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Chang, A.; Rong, Zhao; Ivanchenko, Yu. M.; Lu, Farun; Wolf, E. L.

doi:10.1103/physrevb.46.5692

Cited by 44 publications

(26 citation statements)

References 28 publications

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“…In this way, with only four free parameters, we succeeded to fit almost all of our data. Consulting other reports [1][2][3][4][5]7], we find that our quasiparticle DOS should be widely applicable. The fits are not as good for the double peaked spectrum in YBCO, as in the inset in Fig.2.…”

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confidence: 70%

“…For this reason various methods, such as angle-resolved photoemission (ARPES), tunneling (TS) and Raman spectroscopies, as well as optical conductivity, are extensively used to elucidate the pairing mechanism in cuprates. Among these, scanning tunneling spectroscopy (STS), with its high spatial and energy resolution, emerges as the technique of choice.Using such a local probe at low temperature, reproducible vacuum tunneling spectra have been obtained on many cuprates [1][2][3][4][5][6][7][8], in particular Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) and YBa 2 Cu 3 O 7 (YBCO). However, one still cannot interpret the experimental curves precisely.…”

mentioning

confidence: 99%

“…Using such a local probe at low temperature, reproducible vacuum tunneling spectra have been obtained on many cuprates [1][2][3][4][5][6][7][8], in particular Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) and YBa 2 Cu 3 O 7 (YBCO). However, one still cannot interpret the experimental curves precisely.…”

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confidence: 99%

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Constraints on the quasiparticle density of states in high- T _c superconductors

et al. 2000

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In this Letter we present new tunneling data on YBa2Cu3O7 thin films by low temperature scanning tunneling spectroscopy. Unusual peak-dip-hump features, previously reported in Bi2Sr2CaCu2O 8+δ , are also found in YBa2Cu3O7. To analyse these common signatures we propose a new heuristic model in which, in addition to the d-wave symmetry, the gap function is energy dependent. A simple expression for the quasiparticle density of states is derived, giving an excellent agreement with the experiment. The dynamics of the quasiparticle states and the energy scales involved in the superconducting transition are discussed.Getting to the heart of the quasiparticle density of states (DOS) in cuprate superconductors is an active goal of current theoretical and experimental research. Indeed, in the case of conventional materials, the quasiparticle DOS in the superconducting state contains the key information on the pairing. For this reason various methods, such as angle-resolved photoemission (ARPES), tunneling (TS) and Raman spectroscopies, as well as optical conductivity, are extensively used to elucidate the pairing mechanism in cuprates. Among these, scanning tunneling spectroscopy (STS), with its high spatial and energy resolution, emerges as the technique of choice.Using such a local probe at low temperature, reproducible vacuum tunneling spectra have been obtained on many cuprates [1][2][3][4][5][6][7][8], in particular Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) and YBa 2 Cu 3 O 7 (YBCO). However, one still cannot interpret the experimental curves precisely. The shape of the DOS in BSCCO has a non-trivial dependence on doping [7,9,10], temperature [7,[9][10][11][12][13][14][15][16] and magnetic field [17,18]. The state density is characterized by its large value at the Fermi level, unusual quasiparticle peaks and dip-hump structures at higher energies (see Fig.1). While the T c vs doping curve is bell-shaped, the gap width decreases linearly, as the doping increases from underdoped to overdoped regimes, with no significant change in the DOS shape [7,9,10]. The temperature dependence is also unconventional: The gap does not vanish at the critical temperature and a pseudogap persists at T > T c [7,9,[12][13][14][15]. Finally, a low temperature pseudogap remains when the superconducting order is destroyed, within the vortex core [18], or due to disorder [6]. All these features are difficult to explain with a BCS-type theory.In this Letter we report our new low-temperature STS data on YBCO thin films. We observe strongly pronounced peak-dip-hump structures and a significant state density at zero bias. With previous data on BSCCO, our observations suggest a common mechanism for these features, linked to the superconducting state in cuprates. In order to clarify this effect, we propose a new quasiparticle DOS based on an energy-dependent gap function. A particular form for this function is inferred from the data and has, in addition to d-wave symmetry, a single minimum at a characteristic energy near the gap value. Using such a simple ap...

