- 1 -
Workshop on Simulation and Modeling
of Emerging Electronics (SMEE) 2017
January 11 – 13, 2017
Lecture Theatre P2, LG1/F, Chong Yuet Ming Physics Building, HKU
Organizing Committee
Jian Wang (HKU)
Hong Guo (HKU & McGill U.)
Guanhua Chen (HKU)
Fuchun Zhang (HKU & Zhejiang U.)
Yin Wang (HKU)
Jian Sun (HKU)
Sponsored by
Area of Excellence Project (AoE/P-04/08)
- 2 -
Scientific Program (tentative)
SMEE2017 Program
Wednesday, January 11, 2017
Chairperson: Prof. Hong Guo
08:30 - 09:00 Registration
09:00 - 09:05 Welcome Address: Jian Wang, The University of Hong Kong
09:05 - 09:20 Photo taking
09:20 - 10:05 Keynote Speech 1: James R. Chelikowsky, University of Texas
Computational Tools for Predicting the Properties of Nanostructures
10:05 -10:30 AoE Speech 1: Weng-Cho Chew, University of Illinois at Urbana-Champaign
Quantum Electromagnetics: A New Look
10:30 - 11:00 Tea Break
11:00 - 11:45 Keynote Speech 2: Zhong Fang, Institute of Physics, CAS
Topological Electronic States and Materials
11:45 - 12:10 Invited Speech 1: Wei Ji, Renmin University of China
Interlayer couplings in two-dimensional materials
12:00 - 14:00 Lunch Break
Chairperson: Prof. Xiaodong Cui
14:00 - 14:45 Keynote Speech 3: Robert Wolkow, University of Alberta
Toward Atom Scale Ultra Low Power Classical Circuitry and Quantum Circuitry
14:45 - 15:30 Keynote Speech 4: Xiaofeng Jin, Fudan University
The Spin Hall effect Learnt from the Anomalous Hall Effect
15:30 - 16:00 Tea Break
16:00 - 16:45 Keynote Speech 5: Hongqi Xu, Lund University
Semiconductor Nanowires: Band Structures and Potential Applications in
Nanoelectronics, Optoelectronics and Quantum Technologies
16:45 - 17:10 AoE Speech 2: Xiaodong Cui, The University of Hong Kong
Spin polarization in monolayer tungsten dichalcogenides
- 3 -
Thursday, January 12, 2017
Chairperson: Prof. Wei Ji
09:00 - 09:45 Keynote Speech 6: Tim Mueller, Johns Hopkins University
The effective use of data in materials research
09:45 - 10:30 Keynote Speech 7: Isaac Tamblyn, National Research Council of Canada
Deep learning and computer simulation - learning approximate solutions for rapid
prediction
10:30 - 11:00 Tea Break
11:00 - 11:45 Keynote Speech 8: Christian Flindt, Aalto University
Electron Waiting Times in Mesoscopic Conductors
11:45 - 12:10 Invited Speech 2: Tue Gunst, Technical University of Denmark
Flexural phonon scattering induced by electrostatic gating in graphene
12:00 - 14:00 Lunch Break
Chairperson: Prof. Hong Guo & Jian Wang
14:00 - 15:00 Free Discussion
15:00 - 18:00 Hiking
18:00 - 22:00 Banquet
- 4 -
Friday, January 13, 2017
Chairperson: Prof. Wang Yao
09:00 - 09:45 Keynote Speech 9: Gerrit E.W. Bauer, Tohoku University
Aspects of magnon-phonon transport in magnetic insulators
09:45 - 10:30 Keynote Speech 10: Ke Xia, Beijing Normal University
Magnon-phonon interaction in YIG and effective spin mixing conductance of YIG-
metal interfaces
10:30 - 11:00 Tea Break
11:00 - 11:45 Keynote Speech 11: Can-Ming Hu, University of Manitoba
Cavity Spintronics
11:45 - 12:10 AoE Speech 3: Wang Yao, The University of Hong Kong
Nano-patterned superstructures of topological insulators in the Moire superlattices of
vdW heterobilayers
12:00 - 14:00 Lunch Break
Chairperson: Prof. Jian Wang
14:00 - 14:45 Keynote Speech 12: Xincheng Xie, Peking University
Dephasing and disorder effects in the topological systems
14:45 - 15:30 Keynote Speech 13: Wei Lu, Shanghai Institute of technical physics, CAS
Sub-wavelength opto-electronic device for space application
15:30 - 16:00 Tea Break
16:00 - 16:25 Invited Speech 3: Chao-Cheng Kaun, Academia Sinica
Conductance of Single Molecules on an Insulating Surface
16:25 - 16:50 AoE Speech 4: Hong Guo, McGill University
Applicability of the Chebyshev filtering method in DFPT
16:50 - 17:00 Closing Remarks: Hong Guo, McGill University & The University of Hong Kong
- 5 -
Keynote Speech 1:
Computational Tools for Predicting the Properties of Nanostructures
James R. Chelikowsky
Center for Computational Materials, Institute for Computational Engineering Sciences,
Departments of Physics and Chemical Engineering, University of Texas, Austin, TX 78712
One of the most challenging issues in materials physics is to predict the properties
of matter at the nanoscale. In this size regime, new structural and electronic properties
exist that resemble neither the atomic, nor solid state. These altered properties can have
profound technological implications as quantum confinement can change the role of
“bulk dopants.” Theoretical methods to address such issues face formidable challenges.
