Magnetic properties of iridium pyrochlores R2Ir2O7(R = Y, Sm, Eu and Lu)

Taira, Nobuyuki; Wakeshima, Makoto; Hinatsu, Yukio

doi:10.1088/0953-8984/13/23/312

Cited by 127 publications

(171 citation statements)

References 17 publications

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“…These materials have a large spin orbit couplings and are in a regime of intermediate correlations, making them promising candidates to realize topological insulators [12,13]. They have a magnetic ground state [14,15] and, within a LSDA+U+SO calculations, conjectured to be semi-metals. Most strikingly the low energy physics is described by the Weyl equation, which is the two component version of the Dirac equation.…”

Section: Graphenementioning

confidence: 99%

Adler-Bell-Jackiw anomaly in Weyl semimetals: Application to pyrochlore iridates

2012

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Weyl semimetals are three dimensional analogs of graphene where the energy of the excitations are a linear function of their momentum. Pyrochlore Iridates (A2Ir2O7) with A =yttrium or lanthanide element) are conjectured to be examples of such a system, with the low energy physics described by twenty four Weyl nodes. An intriguing possibility is that these materials provide a physical realization of the Adler-Bell-Jackiw anomaly. In this letter we investigate the properties of pyrochlore iridates in an applied magnetic field. We find that the dispersion of the lowest landau level depends on the direction of the applied magnetic field. Consequently the velocity at low energies can be manipulated by changing the direction of the applied field. The resulting anisotropy in longitudinal conductivity is investigated. [7], and Majorana modes [7,8] are a few examples. A common feature of these systems is that the low energy physics is described by a two component Dirac Hamiltonian with the fermionic momentum is confined to two dimensions. Recently pyrochlore iridates have been conjectured to realize the Adler-Bell-Jackiw (ABJ)[9, 10] chiral anomaly, adding another example to the growing list. GrapheneWan et al.[11] explored the possibility of the three dimensional analog of graphene being realized in the pyrochlore iridates. These materials have a large spin orbit couplings and are in a regime of intermediate correlations, making them promising candidates to realize topological insulators [12,13]. They have a magnetic ground state [14,15] and, within a LSDA+U+SO calculations, conjectured to be semi-metals. Most strikingly the low energy physics is described by the Weyl equation, which is the two component version of the Dirac equation. There are 24 Weyl nodes, three around each L point ([111] and equivalent directions) in the Brilloiun zone (see fig.1). Nodes related either by inversion or reflection about the {xy, yz, zx} planes have opposite chirality. Consequently the material is expected to have an anomalous hall response to applied uniaxial pressure and is susceptible to charge ordering in large magnetic fields [16].In a quantizing magnetic field, the Lowest Landua Level (LLL) is a linear function of the magnitude of a momentum, with the sign determined by the band structure. If an electric field is applied parallel to the magnetic field, the Adler-Bell-Jackiw (ABJ) [9,10] axial anomaly leads to an anomalous magneto-conductance. The origin of this effect is in the production of Weyl fermions of a given chirality and an equivalent annihilation of the opposite chirality [17]. This translates to a transfer of particles from one Weyl node to another of opposite chirality at a constant rate. To reach a steady state, this is balanced by inter-node scattering due to impurities.In the absence of the magnetic field, the intra-node scattering is quite effective in relaxing the momentum. In the presence of a large field, such that only the LLL is occupied, intra-node scattering is suppressed due to a lack of phase space. The...

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Section: Graphenementioning

confidence: 99%

Adler-Bell-Jackiw anomaly in Weyl semimetals: Application to pyrochlore iridates

2012

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“…In the case of R = Nd, Sm, and Eu, this magnetic transition is also accompanied by an electronic transition from metal to insulator. Magnetic susceptibility measurements on R 2 Ir 2 O 7 (R = Y, Sm, Eu, and Lu) reveal a small anomaly at T c and significant hysteresis between field-cooled and zero-field-cooled curves 12,14,15,17 . This has been interpreted as evidence of either a spin glass 12 [18][19][20] .…”

Section: Introductionmentioning

confidence: 98%

“…Magnetic susceptibility measurements on R 2 Ir 2 O 7 (R = Y, Sm, Eu, and Lu) reveal a small anomaly at T c and significant hysteresis between field-cooled and zero-field-cooled curves 12,14,15,17 . This has been interpreted as evidence of either a spin glass 12 [18][19][20] . In a recent analysis by Disseler it is argued that µSR data on Y 2 Ir 2 O 7 and Eu 2 Ir 2 O 7 is only consistent with an all-in/all-out magnetic structure 21 .…”

Section: Introductionmentioning

confidence: 98%

X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

et al. 2016

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We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (∼6 to 300 K) and pressures (∼0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high resolution Ir L3-edge RIXS. In spite of very different ground state properties, we find these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ∼3-5 eV, spin-orbit excitations at ∼0.5-1 eV, and broad low-lying excitations below ∼0.15 eV. In Eu2Ir2O7 we observe highly damped magnetic excitations at ∼45 meV, which display significant momentum dependence. We compare these results with recent dynamical structure factor calculations.

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“…Because of the feature of the Ir 4+ ion, these systems are in a novel regime where strong spin-orbital coupling, strong correlation as well as geometric frustration are present, and new physics may emerge. As temperature is lowered, the A=Eu, Sm, Nd systems experience metalinsulator phase transitions 35 that are clearly associated with a singularity in the magnetic susceptibility, suggesting magnetic ordering [14][15][16] . Recent µSR measurement on A=Eu system, where metal-insulator transition occurs at 120K, suggests large static ordering moment ∼ 1µ B from Ir 4+17 .…”

Section: Introductionmentioning

confidence: 99%

Quantum Hall effects in a Weyl semimetal: Possible application in pyrochlore iridates

2011

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There have been lots of interest in pyrochlore Iridates A2Ir2O7 where both strong spin-orbital coupling and strong correlation are present. A recent LDA calculation 1 suggests that the system is likely in a novel three dimensional topological semi-metallic phase: a Weyl semi-metal. Such a system has zero carrier density and arrives at the quantum limit even in a weak magnetic field. In this paper we discuss two novel quantum effects of this system in a magnetic field: a pressure-induced anomalous Hall effect and a magnetic field induced charge density wave at the pinned wavevector connecting Weyl nodes with opposite chiralities. A general formula of the anomalous hall coefficients in a Weyl semi-metal is also given. Both proposed effects can be probed by experiments in the near future, and can be used to detect the Weyl semi-metal phase.

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Magnetic properties of iridium pyrochlores R₂Ir₂O₇(R = Y, Sm, Eu and Lu)

Cited by 127 publications

References 17 publications

Adler-Bell-Jackiw anomaly in Weyl semimetals: Application to pyrochlore iridates

Adler-Bell-Jackiw anomaly in Weyl semimetals: Application to pyrochlore iridates

X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

Quantum Hall effects in a Weyl semimetal: Possible application in pyrochlore iridates

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