New form of matter ‘excitonium’ discovered

indianexpress.com ^ | December 10, 2017 6:14 pm

[BenLurkin]

Scientists have proven the existence of new form of matter called excitonium – which was first theorised almost 50 years ago. Researchers from University of California Berkeley and University of Illinois at Urbana-Champaign in the US studied non-doped crystals of the transition metal dichalcogenide titanium diselenide (1T-TiSe2).

Excitonium is a condensate – it exhibits macroscopic quantum phenomena, like a superconductor. It is made up of excitons, particles that are formed in a very strange quantum mechanical pairing, namely that of an escaped electron and the hole it left behind.

... when an electron, seated at the edge of a crowded-with-electrons valence band in a semiconductor, gets excited and jumps over the energy gap to the otherwise empty conduction band, it leaves behind a “hole” in the valence band. That hole behaves as though it were a particle with positive charge, and it attracts the escaped electron.

When the escaped electron with its negative charge, pairs up with the hole, the two remarkably form a composite particle, a boson – an exciton. In point of fact, the hole’s particle-like attributes are due to the collective behaviour of the surrounding crowd of electrons. However, that understanding makes the pairing no less strange and wonderful...

Until now, scientists have not had the experimental tools to positively distinguish whether what looked like excitonium was not in fact a Peierls phase. Peierls phases and exciton condensation share the same symmetry and similar observables.

Abbamonte and his team were able to overcome that challenge by using a novel technique they developed called momentum-resolved electron energy-loss spectroscopy (M-EELS). With their new technique, the group was able to measure collective excitations of the low-energy bosonic particles, the paired electrons and holes, regardless of their momentum.

[grey_whiskers]

The "hole" is talking about a missing spot for an electron in the, well, call it a mobile electron lattice in certain metals. Conductivity, you know, means that they electrons are labile rather than more or less strictly localized within a specific orbital as in discrete gaseous molecules.

One analogy might be to those old-fashioned theater marquee lights:

If you look at it, at first it seems like the blacked areas are moving: in fact, it is the activity of the lights that makes it seem so.

The lit-up lights in the marquee are the electrons, the unlit lights are the holes.

[Pontiac]

What I am having trouble with is the idea that an electron jumping from one quantum state to another leaves behind a hole that acts like a particle. For one thing, my understanding is that electrons are not particles as much as they are discreet energy packets. So, how can it leave a hole? And how can a hole behave like an anti-electron?

Actually this is pretty much how semi-conductor theory was explained to me back in the 1980’s.

They even described ‘Hole Flow’ in the opposite direction as electon flow.

[PrairieLady2]

It almost sounds like they figured out how gravity works.

[Windflier]

Here we go again. More fairy dust and pixie sprinkles.

[redfreedom]

Several years ago scientists discovered a sister particle to the electron called the “queertron”. They observed it traveling through electrical circuitry blowing fuses. This explains why home wiring went from fuse boxes to circuit breakers.

[Ceebass]

It seems that many of these scientific articles are written by ordinary journalists. They rewrite the research without any knowledge of the science behind it.

[real saxophonist]

Interviewer: Mr. Welk, what do you think of violence on television?
Lawrence Welk: Violence are the most important part of my orchestra!

[BenLurkin]

QUEER-TRON

[exDemMom]

It seems that many of these scientific articles are written by ordinary journalists. They rewrite the research without any knowledge of the science behind it.

Which is 180 degrees off from what I do, which is understand the science and then write about it so that laypeople can understand. It's pretty hard to write about something when you have no clue what it actually is.

[DeFault User]

Looney Tunes knew about this some 60 years ago. The Portable Hole:

[libh8er]

Electrons absolutely have mass and thus kinetic energy.

[libh8er]

When waiting to make a left turn at an intersection, we don’t really look at oncoming cars so much as the approaching ‘hole’. When the hole is crossing the intersection, we make the left turn !

[Rebelbase]

“Someone needs to explain this to me as if I’m Penny”

Imagine every trashy relationship you’ve ever had rolled into one sordid night...with a bottle of champagne.

[Ozark Tom]

“It is through caffeine alone I set my mind in motion. It is by the juice of Java that thoughts acquire speed, the teeth acquire stains, the dentats acquire profit. It is through caffeine alone I set my mind in motion.” -— brianvds

[Garth Tater]

For one thing, my understanding is that electrons are not particles as much as they are discreet energy packets.

TLDR; Electrons are not particles or "discreet energy packets," they are neither and how we perceive them depends both on the tools we use and by the very act of our perception - and even more strangely - but our potential ability to perform the act of perception. Einstein refused (or at least preferred not) to believe in any quantum spookiness -- but what did he know!

Longer answer:

As with Schrödinger's cat which is not alive or dead or even both (it is, in theory, neither,) electrons are not particles nor "discreet energy packets" (an imprecise description of the probablity distribution of the results that would be returned by measuring the electon's energy field,) and - like the cat - electrons are not one or the other or even both. they are neither.

As you are probably aware, if you wish to set up an experiment to determine the location of an electron viewed as a particle- that can be done. But at the same time if you wish to set up an experiment to determine the probability distribution of the electron's energy field (commonly described as a probability wave) - that can also be done. So an electron is an energy field. But again, nope - a "thing" can not be two separate and distinct "things" at the same time. Only our "view" of whatever it is that we are viewing can allow that apparent impossibility. AND our action of viewing actually impinges on the results returned by our experiments.

But how can our act of viewing affect the outcome of our experiment you might ask as that directly conflicts with our traditional scientific belief in the separation of the experiment and the experimenter? (Does a tree falling in the forest make a noise if there is no one there to hear it? - Of course it does according to traditional scientific thought.)

You are, of course, familiar with the double-slit experiment where a particle is found when detectors are set up to determine which of two slits it traveled through, while an energy field described by its probability wave function is found when no detectors are in place... Well, recent experiments have further mystified this strange behavior. Called the delayed choice double-slit experiment, the results of the experiment (particle or wave) depend not on whether the experimenter determined or did not determine which of the two slits the particle passed through, but rather, whether the experimenter was in any way capable of making that determination (and not that he actually did make the determination.)

A brief synopsis of the weirdness: if a double-slit experiment is set up and detectors are placed on each slit and the data is recorded - BUT NOT VIEWED BY THE EXPERIMENTER - and then the experiment's results (particle or wave) are looked at the results will show that a particle passed through a slit. BUT if the detectors' records are erased before the experiment's results are viewed - then, when viewed, the results will show that a wave passed through both slits. In other words, the results of the experiment are determined by the actions of the experimenter (erase or don't erase the detectors records) AFTER the experiment has been completed.

Now, just for fun, add a second experimenter into the mix who will, based on the flip of a coin, erase or not erase the detectors' records before the first experimenter looks at the results of the experiment. What do you think the first experimenter will see when he looks at the results of the experiment. Yep, quantum weirdness is really weird.

So, is an electron a particle or a "discreet energy packet?" Nope, it's neither. Its nature of being is something that is outside of our plane of existence and our experiments' views of its nature depend on our actions. This coupling of the experimenter and the experiment fly directly in the face of our historic separation of the experimenter and his experiment and throw the very idea of a universe ruled by cause and effect into question. Cool stuff, huh?

_________________________________________________________

Note: please forgive my playing a bit fast and loose with various terms in this post as quantum theory is not my field - just a part time hobby which I am brushing back up on as my son-in-law, a Sheldon Cooper type nerd of the physic community, will be in for Christmas and much whiskey will be consumed while the Tater clan discusses this stuff.