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Feb
4
answered Self-energy of a Fermi liquid
Feb
2
comment Edge states for SSH model?
@buzhidao No. Graphene is not a SPT. It is not gapped in the first place. Its edge state is not stable against disorder.
Feb
1
comment Edge states for SSH model?
@buzhidao The SSH model describes a 1D fermionic SPT state in the symmetry class AIII, so the protecting symmetry is $U(1)\times Z_2^S$, i.e. charge conservation and sub-lattice (chiral) symmetry. The symmetry acts as $U(1):c_i\to e^{i\theta}c_i$ and $Z_2^S:c_i\to(-)^i\mathcal{K}c_i^\dagger$. The sub-lattice symmetry is an antiunitary symmetry that has the effects of particle-hole transform. On the single particle level, the sub-lattice symmetry acts as a unitary operator that anticommute with the Hamiltonian.
Jan
26
reviewed Approve Photon-photon scattering matrix element
Jan
13
revised Green's function for 1 D hubbard model?
deleted 1 character in body
Jan
13
reviewed Approve Acceleration of log moving without slipping with/under a plank
Dec
31
awarded  Nice Question
Dec
23
awarded  Enlightened
Dec
23
awarded  Nice Answer
Dec
17
accepted Is there a 2D manifold on which the Dirac equation has a zero mode?
Dec
11
comment Is there a 2D manifold on which the Dirac equation has a zero mode?
@YingfeiGu I see. So I guess there must be some sense of chirality in order to have protected zero modes. Can the chirality be provided purely by the geometry of the manifold, without the help of gauge field?
Dec
7
comment Seemingly a paradox on the eigenstate thermalization hypothesis (ETH)
Yes, this requirement is general for any ETH state, as long as the region B is small compared to the whole system. You may even think $\rho_B=Z^{-1}e^{-\beta H_B}$ as an equivalent statement of ETH.
Dec
6
comment Is there any one lattice tight banding model (2D) hosts Dirac points as graphene does?
@buzhidao Eq (1) in the paper is exactly the same Hamiltonian as what I have written here. Just set $t_x=t_y=1$ and rename the fermions on A/B sublattice as $a$/$b$ fermion. Or as illustrated in Fig. 1(a) in the paper, it is the $\pi$-flux state with $\pi$ flux through every square. Note that $(-1)^x$ in my Hamiltonian is $1$ if $x$ is even ($a$ fermion), and is $e^{-i\pi}$ if $x$ is odd ($b$ fermion).
Dec
5
answered Is there any one lattice tight banding model (2D) hosts Dirac points as graphene does?
Dec
5
comment Helium 3 atoms as fermions?
Do you think proton is a fermion? If so, why shouldn't we worry about that proton is actually made of quarks there? I think it is the same idea that He3 atom as a whole can be considered as a single fermion, neglecting the internal structure. Because the energy scale in the superfluid problem is too low to resolve the internal structure of He3.
Dec
4
reviewed Approve Is it possible to learn about an event that occurred outside of your observable universe?
Dec
3
comment Dirac monopole of Berry curvature?
Nice answer. However I must say that Weyl nodes are not "low-energy quasi-particles excitations".
Dec
3
answered Dirac monopole of Berry curvature?
Dec
3
revised Why do Weyl points come in pairs in solid state system?
added 20 characters in body
Nov
13
reviewed Approve Simplified rolling tire problem - hollow shell vs solid?