Nanoscale systems may contain thousands of electrons and atoms, and often possess
little symmetry. I will illustrate recent computational advances in this area based on a
real space implementation of pseudopotential-density functional theory. Such methods
can be ideally suited for computing the properties of nanostructured matter. I will
present an overview of our work on new algorithms for this problem and how they can
be applied to nanostructures. Specifically, I will examine the role of quantum
confinement as a function of size and dimensionality, and its role in doping and self-
purification. I will also examine the evolution of interfacial properties at the nanoscale
by focusing on the creation of Schottky barriers wherein we find a fundamental shift
from a “Mott regime” to a “Bardeen” regime.
- 6 -
AOE Speech 1:
Quantum Electromagnetics: A New Look W. C. Chew* and W. E. I. Sha†
*University of Illinois at Urbana-Champaign
†The University of Hong Kong
First, we emphasize the importance of Maxwell’s equations (1865) which have withstood the
test of length scales, special relativity (1905), and quantum theory (1927). Moreover, a
differential geometry description of Maxwell’s equations (1945) had inspired the Yang-Mills
theory (1954), also known as the generalized electromagnetic theory. Its quantum description
(quantum electrodynamics) has inspired quantum field theory. Vacuum space consists of
electron-positron (e-p) pairs that represent nothingness. But when an electromagnetic wave
passes through vacuum, the e-p pairs are polarized to form simple harmonic oscillators. The
propagation of electromagnetic waves through vacuum is due to the coupling of these simple
harmonic oscillators [1]. From this concept, the quantum Maxwell’s equations are derived to
be:
∇ × �̂�(𝐫, 𝑡) − 𝜕𝑡�̂�(𝐫, 𝑡) = �̂�𝑒𝑥𝑡(𝐫, 𝑡), ∇ × �̂�(𝐫, 𝑡) + 𝜕𝑡�̂�(𝐫, 𝑡) = 0, (1)
∇ ⋅ �̂�(𝐫, 𝑡) = �̂�𝑒𝑥𝑡(𝐫, 𝑡), ∇ ⋅ �̂�(𝐫, 𝑡) = 0, (2)
The Green’s function technique applies when the quantum system is linear time
invariant. Hence, past knowledge in computational electromagnetics can be invoked to arrive
at these Green’s functions. These quantum Maxwell’s equations portend well for a better
understanding of quantum effects that are observed in many branches of electromagnetics, as
well as in quantum optics, quantum information, communication, computing, encryption and
related fields. More details about this work can be found in [2-6]. Hence, the combination of
computational electromagnetics with quantum theory is cogent for the development of
computational quantum electromagnetics/optics.
In this talk, a new look at the quantization of electromagnetic field will be presented.
Examples of field-atom interaction using semi-classical calculation as well as fully quantum
calculation will be presented. Connection with computational electromagnetics in these
calculations will be pointed out.
References
[1] T. Lancaster and S. J. Blundell, Quantum Field Theory for the Gifted Amateur, OUP Oxford, 2014.
