Questions tagged [weyl-semimetal]
38 questions
20
votes
2 answers
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.
Hence my question: how is a Lifshitz phase…
Funzies
- 2,950
10
votes
2 answers
Berry curvature concentration around nodal points
It is well-known that in TI-symmetric semi-metals the Berry curvature on the Brillouin torus vanishes away from the nodal points (eg. [XCN10, III.B] [Van18, p. 105]).
But even for non-TI-symmetric semi-metals, the Berry curvature turns out, in…
Urs Schreiber
- 14,227
9
votes
1 answer
What is topological about topological (Dirac or Weyl) semimetals?
The following is my rough understanding of topological phases of matter (please let me know if it is incorrect.) Topologically ordered phases of matter are topological in the sense that they are determined by their topological excitations, and…
d_b
- 8,818
9
votes
2 answers
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? That is to say, given a pair of Weyl points, can…
Aaron
- 3,019
6
votes
0 answers
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 generating functional does not. The non-conservation of…
Hipparkhos
- 71
6
votes
1 answer
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 where this is proved with the machinery of…
S9G
- 135
5
votes
1 answer
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 tilt in the "light" cone of graphene. My doubts…
daemon
- 125
5
votes
0 answers
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
$${\rm sgn}(\mathrm{v}_1 \cdot \mathrm{v}_2 \times…
qc2014
- 541
4
votes
2 answers
Berry curvature flux around a Weyl node
How can I formally show (or at least argue) that, given the crystal Hamiltonian expansion around a Weyl node in a three-dimensional Brillouin Zone located at…
Milarepa
- 902
4
votes
1 answer
Resources on Topological Insulators, Dirac and Weyl semimetals
I want to start studying about topological insulators and go all the way up to Dirac and Weyl semi-metals. What are some good resources(preferable textbooks if there are any) that cover these(don't care If a resource does not cover all of these)? …
TheQuantumMan
- 8,020
4
votes
0 answers
What is a Fermi arc?
What is meant with a Fermi arc in the context of Weyl semimetals?
Is this the just a one-dimensional Fermi surface? For example, in electron-doped graphene, the Fermi surface consists of 2 disjoint circles. Can you then say that in this system, the…
Praan
- 1,167
3
votes
0 answers
Are broken time reversal symmetry and inversion symmetry forbidden in a Weyl semimetal?
In much of the literature floating around, it is commonly implied that an important part of obtaining a Weyl semimetal phase is to break either time reversal symmetry or inversion symmetry.
However, none of the literature I found seems to give a…
induvidyul
- 167
3
votes
1 answer
Application of Sommerfeld model on Weyl semimetals
I'm studying Solid State Physics. I know how to describe the Sommerfeld model, but I don't know how to apply it on Weyl semimetals.
The dispersion relation on Weyl semimetals is the following:
$$\varepsilon(\vec{k})=v_{F}\hbar k $$
I intend do…
Élio Pereira
- 1,102
2
votes
1 answer
Anomalous Hall Effect Saturation Field with Berry Curvature
Whenever you see anomalous Hall effect resistivity/conductivity vs. external magnetic field curves, there is always some low-field part with a greater slope that changes to a lesser slope at some characteristic field. In magnets, this low-field…
Nick Quirk
- 41
- 1
2
votes
1 answer
Weyl point? Weyl node?
I started studying Weyl physics in condensed matters, but I got confusing about the difference between the Weyl point and Weyl node. I understood that when the Weyl points connect continuously, the Weyl node is created. Is it right?
In addition, is…
Y. P
- 148