Questions tagged [weyl-semimetal]

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Validity of Random Phase Approximation in 2D/3D semimetals

In, for instance, this paper and this one the authors look at many-body effects in two- and three-dimensional semimetals, which have a low-energy quasiparticle dispersion relation of the form $\...
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Validity of kinetic theory

I am reading this paper, which uses (chiral) kinetic theory. The authors write: The Boltzmann method is valid only in the semiclassical limit, where $\omega_B \tau \ll 1$, $\omega_B \ll \mu$ and $\...
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Weyl Hamiltonian - Monopole in momentum space

Consider the Weyl Hamiltonian in momentum space: $$ \mathcal{H} = \hbar v_F \chi (\bf{\sigma}\cdot{\bf k}) , $$ where $\sigma^i$ are the Pauli matrices and $\chi$ the chirality of the Weyl node. ...
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What is the difference between metallicity and semimetallicity?

I am looking for a definition of semimetallicity from an experimental point of view ( $\rho(T)$, carrier density, mean free path, scattering time, etc.) and from a theoretical point of view. Can ...
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Are broken time reversal symmetry and inversion symmetry forbidden in a Weyl semimetal?

In much of the literature floating around, it is commonly implied that an important part of obtaining a Weyl semimetal phase is to break either time reversal symmetry or inversion symmetry. However, ...
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Weyl Semimetal and Fermi Velocity

In a Weyl semimetal, the Nielson-Ninomiya theorem enforces the fact that number of positive and negative chirality Weyl points must be equal. Is there any restriction on the form of the Weyl points? ...
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Model of Dirac semimetal without surface states?

There are continuum models of the 3D Dirac semimetal. For example, proposed in this paper, when $k_\pm=k_x\pm ik_y$ and $M=m-|\vec{k}|^2$, $$H=\begin{bmatrix} M & k_+ & 0 & 0 \\ k_- & -...
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PT-symmetry in Energy Band of Crystals

According to this source, it is proved that, in absence of spin-orbit coupling, spatial inversion symmetry (as a part of point-group symmetry which operates as $\hat{S}\psi(\vec{r})=\psi(-\vec{r})$) ...
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Is Weyl semimetal surface state gapless in finite size slab geometry?

For a Weyl semimetal with a pair of Weyl points along $z$ axis, let's consider a slab geometry that is only finite in, say, $x$ direction (infinite in $y,z$). Will the surface state still be gapless? ...
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Why and how Dirac cones are “tilted”?

Given a Weyl Hamiltonian, at rest, $ H = \vec \sigma \cdot \vec{p} $, A Lorentz boost in the x-direction returns $ H = \vec\sigma\cdot\vec {p} - \gamma\sigma_0 p_x $ The second term gives rise to a ...
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What is a Lifshitz phase transition?

In the context of Weyl semimetals, I often read the statement that a Lifshitz phase transition occurs when a Weyl cone is tilted so much that it tips over and crosses through the original Fermi level. ...
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Resources on Topological Insulators, Dirac and Weyl semimetals

I want to start studying about topological insulators and go all the way up to Dirac and Weyl semi-metals. What are some good resources(preferable textbooks if there are any) that cover these(don't ...
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“Mixed anomaly” in Weyl semimetal and its cancellation

The introduction to the problem Suppose the Weyl semimetal (read please briefly the definition before reading the question). Because of the effective nature of the chirality the parameters $b_{0}, \...
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Why Weyl fermion in Weyl semimetals (WSM) have high mobility only at low temperature?

I read several papers reporting high Weyl fermion with very high mobility in WSMs such as TaAs, NbAs, WTe2 and so on. However, this high mobility looks like (=Weyl fermion) always appears at only low ...
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What is a Fermi arc?

What is meant with a Fermi arc in the context of Weyl semimetals? Is this the just a one-dimensional Fermi surface? For example, in electron-doped graphene, the Fermi surface consists of 2 disjoint ...
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What is the reason for chiral anomalies in condensed matter systems?

If you consider a massless relativistic fermion theory and you perform a chiral transformation, then you realize that while the classical action remains invariant under this transformation the ...
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Chiral anomaly in Weyl semimetal

In the presence of electromagnetic fields $E$ and $B$, four current is not conserved in a Weyl semimetal i.e. $\partial_{\mu} j^{\mu}\propto E\cdot B \neq 0$. There are some proofs in the literature ...
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Chirality of Weyl Semimetal

For Weyl semimetal, the effective Hamiltonian reads: $$H=E_0 \mathbb{1} + v_0 \cdot \mathrm{q} \mathbb{1}+\sum_{i=1}^{3} \mathrm{v}_i \cdot \mathrm{q} \sigma_i$$ Why is the chirality given by $${\...