Nome
Anomalous collective modes in Weyl semimetals

Código
2023.15319.PEX

Entidade Beneficiária

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Sumário do Projecto

Recent progress in the field of topological materials results in new opportunities to study emergent phenomena resembling
effects predicted in the context of the Standard Model of particle physics and cosmology. One prominent example is the axial
anomaly manifested through the negative magnetoresistance in Weyl semimetals. Notably, the very same systems can give
access to another effect of a similar nature but never probed experimentally before – the scale or conformal anomaly. In this
project, we propose to study the material realization of the scale anomaly, the related thermoelectric transport, and novel
anomalous collective excitations such as axions and dilatons.
The word "anomaly", in this context, refers to a quantum violation of a classical symmetry. The axial anomaly violates the chiral
symmetry, and related conservation of the axial charge, the difference between the number of right- and left-handed fermions. In
many-body systems, it leads to novel transport phenomena, e.g. an electric current along the magnetic field direction, known as
the negative magnetoresistance in the context of Weyl semimetals or chiral magnetic effect in high-energy physics. In turn, the
scale anomaly violates the conformal invariance, resulting in a non-zero trace of the stress-energy tensor. This modification may
lead to an anomalous contribution to the Nernst effect, and affects the energy-momentum transport in the system.
Recently, it has been shown that the axial anomaly may result in novel axionic mode in Weyl semimetals. This fermion pairing originates in the large distance properties of the anomalous Feynman diagram and corresponding three-point correlation function.
In turn, it is well known that the scale anomaly exhibits the same feature at large distances, and a similar scale anomalous mode
is well-expected to exist. However, this mode, similar to a hypothetical particle, dilaton, widely discussed in the context of
cosmology and astroparticle physics, has not been identified yet, and this is one of the primary goals of the present proposal.
In this proposal, we will extend the EFT description of low-lying excitations in Weyl semimetals, taking into account the effects
sourced by the scale anomaly. We will rely on the EFT approach to the collective axion built by the PI, and include the axionic and
dilatonic modes in Weyl semimetals into the same theoretical framework. We will further investigate the phenomenological
implications of the new excitations in realistic systems, and seek for suggestions for experimental tests.
This ambitious proposal aims to make a major impact, going far beyond the state-of-the-art picture of Weyl semimetals and
suggesting a completely new realization for dilaton. It is structured into four sufficiently independent but synergetic tasks:
(1) Scale anomaly in 2D systems: In 1+1 dimensional (2D) theories, the two anomalies compete, resulting in two possible fermion
pairings. Either of the resulting (pseudoscalar or scalar) bosonic modes are gapless, and saturate the corresponding largedistance
behavior of the 2D anomalous correlators. Utilizing the similarity between the anomalies and studying the scale anomaly
mode in lower-dimensional systems, we will learn about many-body realization of the scale anomaly.
(2) Scale anomaly in 4D systems: Building the EFT description for the low-energy dynamics in Weyl semimetals in the presence of
the scale anomaly, we will identify the key properties of the many-body state supporting the dilatonic mode. Generalizing such a
state to the 4D case, we will study the dynamics of these novel modes, appearing in the system, and related transport
phenomena. We will further construct a unified EFT description for the anomalous modes in 4D.
(3) Phenomenological implications: We will search for potential experimental tests to probe the novel collective modes and
related phenomena in Weyl semimetals. We will attempt to estimate the qualitative effects, sourced by the axionic and dilatonic
modes, further motivating the experimental search in realistic materials.
(4) High-energy sensing: Systems with collective axionic and dilatonic modes could be used to probe the presence of a variety of
hypothetical particles. The resonant transformation of the cosmic axion-like particles or scalar dark matter candidates in Weyl
materials may serve as the basis for the next generation of particle physics experiments. Here, we will consider these
opportunities, relying on the theoretical description developed in the project.

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Suporte sob

Reforçar a investigação, o desenvolvimento tecnológico e a inovação

Região de Intervenção

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Financiamento

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Datas

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