# I Recent (?) noteworthy (?) physics paper

1. Jan 13, 2017

### TeethWhitener

This question is mainly geared toward @ZapperZ, since I know you have a good deal of expertise in superconductivity and in STS/STM. I saw this paper in my journal alerts early early last year:

http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.115.237002 [Broken]
"Mapping the Electronic Structure of Each Ingredient Oxide Layer of High-$T_c$ Cuprate Superconductor $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$"

...and thought it was fascinating (NB--I am a complete outsider to this field). But there seemed to be no mention of it in the APS physics highlights or anything comparable from other journals. It seems to me that one of the main barriers to understanding high-temperature superconductivity comes from detangling the interactions within the millefeuille structure of these compounds, and that this paper takes a big step in that direction. Am I misinterpreting this? Or are these results similar to what the community has been looking at for a while? Just wondering what the thoughts are of people who actually work in this field.

Last edited by a moderator: May 8, 2017
2. Jan 13, 2017

### ZapperZ

Staff Emeritus
It has been years since I was involved actively in High-Tc superconductors, but I did read about this paper quite a while back and had to reacquaint myself on it. Unfortunately, since I no longer attend conferences on this topic, I am not aware of the kind of reception this paper had, or if others have responded or followed up to it.

The question on whether the pseudogap actually plays a role, a red-herring, or even competing with superconductivity has been going on since the day this feature was discovered. Certainly, this paper seems to indicate that the pseudogap is a distraction and "irrelevant" to the superconducting phenomenon. They claim it is from the BiO layer and doesn't do much. However, I've see other papers in which the pseudogap evolves with temperature (see, for example, Miyakawa et al. PRL 83, 1018 (1999)). So this contradiction needs to be reconciled.

It is interesting that they see a van Hove singularity only in the SrO layer, which is strange because the vHs is a feature found in a 2D metallic density of states. It means that this feature should be the strongest in the CuO plane. It should be there above Tc in the normal state, but they don't see it.

But more importantly, why does single layer BSCO have a lower Tc than 2 layer BSCCO, and 3 layer BSCCO having higher Tc than 2 layer BSCCO. According to them, the SrO provides the "charge reservoir" for the CuO layer. So adding more layers to the unit cell shouldn't matter, since each SrO layer only provides charges to the adjacent CuO layer. The BiO layer (the one with the pseudogap) simply isolates all these these layers from one another because they appear to not do anything.

So that's my take on this paper, and like I said, maybe these have been addressed since the paper was published, but I'm out of the loop currently on this topic.

Zz.

3. Jan 13, 2017

### TeethWhitener

Thanks so much for your reply. Interesting about the SrO layer. They measured the two BiO layers and the two CuO2 layers separately, but only one of the SrO layers (the one with a copper oxide layer under it). It might have been nice to see if an SrO layer with BiO under it had a different dI/dV curve than the one with CuO2 underneath it. I guess it's more tightly bound to the CuO2 plane than the BiO plane, and that's why they weren't able to observe it? I'm wondering if maybe the van Hove singularity appeared due to the interplay of SrO and CuO2, and whether this feature would be absent if it were an SrO/BiO stack instead.