Universality of pseudogap and emergent order in lightly doped Mott insulators

Battisti, Irene; Bastiaans, Koen M.; Fedoseev, Vitaly; Torre, A. de la; Iliopoulos, Nikos; Tamai, Anna; Hunter, Emily C.; Perry, Richard; Zaanen, Jan; Baumberger, F.; Allan, Milan P.

doi:10.1038/nphys3894

Cited by 113 publications

(107 citation statements)

References 30 publications

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“…A Dirac cone is not expected in this system due to the breaking of n-glide symmetry by epitaxial constraint, as was shown previously for SrIrO 3 on GdScO 3 [41,42]. However, in a recent work similar V-shaped behavior was found for Sr 2 IrO 4 doped with La 3þ , showing zero DOS at E F [43]. This observation was explained as being a result of charge carriers becoming untrapped for La concentrations exceeding 4%.…”

Section: Spin-orbit Semimetal Sriro 3 In the Two-dimensional Limitmentioning

confidence: 64%

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Autieri²,

et al. 2017

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We investigate the thickness-dependent electronic structure of ultrathin SrIrO 3 and discover a transition from a semimetallic to a correlated insulating state below 4 unit cells. Low-temperature magnetoconductance measurements show that spin fluctuations in the semimetallic state are significantly enhanced while approaching the transition point. The electronic structure is further studied by scanning tunneling spectroscopy, showing that 4 unit cells SrIrO 3 is on the verge of a gap opening. Our density functional theory calculations reproduce the critical thickness of the transition and show that the opening of a gap in ultrathin SrIrO 3 is accompanied by antiferromagnetic order.

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Section: Spin-orbit Semimetal Sriro 3 In the Two-dimensional Limitmentioning

confidence: 64%

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Autieri²,

et al. 2017

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“…Moreover, the phase-separated landscape and the emerging order that we describe in Ref. [32] are not influenced by the presence of the bubbles.…”

Section: Bubbles In the Conductance Layersmentioning

confidence: 89%

“…In Fig. 5(c) we show a conductance layer with a black contour indicating the border between the phase-separated pseudogap and Mott states [32]. As it can be noticed, the bubbles originate from both Mott regions (where there are no dopant atoms) and pseudogap regions (forming around agglomerates of dopant atoms), and when they cross the sharp border between two regions their shape is not affected.…”

Section: Bubbles In the Conductance Layersmentioning

confidence: 94%

“…To what extent this behavior is intrinsic to (Sr 1−x La x ) 2 IrO 4 is not understood. We know from previous STM measurements [32] that the doping concentration is not homogeneous within one sample, but can change on a length scale of hundreds of micrometers, which might complicate the interpretation of transport data. Moreover, for x ≈ 5%, samples show a nanoscale phase separation between Mottinsulating regions with a gap of ∼500 meV and pseudogap regions around clusters of La atoms [30,32].…”

Section: Stm Experiments On the Iridate Sr 2 Iromentioning

confidence: 99%

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Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy

et al. 2017

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The effective Mott gap measured by scanning tunneling microscopy (STM) in the lightly doped Mott insulator (Sr 1−x La x ) 2 IrO 4 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 electric field in this material. Such effects are well known from STM experiments on semiconductors and go under the name of tip-induced band bending (TIBB). We show that this phenomenon also exists in the lightly doped Mott insulator (Sr 1−x La x ) 2 IrO 4 and that, at doping concentrations of x 4%, it causes the measured energy gap in the sample density of states to be bigger than the one measured with other techniques. We develop a model able to retrieve the intrinsic energy gap leading to a value which is in rough agreement with other experiments, bridging the apparent contradiction.At doping x ≈ 5% we further observe circular features in the conductance layers that point to the emergence of a significant density of free carriers in this doping range and to the presence of a small concentration of donor atoms. We illustrate the importance of considering the presence of TIBB when doing STM experiments on correlated-electron systems and discuss the similarities and differences between STM measurements on semiconductors and lightly doped Mott insulators.

