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Nakamura, Fumihiko; Goko, T.; Ito, Masakazu; Fujita, Toshizo; Nakatsuji, Satoru; Fukazawa, Hideto; Maeno, Y.; Alireza, Patricia; Forsythe, D.; Julian, S. R.

doi:10.1103/physrevb.65.220402

Cited by 130 publications

(132 citation statements)

References 20 publications

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“…Ca 2 RuO 4 itself exhibits a peculiar paramagnetic metal-insulator transition [6] (MIT) at T MIT = 360 K, basically concurrent with the change from L-Pbca (long c axis) to S-Pbca (short c axis) structure [8,9] at T S = 356 K. Similar transitions have been reported when Ca is partially replaced by Sr (x 0.2) or under pressure [10,11]. The origin of the MIT has been intensively investigated, both experimentally [5][6][7][8][9][10][11][12][13][14][15] and theoretically [16][17][18][19][20][21][22][23][24][25][26]. Electronically, Ca 2 RuO 4 is characterized by 2/3-filled t 2g bands (t 4 2g e 0 g electronic configuration).…”

Section: Introductionsupporting

confidence: 56%

Mott transition, spin-orbit effects, and magnetism in Ca2RuO4

Zhang

Pavarini

2017

Phys. Rev. B

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In this work, we study the effects of spin-orbit and Coulomb anisotropy on the electronic and magnetic properties of the Mott insulator Ca 2 RuO 4 . We use the local-density approximation + dynamical mean-field approach and spin-wave theory. We show that, contrary to a recent proposal, the Mott metal-insulator transition is not induced by the spin-orbit interaction. We confirm that, instead, it is mainly driven by the change in structure from long to short c-axis layered perovskite. We show that the magnetic ordering and the anisotropic Coulomb interactions play a small role in determining the the size of the gap. The spin-orbit interaction turns out to be essential for describing the magnetic properties. It not only results in a spin-wave gap, but it also enlarges significantly the magnon bandwidth.

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Section: Introductionsupporting

confidence: 56%

Mott transition, spin-orbit effects, and magnetism in Ca2RuO4

Zhang

Pavarini

2017

Phys. Rev. B

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“…In addition, a new phase transition in Ca 2 RuO 4 has been found recently by applying an external hydrostatic pressure [51]. Above a very small pressure (p c = 0.5 GPa) Ca 2 RuO 4 shows metallic properties, and most unusually it becomes a ferromagnetic metal with a Curie temperature T c strongly dependent on pressure.…”

Section: Fig 20mentioning

confidence: 94%

Unconventional superconductivity and magnetism in Sr2RuO4 and related materials

et al. 2004

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Key words unconventional triplet superconductivity, spin fluctuations, strong electronic correlations PACS 74.20.Mn, 74.70.Pq We review the normal and superconducting state properties of the unconventional triplet superconductor Sr2RuO4 with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d-orbitals and a strong magnetic anisotropy occurs (χ +− < χ zz ) due to spin-orbit coupling. The latter results mainly from different values of the g-factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation-induced Cooper-pairing scenario in application to Sr2RuO4 we show how p-wave Cooper-pairing with line nodes between neighboring RuO2-planes may occur.We also discuss the open issues in Sr2RuO4 like the influence of magnetic and non-magnetic impurities on the superconducting and normal state of Sr2RuO4. It is clear that the physics of triplet superconductivity in Sr2RuO4 is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy-fermion systems exhibiting spin fluctuations.

