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A novel artificial condensed matter lattice and a new platform for one-dimensional topological phasesMar 13 2017Engineered lattices in condensed matter physics, such as cold atom optical lattices or photonic crystals, can have fundamentally different properties from naturally-occurring electronic crystals. Here, we report a novel type of artificial quantum matter ... More

Strong phonon softening without Fermi surface nestingSep 03 2009Interactions with electronic excitations can soften and/or broaden phonons. They are greatly amplified at wavevectors Q+- that connect parallel (nested) sheets of the Fermi surface. In such a case, called a Kohn anomaly, the phonon dispersion sharply ... More

A disorder-enhanced quasi-one-dimensional superconductorMar 21 2016Jul 26 2016A powerful approach to analysing quantum systems with dimensionality $d>1$ involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-one-dimensional (q1D) systems can exhibit long-range order at low temperature, but ... More

Evidence for unidirectional nematic bond ordering in FeSeMar 15 2016Apr 09 2016The lifting of $d_{xz}$-$d_{yz}$ orbital degeneracy is often considered a hallmark of the nematic phase of Fe-based superconductors, including FeSe, but its origin is not yet understood. Here we report a high resolution Angle-Resolved Photoemission Spectroscopy ... More

Time-Reversal Symmetry Breaking Type-II Weyl State in YbMnBi2Jul 17 2015Mar 30 2016Detection of Dirac, Majorana and Weyl fermions in real materials may significantly strengthen the bridge between high-energy and condensed-matter physics. While the presence of Dirac fermions is well established in graphene and topological insulators, ... More

Momentum Dependence of Charge Excitations in the Electron-Doped Superconductor Nd1.85Ce0.15CuO4: a RIXS StudyDec 17 2004We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-Tc superconductor Nd1.85Ce0.15CuO4. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning ... More

Anharmonicity due to Electron-Phonon Coupling in MagnetiteMar 12 2013Apr 18 2013We present the results of inelastic x-ray scattering for magnetite and analyze the energies and spectral widths of the phonon modes with different symmetries in a broad range of temperature 125<T<293 K. The phonon modes with X_4 and Delta_5 symmetries ... More

Emergence of Dirac-like bands in the monolayer limit of epitaxial Ge films on Au(111)Jul 14 2017After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic ... More

Short-Range Correlations in Magnetite above the Verwey TemperatureJan 16 2014Magnetite, Fe$_3$O$_4$, is the first magnetic material discovered and utilized by mankind in Ancient Greece, yet it still attracts attention due to its puzzling properties. This is largely due to the quest for a full and coherent understanding of the ... More

Understanding the complex phase diagram of uranium: the role of electron-phonon couplingMay 18 2011We report an experimental determination of the dispersion of the soft phonon mode along [1,0,0] in uranium as a function of pressure. The energies of these phonons increase rapidly, with conventional behavior found by 20 GPa, as predicted by recent theory. ... More

Multiband one-dimensional electronic structure and spectroscopic signature of Tomonoga-Luttinger liquid behavior in K$_2$Cr$_3$As$_3$Oct 13 2016We present Angle-Resolved Photoemission Spectroscopy measurements of the quasi-one dimensional superconductor K$_2$Cr$_3$As$_3$. We find that the Fermi surface contains two Fermi surface sheets, with linearly dispersing bands not displaying any significant ... More

Band Structure and Spin-Orbital Texture of the (111)-KTaO3 Two-Dimensional Electron GasMar 14 2019Two-dimensional electron gases (2DEGs) in oxides show great potential for discovering new physical phenomena and at the same time hold promise for electronic applications. In this work we use angle resolved photoemission to determine the electronic structure ... More

Suppression of orbital ordering by chemical pressure in FeSe1-xSxAug 20 2015We report a high-resolution angle-resolved photo-emission spectroscopy study of the evolution of the electronic structure of FeSe1-xSx single crystals. Isovalent S substitution onto the Se site constitutes a chemical pressure which subtly modifies the ... More

Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1$T$-TiSe$_2$Sep 28 2016Using time- and angle-resolved photoemission spectroscopy with selective near- and mid-infrared photon excitations, we investigate the femtosecond dynamics of the charge density wave (CDW) phase in 1$T$-TiSe$_2$, as well as the dynamics of CDW fluctuations ... More

