ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT ttk.bme.hu>]

Meghívó

BME Elméleti Fizika Szeminárium,

április 29. péntek 10h15,

1111 Budapest, Budafoki út 8., BME F III. magasföldszint 01.,
Elméleti Fizika Tanszék szemináriumi szoba
és
online a Microsoft Teams-ben
<https://teams.microsoft.com/l/meetup-join/19%3ae1a26210676841cdbb27bb01cf353392%40thread.tacv2/1651069093560?context=%7b%22Tid%22%3a%226a3548ab-7570-4271-91a8-58da00697029%22%2c%22Oid%22%3a%22c7eaf7d2-684b-4597-b217-6a9121400219%22%7d>

Angelo Valli (TU Wien):
Hund's physics as a key to understanding emerging quantum phases in
iron-pnictides

The origin of high-temperature superconductivity is one of the most elusive
puzzles of modern solid-state physics. The discovery of materials with
unprecedently high critical temperatures (copper oxides, fullerides, iron
pnictides) which defy the conventional theory of superconductivity, has
fueled an intense research activity for decades. Unconventional
superconducting states arise in the proximity of Mott insulators, i.e.,
states in which the electrons are localized by strong Coulomb repulsion,
and in the iron pnictides, overwhelming evidence identifies the normal
state as bad metal characterized by orbital-selective correlations arising
from the Hund’s exchange interaction. This scenario suggests that a
prominent role is played by many-body effects. At the same time, approaches
based on the exchange of bosons of electronic origin (spin and orbital
fluctuations being the most popular candidates) can predict the emergence
of a variety of phenomena, thus pointing toward a more conventional pairing
mechanism.
We discuss a strategy to reconcile this evidence and show that the nature
of the electronic correlations in the normal state has non-trivial
repercussions on the ordered phases. The inclusion of dynamical
correlations allows the simultaneous description of electronic excitations
living on different energy scales. Within this framework, the Hund's metal
is substantially different from both a weakly interacting metal and an
ordinary correlated metal with a strong effective mass renormalization. We
reveal that Hund’s correlations are counterintuitively beneficial to
boson-mediated superconductivity [1] and that experimental features
observed in the nematic photoemission spectra of FeSe and FeAs compounds
naturally emerge from the orbital-selective behavior [2]. Our analysis
leads to questioning the popular approaches that mainly focus on “who is
the driver?” of the electronic instabilities and calls instead for a more
coherent theoretical description of iron pnictides which must be able to
capture the essence of the correlated metal.

[1] L. Fanfarillo, A. Valli, and M. Capone, Phys. Rev. Lett. 125, 177001
(2020)
[2] L. Fanfarillo, A. Valli, and M. Capone, arXiv:2203.01273 (2022)

Minden érdeklődőt szeretettel várunk.
Asbóth János,
 szemináriumi koordinátor