If you have a glass with some water in it you are left with only that much space. Clearly, if you pour in some more water you will be left with less space. It is a no brainer. However, what is obvious in our daily life may not apply to the exotic realm of atomic scale.
An atom has a well defined set of bands where electrons can be (or move around if you like the idea of electrons orbiting the atoms nucleus). Any given band can contain only as many electrons and no more (K=2, L=8, M=18, N=32, don't confuse the bands with the chemical valence ....) so it should be a no brainer that if you add electrons to a band there will remain less space available. But, as I said, at atomic scale our normal logic gets fuzzy.
Theoretically scientists had found (by playing with math) that certain electronic band configuration might get distorted as more electrons are added and that this distortion, theoretically, should make space for more electrons.
Now researchers at SLAC National Accelerator Laboratory (Stanford, US) have been able to demonstrate that this is indeed what happens. They have been able to "photograph" molecules of Iridium Oxide (Sr3Ir2O7) using x a Synchrotron Radiation Lightsource (xRays). You may read the announcement and the articles if you love this kind of physics (I do, but I recognise that a few may not....).
What is interesting is the implication on the evolution of chips. The miniaturisation is hampered at the construction stage by the need to find ways to etch ever smaller components (we are down to 10 nm), by the fleeting -non deterministic- behaviour of electrons once you reach the nm scale and it is hampered at the operation stage by the heat production. As density increases so the heat density increases and moving to 3D structures make it even worse (dissipation occurs at the surface -square- but heat gets produced by the volume -cube).
The discovery at Stanford opens up a new way to investigate. The possibility of creating conductors inside a chip made by materials having this property (like Iridium Oxide, today copper is being used) that would decrease the energy level hence the heat creation.