[2] Y. P. Chen, W. E.I. Sha, W. C. H. Choy, L. J. Jiang, and W. C. Chew, \Study on Spontaneous Emission
in Complex Multilayered Plasmonic System via Surface Integral Equation Approach with Layered Medium
Green’s Function," Optics Express, vol. 20, no. 18, pp. 20210-20221, Aug. 2012.
[3] C. J. Ryu, A. Y. Liu, W. E. I. Sha, and W. C. Chew, \Finite-Difference Time-Domain Simulation Of The
- 7 -
Maxwell-Schrodinger System," IEEE JMMCT, vol. 1, pp. 40-47, Sep. 2016.
[4] W. C. Chew, A. Y. Liu, C. Salazar-Lazaro, and W. E. I. Sha, \Quantum Electromagnetics: A New Look,
Part I," accepted by IEEE JMMCT.
[5] W. C. Chew, A. Y. Liu, C. Salazar-Lazaro, and W. E. I. Sha, \Quantum Electromagnetics: A New Look,
Part II," accepted by IEEE JMMCT.
[6] W. E. I. Sha and W. C. Chew, \Dissipative and Dispersive Quantum Electromagnetics: A Novel Approach,"
in press.
- 8 -
Keynote Speech 2:
Topological Electronic States and Materials
Zhong Fang
Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
The rapid development in the field of topological states is due both to
conceptual theoretical advances, and to the discoveries of realistic materials where
these exotic states can be hosted. First principles calculations play important roles in
this field. On the theoretical front, the calculations and understanding of Berry
curvature and gauge field established the connection between topology and electronic
structures. On the experimental side, most of materials discovered up to now in this
field are stimulated by computational predictions. In this talk, I will review recent
progresses in this field, with focus on topological semimetals, and address some
recent theoretical and experimental results.
- 9 -
Invited Speech 1
Interlayer couplings in two-dimensional materials
JI, Wei
Department of Physics, Renmin University of China, Beijing 100872, China
In this talk, I briefly summarize our recent progresses on the modelling
of interlayer interactions of various two-dimensional materials, e.g. weakened
van der Waals interaction in twisted graphene1 and ReS22, covalent-like quasi-
bonding in PtS23/PtSe2
4 and BP5,6, and subtle balance between inter- and intra-
layer interactions in organic molecules7. In addition, air stability of BP was
theoretically and experimentally investigated, which reveals the atomic details
for the air degradation of BP8.
References: 1Jiang-Bin Wu et al., ACS Nano 9 (7), pp 7440–7449 (2015).
2Xiaofeng Qiao et al., Nanoscale 8, 8324-8332 (2016)
3Yuda Zhao et al., Advanced Materials 28 (12), 2399–2407 (2016)
4Yuda Zhao et al., Advanced Materials, DOI: 10.1002/adma.201604230
5Jingsi Qiao et al., Nature Commun. 5, 5475 (2014)
6Zhxin Hu et al., Nanoscale 8, 2740 (2016)
7Yuhan Zhang et al., Phys. Rev. Lett. 116, 016602 (2016)
8Yuan Huang et al., Chem. Mater., 28 (22), pp 8330–8339 (2016)
- 10 -
Keynote Speech 3:
Toward Atom Scale Ultra Low Power Classical Circuitry and Quantum Circuitry
Robert Wolkow
Department of Physics, University of Alberta and National Institute for Nanotechnology,
Edmonton, Alberta Canada
Decades of academic study of silicon with scanned probe and related techniques
have made it possible to now envisage a silicon-based, atom-scale, ultra-low power
circuitry that merges with and enhances CMOS electronics technology.
A key step was made in 2008 when single silicon dangling bonds on an
otherwise H-terminated surface were shown to behave as ultimate small quantum
dots1. Because all such dots are identical, and spacing between dots can be identical,
and dots can be placed very closely to achieve strong interaction, and because many,
many dots can be printed easily there appears to be prospects for interesting
circuitry. The same dots can be deployed to make “passive” elements like wires and to
make active elements of diverse kinds including quantum cellular automata with the
prospect of room temperature operation, and single electron transistors (SETs) of
extremely narrow device to device variation.
