On the groupsJ(ℂℙ m ) andJ(ℍℙ n )

Suter, Ulrich W.

doi:10.1007/bf02938493

Bol. Soc. Bras. Mat

1974

DOI: 10.1007/bf02938493

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On the groupsJ(ℂℙ m ) andJ(ℍℙ n )

Ulrich W. Suter

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2000

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“…Our results were obtained by a double irradiation technique which we developed to extract the quadrupolar contribution to the overall NMR relaxation [11]; we sketch this technique as follows. The relaxation of the spin system towards its thermodynamic equilibrium is described by the so-called master equation [12] and, in the interaction representation [13,14], it is given by…”

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confidence: 99%

“…dP(t)/dt = 0), Eq. (1) can be solved exactly [11]. The essential result is that, mainly due to the |∆m| = 2 transitions, the intensities of different lines change compared to a standard detection method (e.g.…”

mentioning

confidence: 99%

“…The spinecho sequence (with S rf =0) provides signals with intensities I se . For the (−3/2, −1/2) transition the enhancement factor, E, is then given by [11]:…”

mentioning

confidence: 99%

“…E is a rather insensitive function with respect to W 1 , since W 1 connects the same energy levels as W , except the (−1/2, 1/2) transition [11]. However, E depends significantly on W 2 which makes the separate detection of quadrupole relaxation possible.…”

mentioning

confidence: 99%

“…More information and details concerning the method and its experimental realization as well as different cross-checks of the results are given in Ref. [11].…”

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confidence: 99%

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Charge Degree of Freedom and the Single-Spin Fluid Model inYBa2Cu4O8

et al. 2000

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We present a 17 O nuclear magnetic resonance study in the stoichiometric superconductor YBa2Cu4O8. A double irradiation method enables us to show that, below around 200 K, the spin-lattice relaxation rate of plane oxygen is not only driven by magnetic, but also significantly by quadrupolar fluctuations, i.e. low-frequency charge fluctuations. In the superconducting state, on lowering the temperature, the quadrupolar relaxation diminishes faster than the magnetic one. These findings show that, with the opening of the pseudo spin gap, a charge degree of freedom of mainly oxygen character is present in the electronic low-energy excitation spectrum.PACS numbers: 74.25.Nf, 74.72.Bk, One of the central issues in understanding cupratebased high-temperature superconductors (HTSC) has been to determine the minimal number of electronic degrees of freedom which are necessary to describe the physics at the atomic scale of these structures. Zhang and Rice proposed that doped holes, which go into oxygen states, form a spin-resonant singlet state with the quasilocalized holes at copper [1]. Therefore, only one spin degree of freedom would be necessary to describe the lowenergy dynamics of the electronic system in the normal state of the HTSC. This scenario is often called singlespin fluid (SSF) and is described within a t-J model. However, as was discussed by various authors [2], this model might be an oversimplification.Due to its local character, nuclear magnetic resonance (NMR) is a very attractive method to address these questions. NMR probes the low-energy excitations of the HTSC electronic system and it provides information about copper and oxygen independently. Studies of the uniform spin susceptibility, Re{χ(q = 0, ω = 0} [3], indicate that only one spin degree of freedom is involved thus supporting the SSF model. On the other hand, oxygen and copper reveal a very different temperature dependence of the spin-lattice relaxation [4] which is related to the dynamic spin susceptibility, Im{χ(q, ω L )} [5]. This could suggest independent spin degrees of freedom. However, as pointed out before [6], the hyperfine field, due to antiferromagnetically correlated copper spins, cancels at the oxygen site and this fact can explain the different temperature dependences within a SSF model.There is, however, evidence that this view is incomplete. The 17 O NMR in Y-Ba-Cu-O HTSC has extensively been studied by various groups. Especially the pronounced temperature dependence of the anisotropy of the experimentally determined effective spin-lattice relaxation rate, 17 W eff , of the plane oxygen is still puzzling [7][8][9] while the SSF model predicts an almost temperature independent rate anisotropy. (The meaning of effective will be discussed below.) As we pointed out in Ref.[8], it is also very difficult to explain, within a simple SSF model, the ratio of this rate and the yttrium rate, namely 17 W eff / 89 W (with the external magnetic field B 0 parallel to the c axis). Furthermore, in a detailed analysis, Walstedt et al.[10] compare...

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mentioning

confidence: 99%

mentioning

confidence: 99%

“…The spinecho sequence (with S rf =0) provides signals with intensities I se . For the (−3/2, −1/2) transition the enhancement factor, E, is then given by [11]:…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…More information and details concerning the method and its experimental realization as well as different cross-checks of the results are given in Ref. [11].…”

mentioning

confidence: 99%

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Charge Degree of Freedom and the Single-Spin Fluid Model inYBa2Cu4O8

et al. 2000

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On the groupsJ(ℂℙ m ) andJ(ℍℙ n )

Cited by 1 publication

References 6 publications

Charge Degree of Freedom and the Single-Spin Fluid Model inYBa2Cu4O8

Charge Degree of Freedom and the Single-Spin Fluid Model inYBa2Cu4O8

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