
FirstPrinciples/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)



FirstPrinciples simulations of electronic structure, excitations and spectral functions are perfomed under the framework of density functional theory (DFT) in the context of topologically nontrivial 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 (ingroup 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:
KarplusLuttinger, AharonovBohm (in Kspace), 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:
Prediction of Quantized circular photogalvanic effect in RhSi chiral conductors ( Phys. Rev. Lett. (2017))
News at Nature Materials on our theroretical prediction of KramersWeyl fermions (2018)
"By considering the topology of chiral crystals, a new type of massless fermion, connected with giant arclike surface states, are predicted. Such Kramersâ€“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 Magnetic Topo. Materials : Princeton News (2019)
Theoretical prediction of novel topological response from topo. semimetals arXiv (2019)
News on ferromagnetic Weyl semimetal discovery (PhysicsWorld 2019)
Theoretical discovery of Weyl semimetal class TaAs (PhysicsWorld 2015)
Theoretical discovery of Topo.Insulator Bi2Se3 class (2008)
"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 spinorbit materials (2018)
Magnetic Weyl semimetal states in CeAlGe family of materials
(Prediction of) Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlX (CeAlGeclass) 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)
Theoretical Prediction of Novel Topo. Materials : News at Berkeley lab
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
PhysicsWorld (2019) Theoretical Prediction of Properties of Topo. Chiral Crystals
Topologically distinct Weylfermion pairs: on the effect of magnetic tunneling (2019)
"Discovery (theoretical prediction and experimental observation) of a largegap topologicalinsulator (Bi2Se3) class with spinpolarized singleDiraccone on the surface" (Submitted 2008)
(Theory & Expts) Bi2Se3 class of Topo.Insulator Materials : Nature Physics News Link (2009)
KramersWeyl Fermions in Topological Chiral Crystals (2018)
Earlier version of Chiral Crystals theory paper arXiv (2016)
Physics World (2016)
MagneticWeyl fermions in spinorbit materials (2017) (also see below)
Nexus Fermions in spinorbit materials (2017) (also see below)
Lorentzviolating 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 nodalline fermions in TlTaSe2
Topological Hopflink semimetals (2017)
 

"Topological Hopflink semimetals"
Guoqing Chang, SuYang Xu, Xiaoting Zhou, ShinMing 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 (PhysicsNext, APSPhysics): ..Quantum Fields to Condensed Matter: New Topological Phases of Matter in Natural and Artificial Materials
Talk at MaxPlanckInstitut (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 nodalline fermion and Chiral anomaly materials and the new physics frontier"
"Theoretical and experimental discovery of Weyl fermion, topological nodalline 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 nodalline fermion and Chiral anomaly materials and the new physics frontier" (Los Alamos Lab 2017)
Discovery of Weyl fermion and topological nodalline 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 nodalline fermion and Chiral anomaly materials and the new physics frontier"
"Theoretical and experimental discovery of New Topological States of Matter (Topo. Semimetals)" (APSPhysics Editorial Office Colloq. 2017)
"Discovery (theoretical and experimental) of Lorentzinvariant and Lorentzviolating emergent Weyl fermions in topological materials (TaAs class & LaAlGe class)"
MIT Chez Pierre Seminar in Condensed Matter Physics: Lecture Link
(Prediction of) HalfHeusler 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, SuYang 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 NodalLine 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 arctunable Weyl Fermion metallic state in Mo_{x}W_{1x}Te_{2}
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 NodalLine Fermions in SpinOrbit Metal PbTaSe_{2}
G. Bian, T.R. Chang, R. Sankar, et al.
Nature Commun. 7:10556 (2016, submitted Nov 2015)








Observation of monolayer valence band spinorbit effect and induced quantum well states in MoX_{2}
Published in Nasser Alidoust, Guang Bian, SuYang Xu, et al., Nature Commun. 5, 4673 (2014)





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).





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



Topological Dirac semimetals (2017)
 

"Topological Dirac semimetals in VAl3 class"
TayRong Chang, SuYang Xu, Daniel S. Sanchez, WeiFeng Tsai, ShinMing Huang, Guoqing Chang, ChuangHan Hsu, Guang Bian, Ilya Belopolski, ZhiMing Yu, Shengyuan A. Yang, Titus Neupert, HorngTay Jeng, Hsin Lin, and M. Zahid Hasan
"TypeII SymmetryProtected Topological Dirac Semimetals"
Phys. Rev. Lett. 119, 026404 (2017)




Mirrorprotected Dirac fermions on Weyl Semimetal Surfaces (2017)
 

(Theoretical prediction and experimental observation of) "Mirror Protected Dirac Fermions on a Weyl Semimetal NbP Surface"
Hao Zheng, Guoqing Chang, ShinMing Huang, Cheng Guo, Xiao Zhang, Songtian Zhang, Jiaxin Yin, SuYang Xu, Ilya Belopolski, Nasser Alidoust, Daniel S. Sanchez, Guang Bian, TayRong Chang, Titus Neupert, HorngTay Jeng, Shuang Jia, Hsin Lin, and M. Zahid Hasan
Phys. Rev. Lett. 119, 196403 (2017)






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



>
 
See theoretical calculations in "Signatures of the AdlerBellJackiw chiral anomaly in a Weyl semimetal".
Nature Communications 7:10735 (2016)





Roomtemperature magnetic topological semimetal state in halfmetallic Heusler Co2TiX (X=Si, Ge, or Sn).
G. Chang, S.Y. Xu, H. Zheng, et al., arXiv:1603.01255





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





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)





Prediction of an arctunable Weyl Fermion metallic state in Mo_{x}W_{1x}Te_{2}
T.R. Chang, S.Y. Xu, G. Chang et al.
Nature Commun. 7:10639 (2016)





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)





HalfHeusler 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).





Topological NodalLine Fermions in SpinOrbit Metal PbTaSe_{2}
G. Bian, T.R. Chang, R. Sankar, et al.
Nature Commun. 7:10556 (2016, submitted Nov 2015)





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 largegap topologicalinsulator class with spinpolarized singleDiraccone on the surface"

