Polarization Analysis of Thermal-Neutron Scattering

Moon, R. M.; Riste, T.; Koehler, W. C.

doi:10.1103/physrev.181.920

Cited by 654 publications

(359 citation statements)

References 10 publications

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“…At a specific momentum and energy transfer, incident neutrons can be polarized along the x, y, and z directions, and the scattered neutrons can have polarizations either parallel (neutron nonspin flip or NSF, ↑↑) or antiparallel (neutron spin flip or SF, ↑↓) to the incident neutrons. Therefore, the six neutron scattering cross sections can be written as σ NSF α and σ SF α , where α = x, y, z 35,37 . If we use M α and N to denote the magnetic response and nuclear scattering, respectively, the neutron scattering cross sections σ NSF α and σ SF α are related to M α and N via Eq.…”

Section: Methodsmentioning

confidence: 99%

Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe1.85Ni0.15As

et al. 2012

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We use polarized inelastic neutron scattering to study low-energy spin excitations and their spatial anisotropy in electron-overdoped superconducting BaFe1.85Ni0.15As2 (Tc = 14 K). In the normal state, the imaginary part of the dynamic susceptibility, χ ′′ (Q, ω), at the antiferromagnetic (AF) wave vector Q = (0.5, 0.5, 1) increases linearly with energy for E ≤ 13 meV. Upon entering the superconducting state, a spin gap opens below E ≈ 3 meV and a broad neutron spin resonance appears at E ≈ 7 meV. Our careful neutron polarization analysis reveals that χ ′′ (Q, ω) is isotropic for the in-plane and out-of-plane components in both the normal and superconducting states. A comparison of these results with those of undoped BaFe2As2 and optimally electron-doped BaFe1.9Ni0.1As2 (Tc = 20 K) suggests that the spin anisotropy observed in BaFe1.9Ni0.1As2 is likely due to its proximity to the undoped BaFe2As2. Therefore, the neutron spin resonance is isotropic in the overdoped regime, consistent with a singlet to triplet excitation.

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Section: Methodsmentioning

confidence: 99%

Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe1.85Ni0.15As

et al. 2012

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“…24 For convenience, we define the neutron polarization directions along Q as x, perpendicular to Q but in the scattering plane as y, and perpendicular to Q and the scattering plane as z, respectively ͓Fig. 1͑c͔͒.…”

Section: B Polarized Neutron Analysismentioning

confidence: 99%

“…The measured neutron cross sections are then accordingly written as ␣ NSF and ␣ SF , where ␣ = x , y , z. 24 With the Cryopad setup, these cross sections can be measured with the sample in a strictly zero magnetic field ͑Ͻ10 mG͒, thus avoiding errors due to flux inclusion or field expulsion in the superconducting phase of the sample.…”

Section: B Polarized Neutron Analysismentioning

confidence: 99%

Anisotropic neutron spin resonance in superconductingBaFe1.9Ni0.1As2

et al. 2010

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We use polarized inelastic neutron scattering to show that the neutron spin resonance below T c in superconducting BaFe 1.9 Ni 0.1 As 2 ͑T c =20 K͒ is purely magnetic in origin. Our analysis further reveals that the resonance peak near 7 meV only occurs for the planar response. This challenges the common perception that the spin resonance in the pnictides is an isotropic triplet excited state of the singlet Cooper pairs, as our results imply that only the S 001 = Ϯ 1 components of the triplet are involved.

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“…In order to determine the direction of the moments for the antiferromagnetic state it is necessary to use polarized neutrons, as outlined by Moon et al in 1969. 12 The crystal used in the experiments is twinned so that a* could not be differentiated from b*.…”

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confidence: 99%

“…12 The crystal used in the experiments is twinned so that a* could not be differentiated from b*. We thus consider the crystal to be tetragonal so that the [1, 1, 0] direction is in the basal plane and the [1, -1, 0] direction perpendicular to the page is also in the basal plane.…”

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confidence: 99%

Polarized neutron measurement of magnetic order inYBa2Cu3O6.45

et al. 2004

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Orbital current order of the d-density-wave type (DDW) has been postulated to explain the pseudogap in the high temperature superconductors. We have performed neutron scattering experiments to search for this order and show here the results obtained on an YBa 2 Cu 3 O 6.45 sample using the best neutron spectrometers available. We argue that the data are consistent with a small, largely c-axis-directed moment, found below about 200K.PACS numbers: 72.15. Gd, 61.12.Ld, 71.30.+h 2 The microscopic origin of the pseudogap is one of the most puzzling attributes of the cuprate superconductors. A review of the various experimental techniques used to determine the pseudogap is given by Timusk and Statt. 1 It is generally considered to stem from pairing above the superconducting transition temperature T C 2,3 or result from another ground-state differentiated from superconductivity by a quantum critical point. 4,5 Chakravarty et al. 6 but a competing phase judged to stem from impurities made the identification of the DDW state difficult. The moments from the bond currents result in peaks at the (h/2, k/2, l) superlattice positions of the reciprocal lattice. This is the position that magnetism is found in the parent compound, YBa 2 Cu 3 O 6.15 , which is an insulator with a Néel transition temperature well above room temperature and has been studied previously. 10,11 The defining attribute of the DDW state is that the moment should be largely along the c-axis. Small moments in the sample crystal originating from the parent compound should be located in the a-b plane as is found for this material. Other magnetic impurity phases could be possible, but to our knowledge no such phases 3 are known to have high temperature (above 50K) magnetic order along the c-axis for the YBa 2 Cu 3 O 6+x system.In order to determine the direction of the moments for the antiferromagnetic state it is necessary to use polarized neutrons, as outlined by Moon et al. in 1969. 12 The crystal used in the experiments is twinned so that a* could not be differentiated from b*. We thus consider the crystal to be tetragonal so that the (1, 1, 0) reflection showed no peak indicating that the higher order scattering from the monochromator was well removed. Figure 1b shows the result of a HF SF measurement through the (1/2, 1/2, 1) position at 20 K. The scan range on the high Q side of the scan is limited by intense NSF scattering that is difficult to correct for with the rather small flipping ratio as seen in Fig 3a. Nevertheless, a peak is observed at (0.5, 0.5, 1) and a Gaussian fit results in a height of 11±2 counts with a width of 0.01±0.002 FWHM at the position 0.5±0.001 r.l.u. The peak is resolution limited, giving a correlation length of about 380Å. Figure 1c shows no evidence for a peak at a temperature of 150K. Multiple runs were averaged to obtain the observed error bars. 5These scans took over two days each and are difficult to improve in a reasonable time period.Also, since the magnetic signal is so small, a higher flipping ratio is des...

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Polarization Analysis of Thermal-Neutron Scattering

Cited by 654 publications

References 10 publications

Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe1.85Ni0.15As

Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe1.85Ni0.15As

Anisotropic neutron spin resonance in superconductingBaFe1.9Ni0.1As2

Polarized neutron measurement of magnetic order inYBa2Cu3O6.45

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