Publications (22)
Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2
D. Qian, L. Wray, D. Hsieh +6
We utilize fine-tuned polarization selection coupled with excitation-energy variation of photoelectron signal to image the \textit{complete d}-band dispersion relation in sodium co…
Charge collective modes in an incommensurately modulated cuprate
L. Wray, D. Qian, D. Hsieh +3
We report the first measurement of collective charge modes of insulating Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete Brillouin zone. Our results show th…
Low-lying quasiparticle states and hidden collective charge instabilities in parent cobaltate superconductors (NaxCoO2)
D. Qian, D. Hsieh, L. Wray +7
We report a state-of-the-art photoemission (ARPES) study of high quality single crystals of the NaxCoO2 series focusing on the fine details of the low-energy states. The Fermi velo…
A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator
D. Hsieh, D. Qian, L. Wray +4
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is genera…
Electrons on the surface of Bi2Se3 form a topologically-ordered two dimensional gas with a non-trivial Berry's phase
Y. Xia, L. Wray, D. Qian +8
The interface between a superconductor and a topological insulator has been proposed to harbor novel quasiparticles that realize physical schemes for fault-tolerant quantum computa…
Time-reversal-protected single-Dirac-cone topological-insulator states in Bi2Te3 and Sb2Te3: Topologically Spin-polarized Dirac fermions with pi Berry's Phase
D. Hsieh, Y. Xia, D. Qian +12
We show that the strongly spin-orbit coupled materials Bi2Te3 and Sb2Te3 (first non-Bi topological insulator) and their derivatives belong to the Z2 (Time-Reversal-Protected, elast…
A topological Dirac insulator in a quantum spin Hall phase (experimental realization of a 3D Topological Insulator)
D. Hsieh, D. Qian, L. Wray +4
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is genera…
First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy
D. Hsieh, Y. Xia, D. Qian +12
Electron systems that possess light-like dispersion relations or the conical Dirac spectrum, such as graphene and bismuth, have recently been shown to harbor unusual collective sta…
Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
Y. Xia, D. Qian, D. Hsieh +8
Recent theories and experiments have suggested that strong spin-orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topo…
Fermi surface topology and low-lying quasiparticle dynamics of parent FeTe/Se Superconductor by orbital-polarization resolved ARPES
Y. Xia, D. Qian, L. Wray +5
We report the first photoemission study of FeTe - the host compound of the newly discovered iron-chalcogenide superconductors (maximum T 27K). Our results reveal…
Experimental determination of the microscopic origin of magnetism in parent iron pnictides
D. Hsieh, Y. Xia, L. Wray +7
Like high Tc cuprates, the newly discovered iron based superconductors lie in close proximity to a magnetically ordered parent phase. However, while the magnetic order in parent cu…
Quasiparticle coherence and the nature of the metal-insulator phase transition in NaCoO
D. Qian, L. Wray, D. Hsieh +7
Layered cobaltates embody novel realizations of correlated quantum matter on a spin-1/2 triangular lattice. We report a high-resolution systematic photoemission study of the insula…
Emergence of Fermi pockets in an excitonic CDW melted novel superconductor
D. Qian, D. Hsieh, L. Wray +5
A superconducting (SC) state (Tc ~ 4.2K) has very recently been observed upon successful doping of the CDW ordered triangular lattice TiSe, with copper. Using high resolution p…
First observation of Spin-Momentum Helical Locking in Bi2Se3 and Bi2Te3, demonstration of Topological-Order at 300K and a realization of topological-transport-regime
D. Hsieh, Y. Xia, D. Qian +14
Both the theoretical and experimental discovery of single-Dirac-cone topological-insulator-class was reported at arXiv:0812.2078 (2008) [Y. Xia et.al., Nature Physics 5, 398-402 (2…
Tightly-bound Cooper pair, quasiparticle kinks and clues on the pairing potential in a high Tc FeAs Superconductor
L. Wray, D. Qian, D. Hsieh +12
We present a systematic photoemission study of the newly discovered high Tc superconductor class (Sr/Ba)1-xKxFe2As2. By utilizing a unique photon energy range and scattering geomet…
Observation of unconventional band topology in a superconducting doped topological insulator, Cux-Bi2Se3: Topological Superconductor or non-Abelian superconductor?
L. Wray, S. Xu, J. Xiong +7
The Cu-doped topological insulator BiSe has recently been found to undergo a superconducting transition upon cooling, raising the possibilities that it is the first known "…
Direct observation of spin-polarized surface states in the parent compound of topological insulator Bi-Sb using spin-resolved-ARPES in a 3D Mott-polarimetry spin mode
D. Hsieh, Y. Xia, L. Wray +9
We report high-resolution spin-resolved photoemission spectroscopy (Spin-ARPES) measurements on the parent compound Sb of the first discovered 3D topological insulator Bi{1-x}Sb{x}…
Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe
Y. Xia, D. Qian, L. Wray +5
We report the first photoemission study of Fe1+xTe - the host compound of the newly discovered iron-chalcogenide superconductors. Our results reveal a pair of nearly electron- hole…
Anisotropic softening of collective charge modes in the vicinity of critical doping in a doped Mott insulator
Y. W. Li, D. Qian, L. Wray +9
Momentum resolved inelastic resonant x-ray scattering is used to map the evolution of charge excitations over a large range of energies, momenta and doping levels in the electron d…
Observation of topologically protected Dirac spin-textures and ÏBerry's phase in pure Antimony (Sb) and topological insulator BiSb
D. Hsieh, Y. Xia, L. Wray +10
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of con…
First direct observation of Spin-textures in Topological Insulators : Spin-resolved ARPES as a probe of topological quantum spin Hall effect and Berry's phase
D. Hsieh, Y. Xia, L. Wray +10
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of con…
Momentum-dependence of Superconducting Gap, strong-coupling dispersion Kink, and tightly bound Cooper pairs in the high-Tc (Sr,Ba)1-x(K,Na)xFe2As2 superconductors
L. Wray, D. Qian, D. Hsieh +13
We present a systematic angle-resolved photoemission spectroscopic study of the high-Tc superconductor class (Sr/Ba){1-x}(K/Na)xFe2As2. By utilizing a photon-energy-modulation cont…