Exploring quasiparticles in high-Tc cuprates through photoemission, tunneling, and x-ray scattering experiments
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Transkript: Englisch(automatisch erzeugt)
00:03
Exploring quasiparticles in high TC cuprates through photoemission, tunneling, and X-ray scattering experiments. The present paper offers an unconventional approach to static, charged modulations recently observed in underdog cuprates.
00:21
Some peer reviewers describe it as thought provocatives, others as well knowingly wrong. Dr. Dallatorre, can you give us more details? Yes, thank you. These results came out as a surprise for us as well. We were working on a phenomenological model that gives a good description of
00:40
STM experiments, and then we found that the same model could describe several other spectroscopic probes as well, like ARPES and X-ray. Our model is actually very simple. It describes the scattering of electrons from local impurities. You see, there is an electron coming in at momentum k, a single scatterer,
01:02
a Lebron approximation, and an outgoing electron at momentum k plus q. Very interesting, but if I'm not mistaken, this is precisely the same mechanism that gives rise to free-dial oscillations in a conventional metal. Cuprates are certainly not conventional metals.
01:22
Indeed, there are important differences. For example, these are actually band electrons or Bogoliubov quasiparticles. Their properties are known from previous measurements. There are no free-fitting parameters in our theory. In underdoped cuprates, the quasiparticles have a relatively short lifetime.
01:41
This is an important ingredient that has been often overlooked. In the STM literature, for example, one often distinguishes between non-dispersive peaks identified with static charge modulations, and dispersive peaks attributed to quasiparticles interference. In this paper, we show that these two effects are, in a sense, adiabatically connected.
02:00
Whether one observes one or the other depends only on the ratio between the pairing gap and the inverse quasiparticle lifetime, you see. The model smoothly connects the two effects, and there is a band structure. Cuprates are not a spherical cow. They have some amount of nesting at the antinodes. This is why normal metals do not display finite x-ray diffraction peaks,
02:23
while cuprates do. You mean that this is not a competing order? In conventional metals, free-dell oscillations are a consequence of Pauli exclusion principle, which leads to a discontinuity in the occupation of the Fermi surface.
02:41
Certainly, free-dell oscillations can act as a seed for the formation of long-range charge density wave, leading to a transition to a Wigner crystal. However, this requires relatively large interactions between the electrons. We rather undertake a weak coupling approach and show that the model of independent short-lived quasiparticles is sufficient
03:01
to quantitatively describe all the experiments. Let's have a look at figure nine of our paper, where we compare our theory with resonant elastic x-ray scattering on three different cuprates. In all cases, the model is in quantitative agreement with the experiment. We can predict both the wave vector and the correlation length of the oscillations.
03:23
But if interactions are not important, what is the reason for the short lifetime of the quasiparticles? Honestly, we don't really know the answer to this question for us. This is the major problem that future experiments will need to clarify.
03:41
From the theoretical side, there are several possible answers on the market. For example, the short lifetime of quasiparticles could be caused by phase fluctuations indeed. We find an interesting relation between quasiparticles lifetime and the critical temperature, which is probably related to the amount of phase fluctuations. But other effects, for example, different competing order, could also be relevant.
04:05
We should throw the ball back to the experiments. Thank you for your attention and enjoy the reading.