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Nature and topology of the low-energy states inZrTe5
Moreschini, L.,Johannsen, J. C.,Berger, H.,Denlinger, J.,Jozwiack, C.,Rotenberg, E.,Kim, K. S.,Bostwick, A.,Grioni, M. American Physical Society 2016 Physical Review B Vol.94 No.8
<P>Long known for its peculiar resistivity, showing a thus far unexplained anomalous peak as a function of temperature, ZrTe5 has recently received rising attention in a somewhat different context. While both theoretical and experimental results seem to point to a nontrivial topology of the low-energy electronic states, there is no agreement on the nature of their topological character. Here, by an angle-resolved photoemission study of the evolution of the band structure with temperature and surface doping, we show that (i) the material presents a van Hove singularity close to the Fermi level, and (ii) no surface states exist at the (010) surface. These findings reconcile band structure measurements with transport results and establish the topology of this puzzling compound.</P>
Bulk and surface band structure of the new family of semiconductors BiTeX (X=I, Br, Cl)
Moreschini, L.,Autes, G.,Crepaldi, A.,Moser, S.,Johannsen, J.C.,Kim, K.S.,Berger, H.,Bugnon, Ph.,Magrez, A.,Denlinger, J.,Rotenberg, E.,Bostwick, A.,Yazyev, O.V.,Grioni, M. Elsevier Scientific Pub. Co 2015 Journal of electron spectroscopy and related pheno Vol.201 No.-
We present an overview of the new family of semiconductors BiTeX (X=I, Br, Cl) from the perspective of angle resolved photoemission spectroscopy. The strong band bending occurring at the surface potentially endows them with a large flexibility, as they are capable of hosting both hole and electron conduction, and can be modified by inclusion or adsorption of foreign atoms. In addition, their trigonal crystal structure lacks a center of symmetry and allows for both bulk and surface spin-split bands at the Fermi level. We elucidate analogies and differences among the three materials, also in the light of recent theoretical and experimental work.
Bilayer splitting and wave functions symmetry inSr3Ir2O7
Moreschini, L.,Moser, S.,Ebrahimi, A.,Dalla Piazza, B.,Kim, K. S.,Boseggia, S.,McMorrow, D. F.,Rønnow, H. M.,Chang, J.,Prabhakaran, D.,Boothroyd, A. T.,Rotenberg, E.,Bostwick, A.,Grioni, M. American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.20
The influence of dimensionality on the electronic properties of layered perovskite materials remains an outstanding issue. We address it here for Sr3Ir2O7, the bilayer compound of the iridate Srn+1IrnO3n+1 series. By angle-resolved photoemission spectroscopy we show that in this material the interlayer coupling is large and that the intercell coupling is, conversely, negligible. From a detailed mapping of the bilayer splitting, and from the intensity modulation of the bonding and antibonding bands with photon energy, we establish differences and similarities with the prominent case of the bilayer superconducting cuprates.
In situ investigation of conducting interface formation in LaAlO3/SrTiO3 heterostructure
유향근,Moreschini Luca,Bostwick Aaron,Walter Andrew L.,노태원,Rotenberg Eli,장영준 한국물리학회 2021 Current Applied Physics Vol.30 No.-
The high-mobility conducting interface (CI) between LaAlO3 (LAO) and SrTiO3 (STO) has revealed many fascinating phenomena, including exotic magnetism and superconductivity. But, the formation mechanism of the CI has not been conclusively explained. Here, using in situ angle-resolved photoemission spectroscopy, we elucidated the mechanisms for the CI formation. In as-grown samples, we observed a built-in potential (Vbi) proportional to the polar LAO thickness starting from the first unit cell (UC) with CI formation appearing above 3 UCs. However, we found that the Vbi is removed by synchrotron ultraviolet (UV)-irradiation; The built-in potential is recovered by oxygen gas (O2(g))-exposure. Furthermore, after UV-irradiation, the CI appears even below 3UC of LAO. Our results demonstrate not only the Vbi-driven CI formation in as-grown LAO/STO, but also a new route to control of the interface state by UV lithographic patterning or other surface modification.
