Download Surface and bulk contributions to SHG from epitaxial topological

Annual
conference
Surface and bulk contributions to SHG from
epitaxial topological insulator films
Hui Shi1 Yu Zhang1 Mengyu Yao2 , Dong Qian2 Shan Qiao1 Weitao Liu1*
1State
Key Laboratory of Surface Physics, Phys. Dept., Fudan Univ., China;
2Phys.Dept., Shanghai Jiaotong Univ.,China
*[email protected]
I. Introduction & Motivation
Conventional transport
and optical techniques
lack surface specificity.
3D topological insulator(Tl):
Unsual surface states protected
by time reversal symmetry[1].
II. Purpose
Nonlinear optical techniques[2] -- surface specificity[3][4]
However, Bulk phase could still contribute to the signal[3].
 Identify the surface contribution to Second Harmonic Generation (SHG) of 3D Tls.
III. Theory
 Theory of nonlinear optics
 Separating surface and bulk contribution
 Modified characteristic matrices with nonlinear boundary conditions
Under the electric-dipole approximation
——Quantitatively calculate the local field of various thicknesses
under different measuring geometry.
Modified nonlinear electromagnetic boundary conditions:
In media with inversion symmetry:
Surface
Local field
Characteristic matrics:
Thin films of different thickness l
Bulk
Surface specificity
Reflected vs. transmitted signals
IV. Sample & Experimental results
 Surface and bulk contributions to SHG
 Crystal structure of Bi2Se3
 Anisotropy of reflected and transmitted SHG signals
Bulk symmetry: D3d
Surface symmetry: C3v
— Reflected
—
 Separation of the surface and bulk contributions
(Output/input/input)
L ~ Fresnel coefficient, which can be deduced from modified characteristic matrices.
Transmitted
centrosymmetric
A
 Linear spectrum of MBE film
Reflected & measured
Reflected & fitting
Transmitted & measured
Transmitted & fitting
B
E
F
Bulk single crystal
C
 Bulk refractive indices [4] apply to MBE film.
D
 Anisotropy of reflected and transmitted SHG signals are obviously different.
 According to Eq(1), there are two kinds of different attribute signals.
 Transport measurements
 Electric-double-layer transistors
(EDLTs) [Fig.G] based on
epitaxial films of Bi2Se3.
G
 Electrostatic gating and bulk
doping affect the SHG signals in
an reversed order [Fig.H,I].
V. Conclusion
References
I
H
 The surface response in SHG signals can be separated from that of the bulk.
 The anisotropic component of SHG signals is both sensitive to the change of the band structure and the carrier density.
[1] Hasan, M.Z., Kane, C.L. Reviews of Modern Physics, 82, 4, pp3045-3067(2010)
[3] D. Hsieh et al., Phys. Rev. Lett. 106, 057401 (2011)
[2] Y. R. Shen, The Principles of Nonlinear Optics (Wiley-InterScience, New York, 1984).
[4]. J.W.McIver, D.Hsieh, Physical Review B 86,035327(2012)