<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>c</mml:mi></mml:math>-axis superfluid response and pseudogap in high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>superconductors

Panagopoulos, C.; Cooper, J. R.; Xiang, Tao; Wang, Y. S.; Chu, C. W.

doi:10.1103/physrevb.61.r3808

Cited by 37 publications

(45 citation statements)

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“…The overall temperature dependence of z A (T ) remarkably resembles that of the c-axis superfluid density measured by Josephson plasma resonance in Bi2212 [18], penetration depth in YBCO [19], and ac susceptibility in LSCO [20]. A possible explanation is that the interlayer tunneling matrix element is enhanced near the (π, 0) point [21] such that the low-temperature QP weight near (π, 0) contributes substantially to the c-axis superfluid density.…”

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confidence: 66%

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Coherent Quasiparticle Weight and Its Connection to High-TcSuperconductivity from Angle-Resolved Photoemission

et al. 2001

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In conventional superconductors, the pairing energy gap (∆) and superconducting phase coherence go hand-in-hand. As the temperature is lowered, both the energy gap and phase coherence appear at the transition temperature T c . In contrast, in underdoped high-T c superconductors (HTSCs), a pseudogap appears at a much higher temperature T * , smoothly evolving into the superconducting gap at T c [1,2]. Phase coherence on the other hand is only established at T c , signaled by the appearance of a sharp quasiparticle (QP) peak [3] in the excitation spectrum. Another important difference between the two types of superconductors is in the ratio of 2∆/T c ≡ R. In BCS theory, R ∼ 3.5, is constant. In the HTSCs this ratio varies widely, continuing to increase in the underdoped region, where the gap increases while T c decreases. Here we report that in HTSCs it is the ratio z A ∆ m /T c which is approximately constant, where ∆ m is the maximum value of the d-wave gap, and z A is the weight of the coherent excitations in the spectral function. This is highly unusual, since in nearly all phase transitions, T c is determined by an energy scale alone. We further show that in the lowtemperature limit, z A increases monotonically with increasing doping x. The growth is linear, i.e. z A (x) ∝ x, in the underdoped to optimally doped regimes, 1

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“…4(b) we compare the T -dependence of z A (T )/z A (0) between an underdoped and an overdoped sample. The coherent weight drops faster in the overdoped sample at low temperatures, once again reminiscent of the c-axis superfluid density in overdoped LSCO and the trend that the c-axis superfluid density is depleted faster upon heating as doping is increased [20].…”

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confidence: 95%

Coherent Quasiparticle Weight and Its Connection to High-TcSuperconductivity from Angle-Resolved Photoemission

et al. 2001

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“…In addition, recent penetration depth measurements in LSCO and HgBa 2 CuO 4ϩ␦ showed that the c-axis penetration depth c Ϫ2 (0) exhibits similar behavior. 15 The apparent competition between quasistatic magnetic correlations and superconductivity thus results in a crossover to weak superconductivity characterized by a strong suppression of the superfluid density. This suppression in the underdoped region can also be directly linked to the strong reduction in entropy and condensation energy associated with the pseudogap.…”

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“…12,15,19 In total, 16 samples were investigated for each doping content. We note that grain agglomerates can be a cause of poor alignment, and to eliminate these, powders were ball milled in ethanol and dried after adding a defloculant.…”

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Evidence for a generic quantum transition in high-Tccuprates