After a quarter century stasis, a flood of new insights into atom scale properties
of silicon has emerged. Among the new results I will describe are; single-electron,
single-atom transport dynamics2, new dangling bond (DB) charge state spectroscopy3,
time-resolved single dopant charge dynamics4, time-resolved imaging of negative
differential resistance on the atomic scale5 and chemical bond contrast in AFM images
of a hydrogen terminated silicon surface6.
[1] M.B.Haider, J.L. Pitters, G.A. DiLabio, L.Livadaru, J.Y.Mutus and R.A. Wolkow, Phys.Rev.Lett.,
102, 046805 (2009), and patent issued recently.
[2] M. Taucer, L.Livadaru, P.G. Piva, R.Achal, H.Labidi, J.L. Pitters and R.A. Wolkow, Phys. Rev.
Lett., 112, 256801 (2014)
[3] H.Labidi, M.Taucer, M.Rashidi, M.Koleini, L.Livadaru, J.Pitters, M.Cloutier, M.Salomons and R.
A. Wolkow, New J. Phys., 17, 073023 (2015)
[4] M. Rashidi, J.A.J. Burgess, M. Taucer, R Achal, J.L. Pitters, S. Loth and R.A. Wolkow, Nature
Comm., 7, 13258 (2016)
[5] M.Rashidi, M.Taucer, I.Ozfidan, E.Lloyd, M.Koleini, H.Labidi, J.L.Pitters, J.Maciejko and R. A.
Wolkow, Phys. Rev. Lett. 117, 276805 (2016)
[6] H.Labidi, M.Koleini, T.Huff, M.Salomons, M.Cloutier, J.Pitters and R.A.Wolkow, accepted
Nature Communications.
- 11 -
Keynote Speech 4:
The Spin Hall effect Learnt from the Anomalous Hall Effect
Xiaofeng Jin
Department of Physics, Fudan University, Shanghai 200433, China
The spin Hall effect (SHE) has recently attracted a great deal of attention in the
spintronics community because of its potential applications utilizing spin current.
Various methods have been developed to produce and detect the SHE, and search for
materials with larger spin Hall angle. Despite these efforts, however, reliable and
accurate determination of spin Hall angle remains challenging. Based on our
understanding of the microscopic mechanisms of the anomalous Hall effect and the
intricate properties of ultrathin Bi films, we have developed a new method to measure
quantities inherent to the spin Hall effect. The present method is much simpler, with far
less complications, and hence more reliable, than those used so far.
- 12 -
Keynote Speech 5:
Semiconductor Nanowires: Band Structures and Potential Applications in
Nanoelectronics, Optoelectronics and Quantum Technologies
Hongqi Xu
Lund University
In this talk, theoretical methods developed in recent years for calculations of
electronic structures of semiconductor nanowires will be reviewed and the
characteristics in the band structures of semiconductor nanowires will be presented and
discussed. The talk will also address potential applications of semiconductor nanowires
in nanoelectronics, optoelectronics and quantum technologies. Particular examples
include piezoelectric photovoltaics with an array of semiconductor core-shell
nanowires, and band inversion and topological properties of core-shell nanowires.
Finally, hybrid semiconductor nanowire-superconductor structures will be addressed,
and the transition to topological superconducting nanowire states, in which Majorana
bound states can be present, as well as its potential applications in topological quantum
computation technology will be discussed.
- 13 -
AoE Speech 2:
Spin polarization in monolayer tungsten dichalcogenides
Xiaodong Cui
The University of Hong Kong
The monolayers of group VI transition metal dichalcogenides feature a valence
band spin splitting with opposite sign in the two valleys located at corners of 1st
Brillouin zone. This spin-valley coupling, particularly pronounced in tungsten
dichalcogenides, can benefit potential spintronics and valleytronics with the important
consequences of spin-valley interplay and the suppression of spin and valley relaxations.
In this talk we discuss the spin-valley coupling in monolayers and multilayers WS2.
We explored the interplay of spin and valley degrees of freedom with photocurrent
experiments. We experimentally demonstrate that this giant spin-valley coupling,
together with the valley dependent physical properties, may lead to rich possibilities for
manipulating spin and valley degrees of freedom in these atomically thin 2D materials.