Enhanced tunability of two-dimensional electron gas on SrTiO3 through heterostructuring
유향근,Luca Moreschini,Aaron Bostwick,Andrew L. Walter,노태원,Eli Rotenberg,장영준 한국물리학회 2020 Current Applied Physics Vol.20 No.11
Two-dimensional electron gases (2DEGs) on the SrTiO3 (STO) surface or in STO-based heterostructures have exhibited many intriguing phenomena, which are strongly dependent on the 2DEG-carrier density. We report that the tunability of the 2DEG-carrier density is significantly enhanced by adding a monolayer LaTiO3 (LTO) onto the STO. Ultraviolet (UV) irradiation induced maximum carrier density of the 2DEG in LTO/STO is increased by a factor of ~4 times, compared to that of the bare STO. By oxygen gas exposure, it becomes 10 times smaller than that of the bare STO. This enhanced tunability is attributed to the drastic surface property change of a polar LTO layer by UV irradiation and O2 exposure. This indicates that the 2DEG controllability in LTO/STO is more reliable than that on the bare STO driven by defects, such an oxygen vacancy.
Evidence for indirect band gap in BaSnO3 using angle-resolved photoemission spectroscopy
주범수,장영준,Luca Moreschini,Aaron Bostwick,Eli Rotenberg,한문섭 한국물리학회 2017 Current Applied Physics Vol.17 No.5
Transparent BaSnO3 thin films have been proposed as an alternative transparent conducting oxide (TCO). Although bulk synthesis and high-quality fabrication of epitaxial films are well established, there are still unsolved aspects about their electronic structure, such as the direct or indirect nature and the size of the band gap. We investigated the electronic structure of epitaxial BaSnO3 thin films using in situ angleresolved photoemission spectroscopy. We directly measured an indirect band gap of 3.7 eV, a value compatible with those of previous reports, but we also identified additional in-gap states at 1.6 eV below the conduction band minimum that we attribute to intrinsic defects, mainly oxygen vacancies.
Insulating-layer formation of metallic LaNiO<sub>3</sub> on Nb-doped SrTiO<sub>3</sub> substrate
Yoo, Hyang Keun,Chang, Young Jun,Moreschini, Luca,Kim, Hyeong-Do,Sohn, Chang Hee,Sinn, Soobin,Oh, Ji Seop,Kuo, Cheng-Tai,Bostwick, Aaron,Rotenberg, Eli,Noh, Tae Won American Institute of Physics 2015 Applied Physics Letters Vol.106 No.12
A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi<sub>4</sub>I<sub>4</sub>
Autè,s, Gabriel,Isaeva, Anna,Moreschini, Luca,Johannsen, Jens C.,Pisoni, Andrea,Mori, Ryo,Zhang, Wentao,Filatova, Taisia G.,Kuznetsov, Alexey N.,Forró,, Lá,szló,Van den Broek, Nature Publishing Group, a division of Macmillan P 2016 NATURE MATERIALS Vol.15 No.2
Recent progress in the field of topological states of matter has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs; refs ,,,), followed by closely related ternary compounds and predictions of several weak TIs (refs ,,). However, both the conceptual richness of Z<SUB>2</SUB> classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z<SUB>2</SUB> topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide Bi<SUB>4</SUB>I<SUB>4</SUB>. The electronic structure of β-Bi<SUB>4</SUB>I<SUB>4</SUB>, characterized by Z<SUB>2</SUB> invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements performed on the (001) surface reveal a highly anisotropic band-crossing feature located at the point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.
Universal Mechanism of Band-Gap Engineering in Transition-Metal Dichalcogenides
Kang, Mingu,Kim, Beomyoung,Ryu, Sae Hee,Jung, Sung Won,Kim, Jimin,Moreschini, Luca,Jozwiak, Chris,Rotenberg, Eli,Bostwick, Aaron,Kim, Keun Su American Chemical Society 2017 NANO LETTERS Vol.17 No.3
<P>van der Waals two-dimensional (2D) semiconductors have emerged as a class of materials with promising device characteristics owing to the intrinsic band gap. For realistic applications, the ideal is to modify the band gap in a controlled manner by a mechanism that can be generally applied to this class of materials. Here, we report the observation of a universally tunable band gap in the family of bulk 2H transition metal dichalcogenides (TMDs) by in situ surface doping of Rb atoms. A series of angle-resolved photoemission spectra unexceptionally shows that the band gap of TMDs at the zone corners is modulated in the range of 0.8-2.0 eV, which covers a wide spectral range from visible to near-infrared, with a tendency from indirect to direct band gap. A key clue to understanding the mechanism of this band-gap engineering is provided by the spectroscopic signature of symmetry breaking and resultant spin-splitting, which can be explained by the formation of 2D electric dipole layers within the surface bilayer of TMDs. Our results establish the surface Stark effect as a universal mechanism of band-gap engineering on the basis of the strong 2D nature of van der Waals semiconductors.</P>