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Graduate Student - Experimental Condensed Matter Physics


Nov
27
awarded  Popular Question
Oct
10
revised Operator that takes us from one density matrix to another?
deleted 5 characters in body
Oct
10
comment Operator that takes us from one density matrix to another?
Hello Mark, thanks for your comment! For 3): Yes, that was a typo, I meant $M_{ij} = <i|M|j>$. For 1) and 2): I admit, I am confused. Let's say we have a STM tip with a single atom at the end and a sample that has a single atom on the surface. Then these two atoms have a spin. If you bring them close enough they can interact (e.g. through the Kondo effect) while at the same time electrons "flow" through the STM from the tip atom to the sample atom. Im struggling to find a way to describe how the electron goes from one state into the other.I will probably write more details in my question tmrw.
Oct
10
asked Operator that takes us from one density matrix to another?
Aug
14
comment How is a Majorana fermion created when a s-wave superconductors is in proximity to a topological insulator (e.g. via an antidot)
Thanks, Looks like a great piece of work!
Aug
13
comment How is a Majorana fermion created when a s-wave superconductors is in proximity to a topological insulator (e.g. via an antidot)
Hello Lababidi, I hope you finished your thesis and had a successful defense! Is there a way to take a look at it?
Aug
12
comment Why does electricity need wires to flow?
Your analogy is good! But why do you assume that the ball will "fall" to the ground of the pool? Depending on the material, the ball can also just float on top of the water or stay somewhere in the middle and dive around. If you increase the voltage, then the air will get ionized and can also conduct electrons, therefore it only depends on the energies and materials involved, but your analogy still holds in terms of a potential field. Even in vacuum, if the energy is high enough, you can create electrons and positrons (pair production).
Aug
11
revised How to transform mechanical work into electrical energy without using piezoelectricity?
edited body
Aug
11
comment How to transform mechanical work into electrical energy without using piezoelectricity?
Bitte ;) und viel Erfolg!
Aug
11
answered How to transform mechanical work into electrical energy without using piezoelectricity?
Jul
19
comment Where does the Berry phase of $\pi$ come from in a topological insulator?
Now I found this argument from Shoucheng Zhang: $\gamma \rightarrow \gamma + 2\pi n$ is invariant because we take it mod 2. Now here's the next step I don't understand: Time reversal takes $\gamma \rightarrow -\gamma$ which is true for $\gamma = 0$ or $\gamma = \pi$.
Jul
19
comment Where does the Berry phase of $\pi$ come from in a topological insulator?
Thanks for continuing this discussion. Yes, I agree that they are always connected. But the Berry phase is explicitly in this equation I posted, when you apply Stokes' theorem you can always bring it in this form: $\gamma = \oint\limits_{\partial(A + B)} d\textbf{k} \cdot \textbf{A} - \iint\limits_{A + B} dk_x dk_y \nabla \times \textbf{A}$.
Jul
18
comment Where does the Berry phase of $\pi$ come from in a topological insulator?
Thanks for pointing this out! Unfortunately he does not explain it in terms of the Berry connection, but he already assumes a correct Hamiltonian that immediately leads to a Dirac cone.
Jul
18
revised Where does the Berry phase of $\pi$ come from in a topological insulator?
added 532 characters in body
Jul
18
revised Where does the Berry phase of $\pi$ come from in a topological insulator?
added 532 characters in body
Jul
17
awarded  Promoter
Jul
9
revised Where does the Berry phase of $\pi$ come from in a topological insulator?
added 185 characters in body
Jul
8
asked Where does the Berry phase of $\pi$ come from in a topological insulator?
Jul
6
awarded  Commentator
Jul
6
comment Topological band structure, difference between a sphere and a donut
@Heidar. What would happen to the bulk-boundary correspondance if we don't have a torus but a sphere? Isn't this the crucial point, why we can consider Laughlin's argument and speak of a charge pump? Because the torus get's transformed into a cylinder due to the two contacts where we must measure the conductance with.