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First-Principles/DFT/TBT Computation Platform used for theoretical prediction of quantum materials and phenomena

(a vast majority of our experimental works are based on our own theoretical predictions)


 
  First-Principles simulations of electronic structure, excitations and spectral functions are perfomed under the framework of density functional theory (DFT) in the context of topologically non-trivial and Berry curvature based states of matter. VASP and ABINIT are the main programs employed in our calculations in combination with topological band theory, homotopy and symmetry related concepts (D. Thouless' 1998 book on Topological Quantum Numbers (1998); Review article by Hasan and Kane, Rev. Mod. Phys 82, 3045 (2010) and Hasan et.al., Ann. Rev. of Cond. Mat. Physics (2017). Theory and experiments working together leading new insights into quantum matter.
The Feynman cluster and other local (in-group lab) resources at Princeton University provide computation power and various resources. We also collaborate with other institutions (including NUS and NEU) for complementary resources.

 
  Ideas from Mathematics (Topology, Homotopy, Symmetry, Knot theory) --> Enrich quantum physics

Concepts in use:

Karplus-Luttinger, Aharonov-Bohm (in K-space), Berry's Phase, Dirac monopole (hedgehog), Chern's Numbers & Parities, Z2, Thouless's pump, Dirac's fermions, Wigner's symmetry, Weyl's chirality, Hopf's link (emergent topological fermions) and more..
Inst. for Advanced Study (IAS, Princeton) School on Topological Matter Relevant Reading List

Some examples of our new materials physics predictions/analytic topological theory:

News at Nature Materials on our theroretical prediction of Kramers-Weyl fermions (2018)
"By considering the topology of chiral crystals, a new type of massless fermion,
connected with giant arc-like surface states, are predicted.
Such Kramers–Weyl fermions should manifest themselves
in a wide variety of chiral materials."
( Nature Materials (2018) )

Our theoretical prediction of magnetic Weyl semimetal materials is noted by PhysicsWorld (2019)

Theoretical prediction of novel topological response from topo. semimetals arXiv (2019)

News on ferromagnetic Weyl semimetal discovery (PhysicsWorld 2019)

"Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet" ( Science 2019 )
is based on our theoretical prediction of Weyl loops and topological surface states in magnets ( PRL 2017 )
Topological Magnets : 2D TopoMagnets, Weyl magnets etc. (APS invited talk)

Chiral Majorana fermions in spin-orbit materials (2018)


Magnetic Weyl semimetal states in CeAlGe family of materials
(Prediction of) Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlX (CeAlGe-class) family of compounds (R=rare earth, Al=aluminium, X=Si, Ge).
G. Chang, B. Singh, S.-Y. Xu, et al., arXiv:1604.02124 (2016)

Our theoretical prediction of Magnetic Weyl Semimetals CeAlGe inspired experiments at MIT (Science (2019))
News at Moore Foundation Prediction & Discovery of Novel Topological Matter and Phenomena (2019)

News at Berkeley lab (California)

Chiral fermions and large topological Fermi arcs in RhSi family (Topological Chiral Crystals) (2017)

News at Princeton Scientists discover chiral crystals exhibiting exotic quantum effects
( Nature (2019) )
News at Berkeley Lab Spiraling Crystal Is the Key to Exotic Discovery

Prediction of Quantized circular photogalvanic effect in RhSi chiral conductors
( Phys. Rev. Lett. )
PhysicsWorld (2019) Theoretical Prediction of Properties of Topo. Chiral Crystals

Topologically distinct Weyl-fermion pairs: on the effect of magnetic tunneling (2019)

"Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator (Bi2Se3) class with spin-polarized single-Dirac-cone on the surface" (Submitted 2008)


(Theory & Expts) Bi2Se3 class of Topo.Insulator Materials : Nature Physics News Link (2009)


Kramers-Weyl Fermions in Topological Chiral Crystals (2018)

Earlier version of Chiral Crystals theory paper arXiv (2016)

Physics World (2016)

Magnetic-Weyl fermions in spin-orbit materials (2017) (also see below)

Nexus Fermions in spin-orbit materials (2017) (also see below)

Lorentz-violating Weyl fermions in magnetic materials (2018)

"(Theoretical prediction) New type of Weyl semimetal with quadratic double Weyl fermions"

(Theoretical Prediction) Drumhead surface states and topological nodal-line fermions in TlTaSe2