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Constraints on the quasiparticle density of states in high- T _c superconductors

et al. 2000

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“…Third, there is neutron spectroscopic evidence for nanoscale cluster formation and percolative superconductivity in various cuprates [2,3]. Fourth, nanoscale spatial variations in the electronic characteristics have been observed in underdoped Bi 2 Sr 2 CaCu 2 O 8+δ with scanning tunnelling microscopy (STM) [4,5,6,7]. They reveal a spatial segregation of the electronic structure into 3nm diameter superconducting domains in an electronically distinct background.…”

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confidence: 99%

Relevance of electron–lattice coupling in cuprate superconductors

Schneider¹,

Khasanov²,

Conder³

et al. 2003

J. Phys.: Condens. Matter

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We study the oxygen isotope ( 16 O, 18 O) and finite size effects in Y1−x PrxBa2Cu3O 7−δ by inplane penetration depth (λ ab ) measurements. A significant change of the length Lc of the superconducting domains along the c-axis and λ 2 ab is deduced, yielding the relative isotope shift ∆Lc/Lc ≈ ∆λ 2 ab /λ 2 ab ≈ −0.14 for x = 0, 0.2 and 0.3. This uncovers the existence and relevance of the coupling between the superfluid, lattice distortions and anharmonic phonons which involve the oxygen lattice degrees of freedom.PACS numbers: 74.72. Bk, 74.25.Kc, 74.62.Yb Since the discovery of superconductivity in cuprates by Bednorz and Müller[1] a tremendous amount of work has been devoted to their characterization. The issue of inhomogeneity and its characterization is essential for several reasons, including: First, if inhomogeneity is an intrinsic property, a re-interpretation of experiments, measuring an average of the electronic properties, is unavoidable. Second, inhomogeneity may point to a microscopic phase separation, i.e. superconducting domains, embedded in a nonsuperconducting matrix. Third, there is neutron spectroscopic evidence for nanoscale cluster formation and percolative superconductivity in various cuprates [2,3]. Fourth, nanoscale spatial variations in the electronic characteristics have been observed in underdoped Bi 2 Sr 2 CaCu 2 O 8+δ with scanning tunnelling microscopy (STM) [4,5,6,7]. They reveal a spatial segregation of the electronic structure into 3nm diameter superconducting domains in an electronically distinct background. On the contrary, a large degree of homogeneity has been observed by Renner and Fischer[8]. As STM is a surface probe the relevance of these observations for bulk and thermodynamic properties remains to be clarified. Fifth, in YBa 2 Cu 3 O 7−δ , MgB 2 , 2H-NbSe 2 and Nb 77 Zr 23 considerably larger domains have been established. The magnetic field induced finite size effect revealed lower bounds ranging from L = 182 to 814A [9,10]. Sixth, since the change of the lattice parameters upon oxygen isotope exchange is negligibly small [11,12], the occurrence of a significant modification of the domains spatial extent, will provide clear evidence for superconductivity mediated by local lattice distortions.This letter concentrates on Y 1−x Pr x Ba 2 Cu 3 O 7−δ with 16 O and 18 O. It addresses these issues by providing clear evidence for a finite size effect on the in-plane London penetration depth, revealing the existence of superconducting domains with spatial nanoscale extent and its significant change upon oxygen isotope exchange.Polycrystalline samples of Y 1−x Pr x Ba 2 Cu 3 O 7−δ (x = 0, 0.2, 0.3) were synthesized by solid-state reactions [13] and their phase-purity was examined using powder xray diffraction. For each doping concentration the samples were reground in a mortar for about 60min. Powder samples with a grain size of < 10µm were obtained by using a system of 20/15/10µm sieves. Oxygen isotope exchange was performed by heating the powder in 18 O 2 gas. In order to en...

