Publications

Cappelli E, Tromp WO, Mckeown Walker S, Tamai A, Gibert Gutierrez M, Baumberger F, Bruno FY.

APL Materials. 2020;8(5):051102

Cucchi I, Marrazzo A, Cappelli E, Ricco S, Bruno F Y, Lisi S, Hoesch M, Kim T K, Cacho C, Besnard C, Giannini E, Marzari N, Gibertini M, Baumberger F, Tamai A.

Physical Review Letters. 2020;124(106402)

Battisti I, Tromp WO, Ricco S, Perry RS, Mackenzie AP, Tamai A, Baumberger F, Allan MP.

npj Quantum Materials. 2020;5(1):91

Discrepancies in the low-energy quasiparticle dispersion extracted from angle-resolved photoemission, scanning tunneling spectroscopy, and quantum oscillation data are common and have long haunted the field of quantum matter physics. Here, we directly test the consistency of results from these…

Lisi S, Lu X, Benschop T, de Jong TA, Stepanov P, Duran JR, Margot F, Cucchi I, Cappelli E, Hunter AS, Tamai A, Kandyba V, Giampietri A, Barinov A, Jobst J, Stalman V, Leeuwenhoek M, Watanabe K, Taniguchi T, Rademaker L, van der Molen SJ, Allan MP, Efetov DK, Baumberger F.

Nature physics. 2020;17(2):189-193

We combine different imaging techniques and angle-resolved photoemission with simultaneous real- and momentum-space resolution (nano-ARPES) to directly map the band dispersion in twisted bilayer graphene devices near charge neutrality. Our experiments reveal large areas with a homogeneous twist…

Cucchi I.

Van der Waals materials can be exfoliated down to atomically thin crystals, offering potential to explore physics in lower dimensionality. In this thesis, I investigated their topological electronic structure with ARPES. I studied mono-, bi- and few-layer Td-WTe2. The small size of exfoliated…

Bruno FY, Mckeown Walker S, Ricco S, De La Torre A, Wang Z, Tamai A, Kim TK, Hoesch M, Bahramy MS, Baumberger F.

Advanced Electronic Materials. 2019;5(1800860):1-7

2D electron gases (2DEGs) in oxides show great potential for the discovery of new physical phenomena and at the same time hold promise for electronic applications. In this work, angle-resolved photoemission is used to determine the electronic structure of a 2DEG stabilized in the (111)-oriented…

Tamai A, Zingl M, Rozbicki E, Cappelli E, Ricco S, De La Torre A, Mckeown Walker S, Bruno FY, King PDC, Meevasana W, Shi M, Radovic M, Plumb NC, Gibbs AS, Mackenzie AP, Berthod C, Strand H, Kim M, Georges A, Baumberger F.

Physical Review X. 2019;9(021048):1-18

We explore the interplay of electron-electron correlations and spin-orbit coupling in the model Fermi liquid Sr2RuO4 using laser-based angle-resolved photoemission spectroscopy. Our precise measurement of the Fermi surface confirms the importance of spin-orbit coupling in this material and reveals…

Vaz DC, Noël P, Johansson A, Göbel B, Bruno FY, Singh G, Mckeown Walker S, Trier F, Vicente-Arche LM, Sander A, Valencia S, Bruneel P, Vivek M, Gabay M, Bergeal N, Baumberger F, Okuno H, Barthélémy A, Fert A, Vila L, Mertig I, Attané J-P, Bibes M.

Nature Materials. 2019;

While spintronics has traditionally relied on ferromagnetic metals as spin generators and detectors, spin–orbitronics exploits the efficient spin–charge interconversion enabled by spin–orbit coupling in non-magnetic systems. Although the Rashba pic- ture of split parabolic bands is often used …

Dashwood CD, Miao H, Vale JG, Ishikawa D, Prishchenko DA, Mazurenko VV, Mazurenko VG, Perry RS, Cao G, De La Torre A, Baumberger F, Baron AQR, McMorrow DF, Dean MPM.

