20140328 TNTL journal club axion electrodynamics, TI-FI interface (nomura, nagaosa)
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Transcript of 20140328 TNTL journal club axion electrodynamics, TI-FI interface (nomura, nagaosa)
TNTL Journal Club
Dongwook Go
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Kentaro Nomura and Naoto Nagaosa
Phys. Rev. Lett. 106, 166802 (2011)Surface-Quantized Anomalous Hall Current and the Magnetoelectric Effect in Magnetically Disordered Topological Insulators
Phys. Rev. B 82, 161401(R) (2010)Electric charging of magnetic textures on the surface of a topological insulator
1
Topological Insulator
Xia et al., (2008), Hsieh, Xia, Qian, Wray, et al., (2009), and Xia, Qian, Hsieh, Wray, et al., (2009). 2
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Hsieh, Xia, Qian, Wray, et al., (2009), Xia, Qian, Hsieh, Shankar, et al., (2009), and Wray et al., (2010).
Topological Insulator
3
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Topological Field Theory
Tight-binding + EM field (minimal coupling limit)
Chern-Simon’s Term (3+1 D)
Integrate-outFermionic DOF
X.-L. Qi et al., PRB (2008).
Time Reversal Symmetry
→ 𝑃3 𝑥, 𝑡 = 0 or 1/2 mod 1
Natural unit ( =c=1)
4
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
1. Half-integer quantum Hall effect2. Topological magnetoelectric effect3. Induced magnetic monopole4. Faraday rotation
Consequences from the Chern-Simon’s term
5
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
X.-L. Qi et al., PRB (2008), Science (2009).
1. Half-integer quantum Hall effect2. Topological magnetoelectric effect3. Induced magnetic monopole4. Faraday rotation
6
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Consequences from the Chern-Simon’s term
X.-L. Qi et al., PRB (2008), Science (2009).
Half-Integer Quantum Hall Effect
Surface Chern-Simon’s term
z-integration
𝑛 ∈ ℤ depends on non-topological details of surface
TI
FI𝟎
𝒛
7
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
X.-L. Qi et al., PRB (2008).
Half-Integer Quantum Hall Effect
𝑗𝜇 =𝛿𝑆𝑠𝑢𝑟𝑓
𝛿𝐴𝜇
𝜎𝐻 =1
2𝜋𝑛 +
1
2
𝜎𝐻 =1
4𝜋sgn(𝑚𝑧)
Natural unit ( =c=1)
8
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
e.g. Massive Dirac Fermion
X.-L. Qi et al., PRB (2008).
9
Topological Magnetoelectric Effect
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Applied Electric Field
Hall Current
Magnetization
Applied Magnetic Field
Induced Electric Field
Charge Polarization(from the Hall current)X.-L. Qi et al., PRB (2008).
10
Topological Magnetoelectric Effect
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
(Gaussian CGS unit)𝜎𝐻 =𝑒2
ℎ𝑐𝑛 +
1
2
From the previous result,
X.-L. Qi et al., PRB (2008).
11
Axion Electrodynamics
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
where , , and
Variation over leads to
X.-L. Qi et al., PRB (2008).
12
Axion Electrodynamics
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
where and
X.-L. Qi et al., PRB (2008).
13
Other Examples
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Faraday Rotation Inducing Magnetic Monopole
X.-L. Qi et al., PRB (2008), Science (2009).
14
T-symmetry Broken Surface State
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
1. External Magnetic Field2. Magnetic Bilayer3. Magnetic Impurity Doping
K. Nomura and N. Nagaosa PRL (2011), PRB Rapid (2010).
15
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Difficulties in realizing TME
1. Get rid of carriers in the bulk
2. Tune the Fermi energy within the gap of surface Dirac cone
3. Attach the insulating ferromagnetic layer with the magnetization perpendicular to the surface
L.-X. Qi et al., PRB (2008).
17K. Nomura and N. Nagaosa PRL (2011).
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Localization of surface states by magnetic impurities
, where
Impurity-averaged Hamiltonian
Exchange interaction betweenmagnetic impurities and electrons
18
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Localization of surface states by magnetic impurities
Gaussian impurity correlation
Random magnetic impurity
Impurity strength ~ 𝑚 :
K. Nomura and N. Nagaosa PRL (2011).
19
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Localization of surface states by magnetic impurities
Full Hamiltonian
=
K. Nomura and N. Nagaosa PRL (2011).
20
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Localization of surface states by magnetic impurities
Numerical Simulation Result
K. Nomura and N. Nagaosa PRL (2011).
21
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Localization of surface states by magnetic impurities
Scaling Analysis
K. Nomura and N. Nagaosa PRL (2011).
22
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Moving a Domain Wall
Electric dipole energy
Uniform magnetization configuration can be achieved!
Larger than other (Zeeman, anisotropy …) energy scales.
K. Nomura and N. Nagaosa PRL (2011).
QH regime
Implication : TME can be realized.
23
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Summary of the previous work
Role of quenched magnetic disorder?
K. Nomura and N. Nagaosa PRL (2011).
24
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Spin textures are charged on TI
K. Nomura and N. Nagaosa PRB Rapid (2010).
Fictitious gauge field Electric field
Magnetic field
Electric charging from spin textures!
QH regime Hall current
Charge pumping
25
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Spin textures are charged on TI
Vortex Domain wall
K. Nomura and N. Nagaosa PRB Rapid (2010).
26
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Derivation : functional path integral approach
K. Nomura and N. Nagaosa PRB Rapid (2010).
(1) Fermion Part
where
27
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Derivation : functional path integral approach
K. Nomura and N. Nagaosa PRB Rapid (2010).
(2) Magnetization Part
+ (anisotropy, DMI … )
28
(3) Integrate-out Fermionic DOF
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Derivation : functional path integral approach
where
K. Nomura and N. Nagaosa PRB Rapid (2010).
, (2+1 D CS term)
29
where
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Derivation : functional path integral approach
K. Nomura and N. Nagaosa PRB Rapid (2010).
Electric charging from spin textures!
Electromagnetic Duality
30
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
K. Nomura and N. Nagaosa PRB Rapid (2010).
L.-X. Qi, Science (2009).
,
generalization of dyons
31
Vortices
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
𝑞 ∈ ℤ, vortex charge
K. Nomura and N. Nagaosa PRB Rapid (2010).
32
Only vortices with 𝑞 = 1, have finite total charge.
Vortices
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Vortex (𝑞 = 1) – anti-vortex (𝑞 = −1) symmetry is broken on TI.
K. Nomura and N. Nagaosa PRB Rapid (2010).
33
Domain Walls
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
K. Nomura and N. Nagaosa PRB Rapid (2010).
Neel wall is charged :
cf. Total charge of Bloch wall =0
34
Domain Walls
K. Nomura and N. Nagaosa PRB Rapid (2010).
As DW velocity is given as under a magnetic field,
Electric field induces DW motion
With typical parameters,
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
35
Summary of the previous work
28 March 2014, Journal Club @ Theoretical Nanoscale Transport Lab, POSTECH
Spin textures are electrically charged on TI, so an electric field can induce motion of spin textures, such as DW.