- 14 -
Keynote Speech 6:
The effective use of data in materials research
Tim Mueller
Johns Hopkins University
Rapid advances in information technology have made it possible to generate,
analyze, and distribute large data sets of material properties. One of the great
challenges in materials research is to effectively make use of these data sets to
accelerate the design and development of new materials. To this end, I will discuss how
machine learning techniques can be used to develop model Hamiltonians and identify
simple descriptors that facilitate rational materials design. I will also demonstrate how
informatics can be used to rapidly generate highly efficient k-point grids, addressing a
longstanding problem in computational materials research. Our group has developed a
publicly accessible k-point grid server backed by a database of hundreds of thousands
of k-point grids, and we estimate that for a broad range of computational methods the
use of this server should nearly double the speed of electronic structure calculations on
crystalline materials.
- 15 -
Keynote Speech 7
Deep learning and computer simulation - learning approximate solutions for
rapid prediction
Isaac Tamblyn
National Research Council of Canada
Within the past decade, the fields of artificial intelligence, computer vision,
and natural language processing have advanced at unprecedented rates. Computerized
identification and classification of images, video, audio, and written text have all
improved to the extent they are now part of everyday technologies such as digital
voice assistants (e.g. Siri), automated banking machines (reading handwritten checks),
and driving assist vehicles (automatic lane change, self-parking, and anticipative
braking). eCommerce and digital media companies such as Amazon and Netflix
routinely use machine learned algorithms for optimizing pricing, product suggestions,
and fraud detection. Impressively, the same algorithms now used for computer vision
and speech recognition have also been applied to complex problems in artificial
intelligence.
Recently, Google’s AlphaGo reached an important milestone in the field of
machine intelligence. Using a combination of deep neural networks (trained by
watching thousands of professional human matches) and Monte Carlo tree-search,
AlphaGo was able to handily beat a 9 dan Go Grandmaster. This machine-over-man
victory took place a full decade before many in the field of artificial intelligence had
anticipated. Unlike DeepBlue’s victory over Kasparov at chess in 1997, the game of
Go cannot be won through brute force search alone. In order to win, AlphaGo had to
develop the same sense of intuition that top human players rely on to assess board
position and strategy. By simple observation and experimentation, modern AI can
learn complex patterns and operations. This knowledge can then be applied to new
situations with impressive results.
In this presentation, I will give an overview of our recent results applying
deep neural networks to classical and quantum mechanical operators. These include
the solving the 2d Ising model and learning the Hamiltonian of an electron in a
confining potential well. The use of Monte Carlo based sampling approaches for
training set generation and our ongoing work on the electronic problem will also be
discussed.
- 16 -
Keynote Speech 8
Electron Waiting Times in Mesoscopic Conductors
Christian Flindt
Aalto University
Investigations of mesoscopic conductors have traditionally involved
measurements of the shot noise and the full counting statistics of transferred charge.
Recently, the distribution of waiting times between consecutive electrons has been
proposed as a complementary view on quantum transport. In my talk, I give an
overview of our efforts to evaluate the electronic waiting time distributions (WTDs) for
mesoscopic conductors. For a voltage-biased quantum point contact, we predict a
crossover in the WTD from Wigner-Dyson statistics at full transmission to Poisson
statistics close to pinch-off. Our theory is extended to periodically driven conductors
and used to analyze a quasi-periodic train of clean single-particle excitations. Finally, I
discuss recent developments in the field and conclude by identifying possible avenues
for further developments.
- 17 -
Invited Speech 2
Flexural phonon scattering induced by electrostatic gating in graphene
Tue Gunst
Technical University of Denmark
Two-dimensional (2D) materials are promising candidates for future electronic
devices with properties that can be tuned by the electrostatic and dielectric environment.
One of the advantages of two-dimensionality is that it allows very precise control of the
carrier density by a gate which enables tuning of the electron-phonon interaction [1].
We have recently theoretically described a new flexural phonon scattering mechanism
induced by the electrostatic gating of a graphene device [2]. Graphene’s extremely high
carrier mobility originates partly from the planar mirror symmetry inhibiting scattering
by the highly occupied acoustic flexural phonons. However, gating graphene can break
the planar mirror symmetry activating one-phonon scattering from flexural phonons
that has detrimental impact on the performance of a graphene device.