Control of a two-dimensional electron gas on SrTiO3(111) by atomic oxygenMay 13 2014We report on the formation of a two-dimensional electron gas (2DEG) at the bare surface of (111) oriented SrTiO3. Angle resolved photoemission experiments reveal highly itinerant carriers with a 6-fold symmetric Fermi surface and strongly anisotropic ... More

Local corrugation and persistent charge density wave in ZrTe3 with Ni intercalationDec 18 2017The mechanism of emergent bulk superconductivity in transition metal intercalated ZrTe3 is investigated by studying the effect of Ni doping on the band structure and charge density wave (CDW). The study reports theoretical and experimental results in ... More

Phonon Softening in Superconducting DiamondDec 18 2005Apr 13 2007We observe strong softening of optical phonon modes in superconducting (Tc = 4.2 K) boron doped diamond near the Brillouin zone center using inelastic x-ray scattering from a CVD-grown highly oriented sample. The magnitude of the softening, and our observation ... More

Effect of nematic ordering on electronic structure of FeSeJun 09 2016Electronically driven nematic order is often considered as an essential ingredient of high-temperature superconductivity. Its elusive nature in iron-based supercon- ductors resulted in a controversy not only as regards its origin but also as to the degree ... More

Fermi arcs and their topological character in the candidate type-II Weyl semimetal MoTe2Apr 27 2016Jul 21 2016We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal MoTe2. Using laser-based angle-resolved photoemission we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface ... More

Reentrant Phase Coherence in Superconducting Nanowire CompositesJan 10 2017Jan 11 2017The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting ... More

Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAsJun 04 2014Jun 05 2014In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface (FS) instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still ... More

Is BaCr$_2$As$_2$ symmetrical to BaFe$_2$As$_2$ with respect to half $3d$ shell filling?Jan 26 2017May 26 2017We have performed an angle-resolved photoemission spectroscopy study of BaCr$_2$As$_2$, which has the same crystal structure as BaFe$_2$As$_2$, a parent compound of Fe-based superconductors. We determine the Fermi surface of this material and its band ... More

In-situ strain-tuning of the metal-insulator-transition of Ca$_{2}$RuO$_{4}$ in angle-resolved photoemission experimentsMar 01 2018Oct 24 2018We report the evolution of the $k$-space electronic structure of lightly doped bulk Ca$_{2}$RuO$_{4}$ with uniaxial strain. Using ultrathin plate-like crystals, we achieve strain levels up to $-4.1\%$, sufficient to suppress the Mott phase and access ... More

A facility for the analysis of the electronic structures of solids and their surfaces by synchrotron radiation photoelectron spectroscopyDec 22 2016A synchrotron radiation beamline in the photon energy range of 18 - 240 eV and an electron spectroscopy end station have been constructed at the 3 GeV Diamond Light Source storage ring. The instrument features a variable polarisation undulator, a high ... More

Direct observation of spin-polarised bulk bands in an inversion-symmetric semiconductorAug 28 2014Methods to generate spin-polarised electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices. This is generally accepted to require breaking global structural inversion ... More

Discovery of switchable weak topological insulator state in quasi-one-dimensional bismuth iodideFeb 12 2018The major breakthroughs in the understanding of topological materials over the past decade were all triggered by the discovery of the Z$_2$ topological insulator (TI). In three dimensions (3D), the TI is classified as either "strong" or "weak", and experimental ... More

Experimental determination of the topological phase diagram in Cerium monopnictidesJul 20 2017We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit ... More

Maximal Rashba-like spin splitting via kinetic energy-driven inversion symmetry breakingAug 13 2017Engineering and enhancing inversion symmetry breaking in solids is a major goal in condensed matter physics and materials science, as a route to advancing new physics and applications ranging from improved ferroelectrics for memory devices to materials ... More

Emergence of the nematic electronic state in FeSeFeb 10 2015We present a comprehensive study of the evolution of the nematic electronic structure of FeSe using high resolution angle-resolved photoemission spectroscopy (ARPES), quantum oscillations in the normal state and elastoresistance measurements. Our high ... More

Nearly-free electrons in a 5d delafossite oxide metalOct 08 2015Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realisation of numerous exotic phases including spin-orbit assisted Mott insulators, correlated topological solids, and prospective new high-temperature ... More

Narrow-band anisotropic electronic structure of ReS$_2$Mar 14 2017We have used angle resolved photoemission spectroscopy to investigate the band structure of ReS$_2$, a transition-metal dichalcogenide semiconductor with a distorted 1T crystal structure. We find a large number of narrow valence bands, which we attribute ... More

