Field-Induced Weyl-Like Crossings and Longitudinal Magnetoconductivity in Dirac Systems

summary

The gist

The gist: The introduction of a pseudoscalar associated to longitudinal photons propagating along a magnetic field B could transforms a Dirac semimetal into a Weyl semimetal with a pair of Weyl nodes

In short

The study uses quantum electrodynamics to investigate how a magnetic field can induce Weyl-like crossings in Dirac systems, transforming them into Weyl semimetals with separated nodes. This topological transition is linked to a pseudoscalar invariant (${f E} imes{f B}$) that generates a chiral current, leading to negative longitudinal magnetoresistance and providing a link between electromagnetic response and transport.

Key concepts

Dirac/Weyl Semimetals: These are materials with linear energy dispersion for their charge carriers, described by Dirac or Weyl equations. They can exhibit unique electronic properties due to the presence of nodes in their energy spectrum, which are crucial for understanding topological phenomena like the one studied here.
Pseudoscalar Invariant (${f E} imes{f B}$): This term represents a combination of electric and magnetic fields that has a specific mathematical property. Its non-vanishing value is key because it drives the topological transition, causing a Dirac semimetal to change its fundamental electronic structure into one resembling a Weyl semimetal with distinct nodes.
Longitudinal Magnetoconductivity: This refers to how the electrical conductivity of a material changes when subjected to both an electric field and a magnetic field applied parallel to each other. The paper derives an analytical expression for this effect, showing it can be negative under certain conditions due to the chiral current generation.
Chiral Current Generation: This describes the process where the magnetic field and electric field together induce a net flow of charge that breaks the statistical balance of particle densities. This is a direct consequence of the topological transition, as it leads to a specific type of current that influences transport properties.

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This episode discusses

Field-Induced Weyl-Like Crossings and Longitudinal Magnetoconductivity in Dirac Systems · Paper Radio

The paper

Field-Induced Weyl-Like Crossings and Longitudinal Magnetoconductivity in Dirac Systems · Read on arXiv

Instituto Superior de Tecnologƭas y Ciencias Aplicadas Instituto de Cibernética, Matemƭica y F༿isica

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: We're looking at the paper: "Field-Induced Weyl-Like Crossings and Longitudinal Magnetoconductivity in Dirac Systems".

Mira: Here's the gist of the paper. The gist: The introduction of a pseudoscalar associated to longitudinal photons propagating along a magnetic field B could transforms a Dirac semimetal into a Weyl semimetal with a pair of Weyl nodes for each point of Dirac, leading to negative longitudinal magnetoresistance in Dirac systems via an axial anomaly relation Theoretical Framework A low-energy model is built to study systems such as Dirac/Weyl semimetals, according to statistical quantum electrodynamics formalism.

Kai: The paper investigates three-dimensional crystals with linear dispersion fermionic excitations, which are describe by the massless 3 + 1 Weyl and Dirac equations Topological Transition The introduction of a pseudoscalar, associated to longitudinal photons propagating along a magnetic field B, could transforms a Dirac semimetal into a Weyl semimetal with a pair of Weyl nodes for each point of Dirac.

Mira: The nodes are separated by a pseudovector electric field induced dynamically along B associated to a chiral effect on the Fermi surface A topological quantum transition is produced between a chiral-and non chiral symmetry phase.

Kai: This Fermi surface modification implies that a Dirac semimetal is transformed into a Weyl semimetal.

Paper summary: Kai: So to recap, this paper investigates three-dimensional crystals with linear dispersion fermionic excitations described by massless three + one Weyl and Dirac equations <ref:2402.16859#pg2,three-dimensional crystals with linear dispersion fermionic excitations>.

Mira: The thesis is that a specific pseudoscalar associated with longitudinal photons propagating along a magnetic field B can transform a Dirac semimetal into one with Weyl nodes, which are paired up for each point of the original Dirac system.

Lev: That transformation happens because there's a pseudovector electric field induced dynamically along B that has an effect on the Fermi surface, leading to this chiral-and non-chiral symmetry phase transition.

Kai: This implies a topological quantum transition between these two phases, which is the main mechanism driving the change in particle behavior.

Mira: The paper then shows how this leads to a general expression for longitudinal magnetoconductivity without needing an independent phenomenological internode relaxation time.

Lev: The crucial part they highlight is that the chiral contribution to this conductivity has an explicit B squared prefactor, and its coefficient depends on the magnetic field and temperature through Landau-level thresholds and Fermi-Dirac occupation factors.

Kai: They also found that the resulting conductivity exhibits a nonmonotonic magnetic field dependence, along with an inverse-temperature regime under appropriate conditions.

Mira: The main significance is that this provides a direct link between the longitudinal electromagnetic response, these field-induced Weyl-like crossings, and longitudinal magnetotransport in Dirac systems.

Lev: It's useful for understanding how to predict transport signatures in materials where we might have these kinds of topological phase boundaries driven by external fields.

Kai: So, they are using this to study things like Na3Bi and ZrTe5, which are real materials in the literature.

Conclusion: Kai: Looking at the paper, I think the real power here is how they tie these fundamental topological concepts—the Weyl nodes—to something incredibly measurable: the longitudinal magnetoconductivity.

Mira: They aren't just doing a calculation; they are proposing a mechanism where the field configuration dictates the topology of the system itself. It’s about controlling phase transitions using electromagnetism in condensed matter.

Lev: If this holds up, it means that you could potentially design materials where changing the magnetic field isn't just nudging some parameters around, but fundamentally altering what kind of excitations are allowed to propagate through them.

Kai: Exactly. It suggests that in systems like these Dirac semimetals, the external fields aren't just causing minor corrections; they’re driving a phase change where new types of nodes appear.

Mira: This has implications for designing sensors or devices where you need to precisely tune transport properties by applying magnetic fields at specific temperatures.

Lev: For error correction, it means we have to be careful because the underlying physics might shift entirely depending on the field strength you're dealing with, which affects how much overhead your code needs.

Kai: So, in short, this paper shows that longitudinal photons interacting with a magnetic field can engineer Weyl nodes and link that directly to measurable conductivity changes.

Mira: It’s a neat piece of condensed matter physics because it connects topology to transport observables in a very concrete way.

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