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Locquet, Jean‐Pierre; Jaccard, Y.; Cretton, Andréas; Williams, E. J.; Arrouy, F.; Machler, E; Schneider, T.; Fischer, Ø.; Martinoli, P.

doi:10.1103/physrevb.54.7481

Cited by 56 publications

(63 citation statements)

References 51 publications

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“…This very surprising result was first obtained by TF-µSR on Tl 2 Ba 2 CuO 6+δ (Tl-2201) [6] and later on (Yb,Ca)-123 and (Y,Ca)-123 [7,8]. Subsequently, it has been confirmed by other experimental techniques [21]. It was previously pointed out that the strong suppression of n o s /m * ab for heavily overdoped samples cannot be understood within a BCS model, unless one assumes that pairbreaking correlations become increasingly important [6,9].…”

supporting

confidence: 54%

Anomalous Peak in the Superconducting Condensate Density of Cuprate High-TcSuperconductors at a Unique Doping State

Tallon²,

et al. 2001

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The doping dependence of the superconducting condensate density, n o s , has been studied by muon-spin-rotation for Y 0. The superconducting condensate density, n s , is proportional to the squared amplitude of the superconducting (SC) order parameter (OP), i.e. of the macroscopic wave function which describes the SC charge carriers. It is thus a fundamental parameter whose variation as a function of temperature (T) and of carrier doping provides important information about the

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supporting

confidence: 54%

Anomalous Peak in the Superconducting Condensate Density of Cuprate High-TcSuperconductors at a Unique Doping State

Tallon²,

et al. 2001

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“…This tendency has been observed subsequently in thin film La 2−x Sr x CuO 4 (LSCO) [13] and bulk YBa 2 Cu 3 O y (YBCO) [14] systems in the OD region. The "coherence peak" in ARPES spectra [15] also follows this behavior of n s /m * in the OD region.…”

mentioning

confidence: 89%

Microscopic phase separation in the overdoped region of high-Tc cuprate superconductors

Uemura

2001

Solid State Communications

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We propose a phenomenological model for high-Tc superconductors (HTSC) assuming: (1) a microscopic phase separation between superconducting and normal-metal areas in the overdoped region; and (2) existence of a homogeneous superconducting phase only below the pseudo-gap T * line, which shows a sharp reduction towards T * ∼ 0 at a mildly overdoped critical concentration xc. This model explains anomalous doping and temperature dependences of ns/m * (superconducting carrier density / effective mass) observed in several overdoped HTSC systems. We point out an analogy to superfluid 4 He/ 3 He films, and discuss an energetic origin of microscopic phase separation. 74.25.Dw, Since the discovery of high-T c cuprate superconductors (HTSC), accumulated studies have revealed unusual phenomena in the underdoped (UD) region, such as, correlations between T c and n s /m * (superconducting carrier density / effective mass) at T → 0 shown by measurements of the magnetic field penetration depth λ [1], and the pseudo-gap phenomena [2]. These results stimulated development of various theories / models for condensation, including Bose-Einstein (BE) to BCS crossover [3,4], phase fluctuations [5,6], XY-model [7] and BE condensation [8]. These models [3][4][5][6][7][8] assume the existence of pre-formed charge pairs above T c . Different pictures, however, assume single charge above T c based on the resonating-valence-bond concepts [9,10].Several anomalous results have been found also in the overdoped (OD) region: µSR studies on Tl 2 Ba 2 CuO 6+δ (Tl2201) [11,12] revealed that n s /m * at T → 0 decreases with increasing hole doping. This tendency has been observed subsequently in thin film La 2−x Sr x CuO 4 (LSCO) [13] and bulk YBa 2 Cu 3 O y (YBCO) [14] systems in the OD region. The "coherence peak" in ARPES spectra [15] also follows this behavior of n s /m * in the OD region. Meanwhile, Tallon and Loram [16] noticed a sharp reduction of the pseudo-gap T * line in the temperature T vs. hole-concentration x phase diagram heading towards T * ∼ 0 at a critical concentration x c ∼ 0.19 holes/Cu which lies in the mildly OD region. In view of the existence of superconductivity in x > x c where the T * line does not exist, Tallon and Loram [16] have advocated a view point that the pseudogap phenomena is not representing pre-cursor superconducting phenomena, but should be ascribed to a tendency towards a ground state competing with superconductivity.We have, however, suggested another possible view point in which T * is ascribed to a signature of a gradual pre-formation of pairs [4] while the anomaly in the OD region to a phase separation [4,11,17,18]. In the present paper, resorting to a model-calculation of n s /m * , comparison with experimental results, a crude estimate of competing electrostatic and condensation/pairing energies, and analogy to 4 He/ 3 He films, we demonstrate that our picture with microscopic phase separation between superconducting and normal-metal regions can quantitatively account for several anomalous results in ...

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“…The T c of these samples typically was about 24 K. This value is comparable to other epitaxial thin film samples but slightly reduced compared to that of the best single crystals of LSCO. This most likely is due to strain at the interface between the substrate and the epitaxial thin film [76,77]. Finally, the NCCO films were deposited similar to the LSCO films by molecular beam epitaxy (MBE) using ozone as oxidation gas [74].…”

Section: Sample Preparation and Experimental Techniquesmentioning

confidence: 99%

Andreev bound states in high temperature superconductors

et al. 1998

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Abstract. Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic field. The tunneling spectra of GBJ formed by YBa2Cu3O 7−δ (YBCO), Bi2Sr2CaCu2O 8+δ (BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4−y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev bound states are discussed and experimental evidence for anomalous Meissner currents is presented.

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Variation of the in-plane penetration depthλabas a function of doping inLa2−

Cited by 56 publications

References 51 publications

Anomalous Peak in the Superconducting Condensate Density of Cuprate High-TcSuperconductors at a Unique Doping State

Anomalous Peak in the Superconducting Condensate Density of Cuprate High-TcSuperconductors at a Unique Doping State

Microscopic phase separation in the overdoped region of high-Tc cuprate superconductors

Andreev bound states in high temperature superconductors

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