Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4

Nakamura, Fumihiko; Sakaki, Mariko; Yamanaka, Yuya; Tamaru, Sho; Suzuki, Takashi; Maeno, Y.

doi:10.1038/srep02536

Cited by 137 publications

(141 citation statements)

References 34 publications

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“…Analogous phenomena can also be triggered using static electric fields. The Mott gap in the multi-orbital Mott insulator Ca 2 RuO 4 , for example, has been reported to collapse under application of a weak electric field (~40 V cm -1 ) 109 far below the energy gap scale. While the exact mechanism is still unsettled, it seems likely that novel phenomena such as a many-body Zener effect and orbital depolarization are at play.…”

Section: Nature Materials Doi: 101038/nmat5017mentioning

confidence: 99%

Towards properties on demand in quantum materials

2017

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Q uantum materials are on the ascent. This term embodies a vast portfolio of compounds and phenomena where ramifications of quantum mechanics are demonstrably real. Quantum materials are in the vanguard of contemporary physics in part because these systems afford an exceptional venue to uncover the many roles of symmetry, topology, dimensionality and strong correlations in macroscopic observables. Here we set out to explore the ways and means of creating new states of matter in quantum materials and manipulating their phases via external stimuli. Practical control of these properties is a precondition for exploiting quantum advantages in new photonic, electronic and energy technologies, a task of significant societal impact 1 . We will primarily focus on the following classes of quantum materials: transition metal oxides, Fe-and Cu-based high-T c superconductors, van der Waals semiconductors, topological insulators and Weyl semimetals, and, finally, graphene.The properties of quantum materials are anomalously sensitive to external stimuli. In these systems, interactions associated with spin, charge, lattice and orbital degrees of freedom are commonly on par with the electronic kinetic energy. A rather fragile balance between coexisting and competing ground states can be readily shifted via external stimuli, leading to a raft of quantum phases and transitions between them 2,3 . Furthermore, certain classes of driven quantum states (Fig. 1a and Box 1) are explicit products of coherent interaction between light and matter 4-6 . Alternatively, the properties of quantum materials can be pre-programmed by directly manipulating the electronic wavefunction and the attendant Berry phase that give rise to the anomalous velocity of electrons in a solid [7][8][9] . These complementary avenues of controls mean that investigations no longer need to be reduced to merely observing (in contrast, for example, to astrophysics). Instead, it is now feasible to attain, in a predictable fashion, 'properties on demand' by steering a quantum material towards a desirable ground, metastable or transient state. The past decade has witnessed an explosion in the field of quantum materials, headlined by the predictions and discoveries of novel Landau-symmetry-broken phases in correlated electron systems, topological phases in systems with strong spin-orbit coupling, and ultra-manipulable materials platforms based on two-dimensional van der Waals crystals. Discovering pathways to experimentally realize quantum phases of matter and exert control over their properties is a central goal of modern condensed-matter physics, which holds promise for a new generation of electronic/photonic devices with currently inaccessible and likely unimaginable functionalities. In this Review, we describe emerging strategies for selectively perturbing microscopic interaction parameters, which can be used to transform materials into a desired quantum state. Particular emphasis will be placed on recent successes to tailor electronic interaction parameters through th...

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Section: Nature Materials Doi: 101038/nmat5017mentioning

confidence: 99%

Towards properties on demand in quantum materials

2017

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“…By the same mechanism, the exchange dominated AF phase also readily switches to FM metal, as observed in La-doped Ca 2 RuO 4 [6,7]. The theory might be relevant also to electric-field-induced FM of Ca 2 RuO 4 [8] and FM state of the RuO 2 planes in oxide superlattices [9]. Further doping suppresses any magnetic order, and we suggest that residual FM correlations may lead to a triplet superconductivity (SC).…”

mentioning

confidence: 98%

Doping-Induced Ferromagnetism and Possible Triplet Pairing ind4Mott Insulators

Chaloupka

Khaliullin

2016

Phys. Rev. Lett.

