Effects of Electron-Electron Interactions on Nuclear Spin-Lattice Relaxation Rates and Knight Shifts in Alkali and Noble Metals

Narath, Albert; Weaver, H. T.

doi:10.1103/physrev.175.373

Cited by 258 publications

(100 citation statements)

References 29 publications

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“…Hence one expects K Ͼ 1 if antiferromagnetic fluctuations are dominant. 41,42 It has been shown 43 that the Korringa ratio is unity when the hyperfine coupling A͑q͒ is momentum independent and the vertex corrections are negligible. The fact that the Korringa ratio is larger than 1 indicates that there are significant vertex corrections when there are large antiferromagnetic fluctuations.…”

Section: Antiferromagnetic Spin Fluctuationsmentioning

confidence: 99%

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Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

2007

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We give a quantitative analysis of the previously published nuclear magnetic resonance ͑NMR͒ experiments in the -͑ET͒ 2 X family of organic charge-transfer salts. The temperature dependence of the nuclear-spin relaxation rate 1 / T 1 , the Knight shift K s , and the Korringa ratio K is compared to the predictions of the phenomenological spin-fluctuation model of Moriya and Millis, Monien, and Pines ͑M-MMP͒, that has been used extensively to quantify antiferromagnetic spin fluctuations in the cuprates. For temperatures above T NMR Ӎ 50 K, the model gives a good quantitative description of the data in the metallic phases of several -͑ET͒ 2 X materials. These materials display antiferromagnetic correlation lengths which increase with decreasing temperature and grow to several lattice constants by T NMR . It is shown that the fact that the dimensionless Korringa ratio is much larger than unity is inconsistent with a broad class of theoretical models ͑such as dynamical mean-field theory͒ which neglects spatial correlations and/or vertex corrections. For materials close to the Mott insulating phase the nuclear-spin relaxation rate, the Knight shift, and the Korringa ratio all decrease significantly with decreasing temperature below T NMR . This cannot be described by the M-MMP model and the most natural explanation is that a pseudogap, similar to that observed in the underdoped cuprate superconductors, opens up in the density of states below T NMR . Such a pseudogap has recently been predicted to occur in the dimerized organic charge-transfer salts materials by the resonating valence bond ͑RVB͒ theory. We propose specific experiments on organic superconductors to elucidate these issues. For example, measurements to see if high magnetic fields or high pressures can be used to close the pseudogap would be extremely valuable.

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Section: Antiferromagnetic Spin Fluctuationsmentioning

confidence: 99%

“…Thus we see that K Ͻ 1 in the presence of ferromagnetic fluctuations. 41,42 So again vertex corrections are important if the system has strong ferromagnetic fluctuations. Recall that, in contrast, for antiferromagnetic fluctuations the Korringa ratio is larger than 1.…”

Section: ͑10͒mentioning

confidence: 99%

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

2007

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“…͑2͒. In terms of the enhancement factor K͑␣͒, where ␣ is associated with the Stoner susceptibility factor, 39 we write = K͑␣͒ o . At temperatures below the Kondo temperature in the case of antiferromagnetic spin fluctuations, K͑␣͒ Ͼ 1, resulting in enhanced values for the Korringa product.…”

Section: ͑2͒mentioning

confidence: 99%

High-field suppression of in-gap states in the Kondo insulatorSmB6

et al. 2007

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The controversial ground-state properties of the Kondo insulator SmB 6 have been investigated using 11 B NMR in very high magnetic fields up to 37 T. We find evidence that, following the development of a gap in the conduction-band density of states below 100 K, the in-gap states dominate the nuclear relaxation at temperatures less than 10 K. The Korringa product 1 / K 2 T 1 T exhibits anomalous behavior in this range and the application of high magnetic fields leads to suppression of nuclear relaxation. The hybridization gap, however, remains open up to 37 T. The behavior of the relaxation at low temperatures suggests a strong field dependence of the in-gap states and rules out the possibility that bound states arise from B 6 vacancies. A simple densityof-states model and a band scheme are introduced to account for these observations.

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“…This particular sample is very close to the theoretical value of for nuclei relaxed by their Fermi contact hyperfine interaction with an electron gas in which electronelectron effects are negligible. When electron-electron effects are included in the analysis, then the theoretical value of the Korringa product K2 TI Tis enhanced [16]. Again, there is some contrast with Si : P results where the measured products are greater [2] than the value of…”

mentioning

confidence: 96%

“…Estimates of the size of this effect [I71 in germanium show that it should be negligible. However, relaxation by the dipolar interaction [16] of the nuclei with the electron spins is a possibility as an explanation of the anomalously low Korringa products.…”

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confidence: 99%

HOST NUCLEAR RESONANCE IN Ge : As

Deshmukh

Tunstall

1976

J. Phys. Colloques

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RBsumB. -On mesure le temps de relaxation spin-rkseau et le dkplacement de Knight du noyau 73Ge dans le systkmes : As. La densit6 du As vhrie de 7,O x 1016 cm-3 jusqu'a 1,75 X 1019 cm3 et les 6chantillons ne sont pas compensbs. La caractkrisation des echantillons est obtenue par des mesures de conductivite et d'effet Hall. Les mesures ne redlent aucun effet des interactions electrons-Blectrons autour de la transition m6tal-non metal. Le deplacement de Knight disparait brusquement k la transition.Abstract. -Measurements of the spin-lattice relaxation time and of the Knight shift of the 73Ge nucleus in &: As are reported. The density range of As is from 7.0 x 1016 cm-3 up to 1.75 x 1019 cm-3 and the samples are uncompensated. The characterization of the samples is supported by conductivity and Hail measurements. There is little or no indication of any electronelectron enhancement of the NMR parameters around the metal-non metal transition. TheKnight shift disappears rather abruptly at the transition.

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Effects of Electron-Electron Interactions on Nuclear Spin-Lattice Relaxation Rates and Knight Shifts in Alkali and Noble Metals

Cited by 258 publications

References 29 publications

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

High-field suppression of in-gap states in the Kondo insulatorSmB6

HOST NUCLEAR RESONANCE IN Ge : As

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