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location Nanjing, China
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visits member for 2 years, 4 months
seen Apr 6 at 10:00

Hi, my name is Kai Li (李凯 in Chinese). Now I'm a doctor in the group of Prof.Jian-Xin Li(李建新), in Nanjing university, China.

Currently, I focus on the interplay of symmetry, gauge structure, topology, and quantum entanglement in condensed matter theory.


Apr
8
awarded  Popular Question
Apr
6
comment Questions on the elementary excitations in the resonating-valence-bond(RVB) states?
Here is a very nice answer by Prof.Wen on overflow: physicsoverflow.org/6327/…
Apr
6
revised Questions on the elementary excitations in the resonating-valence-bond(RVB) states?
edited tags
Apr
6
comment How to understand the entanglement in a lattice fermion system?
Here is a very nice answer by Prof.Wen on overflow: physicsoverflow.org/6359/…
Apr
6
revised How to understand the entanglement in a lattice fermion system?
edited tags
Apr
6
comment Interacting fermionic SPT phases in 2d with time-reversal symmetry
Thanks a lot. Naively thinking, if the fermion Hamiltonian contains terms like $c+c^\dagger$, then it seems that the fermion-number-parity symmetry is explicitly broken, does this situation make sense?
Apr
5
comment Interacting fermionic SPT phases in 2d with time-reversal symmetry
Hi Everett, I have some confusions:(1).As to the notation $Z_2^T$ with $T^2=-1$, the symmetry group generated by TR symmetry seems to be $Z_2^T=[1,T,T^2,T^3]$, which is in fact a $Z_4$ group, so why don't we use the notation $Z_4^T$ instead of $Z_2^T$? (2). Is the fermion-number-parity symmetry mentioned in your comments same as the particle-hole symmetry in the classification table? And should we distinguish them? Thank you very much!
Mar
29
comment Topological ground state degeneracy of SU(N), SO(N), Sp(N) Chern-Simons theory
@Idear And does the level index k=2C (C is the band Chern-number)? Thank you very much!
Mar
29
comment Topological ground state degeneracy of SU(N), SO(N), Sp(N) Chern-Simons theory
@Idear Dear Idear, I don't understand the Chern-Simons theory at all, and here I have a naive question: Consider the Schwinger-fermion mean-field (MF) approach to a lattice spin-1/2 model, if the fermionic MF Hamiltonian describes a spin-liquid (SL) ground-state (GS), where the Invariant Gauge Group (IGG) is IGG=SU(2) and it has a band Chern-number C=2 (assuming the MF Hamiltonian has two no-crossing energy bands, one is positive and the other is negative). Does this imply that the low energy effective theory of this SL GS is a $SU(2)_4$ Chern-Simons theory?
Mar
23
revised What is the first excited state of the honeycomb Kitaev model in its gapped phase?
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Mar
23
revised What is the first excited state of the honeycomb Kitaev model in its gapped phase?
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Mar
20
revised Two puzzles on the Projective Symmetry Group(PSG)?
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Mar
15
comment A naive question about topologically ordered wavefunction?
I see, thank you very much.
Mar
15
comment A naive question about topologically ordered wavefunction?
As to the honeycomb Kitaev model, for the gapless phase (e.g., gapless spin Hamiltonian at $J_x=J_y=J_z$), is the corresponding ground-state also gapless (in the sense that some kind of correlation-length is large as compared to the system size)? If the ground-state is gapless, then is the TEE(=$-ln2$) still well defined?
Mar
15
accepted A naive question about topologically ordered wavefunction?
Mar
15
comment A naive question about topologically ordered wavefunction?
Thanks a lot for your insightful comments and suggested references. The former part in your answer seems deep to me and I may spend more time to understand it. However, I learned from you that the definition of a gapped state $\psi$ is via the correlation length rather than some parent Hamiltonian $H$. So is there a possibility or an example that a gapless Hamiltonian possesses a gapped ground-state?
Mar
15
revised A naive question about topologically ordered wavefunction?
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Mar
14
revised A naive question about topologically ordered wavefunction?
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Mar
14
asked A naive question about topologically ordered wavefunction?
Mar
12
comment Why we call the ground state of Kitaev model a Spin Liquid?
@Xiao-Gang Wen Thank you Prof.Wen. How to see "there is no symmetry breaking in the ground state of Kitaev model" under periodic boundary conditions(PBC)? For example, under open boundary conditions, the ground state is unique and hence preserve all the symmetries of the Hamiltonian; while under PBC, there is a 4-fold ground state degeneracy due to the $Z_2$ gauge structure, and how to understand "no symmetry breaking" in this case. Thank you very much.