Non-Fermi liquid behavior induced by inter-orbital scattering in hole-doped LiFe$_{1-x}$V$_x$AsApr 15 2016We synthesized a series of V-doped LiFe$_{1-x}$V$_x$As single crystals. The superconducting transition temperature $T_c$ of LiFeAs decreases rapidly at a rate of 7 K per 1\% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2\% ... More

Observation of non-Fermi liquid behavior in hole-doped LiFe$_{1-x}$V$_x$AsApr 15 2016Sep 29 2016We synthesized a series of V-doped LiFe$_{1-x}$V$_x$As single crystals. The superconducting transition temperature $T_c$ of LiFeAs decreases rapidly at a rate of 7 K per 1\% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2\% ... More

Observation of Large Topologically Trivial Fermi-Arcs in the Candidate Type-II Weyl Semimetal WTe2Apr 08 2016Sep 12 2016We report angle-resolved photoemission experiments resolving the distinct electronic structure of the inequivalent top and bottom (001) surfaces of WTe2. On both surfaces, we identify a surface state that forms a large Fermi-arc emerging out of the bulk ... More

Absence of Giant Spin Splitting in the Two-Dimensional Electron Liquid at the Surface of SrTiO$_3$ (001)Mar 01 2016We reinvestigate the putative giant spin splitting at the surface of SrTiO$_3$ reported by Santander-Syro $et~al.$ [Nature Mat. 13, 1085 (2014)]. Our spin- and angle-resolved photoemission experiments on (001) oriented surfaces supporting a two-dimensional ... More

Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO$_2$Oct 15 2017We study the electronic structure of the Pd-terminated surface of the non-magnetic delafossite oxide metal PdCoO$_2$. Combining angle-resolved photoemission spectroscopy and density-functional theory, we show how an electronic reconstruction driven by ... More

Collapse of the Mott gap and emergence of a nodal liquid in lightly doped Sr$_2$IrO$_4$Jun 01 2015Superconductivity in underdoped cuprates emerges from an unusual electronic state characterised by nodal quasiparticles and an antinodal pseudogap. The relation between this state and superconductivity is intensely studied but remains controversial. The ... More

Momentum-resolved charge excitations in high-Tc cuprates studied by resonant inelastic x-ray scatteringAug 27 2007We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of high-Tc cuprates. Momentum-resolved charge excitations in the CuO2 plane are examined from parent Mott insulators to carrier-doped superconductors. The Mott gap excitation in undoped ... More

Bulk and surface electronic structure of trigonal structured PtBi2 studied by angle-resolved photoemission spectroscopyJul 12 2016Jul 20 2016PtBi2 with a layered trigonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance, while the mechanism involved is still elusive. Using high resolution angle-resolved photoemission spectroscopy, we present ... More

Experimental realization of type-II Weyl state in non-centrosymmetric TaIrTe$_4$Sep 29 2016Recent breakthrough in search for the analogs of fundamental particles in condensed matter systems lead to experimental realizations of 3D Dirac and Weyl semimetals. Weyl state can be hosted either by non-centrosymmetric or magnetic materials and can ... More

Observation of a van Hove singularity and implication for strong coupling induced Cooper pairing in KFe2As2Dec 02 2014Nov 12 2015Scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) have been investigated on single crystal samples of KFe2As2. A van Hove singularity (vHs) has been directly observed just a few meV below the Fermi level E_F of ... More

Direct Observation of Orbital Hybridisation in a Cuprate SuperconductorJul 26 2017May 29 2018The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates= materials remains heavily debated. Effective low energy single-band models of the copper-oxygen orbitals are widely used because there exists no strong experimental ... More

Giant Kohn anomaly and the phase transition in charge density wave ZrTe_3Feb 05 2009A strong Kohn anomaly in ZrTe_3 is identified in the mostly transverse acoustic phonon branch along the modulation vector q_P with polarization along the a* direction. This soft mode freezes to zero frequency at the transition temperature T_P and the ... More

Spin-valley locking in the normal state of a transition-metal dichalocogenide superconductorMar 16 2016The metallic transition-metal dichalcogenides (TMDCs) are benchmark systems for studying and controlling intertwined electronic orders in solids, with superconductivity developing upon cooling from a charge density wave state. The interplay between such ... More