Physical Review. B, Condensed Matter. 2019;100(085131):1-8

The mixing of orbital and spin character in the wave functions of the 5d iridates has led to predictions of strong couplings among their lattice, electronic, and magnetic degrees of freedom. As well as realizing a novel spin-orbit assisted Mott-insulating ground state, the perovskite iridate…

Ricco S, Kim M, Tamai A, Mckeown Walker S, Bruno FY, Cucchi I, Cappelli E, Besnard C, Kim TK, Dudin P, Hoesch M, Gutmann MJ, Georges A, Perry RS, Baumberger F.

Nature Communications. 2018;9(1):4535

Pressure plays a key role in the study of quantum materials. Its application in angle resolved photoemission (ARPES) studies, however, has so far been limited. Here, we report the evolution of the k-space electronic structure of bulk Ca2RuO4, lightly doped with Pr, under uniaxial strain. Using…

Cucchi I, Gutierrez Lezama I, Cappelli E, Mckeown Walker S, Bruno FY, Tenasini G, Wang L, Ubrig N, Barreteau C, Giannini E, Gibertini M, Tamai A, Morpurgo A, Baumberger F.

Nano Letters. 2018;

Two-dimensional crystals of semi-metallic van der Waals materials hold much potential for the realization of novel phases, as exemplified by the recent discoveries of a polar metal in few-layer 1T′-WTe2 and of a quantum spin Hall state in monolayers of the same material. Understanding these…

Wang K, Bachar N, Teyssier J, Luo W, Rischau W, Scheerer G, De La Torre A, Perry RS, Baumberger F, Van Der Marel D.

Physical Review. B, Condensed Matter. 2018;98(045107):1-12

We studied the in-plane dynamic and static charge conductivity of electron doped Sr2IrO4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La …

He P, Mckeown Walker S, Zhang SS-L, Bruno FY, Bahramy M S, Lee JM, Ramaswamy R, Cai K, Heinonen O, Vignale G, Baumberger F, Yang H.

Physical Review Letters. 2018;120(266802):1-5

We explore the second order bilinear magnetoelectric resistance (BMER) effect in the d-electron-based two-dimensional electron gas (2DEG) at the SrTiO3 (111) surface. We find evidence of a spin-split band structure with the archetypal spin-momentum locking of the Rashba effect for the in-plane…

Pincini D, Boseggia S, Perry R, Gutmann MJ, Ricco S, Veiga LSI, Dashwood CD, Collins SP, Nisbet G, Bombardi A, Porter DG, Baumberger F, Boothroyd AT, McMorrow DF.

Physical Review. B, Condensed Matter. 2018;98(014429):1-9

The chemical and magnetic structures of the series of compounds Ca2−xLaxRuO4 [x = 0, 0.05(1), 0.07(1), 0.12(1)] have been investigated using neutron diffraction and resonant elastic x-ray scattering. Upon La doping, the low-temperature S-Pbca space group of the parent compound is retained in all…

Ricco S.

Ca2RuO4 is a multi-band Mott transition system with a ground state that is known to be sensitive to external perturbations, such as chemical substitution, pressure, strain and electric fields. In this work I utilize such sensitivity to determine its electronic structure evolution by angle-resolved…

Hoesch M, Kim TK, Dudin P, Wang H, Scott S, Harris P, Patel S, Matthews M, Hawkins D, Alcock SG, Richter T, Mudd JJ, Basham M, Pratt L, Leicester P, Longhi EC, Tamai A, Baumberger F.

Review of Scientific Instruments. 2017;88(1):013106

A 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 resolution monochromator, a re-focussing system…

Pincini D, Vale JG, Donnerer C, De La Torre A, Hunter EC, Perry R, Moretti Sala M, Baumberger F, McMorrow DF.

Physical Review. B, Condensed Matter. 2017;96(7)

The collective magnetic excitations in the spin-orbit Mott insulator (Sr1−xLax)2IrO4 (x=0,0.01,0.04,0.1) were investigated by means of resonant inelastic x-ray scattering. We report significant magnon energy gaps at both the crystallographic and antiferromagnetic zone centers at all doping…

Wang Z, Zhong Z, Mckeown Walker S, Ristic Z, Ma J-Z, Bruno FY, Ricco S, Sangiovanni G, Eres G, Plumb NC, Patthey L, Shi M, Mesot J, Baumberger F, Radovic M.