We examine the effect of the gate-induced scattering on the mobility for several
gate geometries and dielectrics using first-principles calculations and the Boltzmann
equation [3, 4]. The mobility degradation is illustrated in Fig. 1. Our findings may
explain the high deformation potential for in-plane acoustic phonons extracted from
experiments at room temperature and furthermore suggest a direct relation between
device symmetry and resulting mobility. The modified temperature and density scaling
of the mobility, allows for its experimental verification. Paradoxically, better sample
quality may show worse performance due to a lower cutoff of the long-wavelength
scattering. Protecting the planar mirror symmetry is therefore of utmost importance to
fully exploit the unique transport properties of graphene.
[1] Dmitri K. Efetov and Philip Kim, “Controlling Electron-Phonon Interactions in Graphene at Ultrahigh Carrier
Densities,” Phys. Rev. Lett., 105, 256805 (2010).
[2] T. Gunst, K. Kaasbjerg, M. Brandbyge, “Flexural phonon scattering induced by electrostatic gating in graphene”,
Physical Review Letters, Accepted, In production (2017).
[3] T. Gunst, T. Markussen, K. Stokbro, M. Brandbyge, “First-principles method for electron-phonon coupling and
electron mobility: Applications to 2D materials”, Phys. Rev. B, 93, 035414 (2016).
[4] Atomistix ToolKit, version 2016, QuantumWise A/S.
Fig.1 Mobility vs temperature at different carrier
densities for a gated graphene device (circles: o) and
isolated graphene with preserved planar mirror
symmetry (triangles: ); i.e., respectively, with and
without field-induced flexural phonon scattering.
- 18 -
Keynote Speech 9
Aspects of magnon-phonon transport in magnetic insulators
Gerrit E.W. Bauer,
Institute for Materials Research, Tohoku University, Sendai, Japan
TU Delft, the Netherlands
Magnetic insulators are a class of versatile materials with great technological
importance. The most important magnetic insulators are arguably the man-made
yttrium iron garnets, ferrimagnets with Curie transitions far above room temperature
and record magnetic quality [1-2]. The discovery by K. Uchida, E. Saitoh c.s. that
magnetic insulators can be actuated thermally and electrically by metallic contacts has
attracted much interest since it allows for their integration into conventional electronic
and thermoelectric devices. The discovery of entirely new phenomena, such as the
spin Seebeck effect, raises the hope for a new and green spintronics based on
insulators.
The transport of magnons from the bulk of the magnet to its interface or between
contacts can dominate the experimental observations thermal and electric magnon
injection. There is much evidence that magnon transport is strongly affected by
interaction with phonons. While a general theory is not yet available, several
experiments can be well described by ad-hoc models for diffuse and ballistic transport
that give insights into the nature of the interaction. This talk will address the evidence
for the formation of hybrid magnon-phonon quasiparticles or “magnon polarons” [3, 4].
This work was supported by the FOM Foundation, EU-FET “InSpin”, DFG Priority
Program 1538 “Spin Caloric Transport”, and JSPS Grants-in-Aid for Scientific
Research (Grant Nos. 25247056, 25220910, 26103006).
[1] V. Cherepanov, I. Kolokolov, V. L'vov, The Saga of YIG: Spectra, Thermodynamics, Interaction and
Relaxation of Magnons in a Complex Magnet, Phys. Rep. 229, 81 (1993).
[2] Recent Advances in Magnetic Insulators -- From Spintronics to Microwave Applications, M. Wu and
A. Hoffmann (eds.), Solid State Physics 64, 1 (2013).
[3] K. Shen and G.E.W. Bauer, “Laser-induced spatiotemporal dynamics of magnetic films”, Phys. Rev.
Lett. 115, 197201 (2015).
[4] T. Kikkawa, K. Shen, B. Flebus, R. A. Duine, K. Uchida, Z. Qiu, G. E. W. Bauer, and E. Saitoh,
“Magnon-Polarons in the Spin Seebeck Effect”, Phys. Rev. Lett. 117, 207203 (2016).
