A fresh twist in chiral topology

Date:
June 22, 2020
Source:
Max Planck Institute for Chemical Physics of Solids
Summary:
Electrons in ''chiral crystals'', solid-state materials with
definite ''handedness'', can behave in unexpected ways. An
interdisciplinary team has realized now a theoretically predicted
peculiar electronic state in a chiral compound, PtGa, from the
class of topological materials. The study allows a fundamental
understanding of the electronic properties of this novel semimetal.



FULL STORY ==========================================================================
The concept of chirality is well-established in science: when an object
cannot be superimposed on its mirror image, both the object and its
mirror image are called chiral. In drug industry, for instance, more than
50% of the pharmaceutically active molecules used nowadays are chiral molecules. While one of the "enantiomers" is life-saving, its counterpart
with opposite handedness may be poisonous. Another concept which has
found widespread interest in contemporary materials science is topology
as many so-called topological materials feature exotic properties. For
example, topological materials can have protected edge states where
electrons flow freely without resistance, as if a superconducting path
of electrons were created at the edge of a material.

Such unconventional properties are a manifestation of the quantum nature
of matter. The topological materials can be classified by a special
quantum number, called the topological charge or the Chern number.


========================================================================== Chiral topological materials have particularly unique properties which
may be useful in future devices for quantum computers which could
speed up computations considerably. An example for such a property
is the long-sought large quantized photogalvanic current. Here a
fixed dc current is generated in a chiral topological material once
exposed to a circularly-polarized light, which is independent of the
strength of incident radiation and its direction can be manipulated by
the polarization of incident light. This phenomenon relies on the fact
that the material possesses a high topological charge of 4, which is
the maximum possible value in any material.

Solid-state chemists and physicists from the Max Planck Institute
for Chemical Physics of Solids (MPI CPfS), the Leibniz Institute
for Solid State and Materials Research (IFW), the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Helmholtz-Zentrum Berlin fuer Materialien
und Energie (HZB) and the University of Science and Technology of China,
Hefei succeeded to realize this peculiar electronic state for the first
time in the new chiral topological compound PtGa. Their results have
been published in Nature Communications1.

In the study, the researchers have used exceptionally strong spin-orbit coupling in PtGa as the key parameter to clearly resolve and count the
number of special topological surface states, called the Fermi arcs, which determine the topological charge. "PtGa is the best compound existing in
nature with chiral B20 structure to observe spin-split Fermi arcs and
realize the maximal Chern number 4 as it has the strongest spin-orbit coupling." says Kaustuv Manna, one of the authors of the study who
works as a scientist at Max Planck Institute for Chemical Physics of
Solids Dresden.

Theoretical calculations performed by Yan Sun and his colleagues suggested
that the compound PtGa is a highly promising candidate to observe the
high topological charge which was experimentally verified by Mengyu Yao
and his colleagues who performed detailed angle-resolved photoemission spectroscopy (ARPES) studies. ARPES is a powerful tool to investigate
the behavior of electrons in solids.

"The work by Yao et al. reveals that PtGa is a topological semimetal
with a maximal chiral charge and has the strongest spin-orbital coupling
among all chiral crystals identified up to date. This observation is significant and has great implications for its transport properties,
such as magnetotransport." explains Ming Shi, a professor and senior
scientist at Paul Scherrer Institute, Switzerland.

The study is an example for an excellent collaboration between research
groups covering different areas of expertise. Within the excellence
cluster ct.qmat, scientists are cooperating to investigate fundamentally
new states of matter.

"We are focusing on novel materials whose observed properties and
functions are driven by quantum mechanical interactions at the atomic
level, with semimetals such as PtGa being one of the most exciting
examples," says Jochen Wosnitza, Director of the Dresden High Magnetic
Field Laboratory (HLD) at HZDR, referring to one of the cluster's main
research topics. Institutes participating in the cluster and collaborating
on the current publication include the DRESDEN- concept partners MPI CPfS,
IFW, and HZDR.


========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Chemical_Physics_of_Solids.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mengyu Yao, Kaustuv Manna, Qun Yang, Alexander Fedorov, Vladimir
Voroshnin, B. Valentin Schwarze, Jacob Hornung, S. Chattopadhyay,
Zhe Sun, Satya N. Guin, Jochen Wosnitza, Horst Borrmann,
Chandra Shekhar, Nitesh Kumar, Jo"rg Fink, Yan Sun, Claudia
Felser. Observation of giant spin-split Fermi-arc with maximal
Chern number in the chiral topological semimetal PtGa. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467- 020-15865-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200622132939.htm

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