Temperature-independent pseudogap and thermally activated c-axis hopping conductivity in layered cuprate superconductors

Dzhumanov, S.; Karimboev, E.X.; Kurbanov, U.T.; Ganiev, O.K.; Djumanov, Sh.S.

doi:10.1016/j.spmi.2014.01.004

Cited by 9 publications

(6 citation statements)

References 56 publications

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“…Thus, HTSCs appear to be quasi two-dimensional systems in the wide temperature range well above T c . In accordance with the theory, Gaussian fluctuations of the order parameter prevent any phase coherency in 2D compounds [46,[83][84][85]. Consequently, the SC critical temperature of an ideal 2D metal is found to be zero (Mermin-Wagner-Hoenberg theorem)…”

Section: Fluctuation Conductivitysupporting

confidence: 61%

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Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc

Solovjov,

Petrenko,

Omelchenko

et al. 2020

Preprint

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Temperature dependencies of excess conductivity, σ ′ , have been studied in detail for three FeSe 0.94 textured polycrystalline samples prepared by partial melting and solid state reaction.It was revealed that both σ ′ and its temperature dependence are extremely sensitive to the method of sample preparation. Then, it was shown that in the range from the superconducting transition temperature T c ∼ 9 K up to the characteristic temperature T 01 ∼ 19 K, σ ′ (T ) obeys the classical fluctuation theories of Aslamazov-Larkin (AL) and Hikami-Larkin (Maki-Thompson (MT) term) pointing to the existence of fluctuating Cooper pairs in FeSe at temperatures exceeding double T c . Like in cuprates, AL-MT crossover at T 0 < T 01 is observed, which means the appearance of 3D-2D dimensional transition at this temperature. This allows us to determine the coherence length along the c-axis, ξ c (0) ∼ 3 Å, and a set of additional samples' parameters, including the phase relaxation time, τ φ , of fluctuating Cooper pairs, within a simple two-dimensional free-carrier picture. It was shown that τ φ in FeSe coincides with that found for YBa 2 Cu 3 O 7−δ suggesting that the nature of superconducting fluctuations is very similar for these high-temperature superconductors of different types.

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Section: Fluctuation Conductivitysupporting

confidence: 61%

“…[36][37][38] and references therein). The main reason for that is related to the nature of the pseudogap (PG), which is known to open below T * , that in underdoped cuprates is much above T c and may have superconducting nature [37,[44][45][46]. Unlike cuprates, there is an obvious lack of research on the SC fluctuations in FeSe.…”

Section: Introductionmentioning

confidence: 99%

Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc

Solovjov,

Petrenko,

Omelchenko

et al. 2020

Preprint

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“…As a result, the proposed new phase diagrams of cuprates are also very different 3–5,9,18,19 . Thus, despite the tremendous efforts towards this end there is still no consensus on the physical nature of the PG (refer to 1–11,18,19,28–32 and references therein).…”

Section: Introductionmentioning

confidence: 99%

Effect of annealing on a pseudogap state in untwinned YBa2Cu3O7−δ single crystals