Fermiology and Superconductivity of Topological Surface States in PdTe$_2$Dec 12 2017Apr 16 2018We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe$_2$ by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing ... More

Ubiquitous formation of bulk Dirac cones and topological surface states from a single orbital manifold in transition-metal dichalcogenidesFeb 27 2017Jul 19 2018Transition-metal dichalcogenides (TMDs) are renowned for their rich and varied properties. They range from metals and superconductors to strongly spin-orbit-coupled semiconductors and charge-density-wave systems, with their single-layer variants one of ... More

Hierarchical spin-orbital polarisation of a giant Rashba systemJul 30 2015The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids, and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a ... More

Hallmarks of Hund's coupling in the Mott insulator Ca$_2$RuO$_4$Oct 10 2016A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realised in Ca$_2$RuO$_4$. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic ... More

Tailoring the nature and strength of electron-phonon interactions in the SrTiO$_3$(001) two-dimensional electron liquidJun 03 2015Feb 19 2016Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO$_3$(001) ... More

Buried double CuO chains in YBa$_2$Cu$_4$O$_8$ uncovered by nano-ARPESFeb 22 2019The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical ... More

Surface vs bulk electronic structures of a moderately correlated topological insulator YbB6 revealed by ARPESMay 01 2014Systematic angle-resolved photoemission spectroscopy (ARPES) experiments have been carried out to investigate the bulk and (100) surface electronic structures of a topological mixed-valence insulator candidate, YbB6. The bulk states of YbB6 were probed ... More

Electronic structure of the candidate 2D Dirac semimetal SrMnSb2: a combined experimental and theoretical studyNov 20 2017Jan 21 2018SrMnSb$_2$ is suggested to be a magnetic topological semimetal. It contains square, 2D Sb planes with non-symmorphic crystal symmetries that could protect band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal in the form of a ... More

The topological surface state of $α$-Sn on InSb(001) as studied by photoemissionNov 29 2017We report on the electronic structure of the elemental topological semimetal $\alpha$-Sn on InSb(001). High-resolution angle-resolved photoemission data allow to observe the topological surface state (TSS) that is degenerate with the bulk band structure ... More

Structural and magnetic phase transitions in Ca$_{0.73}$La$_{0.27}$FeAs$_2$ with electron overdoped FeAs layersMay 21 2015Mar 14 2016We report a study of the Ca$_{0.73}$La$_{0.27}$FeAs$_2$ single crystals. We unravel a monoclinic to triclinic phase transition at 58 K, and a paramagnetic to stripe antiferromagnetic (AFM) phase transition at 54 K, below which spins order 45$^\circ$ away ... More

Massive Dirac Fermion at the Surface of the van der Waals Antiferromagnet MnBi$_2$Te$_4$Mar 28 2019The layered van der Waals compound MnBi$_2$Te$_4$ has been predicted to combine the band ordering of archetypical topological insulators like Bi$_2$Te$_3$ with the magnetism of Mn, making this material a viable candidate for the realization of various ... More

Non-adiabatic Kohn Anomaly in Heavily Boron-doped DiamondJun 07 2017We report evidence of a non-adiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density functional perturbation ... More

Electronic anisotropies revealed by detwinned ARPES measurements of FeSeMay 05 2017Oct 26 2017We report high resolution ARPES measurements of detwinned FeSe single crystals. The application of a mechanical strain is used to promote the volume fraction of one of the orthorhombic domains in the sample, which we estimate to be 80$\%$ detwinned. While ... More

Splitting in the Fermi surface of ZrTe_3: a surface charge density wave systemFeb 28 2009The electronic band structure and Fermi surface of ZrTe_3 was precisely determined by linearly polarized angle-resolved photoelectron spectroscopy. Several bands and a large part of the Fermi surface are found to be split by 100-200 meV into two parallel ... More

Dimensional Crossover in a Charge Density Wave Material Probed by ARPESOct 17 2016High-resolution angle-resolved photoemission spectroscopy (ARPES) data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3. In the low-temperature 3D ... More

$d_{xz/yz}$ Orbital Subband Structures and Chiral Orbital Angular Momentum in the (001) Surface States of SrTiO$_3$Jun 17 2017We have performed angle resolved photoemission spectroscopy (ARPES) experiments on the surface states of SrTiO$_3$(001) using linearly and circularly polarized light to investigate the subband structures of out-of-plane $d_{xz/yz}$ orbitals and chiral ... More

