Adjustable electron chirality in Kagome superconductor CsV3Sb5

Whether the image of an object in a mirror is exactly the same as it is has a very important effect on the physical properties of that object. For example, a basketball player in the mirror looks no different from himself at first glance, but if you look closely, you will see that there is actually still a difference in details: the basketball that was originally in the player’s right hand is converted in the mirror to his left hand. In our daily life, the most representative is our hands, which is why this property is called chiral by scientists.

Chirality is one of the fundamental geometric symmetrical properties that we are often exposed to in our lives, and it has special significance in the fields of biology, chemistry and physics. In materials science, we focus on whether the crystal structure of a solid is chiral. In chiral materials, the motion of electrons and their band properties are inevitably affected by chirality, so they have various novel physical phenomena, thus laying the foundation for the application of new electronic devices.

Electromagnetic chirality is an important property of chiral electronic materials. Similar to the diode effect, it describes that due to the proportionality of the mirror, the direction of the current has a direct effect on the resistance value of the material. Until now, this effect has only occurred in materials with chiral crystal structures. Recently, however, Philip Moll’s team from the Max-Planck-MPSD Institute in Hamburg, Germany, and collaborators from Switzerland, Germany, and Spain first observed this effect in the Kagome superconductor CsV3Sb5, a material with a centrally symmetrical, non-chiral lattice structure, under the title of “Switchable chiral transport in charge-ordered kagome metal.” CsV3Sb5″ was published in the journal Nature.

Chunyu Guo, leader of the MPSD research group, is the first author of the paper, and co-corresponding authors with Mark H. Fischer, Titus Neupert, and Philip J. W. Moll.

Figure 1: Chiral electrons in a Kagome superconductor

This novel phenomenon raises a question with a concise core but profound physical significance: If the arrangement of atoms in a crystal has mirror symmetry, how can the electrons in it not follow lattice symmetry? Obviously, there must be a new effect that is different from the structural chirality. Unlike lattice structures that cannot change the chiral properties – just as we cannot turn the left hand into the right hand and the right hand into the left hand – in CsV3Sb5, this novel electronic chiral property can be adjusted by an applied magnetic field to regulate and convert the chiral properties of the material. Convertible chiral electronic materials represent a new quantum material, and are of great significance for the development of future electronic device technology. Obviously, this extraordinary phenomenon is directly related to the strong electron correlation effect. In this paper, the research team presents a self-consistent theoretical model that directly describes how electrons in materials autonomously constitute a pattern of chiral distribution through the formation of charge density waves without changing atomic structure.

Figure 2: (a) Comparison of ordinary conductors versus chiral conductors. Due to the chipping of the mirror symmetry, the direction of the current and magnetic field directly determines the resistance of the chiral conductor, but it is insignificant for ordinary conductors. (b) In the measurement of electromagnetic anisotropy, we mainly investigate its nonlinear current-voltage dependency. In alternating current measurements, this manifests itself as the appearance of a two-fold signal. (c) Several common causes of electromagnetic anisotropy. (d) In CsV3Sb5 materials, orbital ring currents are spontaneously generated as the temperature decreases, resulting in specific electronic chirality.

In previous studies, CsV3Sb5 has been shown to have a strong electron correlation effect and has a profound effect on its electron band structure, such as the material exhibits a special chiral charge density wave phase as the temperature of the system decreases. Its formation directly leads to the generation of electron orbital ring currents, which further induces a unique electron orbital magnetism, which ultimately causes the spontaneous time inversion symmetry in the material to be broken.

Figure 3: (a) As the direction of the magnetic field changes, the electromagnetic chirality effect changes suddenly, which means that the electron chirality of the material changes. (b) The theoretical model describes the chiral domain in the sample that changes due to the direction of the magnetic field.

In summary, these novel and unique physical effects make CsV3Sb5 a perfect sandbox for exploring the effects of related quantum physics, including the first discovery of controllable electronic chirality. Of course, so far this regulation still needs to be carried out at low temperatures and strong magnetic fields, but with the development of material physics, we may be able to achieve electronic chiral regulation at room temperature in the future. Obviously, such correlated electronic systems with geometric error have great research prospects in the future. (Source: Science Network)

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