Nano Letters. 2017;17(4):2561-2567

Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL…

Bruno FY, Gibert Gutierrez M, Mckeown Walker S, Peil O, De La Torre A, Ricco S, Wang Z, Catalano S, Tamai A, Bisti F, Strocov VN, Triscone J-M, Baumberger F.

APL Materials. 2017;5(1):016101

Battisti I, Fedoseev V, Bastiaans KM, De La Torre A, Perry RS, Baumberger F, Allan MP.

Physical Review. B, Condensed Matter. 2017;95(23)

The effective Mott gap measured by scanning tunneling microscopy (STM) in the lightly doped Mott insulator (Sr1−xLax)2IrO4 differs greatly from values reported by photoemission and optical experiments. Here we show that this is a consequence of the poor electronic screening of the tip-induced…

Mckeown Walker S, Ricco S, Bruno FY, De La Torre A, Tamai A, Golias E, Varykhalov A, Marchenko D, Hoesch M, Bahramy MS, King PDC, Sánchez-Barriga J, Baumberger F.

Physical review. B, Condensed matter and materials physics. 2016;93:245143

Tamai A, Wu QS, Cucchi I, Bruno FY, Ricco S, Kim TK, Hoesch M, Barreteau C, Giannini E, Besnard C, Soluyanov AA, Baumberger F.

Physical review. X. 2016;6:031021

Bruno FY, Tamai A, Wu QS, Cucchi I, Barreteau C, De La Torre A, Mckeown Walker S, Ricco S, Wang Z, Kim TK, Hoesch M, Shi M, Plumb NC, Giannini E, Soluyanov AA, Baumberger F.

Physical review. B, Condensed matter and materials physics. 2016;94:121112(R)

Wang Z, Mckeown Walker S, Tamai A, Wang Y, Ristic Z, Bruno FY, De La Torre A, Ricco S, Plumb NC, Shi M, Hlawenka P, Sánchez-Barriga J, Varykhalov A, Kim TK, Hoesch M, King PDC, Meevasana W, Diebold U, Mesot J, Moritz B, Devereaux TP, Radovic M, Baumberger F.

Nature materials. 2016;15(8):835-839

Battisti I, Bastiaans KM, Fedoseev V, De La Torre A, Iliopoulos N, Tamai A, Hunter EC, Perry R S, Zaanen J, Baumberger F, Allan MP.

Nature physics. 2016;13(1):21-25

Mckeown Walker S.

In this thesis I have investigated the electronic structure of two-dimensional electron liquids (2DEL) induced at different surfaces of the transition metal oxide band insulators SrTiO3, KTaO3 and anatase TiO2 by angle-resolved photoemission spectroscopy (ARPES). I present high-resolution ARPES…

Mckeown Walker S, Bruno FY, Wang Z, De La Torre A, Ricco S, Tamai A, Kim TK, Hoesch M, Shi M, Bahramy MS, King PDC, Baumberger F.

Advanced materials. 2015;27(26):3894-3899

The origin of the 2D electron gas (2DEG)stabilized at the bare surface of SrTiO3 (001) is investigated. Using high-resolution angle-resolved photoemission and core-level spectroscopy, it is shown conclusively that this 2DEG arises from light-induced oxygen vacancies. The dominant mechanism driving…

De La Torre A, Mckeown Walker S, Bruno FY, Ricco S, Wang Z, Gutierrez Lezama I, Scheerer G, Giriat G, Jaccard D, Berthod C, Kim TK, Hoesch M, Hunter EC, Perry RS, Tamai A, Baumberger F.

Physical review letters. 2015;115:176402

We report angle resolved photoemission experiments on the electron doped Heisenberg antiferromagnet Sr1−xLax2IrO4. For a doping level of x 1⁄4 0.05, we find an unusual metallic state with coherent nodal excitations and an antinodal pseudogap bearing strong similarities with underdoped cuprates. …

De La Torre A, Hunter E C, Subedi A, Mckeown Walker S, Tamai A, Kim T K, Hoesch M, Perry R S, Georges A, Baumberger F.

Physical review letters. 2014;113:256402

We characterize the electron doping evolution of (Sr1−xLax)3Ir2O7 by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the…

Mckeown Walker S, De La Torre A, Bruno FY, Tamai A, Kim T K, Hoesch M, Shi M, Bahramy M S, King P D C, Baumberger F.