Shifts and Splittings of the Hole Bands in the Nematic Phase of FeSeFeb 17 2017We report a high-resolution laser-based angle-resolved photoemission spectroscopy (laser-ARPES) study of single crystals of FeSe, focusing on the temperature-dependence of the hole-like bands around the ${\rm \Gamma}$ point. As the system cools through ... More

Sharp optical phonon softening close to optimal doping in La$_{2-x}$Ba$_x$CuO$_{4+δ}$Aug 25 2008Oct 01 2008We report a direct observation of a sharp Kohn-like anomaly in the doubly degenerate copper-oxygen bond-stretching phonon mode occurring at $\mathbf{q}\mathrm{=(0.3, 0,0)}$ in La$_{2-x}$Ba$_x$CuO$_{4+\delta}$ with $\mathrm{x=0.14\pm0.01}$, thanks to the ... More

Phonon anomalies and lattice dynamics in superconducting oxychlorides Ca$_{2-x}$CuO$_2$ClMay 29 2013Jun 05 2013We present a comprehensive study of the phonon dispersion in an underdoped, superconducting Ca$_{2-x}$CuO$_2$Cl$_2$ crystal. We interpret the results using lattice dynamical calculations based on a shell model, and we compare the results, to other hole-doped ... More

Lattice dynamics of the cluster chain compounds M2Mo6Se6Jun 21 2018Jul 09 2018The lattice dynamics of members of the M2Mo6Se6 family of materials with guest ions M = K, Rb, Cs, In, and Tl has been studied using inelastic x-ray scattering and Raman spectroscopy at room temperature, as well as by ab-initio calculations. We find a ... More

Disorder quenching of the Charge Density Wave in ZrTe3Dec 09 2017The charge density wave (CDW) in ZrTe3 is quenched in samples with small amount of Te iso-electronically substituted by Se. Using angle-resolved photoemission spectroscopy we observe subtle changes in the electronic band dispersions and Fermi surfaces ... More

Formation of Hubbard-like bands as a fingerprint of strong electron-electron interactions in FeSeDec 08 2016We use angle-resolved photo-emission spectroscopy (ARPES) to explore the electronic structure of single crystals of FeSe over a wide range of binding energies and study the effects of strong electron-electron correlations. We provide evidence for the ... More

Direct observation of spin-orbit coupling in iron-based superconductorsSep 30 2014Mar 27 2015Spin-orbit coupling (SOC) is a fundamental interaction in solids which can induce a broad spectrum of unusual physical properties from topologically non-trivial insulating states to unconventional pairing in superconductors. In iron-based superconductors ... More

Strongly anisotropic spin-orbit splitting in a two-dimensional electron gasNov 26 2014Near-surface two-dimensional electron gases on the topological insulator Bi$_2$Te$_2$Se are induced by electron doping and studied by angle-resolved photoemission spectroscopy. A pronounced spin-orbit splitting is observed for these states. The $k$-dependent ... More

Holstein polaron in a valley-degenerate two-dimensional semiconductorMay 28 2018Two-dimensional (2D) crystals have emerged as a class of materials with tuneable carrier density. Carrier doping to 2D semiconductors can be used to modulate manybody interactions and to explore novel composite particles. Holstein polaron is a small composite ... More

Probing the reconstructed Fermi surface of antiferromagnetic BaFe$_2$As$_2$ in one domainFeb 26 2019We revisit the electronic structure of BaFe$_2$As$_2$, the archetypal parent compound of the Fe-based superconductors, using angle-resolved photoemission spectroscopy (ARPES). Our high-resolution measurements of samples detwinned by the application of ... More

Phonon dispersion and low energy anomaly in CaC$_6$Nov 11 2009Mar 03 2010We report measurements of phonon dispersion in CaC$_6$ using inelastic X-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. ... More

The three-dimensional electronic structure of the nematic and antiferromagnetic phases of NaFeAs from detwinned ARPES measurementsOct 10 2017We report a comprehensive ARPES study of NaFeAs, a prototypical parent compound of the Fe-based superconductors. By mechanically detwinning the samples, we show that in the nematic phase (below the structural transition at $T_s$ = 54 K but above the antiferromagnetic ... More