- 19 -
Keynote Speech 10
Magnon-phonon interaction in YIG and effective spin mixing conductance of
YIG-metal interfaces
Ke Xia,
Beijing Normal University
Short wave length spin waves excited electrically by metallic contact can also diffuse over
distances of 40 µm, even at room temperature, demonstrating the potential of using spin waves as
information carriers in spintronic applications. The crucial parameters are magnon-phonon interaction
in ferromagnetic insulator and spin mixing conductance of ferromagnet(F)|normal metal(N)
interfaces. However, the spin-mixing conductance is a purely nonrelativistic concept, while there is
mounting evidence that spin-orbit interactions at interfaces generate additional spin-flips and spin-
orbit torques. We have solved this issue by introducing an “effective” spin mixing conductance for
weakly relativistic materials. First ab initio results on ferrite|metal interface indeed indicate an
enhancement that can be very significant for selected crystal orientations. Magnon-phonon
interaction in YIG is also carefully calculated based on realistic electronic structure.
- 20 -
Keynote Speech 11
Cavity Spintronics
Can-Ming Hu
University of Manitoba
Strong coupling between magnons and microwave photons has recently been
theoretically proposed [1] and experimentally investigated using both microwave
transmission [2-4] and electrical detection methods [5]. These works build the
foundation for the emerging field of Cavity Spintronics [6], where the development of
spintronics merges with the advancement in cavity quantum electrodynamics and cavity
polaritons, creating new theoretical and experimental avenues for studying wave
physics, developing quantum technology, and facilitating spintronics applications.
Based on the achievements of pioneers of Cavity Spintronics, this talk aims to
provide a brief introduction of this exciting new frontier of condensed matter physics
research to colleagues working on magnetism, spintronics, microwave and quantum
technologies. Some of the recent work done by our group at the University of Manitoba,
in collaborations with John Xiao’s group at University of Delaware, Chia-Ling Chien’
group at Johns Hopkings University, Hong Guo’s group at McGill University, Wei Lu’s
group at Chinese Academy of Science, Yang Xiao’s group at Nanjing University of
Aeronautics and Astronautics, Jianqiang You’s group at Beijing Computational Science
Research Center, and Sebastian Goennenwein’s group at Walther-Meißner-Institut, will
be reported [5-8].
[1] Ö. O. Soykal and M. E. Flatté, Phys. Rev. Lett. 104, 077202 (2010).
[2] H. Huebl, C.W. Zollitsch, J. Lotze, F. Hocke, M. Greifenstein, A. Marx, R. Gross, and S. T. B.
Goennenwein, Phys. Rev. Lett. 111, 127003 (2013).
[3] Y. Tabuchi, S. Ishino, T. Ishikawa, R. Yamazaki, K. Usami, and Y. Nakamura, Phys. Rev. Lett. 113,
083603 (2014).
[4] X. Zhang, C.-L. Zou, L. Jiang, and H. X. Tang, Phys. Rev. Lett. 113, 156401 (2014).
[5] L.H Bai, M. Harder, Y. P. Chen, X. Fan, J. Q. Xiao, and C.-M. Hu, Phys. Rev. Lett. 114, 227201
(2015).
[6] C.-M. Hu, Phys. Canada, 72, 76 (2016); arXiv: 1508.01966.
[7] B.M. Yao, Y.S. Gui, Y. Xiao, H. Guo, X.S. Chen, W. Lu, C.L. Chien, C.-M. Hu,
Phys. Rev. B, 92, 184407 (2015).
[8] For more information, please check: http://www.physics.umanitoba.ca/~hu/
- 21 -
AoE Speech 3
Nano-patterned superstructures of topological insulators in the Moire
superlattices of vdW heterobilayers
Wang Yao
The University of Hong Kong
In van der Waals heterobilayers, small twisting and/or lattice mismatch leads to
the formation of long-period Moiré pattern where the atomic registry locally
approximates commensurate bilayers but has local-to-local variation over long range.
Such Moiré pattern forms a lateral superlattice modulation of the electronic properties
because the form and strength of interlayer coupling is controlled by atomic registry.
In heterobilayers of transition metal dichalcogenides, when the type-II band alignment
is tuned into the inverted regime by an interlayer bias, we find the system can undergo
a topological phase transition depending on the interlayer atomic registry. The Moire
superlattice then leads to mosaic pattern of topological insulator (TI) regions and
normal insulator regions in Moiré superlattices. This points to a new means of realizing
programmable and electrically switchable topological superstructures from 2D arrays
of TI nano-dots to 1D arrays of TI nano-stripes.