Physical review letters. 2014;113(17):177601

We 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 sixfold symmetric Fermi surface and strongly anisotropic effective masses. The electronic structure of…

Eknapakul T, King PDC, Asakawa M, Buaphet P, He R-H, Mo S-K, Takagi H, Shen KM, Baumberger F, Sasagawa T, Jungthawan S, Meevasana W.

Nano letters. 2014;14(3):1312-1316

Several transition-metal dichalcogenides exhibit a striking crossover from indirect to direct band gap semiconductors as they are thinned down to a single monolayer. Here, we demonstrate how an electronic structure characteristic of the isolated monolayer can be created at the surface of a bulk…

King PDC, Mckeown Walker S, Tamai A, De La Torre A, Eknapakul T, Buaphet P, Mo S-K, Meevasana W, Bahramy MS, Baumberger F.

Nature communications. 2014;5(3414):5

Two-dimensional electron gases (2DEGs) in SrTiO3 have become model systems for engineering emergent behaviour in complex transition metal oxides. Understanding the collective interactions that enable this, however, has thus far proved elusive. Here we demonstrate that angle-resolved photoemission…

Allan MP, Tamai A, Rozbicki E, Fischer MH, Voss J, King PDC, Meevasana W, Thirupathaiah S, Rienks E, Fink J, Tennant DA, Perry RS, Mercure JF, Wang MA, Lee J, Fennie CJ, Kim E-A, Lawler MJ, Shen KM, Mackenzie AP, Shen Z-X, Baumberger F.

New journal of physics. 2013;15(6):063029

The phase diagram of Sr3Ru2O7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron…

King PDC, Takayama T, Tamai A, Rozbicki E, Mckeown Walker S, Shi M, Patthey L, Moore RG, Lu D, Shen KM, Takagi H, Baumberger F.

Physical review. B, Condensed matter and materials physics. 2013;87(24)

We investigate the bilayer Ruddlesden-Popper iridate Sr3Ir2O7 by temperature-dependent angle-resolved photoemission. At low temperatures, we find a fully gapped correlated insulator, characterized by a small charge gap and narrow bandwidths. The low-energy spectral features show a pronounced…

Tamai A, Meevasana W, King PDC, Nicholson CW, De La Torre A, Rozbicki E, Baumberger F.

Physical review. B, Condensed matter and materials physics. 2013;87(07):075113

We present angle-resolved photoemission data from Cu(111). Using a focused 6 eV continuous-wave laser for photoexcitation, we achieve a high effective momentum resolution, enabling detection of the Rashba spin splitting in the Shockley surface state on Cu(111). The magnitude of the spin splitting…

Scanlon DO, King PDC, Singh RP, De La Torre A, Mckeown Walker S, Balakrishnan G, Baumberger F, Catlow CRA.

Advanced materials. 2012;24(16):2154-2158

Intrinsic topological insulators are realized by alloying Bi2Te3 with Bi2Se3. Angle-resolved photoemission and bulk transport measurements reveal that the Fermi level is readily tuned into the bulk bandgap. First-principles calculations of the native defect landscape highlight the key role of…

Bahramy MS, King PDC, De La Torre A, Chang J, Shi M, Patthey L, Balakrishnan G, Hofmann P, Arita R, Nagaosa N, Baumberger F.

Nature communications. 2012;3(1159)

Bismuth-chalchogenides are model examples of three-dimensional topological insulators. Their ideal bulk-truncated surface hosts a single spin-helical surface state, which is the simplest possible surface electronic structure allowed by their non-trivial Z2 topology. However, real surfaces of such…

King PDC, He RH, Eknapakul T, Buaphet P, Mo S-K, Kaneko Y, Harashima S, Hikita Y, Bahramy MS, Bell C, Hussain Z, Tokura Y, Shen Z-X, Hwang HY, Baumberger F, Meevasana W.

Physical review letters. 2012;108(11):117602

We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of…

Meevasana W, King PDC, He RH, Mo S-K, Hashimoto M, Tamai A, Songsiriritthigul P, Baumberger F, Shen Z-X.