A weakly correlated Fermi liquid state with a small Fermi surface in lightly doped Sr$_3$Ir$_2$O$_7$Sep 24 2014We characterize the electron doping evolution of (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ by means of angle-resolved photoemission. Concomitant with the metal insulator transition around $x\approx0.05$ we find the emergence of coherent quasiparticle states forming ... More

Generation and evolution of spin-, valley- and layer-polarized excited carriers in inversion-symmetric WSe2Jun 10 2016Manipulation of spin and valley degrees of freedom is a key step towards realizing novel quantum technologies, for which atomically thin transition metal dichalcogenides (TMDCs) have been established as promising candidates. In monolayer TMDCs, the lack ... More

Surface structure of Bi2Se3(111) determined by low-energy electron diffraction and surface X-ray diffractionJun 14 2013The surface structure of the prototypical topological insulator Bi2Se3 is determined by low-energy electron diffraction and surface X-ray diffraction at room temperature. Both approaches show that the crystal is terminated by an intact quintuple layer. ... More

Generation and evolution of spin-, valley- and layer-polarized excited carriers in inversion-symmetric WSe2Jun 10 2016Jan 02 2017Manipulation of spin and valley degrees of freedom is a key step towards realizing novel quantum technologies, for which atomically thin transition metal dichalcogenides (TMDCs) have been established as promising candidates. In monolayer TMDCs, the lack ... More

Orbitally selective breakdown of Fermi liquid quasiparticles in Ca$_{1.8}$Sr$_{0.2}$RuO$_4$Apr 16 2019We present a comprehensive angle-resolved photoemission spectroscopy study of Ca$_{1.8}$Sr$_{0.2}$RuO$_4$. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis ... More

Massive Neutrino in Non-commutative Space-timeDec 24 2007Apr 01 2008We consider the noncommutative standard model based on $SU(3)\times SU(2)\times U(1)$. We study the gauge transformation of right handed neutrino and its direct interaction with photon in the noncommutative space-time. We show that the massive Dirac neutrinos, ... More

Infinite order excitonic Bloch equations for asymmetric nanostructuresJul 04 2003We present a new exciton-based formalism for calculating the coherent response of asymmetric semiconductor multiple quantum well structures to ultra-short optical pulses valid to infinite order in the optical field and including the self-generated intraband ... More

Scalar StoponiumAug 18 1993We study the decays of a scalar \stst\ bound state \sigst, where \st\ is the lighter stop eigenstate. If \st\ has no tree--level 2--body decays, the dominant decay modes of \sigst\ are $gg$ or, if $m_h < \mst \ll \mstt$, a pair of light scalar Higgs bosons ... More

Production and Decay of Scalar Stoponium Bound StatesDec 02 1993In this paper we discuss possible signatures for the production of scalar \stst\ (stoponium) bound states \sigst\ at hadron colliders, where \st\ is the lighter scalar top eigenstate. We first study the decay of \sigst; explicit expressions are given ... More

Parton Model in Lorentz Invariant Non-Commutative SpaceMay 26 2004Aug 22 2004We consider the Lorentz invariant non-commutative QED and complete the Feynman rules for the theory up to the order $\theta^2$. In the Lorentz invariant version of the non-commutative QED the particles with fractional charges can be also considered. We ... More

Electromagnetic Response of Weyl SemimetalsMar 22 2013Jun 27 2013It has been suggested recently, based on subtle field-theoretical considerations, that the electromagnetic response of Weyl semimetals and the closely related Weyl insulators can be characterized by an axion term E.B with space and time dependent axion ... More

The Charm Quark Contribution to the Proton Structure FunctionOct 14 2006Dec 27 2006The charm quark structure function $F^c_2$ and the longitudinal structure function $F_l^p$ are directly sensitive to the gluon content of proton and therefore are crucial in understanding of proton structure function, in particular at low momentum transfer ... More

Photon Neutrino Scattering in Non-Commutative SpaceNov 04 2005Jan 19 2006We extend the non-commutative standard model based on the minimal $SU(3)\times SU(2)\times U(1)$ gauge group to include the interaction of photon with neutrino. We show that, in the gauge invariant manner, only the right handed neutrino can directly couple ... More

On the effect of the thermal gas component to the stability of vortices in trapped Bose-Einstein condensatesMar 12 2002We study the stability of vortices in trapped single-component Bose-Einstein condensates within self-consistent mean-field theories--especially we consider the Hartree-Fock-Bogoliubov-Popov theory and its recently proposed gapless extensions. It is shown ... More