- 22 -
Keynote Speech 12
Dephasing and disorder effects in the topological systems
Xincheng Xie
Peking University
The influence of dephasing and disorder effects in the topological systems, such
as the quantum spin Hall effect (QSHE) system, the surface states of 3D topological
insulators, and the Weyl semimetals (WSMs) is studied. For the 2D QSHE system, we
find that the quantum conductance plateaus are robust against the normal dephasing but
fragile with the spin dephasing, and thus these quantum plateaus only survive in
mesoscopic samples. For the surface states of 3D topological insulators, we show that
the combination of dephasing and impurity scattering can cause backscattering in the
helical states. In WSMs, we predict the Goos-Hänchen and the Imbert-Fedorov shifts
exist for the reflection at the interface of two WSMs. We find that the IF shift originates
from the topological effect of the system, and can be utilized to characterize the Weyl
semimetals, to design valleytronic devices, and to measure the Berry curvature of the
system. We also study the impurity scattering and disorder effects in the WSMs. We
show that the topological IF shift also influences the single impurity scattering cross-
section and gives rise to exotic transport properties of WSMs. Furthermore, we study
the disorder induced localization in WSMs, and find three exotic quantum phase
transitions.
- 23 -
Keynote Speech 13
Sub-wavelength opto-electronic device for space application
Wei Lu
Shanghai Institute of technical physics, CAS
The opto-electrical technology for space includes the detection of light from target
and illumination on the target. The driving force for this technology is from the opto-
electronic device. The new phenomenon of sub-wavelength structure gives the light on
the high performance device improvement. When the space opto-electrical technology
meets the sub-wavelength structure, some new technology chance is emerged:
(1) The manipulation on the capture of electron by 3 dimensional electron sub-
wavelength structure has been used on the space used GaN-LED, and the LED is used
in satellite as the first time on 2006.
(2) The optical sub-wavelength resonant cavity chip is developed, it is used on the
satellite as the multispectral camera by reducing the dispersive volume about 4 orders.
(3) By integrating the different electron sub-wavelength structures, the long
wavelength infrared to visible conversion device gives a way to develop the very large
format infrared focal plan array. The high gain detection behavior is achieved by the
photo-nano-gate effect to give a way for high sensitive detector.
(4) By integrating both the electron and optical sub-wavelength structures, the
operation temperature is increased for very long wavelength infrared focal plan array.
The long wavelength infrared polarization sensitive detector has been developed with
the extinction ratio of 65.
(5) The 2D material, as an extreme electron sub-wavelength structure, has also
shown a good light detection behavior, which may useful for the flexible focal plan
array device technology in future.
In conclusion, as meeting with the space opto-electrical technology, the solid sub-
wavelength structure has shown and is showing and will show its fascination.
- 24 -
Invited Speech 3
Conductance of Single Molecules on an Insulating Surface
Chao-Cheng Kaun
Academia Sinica
Using first-principles calculations, we study the electron transport through
single molecules, magnesium porphine and phthalocyanine, adsorbed on a NaCl bilayer
on a metal substrate. The conductance of the tip–vacuum–molecule–NaCl–metal
junctions depend on the orientation of the molecule on the insulating surface, the tip
position above the molecule, and the configuration of the molecule, due to changes of
the spatial extensions of the molecular orbitals. Shifting the molecule to locate on
different ions also varies the conductance.
- 25 -
AoE Speech 4
Applicability of the Chebyshev filtering method in DFPT
Hong Guo
McGill University
The Chebyshev filtering method was introduced in the field of density functional theory
(DFT) by Zhou et al. in 2006. It has been used to solve problems of unprecedented size
(Si9041H1860 and Fe360 clusters) using a relatively small number of processors. The method was
originally implemented in the real space pseudopotential code PARSEC. Since then, the method
has been adapted in finite-elements, projector-augmented waves (ABINIT) and full-potential
linearized augmented planewaves (FLEUR) implementations. In density functional
perturbation theory (DFPT), the fundamental function ∆ρ is updated using a direct summation
over all states or by solving the Sternheimer equation. I will discuss the applicability of the
Chebyshev filtering method in the field of DFPT. In particular, I will demonstrate how to solve
the Sternheimer equation in periodic systems using Chebyshev filtering. I will present the
results of dielectric tensor calculation as a proof-of-concept.