Nature materials. 2011;10(2):114-118

Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity1, colossal magnetoresistance2 or multiferroicity 3. The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the…

King PDC, Hatch RC, Bianchi M, Ovsyannikov R, Lupulescu C, Landolt G, Slomski B, Dil JH, Guan D, Mi JL, Rienks EDL, Fink J, Lindblad A, Svensson S, Bao S, Balakrishnan G, Iversen BB, Osterwalder J, Eberhardt W, Baumberger F, Hofmann P.

Physical review letters. 2011;107(09):096802

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi2Se3 from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger…

King PDC, Rosen JA, Meevasana W, Tamai A, Rozbicki E, Comin R, Levy G, Fournier D, Yoshida Y, Eisaki H, Shen KM, Ingle NJC, Damascelli A, Baumberger F.

Physical review letters. 2011;106(12):127005

We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission. From detailed low-energy electron diffraction measurements and an analysis of the angle-resolved photoemission polarization dependence, we show that these…

Tamai A, Baumberger F, Hengsberger M, Lobo-Checa J, Muntwiler M, Corso M, Cirelli C, Patthey L, Shen Z-X, Greber T, Osterwalder J.

Physical review. B, Condensed matter and materials physics. 2010;81(04):045423

The low-energy single-particle excitations of highly ordered C60 chains adsorbed on a vicinal copper substrate are investigated by angle-resolved photoemission spectroscopy. The interface state previously identified on C60/Cu(111) shows a one-dimensional dispersion on Cu(553). In contrast, no…

Tamai A, Ganin AY, Rozbicki E, Bacsa J, Meevasana W, King PDC, Caffio M, Schaub R, Margadonna S, Prassides K, Rosseinsky MJ, Baumberger F.

Physical review letters. 2010;104(09):097002

We investigate the normal state of the “11” iron-based superconductor FeSe0.42Te0.58 by angle-resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between…

Meevasana W, Zhou XJ, Moritz B, Chen C-C, He RH, Fujimori S-I, Lu DH, Mo S-K, Moore RG, Baumberger F, Devereaux TP, Van Der Marel D, Nagaosa N, Zaanen J, Shen Z-X.

New journal of physics. 2010;12(2):023004

Lee J, Allan MP, Wang MA, Farrell J, Grigera SA, Baumberger F, Davis JC, Mackenzie AP.

Nature physics. 2009;5(11):800-804

The intriguing idea that strongly interacting electrons can generate spatially inhomogeneous electronic liquid-crystalline phases is over a decade old1, 2, 3, 4, 5, but these systems still represent an unexplored frontier of condensed-matter physics. One reason is that visualization of the…

De La Torre A.

This thesis reports the doping evolution of the electronic structure of the single and bilayer idridates Sr2IrO4 and Sr3Ir2O7 from angle resolved photoemission (ARPES) experiments.

Cappelli E.

In this thesis, I present my research work on epitaxial thin films of LaNiO3 and SrMoO3, investigated by angle-resolved photoemission spectroscopy (ARPES), which yields a direct measurement of the interacting electronic structure. Thin films of the correlated transition-metal oxide LaNiO3 undergo a …

Cucchi I.

Van der Waals materials can be exfoliated down to atomically thin crystals, offering potential to explore physics in lower dimensionality. In this thesis, I investigated their topological electronic structure with ARPES. I studied mono-, bi- and few-layer Td-WTe2. The small size of exfoliated…

Ricco S.

Ca2RuO4 is a multi-band Mott transition system with a ground state that is known to be sensitive to external perturbations, such as chemical substitution, pressure, strain and electric fields. In this work I utilize such sensitivity to determine its electronic structure evolution by angle-resolved…

Mckeown Walker S.

In this thesis I have investigated the electronic structure of two-dimensional electron liquids (2DEL) induced at different surfaces of the transition metal oxide band insulators SrTiO3, KTaO3 and anatase TiO2 by angle-resolved photoemission spectroscopy (ARPES). I present high-resolution ARPES…

De La Torre A.

This thesis reports the doping evolution of the electronic structure of the single and bilayer idridates Sr2IrO4 and Sr3Ir2O7 from angle resolved photoemission (ARPES) experiments.