fractionalization and hidden symmetry in topological...
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Fractionalization and Hidden Symmetry in Topological Orders
ISSP, The University of Tokyo, Masatoshi Sato
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• MS, M.Kohmoto, Y.-S.Wu, “Braid Group, Gauge Invariance, and Topological Order”, Phys. Rev. Lett. 97, 010601, (2006).• MS, “ Topological discrete algebra, ground state degeneracy, and quark confinement”, Phys. Rev. D77, 045013, (2008).
•Mahito Kohmoto, ISSP, University of Tokyo•Yong-Shi Wu, Utah University
In collaboration with
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Outline
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1. What is topological order ?
2. Fractionalization (charge, statistics, quantum Hall effect) and hidden symmetry
3. Topological degeneracy
4. Hidden symmetry in quark unconfinement phase
5. Summary
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Gapped quantum phase with ground state degeneracy depending on topology of the system(topological degeneracy)
What is topological order? Wen ‘90
Topological orders cannot be understood by a conventional spontaneously symmetry breaking
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Ex.) fractional quantum Hall state
topological degeneracy
Laughlin state
Wen-Niu ‘90
• FQH states do not break symmetry of the Hamiltonian• They can be characterized by topological degeneracy.
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charge fractionalization
fractional anyon statistics
fractional quantum Hall effect
In the following, I present a simple connection between topological orders and fractionalization.
Ex.) Laughlin state
D.Arovas, J.Schrieffer, F.Wilczek, ‘84
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Outline
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1. What is topological order ?
2. Fractionalization (charge, statistics, quantum Hall effect) and hidden symmetry
3. Topological degeneracy
4. Hidden symmetry in quark unconfinement phase
5. Summary
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① The system is on a torus.② The system is gapped.③ Charge fractionalization occurs.
We consider the following 2+1d system
Fractionalization and hidden symmetry[Einarsson (90), Wen-Niu (90), Wen-Dagotto-Fradkin (90),Wu-Hatsugai-Kohmoto (91), Oshikawa-Senthil (06),MS-Kohmoto-Wu (06)]
quasiparticle excitation
anti-quasiparticle excitation
: charge of the constituent particle
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We consider the following three adiabatic processes on a torus
A) movement of i-th quasi-particle excitation along loops of torus
loop op.
B) exchange between i-th and (i+1)-th quasi-particle excitations
exchange op.
C) unit flux insertions through holes of torus
a unit flux
flux op.
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The spectrum of the system is invariant under these processes(in the thermodynamic limit).
constituent particle
AB phase
For c), this is because the constituent particle cannot detect the inserted unit flux.
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Laughlin (81)
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We can show that these processes satisfy the following algebra
MS.M.Kohmoto, Y.S.Wu (06)
① Braid Group
② Aharanov-Bohm effect
③ Schur’s lemma
loop op.
exchange op.
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Loop op. after flux insertion give rise to non-trivial AB phase
In a similar manner, we obtain
AB effect
loop op. after flux insertionAB phase
A quasiparticle with a fractional charge can detect the inserted unit flux.
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① Braid Group
② Aharanov-Bohm effect
③ Schur’s lemma
loop op.
exchange op.
These processes satisfy the following algebra
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commutes with all the braid group operators
Schur’s lemma
To obtain consistency between them,
By taking into account the AB effect,
In a similar manner, we can show
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① Braid Group
② Aharanov-Bohm effect
③ Schur’s lemma
loop op.
exchange op.
From these considerations, we completely determine the algebrasatisfied by these operators
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If we assume that the quasi-particle obeys abelian statistics, the algebra is simplified.
The solution of braid group is
① Braid Group② Aharanov-Bohm effect③ Schur’s lemma
Hidden symmetry from fractionalization
loop ops.
MS,Kohmoto,Wu (06)
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From the hidden symmetry, we can obtain these two results.
Topological degeneracy
Existence of nonzero Chern (or Thouless-Kohmoto-Nightingale-den Nijs) numbers of the wave function
fractional quantum Hall effect
nonzero Chern# of ground states
Niu-Thouless-Wu (84)
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nonzero Chern # of quasiparticle statesnonzero Chern # of quasiparticle states
Phase with fractionalization Phase with non-trivial topological #
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Outline
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1. What is topological order ?
2. Fractionalization (charge, statistics, quantum Hall effect) and hidden symmetry
3. Topological degeneracy
4. Hidden symmetry in quark unconfinement phase
5. Summary
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To count ground state degeneracy, we define Tx on the ground state as follows
pair-creation pair-annihilation
In a similar manner, we define Ty on the ground state
Topological degeneracy
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To be consistent with non-trivial hidden symmetry, the ground state must be degenerated.
The minimal ground state degeneracy is
Topological degeneracy
specific to torus geometry
MS,Kohmoto,Wu (06)
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Even for this definition of Tx and Ty, we have the same hidden sym.
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Outline
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1. What is topological order ?
2. Fractionalization (charge, statistics, quantum Hall effect) and hidden symmetry
3. Topological degeneracy
4. Hidden symmetry in non-abelian gauge theories
5. Summary
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Hidden symmetry in quark unconfinementphase
Question: Is it possible to generalize hidden symmetry to non-abelian gauge theories such as QCD ?
Answer: Yes
However, fractionalization of the constituent particle is not necessary, but unconfinement of quarks (fractionalization of baryon #) is enough.
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An important distinction from the previous argument is the existence of quatum fluctuations of gluon
insertion of flux coupled to baryon #
The spectrum is invariant under flux insertion
center of SU(3)
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1) If quark is unconfined, we have the non-trivial AB phase
quark
AB phase
2) On the other hand, if quark is confined, only trivial AB phase
baryon
AB phase
trivial
hidden symmetry
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Because the unit flux is reduced, the constituent particle can feel the inserted flux.
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quark loop op.
On D dimensional torus
flux op.
the minimal topological degeneracy
hidden symmetry
On the other hand, no topological degeneracy if quark is confined
MS (08)
c.f.) Z2 gauge theorySenthil-Fisher (01), Kitaev(02),
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The topological degeneracy obtained from hidden symmery is consistent with the Wilson’s criterion of quark confinement in the static limit of quarks
In the static limit, QCD reduces to pure YM theory, so the system on a torus has a (spatial ) center symmetry
① If quark is unconfined
perimeter law breaking center symmetry
② If quark is confined
area law preserving center symmetry
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Summary
Hidden symmetry is derived from fractionalization (charge fractionalization, fractional anyon statistics, FQH effect) .
Completely characterize a generic 2D Abelian topological order Formula for topological degeneracy on 2D torusNon trivial topological # of wave function
Hidden symmetry can be generalized to non-abelian gauge theories .
Topological degeneracy gives a gauge-invariant characterization of the quark (un)confinement phase ( in the zero temperature )
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