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Martin, Aírton Abrahão; Ruf, T.; Strach, T.; Cardona, M.; Wolf, Th.

doi:10.1103/physrevb.58.14349

Cited by 8 publications

(10 citation statements)

References 24 publications

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“…These results are somewhat surprising in view of several theoretical predictions [2,3,5,13] and what has been observed in most of the HTS. [19,20,21] As pointed out by several authors, the linewidth of this mode is extremely large, indicating strong anharmonicity for this mode. Particularly, Goncharov et al [9] have shown that the Grüneisen parameter related to the E 2g mode is very large, γ E2g = 3.9 ± 0.4.…”

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confidence: 99%

“…[17,18] These behaviors have been observed in most of the HTS. [19,20,21] Besides, the temperature dependence of the phonon frequency and linewidth measured by Raman scattering can give some insight about the anharmonicity of the E 2g mode. In general, due to the lattice expansion contribution, [22] the harmonic phonon frequency is temperature-dependent and in the lowest order is given by:…”

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confidence: 99%

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Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Martinho

Rettori

Pagliuso

et al. 2003

Solid State Communications

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Temperature-dependent Raman scattering studies in polycrystalline MgB2 (10 < T < 300 K) reveal that the E2g phonon does not experience any self-energy renormalization effect across the superconducting critical temperature TC ≈ 39 K, in contrast with most of the current theoretical models. In the presence of our results, those models must be reviewed. The analysis of the temperature dependence of the E2g phonon frequency yields an isobaric Grüneisen parameter of | γE 2g | 1, smaller than the value of 3.9 obtained from isothermal Raman experiments under pressure. It is suggested that this apparent disagreement can be explained in terms of pressureinduced changes of the topology of the Fermi surface. MgB 2 has attracted much recent interest due to its remarkable physical properties such as: i) relatively high superconducting transition, T C = 39 K, for a binary compound with a simple crystal structure, ii) large and anisotropic coherence lengths, critical fields and current densities, and iii) critical currents that are not limited by grain boundaries (absence of weak link effects). [1] MgB 2 forms in a hexagonal structure with space group P6/mmm (D 1 6h ). The B atoms are located on a primitive honeycomb lattice consisting of graphite-type sheets. The B 2 -layers are intercalated with Mg-layers that also form a honeycomb lattice with a Mg atom in the center. For this space group, factor-group analysis predicts four modes at the Γ point: E u + A 2u + E 2g + B 1g , where only the E 2g mode is Raman-active and the B 1g mode is silent. The E 2g phonon is a doubly degenerate in-plane B-B bond-stretching mode[2] with nonvanishing Raman tensor elements (α xx − α yy ) and α xy . First principles lattice dynamics calculations indicate that these modes would be observed at 327 cm −1 (E u ), 405 cm −1 (A 2u ), 572 cm −1 (E 2g ) and 702 cm −1 (B 1g ). [3] In analogy with high T C superconductors (HTS), Hall effect measurements [4] indicate that the charge carriers in MgB 2 are holes with a hole density at 300 K of 1.7 − 2.8×10 23 holes/cm 3 . In fact, hole-mediated su- * Electronic address: hercules@ifi.unicamp.br; URL: http://www.ifi.unicamp.br/gpoms perconductivity has been proposed by An and Pickett for MgB 2 .[5] These authors attribute the relatively high value of T C to the strong coupling between holes and the in-plane boron phonon, E 2g modes. According to this model, the holes originate in the σ (sp 2 orbitals) bands due to charge transfer from the σ bands to the π (p z orbitals) bands. Based on this model, several papers have discussed the possibility of E 2g phonon being a frozen-in mode, strongly coupled to the σ electronic bands near the Fermi level. [2,3,6,7] It is claimed that the E 2g phonon, due to its rather strong coupling to the σ electronic bands, would be highly anharmonic, presenting a very large linewidth. However, Boeri et al [8] pointed out that neither the presence at the Fermi level of the σ bands nor their strong coupling to the E 2g phonon are sufficient to induce such anharmonic effects, and the...

