Axions, Weyl and Beyond

31 Aug 2023, 13:40 → 1 Sept 2023, 19:00 Asia/Seoul

The Westin Josun Busan (Busan, South Korea)

Deog Ki Hong (Pusan National University (KR)), Ki-Seok Kim (POSTECH), Sang-Jin Sin (Hanyang Universty)

We gather experts in particle physics and condensed matter physics to study a common theme around axion physics. With the dialogue at this workshop we seek possible future collaborations between two displines. 

Thursday 31 August

13:40 → 14:00 Registration and Opening remark (Deog Ki Hong)

14:00 → 14:45 Recent progress in Weyl and topological semimetals

Wey semimetal is an interesting class of topological materials that harbors chiral fermions as the low energy excitations. In this talk, I will give a comprehensive review of the Weyl semimetallic phase. Starting from exotic transport and experimental phenomena of such matter, I will discuss the dimensional hierarchy and the relation with the topological insulator phase in higher-dimensions. Finally, I will introduce the recent progress in the fields of topological semimetals that attempt to generalize the concept of Weyl fermions.

Speaker: Prof. Moon Jip Park (Hanyang University)

14:45 → 15:30 A Review of Axion Physics

Axion is one of the most compelling candidate particles for new physics beyond the Standard model. It is ubiquitous in a variety of well-motivated new physics scenarios and can address conundrums in the Standard Model, e.g., the strong CP problem. Indeed, research on axions is actively ongoing worldwide. In this talk, I will briefly overview axion physics and the current status of phenomenological research on axions. If I have enough time, I will introduce my recent work on ‘Axion magnetic resonance’.

Speaker: Dr Seokhoon Yun (University of Padova)

axo=ion_S.Yun.pdf

15:30 → 16:00 Coffee break

16:00 → 16:45 Exploring the nontrivial topology of topological metals using electrical and thermal transport

Experimental techniques to reveal the topology of materials and related properties are limited. Angle-resolved photoemission spectroscopy (ARPES) is a direct way to probe the band structure, but it cannot detect novel transport phenomena in a topological material. Electrical and thermal characterization techniques are therefore useful and necessary. In this talk, I will review experimental characterization methods based on electrical and thermal transports, and present some examples to show how these techniques reveal the nontrivial topological properties of materials. I will specifically emphasize the use of AC transport techniques, which can be used to investigate both the equilibrium properties of a system and the nonequilibrium steady state driven by AC perturbations. The discussions in this talk will demonstrate the power and usefulness of electrical and thermal transport measurements in revealing the topology of materials.

Speaker: Prof. Heon-Jung Kim (Daegu University)

16:45 → 17:00 discussions

17:00 → 17:45 Review on Axion search experiment

The axion is a hypothetical particle motivated from the Peccei-Quinn solution to the strong CP problem. Light axions, particularly those with masses below meV, exhibit feeble interactions with the standard model particles, rendering them compelling candidates for cold dark matter. Despite their flimsy interactions, numerous innovative methodologies have been proposed and implemented to directly detect their existence. In this presentation, we examine the physics of axions and introduce a range of proposed experimental approaches for dark matter axion searches.

Speaker: Dr Junu Jeong (CAPP, IBS)

Junu_AxionExpReview.pdf

Review of Axion Experiment

17:45 → 18:00 discussions

18:00 → 20:00 Dinner

20:00 → 20:45 Detecting axion dark matter with chiral magnetic effects

We show that dark matter axions or axion-like particles (ALP) induce spontaneously alternating electric currents in conductors along the external magnetic fields due to the (medium) axial anomaly, realizing the chiral magnetic effects. We propose a new experiment to measure this current to detect the dark matter axions or ALP. These induced currents are the electron medium effects, directly proportional to the axion or ALP coupling to electrons, which depends on their microscopic physics, and also suppressed by the Fermi velocity.

Speaker: Dr Sang Hui Ihm (CTPU, IBS)

20:45 → 21:00 Coffeee break

21:00 → 22:00 Brain Storming Discussions

Discussions on axions and Weyl metal

Speakers: Deog Ki Hong (Pusan National University (KR)), Prof. Ki-Seok Kim (POSTECH)

Friday 1 September

09:00 → 09:45 Topological Fermi-liquid theory: Dynamics of collective modes and their instabilities in Weyl metals (Role of emergent axions in interacting Weyl metals)

1. Introduction of topological classification of electronic band structure based on historical perspectives: Paper reviews
   2.Emergent axions in ferromagnetic Weyl metals, antiferromagnetic topological insulators, and superconducting Weyl metals: From microscopic lattice models to effective field theories with symmetry breaking ➔ Novel non-equilibrium phase transitions
2. Introduction of Berry curvature into Landau’s Fermi-liquid theory = Topological Fermi-liquid theory (Haldane): Dynamics of l=1 & l=2 collective modes and their instabilities in interacting Weyl metals
3. Role of effective axion dynamics in potential instabilities of topological Fermi liquid theory: Generalization of composite Fermion theory in two spatial dimensions (From EM CS + gravitational CS + Wen-Zee CS to EM theta + gravitational theta + mixed anomaly theta terms)

Speaker: Prof. Ki-Seok Kim (POSTECH)

09:45 → 10:30 A Short Review of Time-Resolved and Angle-Resolved PES Studies on a few Weyl Systems

In this short review presentation, I would like to talk about the basic concept of time-resolved photoemission and angle-resolved photoemission spectroscopy as the fittest observation tool for Dirac/Weyl systems, and present a few prototypical successful examples in chronological order to observe Dirac/Weyl quasi-particles in condensed matter systems via TR-/ARPES, expecting vivid discussion for the future research direction.

Speaker: Prof. Han-Jin Noh (Chonnam National University)

10:30 → 11:00 Coffee break

11:00 → 11:45 Generalized Global Symmetries of Axion

In this talk, I will describe various generalized global symmetries of axion-Maxwell theory.
This includes 0-, 1-, and 2-form symmetries, non-invertible symmetries and 3-group symmetry. If time permits, I will briefly mention how the symmetry structure changes for axion-YM and axion-QCD theory.

Speaker: Prof. Sungwoo Hong (KAIST)

11:45 → 12:00 discussions

12:00 → 14:00 Lunch

14:00 → 14:45 Weyl Fermion in holography and the fate of the topology under the presence of the strong interaction.

We examine how to realize the Weyl Fermion in holography, which describe a strongly interacting system. We then study whether the topology of the Weyl Fermion realized in holographic set up to answer the question whether it remains in the presence of the interaction. Finally, we try to understand the topology as a consequence of the symmetry breaking.

Speaker: Prof. Sang-Jin Sin (Hanyang University)

14:45 → 15:30 Axions and atomic spectra

Speaker: Deog Ki Hong (Pusan National University (KR))

15:30 → 16:00 Coffee break

16:00 → 17:00 Brain storming discussions

Speaker: Deog Ki Hong (Pusan National University (KR))