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T.
Shiroka
,
R.
Fittipaldi
,
M.
Cuoco
,
R.
De Renzi
,
Y.
Maeno
,
R. J.
Lycett
,
Silvia
Ramos
,
E. M.
Forgan
,
C.
Baines
,
A.
Rost
,
V.
Granata
,
A.
Vecchione
Abstract: The low-temperature magnetic behavior of the double-layered ruthenate Sr3Ru2O7, as grown from a eutectic Sr2RuO4-Sr3Ru2O7 system, was investigated via zero-and transverse-field muon-spin rotation. The gradual increase of the muon relaxation rate observed below 2.5 K, even in the absence of applied magnetic fields, indicates the occurrence of a spontaneous breaking of time-reversal symmetry. The onset of the latter at a temperature above 1.5 K, the T-c of the single phase Sr2RuO4, provides evidence about an unconventional superconducting state in the eutectic phase, which most likely takes place at the interface between the Sr2RuO4 and Sr3Ru2O7 domains, or even inside the Sr3Ru2O7 phase. We show that the superconducting state manifests a two-component behavior in the transverse-field response with change-over at about T = 2.5 K and T = 1.5 K. The comparison with zero-field mu SR data in the Ru-Sr2RuO4 eutectic system rules out the possibility of spurious effects due to embedded Ru islands.
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Apr 2012
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Sergey
Borisenko
,
Volodymyr B.
Zabolotnyy
,
Alexander A.
Kordyuk
,
Danil V.
Evtushinsky
,
Timur K.
Kim
,
Emanuela
Carleschi
,
Bryan P.
Doyle
,
Rosalba
Fittipaldi
,
Mario
Cuoco
,
Antonio
Vecchione
,
Helmut
Berger
Abstract: The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (ω) and momentum (k) and the probability to find them in a particular state with given ω and k is described by the spectral function A(k, ω). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
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Oct 2012
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Abstract: We derive an effective quasiparticle tight-binding model which is able to describe with high accuracy the low-energy electronic structure of Sr2RuO4 obtained by means of low temperature angle resolved photoemission spectroscopy. Such an approach is applied to determine the momentum and orbital dependent effective masses and velocities of the electron quasiparticles close to the Fermi level. We demonstrate that the model can provide, among the various computable physical quantities, a very good agreement with the experimentally measured specific heat coefficient and compares well with the plasma frequency estimated from local density calculations. Its use is underlined as a realistic input in the analysis of the possible electronic mechanisms related to the superconducting state of Sr2RuO4.
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Oct 2013
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I05-ARPES
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D.
Sutter
,
C. G.
Fatuzzo
,
S.
Moser
,
M.
Kim
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
Y.
Sassa
,
F.
Cossalter
,
G.
Gatti
,
M.
Grioni
,
H. M.
Rønnow
,
N. C.
Plumb
,
C. E.
Matt
,
M.
Shi
,
M.
Hoesch
,
T. K.
Kim
,
T.-R.
Chang
,
H.-T.
Jeng
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
A.
Georges
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[14617, 12926]
Open Access
Abstract: A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund’s coupling that together generate the Mott insulating state of Ca2RuO4.
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May 2017
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[16576, 17569, 18967]
Open Access
Abstract: We review the magnetic and orbital ordered states in Ca2RuO4 by performing resonant elastic x-ray scattering (REXS) at the Ru L2,3 edges. In principle, the point symmetry at Ru sites does not constrain the direction of the magnetic moment below TN. However early measurements reported the ordered moment entirely along the b orthorhombic axis. Taking advantage of the large resonant enhancement of the magnetic scattering close to the Ru L2 and L3 absorption edges, we monitored the azimuthal, thermal, and energy dependence of the REXS intensity and find that a canting (m_c≃0.1 m_b) along the c-orthorhombic axis is present. No signal was found for m_a despite this component also being allowed by symmetry. Such findings are interpreted by a microscopic model Hamiltonian and pose new constraints on the parameters describing the model. Using the same technique we reviewed the accepted orbital ordering picture. We detected no symmetry breaking associated with the signal increase at the “so-called” orbital ordering temperature (≃260K). We did not find any changes of the orbital pattern even through the antiferromagnetic transition, suggesting that, if any, only a complex rearrangement of the orbitals, not directly measurable using linearly polarized light, can take place.
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Sep 2018
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I05-ARPES
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D.
Sutter
,
M.
Kim
,
C. E.
Matt
,
M.
Horio
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
K.
Hauser
,
Y.
Sassa
,
G.
Gatti
,
M.
Grioni
,
M.
Hoesch
,
T. K.
Kim
,
E.
Rienks
,
N. C.
Plumb
,
M.
Shi
,
T.
Neupert
,
A.
Georges
,
J.
