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Ranku
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Do positively charged holes have any other quantum numbers assigned to them? What are the similarities and differences between a hole and a positron?
Ranku said:Do positively charged holes have any other quantum numbers assigned to them? What are the similarities and differences between a hole and a positron?
SpectraCat said:Electron "holes" are a semantic convenience used to represent electronic vacancies in explanations of physical phenomena. You can think of them like the placeholder zeros in a number like, 18057604. In principle there could be values in the [tex]10^{1}[/tex] and [tex]10^{5}[/tex] places, but in this particular instance, there aren't. Depending on the specific context in which they are used, it sometimes makes sense to associate quantum numbers with holes. For example, a chlorine atom is one 3p electron short of having a complete n=3 shell. Therefore it is semantically consistent to say that it has an "n=3, l=1" hole.
Having said all of that, holes do not really have any independent reality. Positrons, on the other hand, are real particles ... they are the antiparticles of electrons, and have precisely the same set of quantum numbers, but with a positive charge. They have independent reality, that is, they exist and can be isolated experimentally.
Ranku said:So holes are independently introduced conceptual constructs, that are not part of the particle standard model?
f95toli said:Yes, holes are not "real" as such . They are mathematical constructs that are useful because they simplify our calculations.
Frame Dragger said:Holes are very much like Virtual Particles in that their effect seems obvious, but they are really just a trick of the math. That said, they are a trick which does a good job describing the situation for people who don't think in dimensions higher than 3![]()
Galap said:I'd like to hear more in depth about the more-than-3d explanation you imply :)
ArjenDijksman said:I see no inconsistency in thinking of holes as ordinary locations left vacant by electrons in a lattice. An electron is attracted to a hole, because there's more place for the electron around holes then elsewhere in the lattice, it can reoccupy the hole ("recombine"), it can "circle" around it (forming an exciton)... It is above all a physical reality and incidentally a mathematical trick...
Frame Dragger said:? I mean to say that human beings can't imagine structures in more than the 3 spatial dimensions we experience daily. Given that, we get gravity "wells" and and electron "holes". What else can we say unless people simply spoke in equations?
ZapperZ said:I think this is an excellent view of it.
Claiming that holes aren't real is analogous to saying a "bubble" in water isn't real. It is as much a "real" object as the glob of water that left it and went up above the surface. The fact that we can "renormalize" the environment in the filled band and to consider such holes as having not only a positive charge, but also to have spin, etc., means that below the Fermi level, they are as real as the "vacuum excitation" that we call 'electron'.
In condensed matter physics, there is never any demotion of the concept of "holes" with respect to "electrons". YBCO and LACO and BCCO are all hole-doped superconductors, while NCCO is an electron-doped superconductor, for example. In Andreev scattering, it does makes a difference if a hole is reflected at the interface. There are plenty more examples where this came from.
Zz.
SpectraCat said:I think this is kind of a "potato/potahtoe" thing, and the differences in description are mostly semantic. Holes are semantically and mathematically convenient for sure, but they are an "extra" concept. What I mean by this is that the properties of what we call a hole or vacancy could be obtained simply from the properties of the electrons that are actually there. This is true in the atomic case (where it is simple to prove), and while I am less familiar with solid-state physics, I suspect it is true there as well, although it is probably *way* less tractable to deal with.
Note that I am not disputing the reality of holes ... of course they are real, as much as the hole in a doughnut is real ... but it requires the doughnut for its existence. If you excite an electron out of a filled band, then you create a higher energy configuration, which has a vacancy in the filled band that "wants" to have an electron in it. Therefore it seems to have a positive charge, and will act as ArjenDijksman described. If the band is spin polarized, then only an electron with a particular spin can fill the hole. The properties of spin and charge are also only relevant with respect to some lower energy reference state. That is what I meant earlier when I said they have no independent reality.
ZapperZ said:But within context to condensed matter physics, an "electron" also relies on the vacuum state, i.e. a background of "holes" for its existence! That's why I called an electron a "vacuum excitation"! In fact, both holes and electrons are "quasiparticles" in a many-body interaction. They are not different.
Zz.
SpectraCat said:Ok .. I guess I see what you are saying, but there still seems to be a significant difference to me. Electrons and holes both "exist" in a solid state electrical conductor, however, if we use that conductor as the emission element of a beam source, it is straightforward to make a beam of electrons, but to my knowledge, no one has ever made a beam of holes.
I am a rank novice when it comes to high-energy physics, so I will have to take the word of those more knowledgeable than myself about "vacuum holes". I am also willing to accept that we can only make an electron beam because we live in and experience the "low energy" case, as suggested by Physics Monkey.
ZapperZ said:The fact that we can "renormalize" the environment in the filled band and to consider such holes as having not only a positive charge, but also to have spin, etc., means that below the Fermi level, they are as real as the "vacuum excitation" that we call 'electron'.
SpectraCat said:Ok .. I guess I see what you are saying, but there still seems to be a significant difference to me. Electrons and holes both "exist" in a solid state electrical conductor, however, if we use that conductor as the emission element of a beam source, it is straightforward to make a beam of electrons, but to my knowledge, no one has ever made a beam of holes.
SpectraCat said:Ok .. I guess I see what you are saying, but there still seems to be a significant difference to me. Electrons and holes both "exist" in a solid state electrical conductor, however, if we use that conductor as the emission element of a beam source, it is straightforward to make a beam of electrons, but to my knowledge, no one has ever made a beam of holes.
ArjenDijksman said:Well said. That's clear indeed apart from the fact that the term "holes" applies generally to semiconductors. In conductors (read: good conductors), it doesn't make much sense to speak of holes, because the electron is almost free. As an analogy, if soccer players are electrons, the soccer field is a metal where the player has plenty of space to circulate (occasionally colliding with other electrons or objects that compose the lattice). But if the player is in the crowded changing room, he will be attracted to the vacant places (=the holes). The changing room can then be seen as a semiconductor.
Arjen
I'm not well acquainted with superconductivity, so I didn't know that. Isn't that hole doping just analogous to doping with atoms with unfilled electron shells, like for p-type semiconductors?ZapperZ said:That isn't quite true. The cuprate superconductors, for example, in the normal state, are "bad metals". They get to become that by doping the insulating parent compound with holes, not electrons (that's why I earlier called some of them as hole-doped superconductors). So the charge carrier that is moving in this "conductor" are holes, not electrons. We do not always have to have a semiconductor to get the presence of holes.
ArjenDijksman said:I'm not well acquainted with superconductivity, so I didn't know that. Isn't that hole doping just analogous to doping with atoms with unfilled electron shells, like for p-type semiconductors?
ZapperZ said:It certainly is, but it is still not a "semiconductor". It is a metal (i.e. the resistivity vs. temp. curve has a positive slope), but yet, it becomes more conducting with more hole doping.
Zz.
DrDu said:What tends to make the hole concept very usefull both in particle and in solid state physics is the fact that an electron near the upper end of the valence (negative energy) band, has a negative effective mass. A hole then has a positive mass, which is what we are more used to from free particles.
SpectraCat said:Really? I find that hard to understand, but I guess it must be all in the definition of "effective mass". I will check it out in my Ashcroft and Mermin when I have time.