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“…Experimentally, V-shaped gaps are indeed commonly observed in c-axis tunneling measurements [7,11,14,19,20,21,22]. Recently, however, U-shaped gaps were observed in tunneling spectra acquired on the (001) Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) surface [17].…”

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confidence: 99%

Scanning tunneling spectroscopy of a -axis YBa ₂ Cu ₃ O _{7 − δ} films: k -selectivity and the shape of the superconductor gap

Sharoni¹,

Leibovitch²,

Kohen³

et al. 2003

Europhys. Lett.

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Abstract. -Tunneling spectroscopy of epitaxial (100) oriented YBa2Cu3O 7−δ films was performed using an STM at 4.2 K. On atomically smooth areas, tunneling spectra revealing clear U-shaped gaps with relatively low zero bias conductance were measured. These spectra can be well fitted to the tunneling theory into a d-wave superconductor only when introducing a strong dependence of the tunneling probability on the wave-vector k. Possible origins for this k -selectivity in STM measurements will be discussed. On other areas, V-shaped gaps as well as zero bias conductance peaks are observed, indicating relaxation of k -selectivity and the effect of nanofaceting, respectively.The d -wave symmetry of the order parameter of YBa 2 Cu 3 O 7−δ (YBCO) [1, 2, 3] has a special signature in the tunneling spectra measured for these superconductors. The hallmark of this is the zero bias conductance peak (ZBCP) that appears when tunneling along or near the nodal direction ([110] for YBCO). This reflects the existence of Andreev bound states at the Fermi level residing on the pair-breaking (110) surface [4,5,6,7,8]. The ZBCP was measured by numerous groups, using both macroscopic and microscopic (STM) tunnel junctions [9,10,11,12,13,14,15]. Manifestation of the d -wave order parameter in the tunneling spectra acquired along the anti-nodal ([100] for YBCO) and the c-axis directions is more controversial. The theory of tunneling into a d -wave superconductor predicts a V-shaped gap structure for both tunneling directions in the case where the density of states (DOS) is isotropically averaged over the Fermi surface [6,7]. Here, quasi-particle excitations are observed at any finite energy, since the nodal directions in k -space are monitored, resulting in a linear dependence of the dI/dV vs. V tunneling spectra on energy around the Fermi energy (zero bias). Such isotropic tunneling scenario is believed to apply to STM measurements [16]. In contrast, U-shaped gaps are predicted to appear when k -vectors along the anti-nodal direction are preferentially monitored in the tunneling process [7,11,14,17,18]. Resolving this issue is thus important for

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Observation of large tunneling-conductance variations in direct mapping of the energy gap of single-crystalBi2Sr2

Cited by 44 publications

References 28 publications

Constraints on the quasiparticle density of states in high- T _c superconductors

Constraints on the quasiparticle density of states in high- T _c superconductors

Relevance of electron–lattice coupling in cuprate superconductors

Scanning tunneling spectroscopy of a -axis YBa ₂ Cu ₃ O _{7 − δ} films: k -selectivity and the shape of the superconductor gap

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Observation of large tunneling-conductance variations in direct mapping of the energy gap of single-crystalBi2Sr2

Cited by 44 publications

References 28 publications

Constraints on the quasiparticle density of states in high- T c superconductors

Constraints on the quasiparticle density of states in high- T c superconductors

Relevance of electron–lattice coupling in cuprate superconductors

Scanning tunneling spectroscopy of a -axis YBa 2 Cu 3 O 7 − δ films: k -selectivity and the shape of the superconductor gap

Contact Info

Product

Resources

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Constraints on the quasiparticle density of states in high- T _c superconductors

Constraints on the quasiparticle density of states in high- T _c superconductors

Scanning tunneling spectroscopy of a -axis YBa ₂ Cu ₃ O _{7 − δ} films: k -selectivity and the shape of the superconductor gap