Electrical current in metals | energy bands

Click For Summary

Discussion Overview

The discussion revolves around the nature of electrical current in metals and the role of energy bands versus discrete energy levels. Participants explore theoretical concepts related to electron behavior, energy states, and the conditions necessary for current flow in different materials, including conductors and insulators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that electrical current requires energy bands because discrete energy levels prevent electrons from jumping between atoms due to the Pauli exclusion principle.
  • Others argue that electrons can transition to free states regardless of whether they are in a band or not, noting that both conductors and insulators can exist with or without band gaps.
  • A participant suggests that in Beryllium, an electron must change its quantum state to move from a fully occupied s orbital to a higher energy state, raising questions about the mechanisms that facilitate this change.
  • It is mentioned that electrons can acquire energy from various sources, such as photons or applied electrical bias, to change their states.
  • Another participant clarifies that the concept of principal quantum numbers is less relevant for free electrons, as bands represent energy regions with closely spaced states, allowing for easier transitions.
  • Confusion arises regarding the definition of "state" and the criteria for when a band is fully packed, with references to the Kronig-Penney model and the relationship between electron count and available energy levels.

Areas of Agreement / Disagreement

Participants express differing views on the implications of energy bands versus discrete energy levels for electrical current. There is no consensus on the mechanisms of electron state changes or the definitions of key concepts, indicating ongoing debate and exploration of the topic.

Contextual Notes

Limitations include varying interpretations of energy states, the role of quantum numbers, and the conditions under which bands are considered fully packed. The discussion does not resolve these complexities.

Goodver
Messages
101
Reaction score
1
Why electrical current is possible only with the presence of energy BANDs, rather than discrete energy levels.

Thank you.
 
Last edited:
Physics news on Phys.org
Why do you think discrete energy levels do not allow currents?
 
As far as I understand now, in case of discrete energy levels, electrons can not jump from one atom to another because it would violate Pauli exclusion principle, but in case of energy bands, it is somehow possible. And I am not sure about why is it possible.
 
They can always go to free states, it does not matter if they are in a band or not. Most solids form bands, and you still have good conductors (like metals, no band gap) and good insulators (with a band gap) there.
 
  • Like
Likes   Reactions: Goodver
Suppose we have Beryllium (2s2). As far as I understand electron can jump to the free state without changing its quantum numbers. In case of Beryllium s orbital is fully occupied, thus electron can not jump to s orbital again, and only possibility if it would jump to p orbital, which will require change of L quantum number and change of electron's state. What makes electron to change it's state?

Insulators topic, seems to be more less clear to me.
 
The electron can change its state by acquiring energy from somewhere. This can be from a photon, a phonon or an applied electrical bias.
 
yehokhenan said:
The electron can change its state by acquiring energy from somewhere.
Change of energy would mean change of energy level (principal quantum number), as far as I understand, electrical current is due to jump of electrons within degenerate states, that's why electrical current possible in metals and not in insulators (without changing of energy level).
 
The concept of principal quantum numbers does not make sense if the electron is not bound to a specific atom.
Bands are simply energy regions where the states are extremely close together, so even tiny energy changes are sufficient to reach a different state.
 
Ok, I am confused now. What is meant by the state then? And what determines when the band is fully packed and when not?

As far as I understand, electrons can be in one of the energy bands which are separated by energy gaps (Kronig Penney model). On each energy band/level can be only certain amount of electrons. In insulators we have elements for which energy bands are fully packed, therefore to conduct a current electron must be excited to the higher energy band, which requires overcoming of energy gap. In case of conductors, energy bands are not packed fully, thus electrons do not have to overcome energy gap to conduct.

Is this correct?
 
  • #10
Goodver said:
What is meant by the state then?
An energy level that can get occupied by an electron.
Goodver said:
And what determines when the band is fully packed and when not?
The number of electrons compared to the number of available energy levels.
Goodver said:
As far as I understand, electrons can be in one of the energy bands which are separated by energy gaps (Kronig Penney model).
The gap does not have to exist.

Right.
 
  • Like
Likes   Reactions: Goodver

Similar threads

Undergrad Emission of light from incandescence of metals
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Carrier relaxation within a quantum well
  • · Replies 4 ·
Replies
4
Views
3K
Graduate Energy of valence electrons from period of the periodic table
  • · Replies 2 ·
Replies
2
Views
1K
Graduate Band Structure in solids versus Superconductivity
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Can Having Electrons in Energy Levels Indicate Ionisation of Atoms?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Are the electrons in the conduction band completely free?
  • · Replies 11 ·
Replies
11
Views
4K
High School PV cell charge separation by an external electric field
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad Question about Electronic Band Structure
  • · Replies 3 ·
Replies
3
Views
2K
High School Doping in semicondctors (n type)
  • · Replies 2 ·
Replies
2
Views
3K
Graduate Explaining the Absence of Band Gaps in Superconductors
  • · Replies 5 ·
Replies
5
Views
7K