Solovjov

Petrenko

Omelchenko

et al. 2019

Sci Rep

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The effect of annealing both in the oxygen atmosphere and at room temperatures on physical properties such as the pseudogap (Δ*(T)) and excess conductivity (σ′(T)) of untwined YBa 2 Cu 3 O 7−δ (YBCO) single crystal with a small deviation from oxygen stoichiometry is studied. It was revealed that as the charge carrier density, n f , increases, Т с also slightly increases, whereas the temperature of the pseudogap opening, T*, decreases noticeably, which is consistent with the phase diagram (PD) of cuprates. The excess conductivity in the vicinity of T c is represented by the Aslamazov-Larkin and Hikami-Larkin fluctuation theories, illustrating the three-dimensional to two-dimensional (i.e. 3D-2D) crossover with an increase in temperature. The crossover temperature T 0 determines the coherence length along the c axis is ξ c (0) = 0.86 Å, that is 2.6 times larger than for optimally doped YBCO single crystals with defects. Taking into account the short coherence length in high-temperature superconductors, in the model of free charge carriers the phase relaxation time of fluctuating Cooper pairs is determined, τ φ (100 K) = (4.55 ± 0.4) · 10 −13 s, which is slightly (1.2 times) larger than in well-structured YBCO films, and as in films, does not depend on n f . It is shown that Δ*(T) at different annealing stages practically does not change its shape. As in the well-structured YBCO films, Δ*(T) demonstrates maximum at T pair ~124 K which depends weakly on n f . However, the maximum value of Δ*(T pair ) increases with increasing n f , as it follows from the PD of cuprates. Comparing the experimental data with the Peters-Bauer theory we estimated the density of local pairs ≈ 0.3 near T c that is a common value for high-temperature superconductors.

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“…A key issue of HTSCs physics is the study of the anomalies of the pseudogap state [1][2][3][4][5][9][10][11][12][13][14][15], which is observed below the PG opening temperature, T * >> T c , in the range of the phase diagram with a concentration of charge carriers less than the optimal one, which is usually called the range of "underdoped states". In this region, numerous anomalies of electronic properties are observed, associated with a decrease in the density of single-particle excitations and anisotropic rearrangement of the spectral density of charge carriers, most likely due to the rearrangement of the Fermi surface [9,10,16].…”

Section: Introductionmentioning

confidence: 99%

Influence of electron irradiation on fluctuation conductivity and pseudogap in YBa2Cu3O7−δ single crystals

Solovjov

Omelchenko

Petrenko

et al. 2022

Low Temperature Physics

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The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity ρ(T) of an optimally doped YBa 2 Cu 3 O 7-δ single crystal has been studied. The temperature dependences of both fluctuation conductivity σ΄(T) and the pseudogap Δ * (T) on irradiation dose φ have been calculated within the local pair model. Here we show that with an increase in φ, the value of ρ(300 K) increases linearly, while T c decreases linearly. Concurrently, the value of ρ(100 K) increases nonlinearly, demonstrating a feature for φ 3 = 4.3•10 18 e/cm 2 , which is also observed in the number of other dose-dependent parameters. Regardless of the irradiation dose, in the temperature range from T c up to T 01 , σ΄(T) obeys the classical fluctuation theories of Aslamazov-Larkin (3D-AL) and Maki-Thompson (2D-MT), demonstrating 3D-2D crossover with increasing temperature. The crossover temperature Т 0 makes it possible to determine the coherence length along the с axis, ξ с (0), which increases by ~ 3 times under irradiation. Furthermore, the range of superconducting fluctuations above T c also noticeably increases. At φ 1 = 0, the dependence Δ * (T) typical for single crystals containing pronounced twin boundaries is observed with a maximum at T pair ~ 120 K and a distinct minimum at T = T 01 . It was determined for the first time that at φ 3 = 4.3•10 18 e/cm 2 the shape of Δ * (T) changes strongly and becomes the same as in optimally doped YBa 2 Cu 3 O 7-δ single crystals with a very low pseudogap opening temperature T * and noticeably reduced T pair , while at T c (φ) there are no singularities. With an increase in the irradiation dose up to φ 4 = 8.8•10 18 e/cm 2 , the shape of Δ * (T) is restored and becomes the same as in well-structured YBa 2 Cu 3 O 7-δ films and untwined single crystals. Moreover, in this case, T pair and Т * increase noticeably.

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Temperature-independent pseudogap and thermally activated c-axis hopping conductivity in layered cuprate superconductors

Cited by 9 publications

References 56 publications

Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc

Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc

Effect of annealing on a pseudogap state in untwinned YBa2Cu3O7−δ single crystals

Influence of electron irradiation on fluctuation conductivity and pseudogap in YBa2Cu3O7−δ single crystals

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