stability of various crystal phases.

Pressure: Applying pressure can lead to lattice collapse or structural phase transitions. For instance, NbTe2 undergoes a lattice-collapse phase transition at approximately 20 GPa, which is accompanied by Nb dimerization. This transition can enhance superconductivity, as seen in TaTe2, which exhibits multiple superconducting phases under pressure. The application of pressure can also modify the Fermi surface topology, potentially leading to new quantum phenomena.

Strain: Strain can induce anisotropic changes in the electronic structure, particularly in materials with quasi-one-dimensional characteristics like the ribbon-chain structures in MTe2. Strain can enhance or suppress the formation of flat bands, which are crucial for electronic properties such as conductivity and superconductivity. The ability to tune the strain allows for the manipulation of the electronic states and can lead to the emergence of new phases or enhance existing properties.

Doping: Doping with different elements (e.g., Ti in VTe2) can suppress or stabilize certain phases, such as the 1T-1T” transition in VTe2. Doping alters the charge carrier concentration, which can lead to significant changes in the Fermi surface and the associated electronic properties. For example, Ti doping can shift the transition temperature and modify the electronic band structure, impacting the material's conductivity and potential for superconductivity.

These external perturbations provide a powerful means to tune the functional properties of MTe2 materials, enabling the exploration of novel quantum phenomena and applications in electronic devices.

What are the potential mechanisms behind the kink-like band reconstruction observed in TaTe2, and how do they relate to the structural and electronic fluctuations in this material?

The kink-like band reconstruction observed in TaTe2 is a complex phenomenon that can be attributed to several interrelated mechanisms:

Orbital-dependent interactions: The kink-like structure is primarily associated with the dXY-derived bands at the Brillouin zone boundary. The transformation from a linear band to a kink-like structure indicates a significant change in the electronic interactions, likely due to the coupling between different orbital states (dXY, dYZ, dZX) as the material transitions from the ribbon-chain to the butterfly-like-cluster phase.

Structural fluctuations: The transition from the ribbon-chain to the butterfly-like-cluster phase involves substantial atomic displacements and the formation of butterfly-like clusters. These structural changes can lead to variations in the electronic environment, affecting the band structure and resulting in the observed kink-like features. The temperature-dependent structural fluctuations may also contribute to the energy scale of the kink, as the electronic states adapt to the new local bonding configurations.

Charge density variations: The splitting of core-level spectra, such as the Ta 4f core-level spectra, indicates variations in electron density among inequivalent Ta sites. This charge density variation can influence the electronic states and contribute to the kink-like band reconstruction. The observed energy shifts in the core-level spectra suggest that the chemical potential is also affected by these fluctuations, further influencing the electronic structure.

Overall, the kink-like band reconstruction in TaTe2 is a manifestation of the interplay between electronic and structural fluctuations, highlighting the importance of local bonding and orbital interactions in determining the material's electronic properties.

Given the importance of local molecular-like bonding in organizing the complex electronic structures, are there other classes of inorganic materials where similar concepts could be applied to understand their emergent phenomena?

Yes, the concept of local molecular-like bonding is applicable to various classes of inorganic materials, particularly those exhibiting complex electronic structures and emergent phenomena. Some notable examples include:

Transition Metal Oxides: Many transition metal oxides, such as cuprates and manganites, exhibit rich electronic phenomena, including high-temperature superconductivity and colossal magnetoresistance. The local bonding characteristics, such as dimerization and orbital ordering, play a crucial role in determining their electronic properties and phase transitions.

Spinels and Perovskites: In materials like spinel oxides (e.g., LiMn2O4) and perovskites (e.g., LaMnO3), local bonding configurations and orbital hybridization significantly influence their magnetic and electronic properties. The interplay between local bonding and long-range order can lead to phenomena such as charge ordering and orbital ordering.

Layered Materials: Other layered materials, such as transition metal dichalcogenides (TMDs) and black phosphorus, also exhibit local bonding characteristics that affect their electronic properties. The formation of flat bands and the emergence of topological states in these materials can be understood through the lens of local molecular-like bonding.

Metal-Organic Frameworks (MOFs): In MOFs, the coordination of metal ions with organic ligands can lead to complex electronic structures and emergent properties, such as gas adsorption and catalysis. The local bonding interactions within these frameworks can be crucial for tuning their functional properties.

In summary, the principles of local molecular-like bonding can be extended to a wide range of inorganic materials, providing a framework for understanding their complex electronic structures and the emergent phenomena that arise from them.