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Song, Yi‐Qiao; Lee, Moohee; Halperin, W. P.; Tonge, L. M.; Marks, Tobin J.

doi:10.1103/physrevb.45.4945

Phys. Rev. B

1992

DOI: 10.1103/physrevb.45.4945

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Determination of magnetic penetration depth from saddle-point field analysis inTl2Ba2

Yi‐Qiao Song

Moohee Lee

W. P. Halperin

et al.

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Cited by 12 publications

(10 citation statements)

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“…In the weak coupling limit the low temperature slope of the susceptibility of a d-wave superconductor with T c = 80 K corresponds to a Gd K shift of 10 ppm/K [16]. Diamagnetic corrections are not negligible for lower fields and in the c direction, and we estimate the field dependence of B c dia from classical expressions and recent numerical results [18][19][20][21][22]. Above the vortex lattice melting temperature the magnetic field inhomogeneity due to vortices is motionally averaged and B bulk demagnetization, which is roughly proportional to ln(H c2 /B) [18][19][20].…”

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confidence: 91%

“…A shift, ∆B saddle , in addition to demagnetization appears when the vortex lattice freezes, because the magnetic field distribution is asymmetric and peaked at the saddle point, which is different from the average field. For zero superconducting coherence length, ξ ab = 0, ∆B (0) saddle ≈ 0.037Φ 0 /λ 2 ab ≈ 3 mT in a triangular vortex lattice with λ ab = 160 nm [21]. However, numerical studies show [20,22] that already in fields where the distance between vortices is much larger than ξ ab , ∆B saddle is reduced significantly.…”

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confidence: 95%

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Magnetic-Field-Induced Low-Energy Spin Excitations inYBa2Cu4O8Measured b

et al. 2000

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We have measured the spin susceptibility of the underdoped high temperature superconductor, YBa2Cu4O8 by Gd 3+ electron spin resonance in single crystals and aligned powders at several magnetic fields between 3 and 15.4 T. At low temperatures and high fields, the spin susceptibility of the CuO2 planes is enhanced slightly in the B c orientation with respect to the B ⊥ c orientation. The enhancement in an applied field of 15.4 T (≈ 0.15 Hc2) at 16 K (0.2 Tc) is approximately 10 percent of the susceptibility measured at Tc. Such a small magnitude suggests that the second critical field of superconductivity, Hc2 ≈ 100 T, would not suppress the pseudogap. This work demonstrates the potential of high field ESR in single crystals for studying high Tc superconductors. 74.25.Nf, 74.72.Bk, 76.30.Kg The structure of vortex lines in high temperature superconductors (HTSCs) may shed light on the microscopic mechanism of superconductivity. The earliest dwave pairing theories implied that the zero temperature spin susceptibility should scale with magnetic field as (B/H c2 ) 1/2 [1,2] in contrast to the linear dependence in an s-wave superconductor. A rigorous solution of the Bogoliubov-de Gennes equations in the mixed state [3] reveals that quasiparticles in d-wave superconductors are not bound to vortices, and predict a space averaged density of states (DOS) N (0) ∝ (B/H c2 ) γ , where 0.4 ≤ γ ≤ 1 depending on the temperature and the model used [4,5]. A number of experiments were targeted at the field dependence of the DOS in YBa 2 Cu 3 O 7−δ . Scanning tunneling microscopy [6] resolves the DOS at and around vortices, but is unsuitable to measure the total DOS [7]. Bulk experiments on nearly optimally doped YBa 2 Cu 3 O 7−δ include heat capacity [8], infrared transmission [9], thermal conductivity [10], and high field muon spin rotation [11]. Most of these experiments, together with early NMR on planar copper and oxygen [12], indicated some increase in the DOS with magnetic field but were inconclusive about its magnitude.Underdoped HTSCs-which also possess a pseudogap in the normal state-are of special interest, as it is unclear how the pseudogap is related to the d-wave superconducting gap. An indication whether high magnetic fields suppress the pseudogap or not may contribute to understanding its nature. Also, most theoretical calculations of the quasiparticle spectra in HTSCs depend on the assumption that Landau's theory of the Fermi-liquid is applicable below T c , which is still to be justified by experiments. A recent 63 Cu NMR study on YBa 2 Cu 4 O 8 at high fields [13] reports a sizeable field induced DOS for B in the (a, b) plane, implying a large enhancement for B c. In contrast, we show that for B c the DOS enhancement is small and incompatible with a suppression of the pseudogap at B = H c2 .In this Letter, we report the spin susceptibility of YBa 2 Cu 4 O 8 obtained by high field electron spin resonance (ESR) spectroscopy of Gd 3+ in Gd:3+ is a non-perturbing probe of the CuO 2 spin polarization [14]. We se...

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Magnetic-Field-Induced Low-Energy Spin Excitations inYBa2Cu4O8Measured b

et al. 2000

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“…205 T1 spectra were recorded with a spin-echo sequence and by shifting the spectrometer frequency through the resonance. Typical delay times for echo formation were r e & 40-60 /xs.We have studied the c-axis alignment by 205 T1 NMR in the normal state [6,7]. Prom the analysis of the spectra for H || c, H _L c, and the random powder, we found that in this sample (48±2)% of the Tl-2223 crystallites were aligned and the rest randomly oriented.…”

mentioning

confidence: 97%

“…We have studied the c-axis alignment by 205 T1 NMR in the normal state [6,7]. Prom the analysis of the spectra for H || c, H _L c, and the random powder, we found that in this sample (48±2)% of the Tl-2223 crystallites were aligned and the rest randomly oriented.…”

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Low temperature fluctuations of vortices in layered superconductors

et al. 1993

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Data on the 205 T1 NMR frequency shift and linewidth due to the magnetic field variation in the mixed state of Tl2Ba2Ca2Cu30io are presented. These data, which are commonly used to extract the London penetration depth, show a near linear temperature dependence at T < T c . We offer an explanation of this effect as being caused by thermal fluctuations of vortices in weakly coupled layered systems. We argue that the fluctuations cannot be ignored in interpretation of NMR and muon-spin-resonance data for materials with large penetration depths even at low T. PACS numbers: 74.25.Nf, 74.40.+k In weakly coupled layered superconductors, thermal fluctuations of vortices strongly influence the thermodynamics of the system in a magnetic field. This has been observed in "non-mean-field" dependence of the magnetization M on temperature T and magnetic field H in Bi 2 Sr 2 CaCu 2 0 8 (Bi-2212) and Bi 2 Sr2Ca 2 Cu30io (Bi-2223) well under the mean-field transition temperature T C Q. At a temperature T*, a few kelvins below T c o, M is field independent [1-3], The effect has been explained quantitatively by the contribution of fluctuating vortices to the system entropy [4].For high anisotropies and H

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205Tl NMR in oxygen depleted cuprate superconductors Tl2Ba2CaCu2O8−δ

Winzek

Mattausch

Eriksson

et al. 1993

Physica C: Superconductivity

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Determination of magnetic penetration depth from saddle-point field analysis inTl2Ba2

Cited by 12 publications

References 24 publications

Magnetic-Field-Induced Low-Energy Spin Excitations inYBa2Cu4O8Measured b

Magnetic-Field-Induced Low-Energy Spin Excitations inYBa2Cu4O8Measured b

Low temperature fluctuations of vortices in layered superconductors

205Tl NMR in oxygen depleted cuprate superconductors Tl2Ba2CaCu2O8−δ

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