Chang
Diamond Proposal Number(s):
[15296]
Abstract: We 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 and comparison to dynamical mean-field theory calculations. Bands assigned to
d
x
z
,
d
y
z
orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions—associated with a predominantly
d
x
y
band character—are shown to display non-Fermi-liquid behavior. We thus demonstrate that
Ca
1.8
Sr
0.2
RuO
4
is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.
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Mar 2019
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I05-ARPES
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M.
Horio
,
Q.
Wang
,
V.
Granata
,
K. P.
Kramer
,
Y.
Sassa
,
S.
Jöhr
,
D.
Sutter
,
A.
Bold
,
L.
Das
,
Y.
Xu
,
R.
Frison
,
R.
Fittipaldi
,
T. K.
Kim
,
C.
Cacho
,
J. E.
Rault
,
P. Le
Fèvre
,
F.
Bertran
,
N. C.
Plumb
,
M.
Shi
,
A.
Vecchione
,
M. H.
Fischer
,
J.
Chang
Diamond Proposal Number(s):
[20259]
Open Access
Abstract: Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.
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Mar 2021
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[22052, 18967]
Open Access
Abstract: Understanding and controlling the transition between antiferromagnetic states having different symmetry content with respect to time-inversion and space-group operations are fundamental challenges for the design of magnetic phases with topologically nontrivial character. Here, we consider a paradigmatic antiferromagnetic oxide insulator, Ca2RuO4, with symmetrically distinct magnetic ground states and unveil a novel path to guide the transition between them. The magnetic changeover results from structural and orbital reconstruction at the transition metal site that in turn arise as a consequence of substitutional doping. By means of resonant X-ray diffraction we track the evolution of the structural, magnetic, and orbital degrees of freedom for Mn doped Ca2RuO4 to demonstrate the mechanisms which drive the antiferromagnetic transition. While our analysis focuses on a specific case of substitution, we show that any perturbation that can impact in a similar way on the crystal structure, by reconstructing the induced spin–orbital exchange, is able to drive the antiferromagnetic reorganization.
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Jun 2022
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I05-ARPES
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Masafumi
Horio
,
Filomena
Forte
,
Denys
Sutter
,
Minjae
Kim
,
Claudia G.
Fatuzzo
,
Christian E.
Matt
,
Simon
Moser
,
Tetsuya
Wada
,
Veronica
Granata
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Gianmarco
Gatti
,
Henrik M.
Ronnow
,
Moritz
Hoesch
,
Timur K.
Kim
,
Chris
Jozwiak
,
Aaron
Bostwick
,
Eli
Rotenberg
,
Iwao
Matsuda
,
Antoine
Georges
,
Giorgio
Sangiovanni
,
Antonio
Vecchione
,
Mario
Cuoco
,
Johan
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: Doped Mott insulators are the starting point for interesting physics such as high temperature superconductivity and quantum spin liquids. For multi-band Mott insulators, orbital selective ground states have been envisioned. However, orbital selective metals and Mott insulators have been difficult to realize experimentally. Here we demonstrate by photoemission spectroscopy how Ca2RuO4, upon alkali-metal surface doping, develops a single-band metal skin. Our dynamical mean field theory calculations reveal that homogeneous electron doping of Ca2RuO4 results in a multi-band metal. All together, our results provide evidence for an orbital-selective Mott insulator breakdown, which is unachievable via simple electron doping. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states.
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Nov 2023
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I05-ARPES
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Carolina A.
Marques
,
Philip A. E.
Murgatroyd
,
Rosalba
Fittipaldi
,
Weronika
Osmolska
,
Brendan
Edwards
,
Izidor
Benedičič
,
Gesa-R.
Siemann
,
Luke C.
Rhodes
,
Sebastian
Buchberger
,
Masahiro
Naritsuka
,
Edgar
Abarca-Morales
,
Daniel
Halliday
,
Craig
Polley
,
Mats
Leandersson
,
Masafumi
Horio
,
Johan
Chang
,
Raja
Arumugam
,
Mariateresa
Lettieri
,
Veronica
Granata
,
Antonio
Vecchione
,
Phil D. C.
King
,
Peter
Wahl
Diamond Proposal Number(s):
[28412]
Open Access
Abstract: Van Hove singularities (VHss) in the vicinity of the Fermi energy often play a dramatic role in the physics of strongly correlated electron materials. The divergence of the density of states generated by VHss can trigger the emergence of phases such as superconductivity, ferromagnetism, metamagnetism, and density wave orders. A detailed understanding of the electronic structure of these VHss is therefore essential for an accurate description of such instabilities. Here, we study the low-energy electronic structure of the trilayer strontium ruthenate Sr4Ru3O10, identifying a rich hierarchy of VHss using angle-resolved photoemission spectroscopy and millikelvin scanning tunneling microscopy. Comparison of k-resolved electron spectroscopy and quasiparticle interference allows us to determine the structure of the VHss and demonstrate the crucial role of spin-orbit coupling in shaping them. We use this to develop a minimal model from which we identify a mechanism for driving a field-induced Lifshitz transition in ferromagnetic metals.
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Apr 2024
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