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We study the effects of electron doping in Mott insulators containing d 4 ions such as Ru 4+ , Os 4+ , Rh 5+ , and Ir 5+ with J = 0 singlet ground state. Depending on the strength of the spin-orbit coupling, the undoped systems are either nonmagnetic or host an unusual, excitonic magnetism arising from a condensation of the excited J = 1 triplet states of t 4 2g . We find that the interaction between J-excitons and doped carriers strongly supports ferromagnetism, converting both the nonmagnetic and antiferromagnetic phases of the parent insulator into a ferromagnetic metal, and further to a nonmagnetic metal. Close to the ferromagnetic phase, the low-energy spin response is dominated by intense paramagnon excitations that may act as mediators of a triplet pairing.PACS numbers: 75.10. Jm, 75.25.Dk, 75.30.Et, 74.10.+v A distinct feature of Mott insulators is the presence of low-energy magnetic degrees of freedom, and their coupling to doped charge carriers plays the central role in transition metal compounds [1]. In large spin systems like manganites, this coupling converts parent antiferromagnet (AF) into a ferromagnetic (FM) metal and gives rise to large magnetoresistivity effects. The doping of spin one-half compounds like cuprates and titanites, on the other hand, suppresses magnetic order and a paramagnetic (PM) metal emerges. In general, the fate of magnetism upon charge doping is dictated by spin-orbital structure of parent insulators.In compounds with an even number of electrons on the d shell, one may encounter a curious situation when the ionic ground state has no magnetic moment at all, yet they may order magnetically by virtue of low-lying magnetic levels with finite spin, if the exchange interactions are strong enough to overcome single-ion magnetic gap. The d 4 ions such as Ru 4+ , Os 4+ , Rh 5+ , Ir 5+ possess exactly this type level structure [2] due to spin-orbit coupling λ(S ·L): the spin S = 1 and orbital L = 1 moments form a nonmagnetic ground state with total J = 0 moment, separated from the excited level J = 1 by λ. A competition of the exchange and spin-orbit couplings results then in a quantum critical point (QCP) between nonmagnetic Mott insulator and magnetic order [3,4]. Since magnetic order is due to condensation of the virtual J = 1 levels and hence "soft", the amplitude (Higgs) mode is expected. The corollary of the "d 4 excitonic magnetism" [3] is the presence of magnetic QCP that does not require any special lattice geometry, and the energy scales involved are large. The recent neutron scattering data [5] √ 2, and T z = iT 0 , it can be written aswhere γ is determined by the bond direction. The model shows AF transition due to a condensation of T at a critical value K c = 6 11 λ of the interaction parameter K = 4t 2 0 /U . The degenerate T x,y,z levels split upon material-dependent lattice distortion, affecting the details of the model behavior [19]. We will consider the cubic symmetry case and make a few comments on the possible effects of the tetragonal splitting.The d 4 system...

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“…Similarly, FM-M behavior is observed in Ca 2 RuO 4 thin films, where in-plane epitaxial stress leads to a structural change 14,15 . Recently-discovered electric-fieldinduced Mott transition in Ca 2 RuO 4 is also accompanied by a change of the lattice distortion 16 . Theoretical studies on relations between the lattice distortions and electronic states are also actively performed [17][18][19][20][21][22][23][24][25][26][27] .…”

Section: Introductionmentioning

confidence: 99%

“…As revealed in previous experiments 6,9,[12][13][14][15][16] , the flattening distortion needs to be released for inducing the metallic state. Therefore, we expect that in-plane pressure, where the crystal is free to expand along the c axis, is more effective than P hydro to change the electronic state in Ca 2 RuO 4 .…”

Section: Introductionmentioning

confidence: 99%

Anisotropic uniaxial pressure response of the Mott insulator Ca2RuO4

et al. 2013

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We have investigated the in-plane uniaxial pressure effect on the antiferromagnetic Mott insulator Ca 2 RuO 4 from resistivity and magnetization measurements. We succeeded in inducing the ferromagnetic metallic phase at lower critical pressure than by hydrostatic pressure, indicating that the flattening distortion of the RuO 6 octahedra is more easily released under in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the pressure responses of various magnetic phases: Although the magnetization increases monotonically with pressure diagonal to the orthorhombic principal axes, the magnetization exhibits peculiar dependence on pressure along the in-plane orthorhombic principal axes. This peculiar dependence can be explained by a qualitative difference between the uniaxial pressure effects along the orthorhombic a and b axes, as well as by the presence of twin domain structures.

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Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4

Cited by 137 publications

References 34 publications

Towards properties on demand in quantum materials

Towards properties on demand in quantum materials

Doping-Induced Ferromagnetism and Possible Triplet Pairing ind4Mott Insulators

Anisotropic uniaxial pressure response of the Mott insulator Ca2RuO4

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