Pressure-tuned Frustration of Magnetic Coupling in Elemental Europium

Pi, Shu-Ting; Savrasov, S. Y.; Pickett, Warren E.

doi:10.1103/physrevlett.122.057201

Cited by 9 publications

(9 citation statements)

References 40 publications

(51 reference statements)

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“…The result is to remain spin disordered but with AFM correlations, i.e., incipient AFM order, that will reduce the spin free energy. This correlated spin-liquid phase, the Sachdev-Read MQPM phase that has been proposed in another disordered moment superconductor [35], provides the platform for the superconductivity that appears upon hole doping. None of these complications occur in CaCuO 2 .…”

Section: Discussion: Avoidance Of the Afm Phasementioning

confidence: 86%

“…No items, however, seem as fundamental as the difference in ground states of the undoped materials: antiferromagnetic (AFM) insulator for CCO, and disordered moment conductor for NNO, the latter being a conducting quantum paramagnetic (MQPM) phase in the Sachdev-Read classification [32]. Based on an interacting two-band model, Werner and Hoshino [5] discussed NNO in terms of the spin-freezing theory of unconventional superconductivity [33,34], and the potentially simpler case of superconductivity at high pressure in elemental Eu with disordered f 7 moments [35] might share in this behavior.…”

Section: Introductionmentioning

confidence: 99%

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Fluctuation-frustrated flat band instabilities in NdNiO2

Choi

Pickett

Lee

2020

Phys. Rev. Research

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The discovery that Nd 1−x Sr x NiO 2 , with the CaCuO 2 infinite-layer structure, superconducts up to 15 K around the hole-doping level x = 0.2 raises the crucial question of its fundamental electronic and magnetic processes. The unexplained basic feature that we address is that, for x = 0 and as opposed to strongly antiferromagnetic (AFM) CaCuO 2 , NdNiO 2 with the same structure and formal d 9 configuration does not undergo AFM order. We study this issue not in the conventional manner, as energetically unfavored or as frustrated magnetic order, but as an instability of the AFM phase itself. We are able to obtain the static AFM ordered state, but find that a flat band, one-dimensional-like van Hove singularity (vHs) is pinned to the Fermi level. This situation is unusual in a non-half-filled, effectively two-band system. The vHs makes the AFM phase unstable to spindensity disproportionation, breathing, and half-breathing lattice distortions, and (innate or parasitic) chargedensity disproportionation. These flat band instabilities, distant relatives of single-band cuprate models, thereby inhibit but do not eliminate incipient AFM tendencies at low temperature. The primary feature is that a pair of active bands (d x 2 −y 2 , d z 2) eliminate half-filled physics and, due to instabilities, preclude the AFM phase seen in CaCuO 2. This strongly AFM correlated, conducting spin-liquid phase with strong participation of the Ni d z 2 orbital forms the platform for superconductivity in NdNiO 2 .

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Section: Discussion: Avoidance Of the Afm Phasementioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Fluctuation-frustrated flat band instabilities in NdNiO2

Choi

Pickett

Lee

2020

Phys. Rev. Research

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“…This system displays strong interplay and competition between the R 4f magnetic moment and the conduction states with heavy Ni character, with the R 5d playing an important role in coupling the local moments to the itinerant states. [25,26] Elemental europium at high pressure but retaining a f 7 local moment, switches from metallic and magnetically ordered to superconducting and magnetically disordered around 80 GPa, [27,28] providing its own questions about the effect of 4f moments on pairing, a coupling that must proceed through the Eu 5d states.…”

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confidence: 99%

Role of 4f states in infinite-layer NdNiO2

2020

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Atomic 4f states have been found to be essential players in the physical behavior of lanthanide compounds, at the Fermi level EF as in the proposed topological Kondo insulator SmB6, or further away as in the magnetic superconductor system RNi2B2C (R=rare earth ion) and in Y1−xPrxBa2Cu3O7, where the 4f shell of Pr has a devastating effect on superconductivity. In hole-doped RNiO2, the R=Nd member is found to be superconducting while R=La is not, in spite of the calculated electronic structures being nearly identical. We report first principles results that indicate that the Nd 4f moment affects states at EF in infinite-layer NdNiO2, an effect that will not occur for LaNiO2. Treating 20% hole-doping in the virtual crystal approach indicates that 0.15 holes empty the Γ-centered Nd-derived electron pocket while leaving the other electron pocket unchanged; hence Ni only absorbs 0.05 holes; the La counterpart would behave similarly. However, coupling of 4f states to the electron pockets at EF arises through the Nd intra-atomic 4f − 5d exchange coupling K ≈ 0.5 eV and is ferromagnetic (FM), i.e. anti-Kondo, in sign. This interaction causes spin-disorder broadening of the electron pockets and should be included in models of the normal and superconducting states of Nd0.8Sr0.2NiO2. The Ni moments differ by 0.2µB for FM and antiferromagnetic alignment (the latter are larger), reflecting some itineracy and indicating that Heisenberg coupling of the moments may not provide a quantitative modeling of Ni-Ni exchange coupling.

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“…incipient AFM order, that reduce the free energy. This correlated spin liquid phase, the Sachdev-Read MQPM phase that has been proposed in another disordered moment superconductor, [34] provides the platform for the superconductivity that appears upon hole doping.…”

mentioning

confidence: 93%

“…No items however seem as fundamental as the difference in ground states of the undoped materials: antiferromagnetic (AFM) insulator for CCO, and disordered moment conductor for NNO, the latter being a conducting quantum paramagnetic (MQPM) phase in the Sachdev-Read classification. [31] Based on an interacting two-band model, Werner and Hoshino [4] discussed NNO in terms of the spin-freezing theory of unconventional superconductivity, [32,33] and the potentially simpler case of superconductivity at high pressure in elemental Eu with disordered f 7 moments [34] might share in this behavior.…”

mentioning

confidence: 99%

Fluctuation-frustrated flat band instabilities in NdNiO2

Choi,

Pickett,

Lee

2020

Preprint

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The discovery that Nd1−xSrxNiO2, with the CaCuO2 infinite-layer structure, superconducts up to 15 K around the hole-doping level x=0.2, raises many important questions about its fundamental electronic and magnetic processes. One unexplained feature is that, for x=0 and as opposed to CaCuO2, NdNiO2 with the same formal d 9 configuration does not order antiferromagnetically (AFM). We study the experimentally inaccessible AFM phase, finding for the static lattice, a flatband, one-dimensional van Hove singularity (vHs) pinned to the Fermi level is unstable to charge, spin, and lattice orders. These flat-band instabilities thereby limit incipient AFM order at low temperature and, being assisted by zero point fluctuations of the oxygen lattice, preclude the AFM phase seen in CaCuO2. This strongly AFM correlated, conducting spin-liquid phase forms the platform for superconductivity in NdNiO2.

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Pressure-tuned Frustration of Magnetic Coupling in Elemental Europium

Cited by 9 publications

References 40 publications

Fluctuation-frustrated flat band instabilities in NdNiO2

Fluctuation-frustrated flat band instabilities in NdNiO2

Role of 4f states in infinite-layer NdNiO2

Fluctuation-frustrated flat band instabilities in NdNiO2

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