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confidence: 99%

Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Martinho

Rettori

Pagliuso

et al. 2003

Solid State Communications

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“…However, when this CFphonon coupling is taken into account, the B 1g phonon softening can be identified and analyzed. 8,9 The temperature behavior of the B 1g phonon in SmBa 2 Cu 3 O y ͑Sm123͒ resembles rather closely that in Nd123, i.e., the B 1g phonon anomalously hardens when the temperature decreases. In this paper we present evidence that the anomalous hardening of the B 1g phonon in Sm123 is due to its coupling to a CF excitation, similar to Nd123.…”

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confidence: 74%

“…The temperature behavior of the peaks at 200 and 319 cm Ϫ1 in the spectra of SmBa 2 Cu 3 O 6.0 , however, resembles more that of the coupled-phonon-CF excitation in Nd123. 6,8,9 We thus focus our attention on the 4 f excitations in Sm123.…”

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“…A strong renormalization, however, seems unlikely at first sight due to the much larger energy difference of these states compared to the case of Nd123. 6,8,9 Nevertheless, since the symmetry requirements are satisfied, the O2-O3 B 1g phonon should harden and the CF peak should soften with decreasing temperature while gaining intensity, provided the coupling is strong enough.…”

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Anomalous phonon self-energy effects inSmBa2Cu3O
Martin
¹
,
Hadjiev
²
,
Ruf
³

et al. 1998
Phys. Rev. B
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We present a Raman study of the variation of the B 1g O2-O3 out-of-phase plane-oxygen vibration in SmBa 2 Cu 3 O y with temperature. This mode shows an anomalously strong hardening of about 10-13 cm Ϫ1 between 300 and 10 K for both the nonsuperconducting (yϷ6.0) and superconducting (yϷ6.9) samples. At low temperature, new excitations at 90 and 187 cm Ϫ1 were detected in the Raman spectra of the SmBa 2 Cu 3 O 6.0 crystal. Their position and intensity change with temperature in a manner typical for coupledphonon-crystal-field ͑CF͒ excitations. Based on these findings we suggest that the anomalous hardening of the B 1g phonon in SmBa 2 Cu 3 O y is mostly due to its coupling to a Sm 3ϩ CF transition at 193 cm Ϫ1 found earlier in inelastic-neutron-scattering experiments. ͓S0163-1829͑98͒06145-1͔

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Optical Study of Crystal-Field Excitation in (R)Ba2Cu3O7-δ Single Crystals

Martin¹,

Cardona²,

Jandl³

et al. 2000

phys. stat. sol. (b)

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A large number of high‐temperature superconductors (HTS) contain rare‐earth (R) ions with 4f‐electron multiplets which are split by the crystal field (CF) of the neighboring ligands and, in many cases, their energy differences are in the range of optical phonons. When these two excitations (phonons and CF) have the same symmetry and are close in energy they can couple to each other, leading to a doublet structure at low temperature. Since the R ions are located between the CuO2 superconducting planes, this crystal‐field–phonon coupling can be used as a probe to investigate superconductivity related phenomena. In this paper, we discuss the coupling of phonons to CF excitations in (R)Ba2Cu3O7–δ and demonstrate that Raman and infrared spectroscopy can be successfully used as a novel tool for CF studies in HTS, since they are not limited to low energy transfer and can be applied to study small single crystals.

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Raman study of coupled-phonon–crystal-field excitations inNd1+xBa2−x

Cited by 8 publications

References 24 publications

Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Anomalous phonon self-energy effects inSmBa2Cu3O
Martin
¹
,
Hadjiev
²
,
Ruf
³

et al. 1998
Phys. Rev. B
Self Cite

Optical Study of Crystal-Field Excitation in (R)Ba2Cu3O7-δ Single Crystals

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Raman study of coupled-phonon–crystal-field excitations inNd1+xBa2−x

Cited by 8 publications

References 24 publications

Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Anomalous phonon self-energy effects inSmBa2Cu3OMartin1, Hadjiev2, Ruf3 et al. 1998Phys. Rev. BSelf Cite

Optical Study of Crystal-Field Excitation in (R)Ba2Cu3O7-δ Single Crystals

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Product

Resources

About

Anomalous phonon self-energy effects inSmBa2Cu3O
Martin
¹
,
Hadjiev
²
,
Ruf
³

et al. 1998
Phys. Rev. B
Self Cite