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“…Therefore, the nodal liquid state seems to evolve from the remnant Fermi-surface state in electron-doped Sr 2 IrO 4 . Our observation of the coexistence of LHB and the remnant Fermi-surface state might correspond to scanning tunneling microscopy results on Sr 2−x La x IrO 4 where a static phase separation between the large gap state and the small gap state has been observed [26,27], while the present result is hardly reconciled with a simple phase separation of the parent material and the metallic state with a fixed doping level since the spectral line shape and gap size change with La doping, as shown in Fig. 3 [28].…”

mentioning

confidence: 95%

Evolution of the remnant Fermi-surface state in the lightly doped correlated spin-orbit insulator Sr2−xLaxIrO4

et al. 2017

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The electronic structure of the lightly electron-doped correlated spin-orbit insulator Sr 2 IrO 4 has been studied by angle-resolved photoelectron spectroscopy. We have observed the coexistence of a lower Hubbard band and an in-gap band; the momentum dependence of the latter traces that of the band calculations without on-site Coulomb repulsion. The in-gap state remained anisotropically gapped in all observed momentum areas, forming a remnant Fermi-surface state, evolving towards the Fermi energy by carrier doping. These experimental results show a striking similarity with those observed in deeply underdoped cuprates, suggesting the common nature of the nodal liquid states observed in both compounds. DOI: 10.1103/PhysRevB.96.041106 Unconventional physics of superconductivity near the metal-insulator transition in strongly correlated Mott insulators has been one of the major themes in a variety of systems, such as cuprates, iron-based compounds, heavyelectron systems, and organic materials [1]. Recently, much attention has been given to 5d-electron systems in which the magnitude of spin-orbit coupling is comparable to the transfer-integral and Coulomb repulsion energies, and this interplay may produce possible novel phases. Sr 2 IrO 4 is a good example of such a system for which the electronic states can be well described by considering spin-orbit coupling as well as Coulomb repulsion energy U [2,3].Sr 2 IrO 4 is an antiferromagnetic insulator with T N = 240 K, and is isostructural to one of the parent compounds of cuprate superconductors, namely, La 2 CuO 4 [4]. Similar to the cuprates, the electronic structure is highly two dimensional, as revealed by angle-resolved photoelectron spectroscopy (ARPES) [5,6]. Unlike cuprates, to date, Sr 2 IrO 4 has not shown superconductivity, although a possible emergence of superconductivity in this system has been theoretically predicted by carrier doping [7][8][9][10]. On the other hand, a d-wave gapped state and Fermi arc behavior have been observed in both the bulk [11] and surface [12][13][14] electronic structures of doped Sr 2 IrO 4 , similar to the cuprates. Such a similarity is puzzling and raises several questions, but this is merely due to the lack of momentum-resolved data in a wide range of doping, especially in the deeply underdoped regime. This is indeed crucial to explore if this anisotropic gap has the same origin as the pseudogap in cuprate superconductors and if the gap is related to superconductivity.To address these unsettled issues, we have studied how this d-wave gapped state evolves by doping in lightly doped Sr 2−x La x IrO 4 (x = 0, 0.04, 0.08) using ARPES. We have observed a dispersive in-gap state that evolves by carrier doping and coexists with the lower Hubbard band (LHB) seen (Fig. S1).ARPES experiments were performed at the 1-squared beamline of BESSY II, using a Scienta-Omicron R8000 analyzer. Circularly polarized light with hν = 100 eV was used to excite the photoelectrons. Clean surfaces for measurements were obtained by in situ cleaving ...

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Universality of pseudogap and emergent order in lightly doped Mott insulators

Cited by 113 publications

References 30 publications

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy

Evolution of the remnant Fermi-surface state in the lightly doped correlated spin-orbit insulator Sr2−xLaxIrO4

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