Direct observation of coherence energy scale of Hund's metal

Date:
March 9, 2021
Source:
Pohang University of Science & Technology (POSTECH)
Summary:
A research team has directly observed the coherence energy scale
suppressed by Hund's coupling on approach to the metal-insulator
transition of strongly correlated multiband material.



FULL STORY ========================================================================== Strongly correlated systems are materials that exhibit strong interactions between electrons, a property unseen in ordinary conductors or insulators.

Typical examples include metal-insulator transitions or unconventional
high- temperature superconductivity where the resistance becomes zero
at high temperatures.


========================================================================== There have been studies to explain this strong interaction between
electrons and their characteristic energy scales, but no direct
observation on such energy scales through theory or experiments has been reported. To this, the POSTECH-IBS joint research team has succeeded
in directly observing the evolution of coherence energy scale of the
Hund's metal in its electronic structure and as a result, clarifying
the principle behind it.

The joint research team -- consisting of Professor Ji Hoon Shim and
Dr. Bo Gyu Jang of POSTECH's Department of Chemistry, and Professor
Changyoung Kim and Dr.

Garam Han of Center for Correlated Electron Systems at the Institute for
Basic Science (IBS) -- has discovered that the kink behavior of electronic
band structure of NiS2-xSex, changes according to the degree of selenium
(Se) doping. The researchers used the angle-resolved photoemission
spectroscopy (ARPES) to verify this. Using the first-principle
calculation, they proved for the first time that this kink is due to the
Hund's coupling and that it is linked to the characteristic coherence
energy scale in matters. These research findings were recently published
in Nature Communications.

Until now, the unique phenomenon that occurs in strongly correlated
materials have been usually explained by the electron interactions in single-band model.

However, most materials have multiband nature and this has limited understanding the Hund's coupling effect which should be taken into consideration.

The research team controlled the intensity of the interaction between
electrons by controlling the selenium (Se) doping in NiS2-xSex, a Hund's
metal. The researchers observed the evolution of kink behavior in the electronic structure at low temperatures and confirmed that this kink
is directly related to the coherence temperature scale of the system, suppressed by the Hund's coupling.

This study suggests that the traditional picture studied based on a
single-band model should be modified in multiband systems in which the
Hund's coupling plays an important role. It is attracting the attention of academic circles for its direct observation of a matter's characteristic
energy scale through its electronic structure at low temperatures.

This research was conducted with the support from the SRC Quantum Dynamics Research Center, the Nano-New Materials Core Technology Development
Program and the Institute for Basic Science.

========================================================================== Story Source: Materials provided by Pohang_University_of_Science_&_Technology_(POSTECH).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Bo Gyu Jang, Garam Han, Ina Park, Dongwook Kim, Yoon Young Koh,
Yeongkwan
Kim, Wonshik Kyung, Hyeong-Do Kim, Cheng-Maw Cheng, Ku-Ding
Tsuei, Kyung Dong Lee, Namjung Hur, Ji Hoon Shim, Changyoung Kim,
Gabriel Kotliar.

Direct observation of kink evolution due to Hund's coupling
on approach to metal-insulator transition in NiS2-xSex. Nature
Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-21460-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210309105155.htm

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