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confidence: 99%

“…In this limit, the ground state is non-magnetic with zero total angular momentum, and therefore a QCP separating it from a magnetically ordered phase is expected as a matter of principle. Although this QCP can be pre-empted by an insulator-metal transition 17,18 or rendered first-order by coupling to the lattice or other extraneous factors, it is sufficient that the system is reasonably close to the hypothetical QCP.To assess the proximity to the QCP and the possibility of finding the Higgs mode, we first reproduce the observed transverse spin-wave modes by applying the spin-wave theory 19,20 to the following phenomenological Hamiltonian dictated by general symmetry considerations:Here,S denotes a pseudospin-1 operator describing the entangled spin and orbital degrees of freedom. This model includes single-ion terms (E and ) of tetragonal (z c) and orthorhombic (x a) symmetries, correspondingly, as well as an XY-type exchange anisotropy (α > 0) and the bond-directional pseudodipolar interaction (A); note that its sign depends on the bond.…”

mentioning

confidence: 99%

Higgs mode and its decay in a two-dimensional antiferromagnet

et al. 2017

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Condensed-matter analogues of the Higgs boson in particle physics allow insights into its behaviour in di erent symmetries and dimensionalities 1 . Evidence for the Higgs mode has been reported in a number of di erent settings, including ultracold atomic gases 2 , disordered superconductors 3 , and dimerized quantum magnets 4 . However, decay processes of the Higgs mode (which are eminently important in particle physics)have not yet been studied in condensed matter due to the lack of a suitable material system coupled to a direct experimental probe. A quantitative understanding of these processes is particularly important for low-dimensional systems, where the Higgs mode decays rapidly and has remained elusive to most experimental probes. Here, we discover and study the Higgs mode in a two-dimensional antiferromagnet using spin-polarized inelastic neutron scattering. Our spin-wave spectra of Ca 2 RuO 4 directly reveal a well-defined, dispersive Higgs mode, which quickly decays into transverse Goldstone modes at the antiferromagnetic ordering wavevector. Through a complete mapping of the transverse modes in the reciprocal space, we uniquely specify the minimal model Hamiltonian and describe the decay process. We thus establish a novel condensed-matter platform for research on the dynamics of the Higgs mode.For a system of interacting spins, amplitude fluctuations of the local magnetization-the Higgs mode-can exist as well-defined collective excitations near a quantum critical point (QCP). We consider here a magnetic instability driven by the intra-ionic spinorbit coupling, which tends towards a non-magnetic state through complete cancellation of orbital (L) and spin (S) moments when they are antiparallel and of equal magnitude 5,6 . This mechanism should be broadly relevant for d 4 compounds of such ions as Ir(V), Ru(IV), Os(IV) and Re(III) with sizable spin-orbit coupling but remains little explored. We investigate the magnetic insulator Ca 2 RuO 4 , a quasi-two-dimensional antiferromagnet 7 with nominally L = 1 and S = 1 (Fig. 1). Because the local symmetry around the Ru(IV) ion is very low 8,9 (having only inversion symmetry), it is widely believed that the orbital moment is completely quenched by the crystalline electric field 10-13 , which is dominated by the compressive distortion of the RuO 6 octahedra along the c-axis (Fig. 1). In the absence of an orbital moment, the nearest-neighbour magnetic exchange interaction is necessarily isotropic. Deviations from this behaviour are a sensitive indicator of an unquenched orbital moment. If this moment is sufficiently strong, it can drive Ca 2 RuO 4 close to a QCP with novel Higgs physics.Our comprehensive set of time-of-flight (TOF) inelastic neutron scattering (INS) data over the full Brillouin zone (Fig. 2a) indeed reveal qualitative deviations of the transverse spin-wave dispersion from those of a Heisenberg antiferromagnet. In particular, the global maximum of the dispersion is found at q = (0,0), in sharp contrast to a Heisenberg antiferromagnet, which has a...

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From Mott insulator to ferromagnetic metal: A pressure study ofCa2RuO4

Cited by 130 publications

References 20 publications

Mott transition, spin-orbit effects, and magnetism in Ca2RuO4

Mott transition, spin-orbit effects, and magnetism in Ca2RuO4

Unconventional superconductivity and magnetism in Sr2RuO4 and related materials

Higgs mode and its decay in a two-dimensional antiferromagnet

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