Lorentz Conserving Noncommutative Standard ModelMar 29 2007May 10 2007We consider Lorentz conserving noncommutative field theory to construct the Lorentz conserving noncommutative standard model based on the gauge group $SU(3)\times SU(2)\times U(1)$. We obtain the enveloping algebra-valued of Higgs field up to the second ... More

Shelving and Probe Efficiency in Trapped Ion ExperimentsFeb 24 2014A generalized probe sequence typical of trapped ion experiments using shelving is studied. Detection efficiency is analyzed for finite shelved state lifetimes and using multi-modal count distributions. Multi-modal distributions are more appropriate for ... More

The Neutralino Relic Density in Minimal N=1 SupergravityJul 10 1992We compute the cosmic relic (dark matter) density of the lightest supersymmetric particle (LSP) in the framework of minimal $N=1$ Supergravity models with radiative breaking of the electroweak gauge symmetry. To this end, we re--calculate the cross sections ... More

Quantization and $2π$ Periodicity of the Axion Action in Topological InsulatorsJun 17 2010Nov 10 2010The Lagrangian describing the bulk electromagnetic response of a three-dimensional strong topological insulator contains a topological `axion' term of the form '\theta E dot B'. It is often stated (without proof) that the corresponding action is quantized ... More

Neutralino-Nucleon Scattering RevisitedJul 01 1993We present a detailed discussion of the elastic scattering of a supersymmetric neutralino off a nucleon or nucleus, with emphasis on the spin--independent interaction. We carefully treat QCD effects on the squark exchange contribution. In particular, ... More

Quantum information processing: The case of vanishing interaction energyOct 27 2002We investigate the rate of operation of quantum "black boxes" ("oracles") and point out the possibility of performing an operation by a quantum "oracle" whose average energy equals zero. This counterintuitive result not only presents a generalization ... More

Self-Organized Topological State with Majorana FermionsJul 08 2013Nov 06 2013Topological phases, quite generally, are difficult to come by. They either occur under rather extreme conditions (e.g. the quantum Hall liquids, which require high sample purity, strong magnetic fields and low temperatures) or demand fine tuning of system ... More

Spin Response of Electrons on the Surface of a Topological InsulatorJan 11 2012The surface of a topological insulator hosts a very special form of a quasi-two dimensional metallic system when it is embedded in a topologically trivial medium like the vacuum. The electronic properties of this unusual 2D metal are distinct in many ... More

Electroweak Baryogenesis in the MSSMMar 05 1999Mar 24 1999We review the baryogenesis scenario in the MSSM at the perturbative level and, in particular, the impact of two-loop corrections on the strength of the phase transition and the amount of generated baryon asymmetry. We confirm the baryogenesis window, ... More

Cosmic Variance and Its Effect on the Luminosity Function Determination in Deep High z SurveysDec 03 2007We study cosmic variance in deep high redshift surveys and its influence on the determination of the luminosity function for high redshift galaxies. For several survey geometries relevant for HST and JWST instruments, we characterize the distribution ... More

Periodic Solutions of Abel Differential EquationsMay 05 2006Jun 09 2006For a class of polynomial non-autonomous differential equations of degree n, we use phase plane analysis to show that each equation in this class has n periodic solutions. The result implies that certain rigid two-dimensional systems have at most one ... More

Hydrogen and muonic-Hydrogen Atomic Spectra in Non-commutative Space-TimeOct 03 2014Dec 16 2014Comparing electronic Hydrogen with muonic Hydrogen shows that the discrepancy in measurement of the Lamb shift in the both systems are relatively of order of $(\frac{m_\mu}{m_e})^{4-5}$. We explore the spectrum of Hydrogen atom in noncommutative $QED$ ... More

Pair excitations and the mean field approximation of interacting Bosons, IAug 18 2012Mar 16 2013In our previous work \cite{GMM1},\cite{GMM2} we introduced a correction to the mean field approximation of interacting Bosons. This correction describes the evolution of pairs of particles that leave the condensate and subsequently evolve on a background ... More

Color-Flavor (Un)lockingFeb 11 2002The structure of the phase diagram of strongly interacting matter at moderate densities is calculated within a 3-flavor NJL-type quark model with realistic quark masses. We focus on the influence of the selfconsistently determined effective strange quark ... More