Topological Hopf-link semimetals (2017)


DS
 
 
"Topological Hopf-link semimetals"
Guoqing Chang, Su-Yang Xu, Xiaoting Zhou, Shin-Ming Huang, Bahadur Singh, Baokai Wang, Ilya Belopolski, Jiaxin Yin, Songtian Zhang, Arun Bansil, Hsin Lin, and M. Zahid Hasan
"Topological Hopf and Chain Link Semimetal States and Their Application to Co2MnGa"
Phys. Rev. Lett. 119, 156401 (2017)


Weyl semimetals: Massless Yet Real (2015);

PhysicsWorld (March, 2016)

PhysicsWorld (July, 2015)

Topo.Insulators: Nature Physics News Link (2009)

Pedagogical Lectures

Invited Reviews

Science Talk (Physics-Next, APS-Physics): ..Quantum Fields to Condensed Matter: New Topological Phases of Matter in Natural and Artificial Materials

Talk at Max-Planck-Institut (Germany) "New Forms of Matter: Topological Insulators and Superconductors"

Keynote Talk at Hubbard Theory consortium summer school (London)

Sir Nevill Mott Lecture (London)

Pedagogical talk on Topological Matter at ICTP Conference on "Ultracold Atoms & Gauge Theories"

Keynote Talk at Conference on New Trends in Topological Insulators (Germany): Topological Surface States : Discovery and Recent Results

Moore foundation Symposium talk : "Theoretical and experimental discovery of Weyl fermion, topological nodal-line fermion and Chiral anomaly materials and the new physics frontier"

"Theoretical and experimental discovery of Weyl fermion, topological nodal-line fermion and Chiral anomaly materials and the new physics frontier" (Rutgers 2016)

"Discovery of New Topological Phases of Matter" (Lawrence Berkeley Lab, 2017)

"Theoretical and experimental discovery of Weyl fermion, topological nodal-line fermion and Chiral anomaly materials and the new physics frontier" (Los Alamos Lab 2017)

Discovery of Weyl fermion and topological nodal-line fermions as emergent excitations in topological materials (JQI)


American Physical Society Talk:
"Discovery (Theoretical and Experimental) of Weyl fermion semimetal and topological Fermi arc quasiparticles in TaAs, NbAs, NbP, TaP and related materials"

Princeton theory center (PCTS) talk : "Theoretical and experimental discovery of Weyl fermion, topological nodal-line fermion and Chiral anomaly materials and the new physics frontier"

"Theoretical and experimental discovery of New Topological States of Matter (Topo. Semimetals)" (APS-Physics Editorial Office Colloq. 2017)

"Discovery (theoretical and experimental) of Lorentz-invariant and Lorentz-violating emergent Weyl fermions in topological materials (TaAs class & LaAlGe class)"

MIT Chez Pierre Seminar in Condensed Matter Physics:
Lecture Link


(Prediction of) Half-Heusler ternary compounds as new multifunctional experimental platforms for topological quantum phenomena.
Published in H. Lin, L. A. Wray, Y. Xia, et al., Nature Materials 9, 546 (2010).


(Prediction of) Nexus fermions in topological symmorphic crystalline metals Published in Guoqing Chang, Su-Yang Xu et al., Scientific Reports 7, 1688 (2017).

Some recent theoretical predictions: S.-M. Huang, S.-Y. Xu, I. Belopolski, et al., Nature Commun. 6:7373 (2015).

(Prediction of) Drumhead Surface States and Topological Nodal-Line Fermions in TlTaSe2.
G. Bian.,T.-R. Chang., H. Zheng, et al., arXiv:1508.07521 (2015).

(Prediction of) A strongly robust Weyl fermion semimetal state in Ta3S2.
G. Chang, S.-Y. Xu, D. S. Sanchez, et al., Science Advances (2015).

