Topological New Fermions under Laser and New Topological Material Exploring via Machine Learning

Project Information

TNFL-TMML

Grant agreement ID: 793609

DOI

10.3030/793609

Project closed

EC signature date 27 February 2018

Start date 1 April 2018

End date 31 March 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 171 460,80

EU contribution

€ 171 460,80

Coordinated by

MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV
Germany

Periodic Reporting for period 1 - TNFL-TMML (Topological New Fermions under Laser and New Topological Material Exploring via Machine Learning)

Reporting period: 2018-04-01 to 2020-03-31

Summary of the context and overall objectives of the project

In this project, we focus on 3 topics: 1) the Floquet engineering of topological states, including the laser induced anomalous Hall conductance on monolayer graphene, and the topological phase transitions induced by the driving laser in magnetically doped topological insulator (TI) thin films; 2) the search of new topological states and electric engineering for antiferromagnetic (AFM) TI thin films; and 3) material searching via machine learning.
In the first and second topics, we aim to bring together 2 exciting fields of frontier condensed matter researches and material science: i) the studies of topological materials and ii) the novel control opportunities offered by strong lasers. In the last decade, tremendous progresses have been made in these fields both from theoretical and experimental points of views. The great success in this field further inspires new studies to understand the underlying physics and potential applications to use these exotic effects for electronic and spintronic device design. On the other hand, fast development of laser technology provides the possibility to control, modify, and steer the electronic properties of solid states precisely on ultra-fast (femto to pico-second) time scales in a reversible and flexible manner way beyond the possibilities in equilibrium. These properties of control are highly beneficial to many of the emerging quantum technologies. However, in this rich field theoretical approaches to describe the light matter interaction in topological systems and efficiently engineering the topological properties are urgently needed, which we will provide within our research endeavor.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main results are concluded following: we employed the quantum Liouville equation with phenomenological dissipation to investigate the transport properties of massless and massive Dirac fermion systems that mimics graphene and TIs, respectively. Graphene does not show an intrinsic Hall effect, but shows a Hall current under the presence of circularly-polarized laser fields as a nature of a optically-driven non-equilibrium state. Based on the microscopic analysis, we find that the light induced Hall effect mainly originates from the imbalance of photocarrier distribution in momentum space although the emergent Floquet–Berry curvature also has a non-zero contribution. In our last manuscript, we demonstrated that the magnetism in TI thin film could be dynamically manipulated via a Floquet engineering approach using circularly polarized light. Increasing the strength of the laser field, besides the expected topological phase transition, the magnetically doped TI thin film also undergoes a magnetic phase transition from ferromagnetism to paramagnetism, whose critical behavior strongly depends on the quantum quenching.
We systematically studied the electronic properties of Bi(111) thin films grown on a NbSe2 substrate. Combined with STM and the first-principles calculations, we found two types of non-magnetic edge structures coexist alternately at the boundaries of singe-bilayer islands, whose topological edge states exhibit remarkably different energy and spatial distributions. Prominent edge states are persistently visualized at the edges of both single and double bilayer Bi islands, regardless of the underlying thickness of Bi(111) thin films. Our work clarified the long-standing controversy regarding the topology of Bi(111) thin films and reveals the tunability of topological edge states via edge modifications. We also found that the dual-gate technology can well tune the electronic and topological properties of AFM even septuple-layer (SL) MnBi2Te4 thin films. Under an out-of-plane electric field, the Berry curvature of thin film could be engineered efficiently, resulting in a huge change of anomalous Hall signal. Beyond the critical electric field, the double-SL MnBi2Te4 thin film becomes a Chern insulator with a high Chern number of 3. These discoveries inspired the design of low-power memory prototypes for future AFM spintronic applications.
During the projects, we published four papers and one paper is under preparation. Our work was published in renowned Journals such like Physical Review Research, Physical Review B and New Journal of Physics
Furthermore the researcher participated in 7 dissemination activities i.e. conferences, seminars, invited talks and workshops in Germany, Spain, Belgium and USA (see list below) and also participated in the activities organized by the MPSD Theory Department for the DESY Open Day and Science Night, Hamburg, (2019 Nov.)

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Following the results that we have achieved, we continue to propose new way to manipulate the topological and electronic properties in the topological materials via non-equilibrium methods, such as the classic light and quantum light. When we apply the lase to solid states, the light will couple to electronic degrees of freedom directly or the quasiparticles. Therefore, we will distinguish two levels of accuracy of modeling the light field: either neglecting or keeping its quantum nature. In the former case one can model the light field simply as a periodic driving force on the electrons. This is sometimes referred to as Floquet engineering and has emerged as a viral field of physics. Our past studies are mainly focusing on the classic light tuning. And in our on-going project, we continue the research on this path, but use some different physical proposals, such as non-linear phononic control.
On the other hand, In the case where the full quantum nature of the light field is kept, i.e. one treats the particle nature of the photon, we require a theory of quantum electrodynamics and the treatment becomes much more complicated. However, this complication also comes with the benefit of enlarged possibilities of control. Hybrid light-matter states can display an interesting mixture of properties between the fermionic and bosonic ones. Exploring this so-called cavity-control is relatively young in the solid-state context and will be an ambitious goal in this proposal. We are going on in this field by using the experience grained from this project.

The Berry curvature induced by out-of-plane electric field shown in double-SL MnBi2Te4 thin films.