Tallon²,

et al. 2002

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We study the low-energy spin fluctuations and superfluid density of a series of pure and Zn-substituted high-T c superconductors ͑HTS͒ using the muon spin relaxation and ac-susceptibility techniques. At a critical doping state, p c , we find ͑i͒ simultaneous abrupt changes in the magnetic spectrum and in the superconducting ground state and ͑ii͒ that the slowing down of spin fluctuations becomes singular at Tϭ0. These results provide experimental evidence for a quantum transition that separates the superconducting phase diagram of HTS into two distinct ground states. DOI: 10.1103/PhysRevB.66.064501 PACS number͑s͒: 74.72.Ϫh, 74.25.Ha, 75.40.Ϫs, 76.75.ϩi Quantum phase transitions occur at zero temperature at a critical electron density separating distinct ground states. Near a quantum critical point, electrons in metals are highly correlated and the diverging fluctuations may induce unconventional superconductivity. [1][2][3][4][5][6][7][8] For example, in certain heavy fermion compounds a ''bubble'' of superconductivity occurs around the quantum critical point at which itinerant antiferromagnetism is suppressed by applied pressure. 9 The search for an underlying quantum phase transition in high-T c superconductors ͑HTS͒ is motivated by the potential for quantum fluctuations to bind electronic carriers into superconducting Cooper pairs and also to cause the celebrated linear temperature dependence of their electrical resistivity. [1][2][3][4][5][6][7][8]10 HTS exhibit a common generic phase diagram in which the superconducting transition temperature, T c , rises to a maximum at an optimal doping of approximately 0.16 holes per planar copper atom and then falls to zero on the overdoped side. In addition the underdoped normal state exhibits correlations, which introduce a gap in the density of states that strongly affects all physical properties. There is no phase transition associated with the opening of this gap and so it is called a pseudogap. Analysis of specific heat data, for example, suggests that the pseudogap energy decreases with doping and falls to zero at a critical doping of p c Ӎ0.19, just beyond optimal doping, 10,11 a behavior rather analogous to the quantum-critical heavy-fermion materials. 9 Many fundamental physical quantities such as the superconducting condensation energy, 10,11 the superfluid density, 12,13 and the quasiparticle weight, 10,14 show abrupt changes as p→p c . While compelling in their totality, 10,11 none of the results can be considered as evidence of a quantum transition. In particular there is no evidence for an associated order parameter and slowing down of the relevant fluctuations. With this in mind we examined the evolution with doping of the low-energy spin fluctuation spectrum using muon spin relaxation ( SR) combined with low-field ac-susceptibility measurements of the superfluid density.The samples studied were: ͑i͒ La 2Ϫx Sr x Cu 1Ϫy Zn y O 4 ͑LSCO͒ (xϭ0.03-0.24 and yϭ0, 0.01, and 0.02͒. Samples were synthesized using solid-state reaction and where necessary follow...

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“…For instance La 2 CuO 4 can be doped either by alkaline earth ions or oxygen to exhibit superconductivity. The empirical phase diagram of La 2-x Sr x CuO 4 [3][4][5][6][7][8][9][10][11], depicted in …”

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Universal properties of cuprate superconductors

Schneider

2003

Physica B: Condensed Matter

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To provide an understanding of the universal properties emerging from the empirical correlations and phase diagrams of cuprate superconductors , we invoke the scaling theory of finite temperature and quantum critical phenomena. The universal features are traced back to the existence of quantum critical lines, representing the end lines of the finite temperature transition surface. At the respective quantum critical lines two dimensional superconductor to insulator (2D-QSI) transitions and three dimensional superconductor to normal state (3D-QSN) transitions occur. The flow to this quantum critical points is tuned by doping, substitution and anisotropy. It is shown that the empirical correlations, like the dependence of T c on dopant and substitution concentration, the dependence of T c on zero temperature in-plane penetration depth, etc., reflect universal properties associated with the flow to these quantum critical points and of the crossover from one to the other. A detailed account of the flow to 2D-QSI and 3D-QSN criticality is a challenge for microscopic theories attempting to solve the puzzle of superconductivity in these materials. Key words: Cuprate superconductors, universal propertiesThe evidence for and the implications of critical fluctuations near the superconducting phase transition have been revisited quite often since the discovery of materials which exhibit high temperature superconductivity. Although it has been difficult to confront experiment with the zoo of microscopic theories and models, there have been notable successes in understanding the phenomenology of zero and finite temperature phase 1

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c-axis superfluid response and pseudogap in high-Tcsuperconductors

Cited by 37 publications

References 33 publications

Coherent Quasiparticle Weight and Its Connection to High-TcSuperconductivity from Angle-Resolved Photoemission

Coherent Quasiparticle Weight and Its Connection to High-TcSuperconductivity from Angle-Resolved Photoemission

Evidence for a generic quantum transition in high-Tccuprates

Universal properties of cuprate superconductors

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