Prediction of an arc-tunable Weyl Fermion metallic state in MoxW1-xTe2
T.-R. Chang, S.-Y. Xu, G. Chang et al. Nature Commun. 7:10639 (2016)

(Prediction of) A new type of Weyl semimetal with quadratic double Weyl fermions in SrSi2
S.-M. Huang, S.-Y. Xu, I. Belopolski et al., PNAS 113, 1180 (2015)

(Prediction & Experiment together) Topological Nodal-Line Fermions in Spin-Orbit Metal PbTaSe2

G. Bian, T.-R. Chang, R. Sankar, et al. Nature Commun. 7:10556 (2016, submitted Nov 2015)

   
 
  MoS21  
 
Observation of monolayer valence band spin-orbit effect and induced quantum well states in MoX2
Published in Nasser Alidoust, Guang Bian, Su-Yang Xu, et al.,
Nature Commun. 5, 4673 (2014)

 
  DS  

A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class.
Published in S.-M. Huang, S.-Y. Xu, I. Belopolski, et al., Nature Commun. 6:7373 (2015).

 
  DS
DS
 
Drumhead Surface States and Topological Nodal-Line Fermions in TlTaSe2.
G. Bian.,T.-R. Chang., H. Zheng, et al., arXiv:1508.07521 (2015).

 
 

Topological Dirac semimetals (2017)


DS
 
 
"Topological Dirac semimetals in VAl3 class"
Tay-Rong Chang, Su-Yang Xu, Daniel S. Sanchez, Wei-Feng Tsai, Shin-Ming Huang, Guoqing Chang, Chuang-Han Hsu, Guang Bian, Ilya Belopolski, Zhi-Ming Yu, Shengyuan A. Yang, Titus Neupert, Horng-Tay Jeng, Hsin Lin, and M. Zahid Hasan
"Type-II Symmetry-Protected Topological Dirac Semimetals"
Phys. Rev. Lett. 119, 026404 (2017)
 
 
 

Mirror-protected Dirac fermions on Weyl Semimetal Surfaces (2017)


DS
 
 
(Theoretical prediction and experimental observation of) "Mirror Protected Dirac Fermions on a Weyl Semimetal NbP Surface"
Hao Zheng, Guoqing Chang, Shin-Ming Huang, Cheng Guo, Xiao Zhang, Songtian Zhang, Jiaxin Yin, Su-Yang Xu, Ilya Belopolski, Nasser Alidoust, Daniel S. Sanchez, Guang Bian, Tay-Rong Chang, Titus Neupert, Horng-Tay Jeng, Shuang Jia, Hsin Lin, and M. Zahid Hasan
Phys. Rev. Lett. 119, 196403 (2017)
 
 
  DS
DS
 
Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlX family of compounds (R=rare earth, Al=aluminium, X=Si, Ge).
G. Chang, B. Singh, S.-Y. Xu, et al., arXiv:1604.02124

 
 

DS
>
 
See theoretical calculations in "Signatures of the Adler-Bell-Jackiw chiral anomaly in a Weyl semimetal".
Nature Communications 7:10735 (2016)

 
  DS
DS
 
Room-temperature magnetic topological semimetal state in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn).
G. Chang, S.-Y. Xu, H. Zheng, et al., arXiv:1603.01255

 
  DS
DS
 
A strongly robust Weyl fermion semimetal state in TaS.
G. Chang, S.-Y. Xu, D. S. Sanchez, et al., arXiv:1512.08781 (2015).

 
  DS  

Criteria for Directly Detecting Topological Fermi Arcs in Weyl Semimetals
I. Belopolski, S.-Y. Xu, D. S. Sanchez et al. Phys. Rev. Lett. 116, 066802 (2016)

 
  DS
DS
 
Prediction of an arc-tunable Weyl Fermion metallic state in MoxW1-xTe2
T.-R. Chang, S.-Y. Xu, G. Chang et al. Nature Commun. 7:10639 (2016)

 
  DS
DS
 
A new type of Weyl semimetal with quadratic double Weyl fermions in SrSi2
S.-M. Huang, S.-Y. Xu, I. Belopolski et al., PNAS 113, 1180 (2015)

 
  NbSe2  
Half-Heusler ternary compounds as new multifunctional experimental platforms for topological quantum phenomena.
Published in H. Lin, L. A. Wray, Y. Xia, et al., Nature Materials 9, 546 (2010).

  DS
DS
 
  Topological Nodal-Line Fermions in Spin-Orbit Metal PbTaSe2
G. Bian, T.-R. Chang, R. Sankar, et al. Nature Commun. 7:10556 (2016, submitted Nov 2015)

 
  DS  
Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP
G. Chang, S.-Y. Xu, H. Zheng et al., Phys. Rev. Lett. 116, 066601 (2016)


 
  Bi2Se3 class of Topo.Insulator Materials : Nature Physics News Link (2009)


"Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface"