arXiv subjects

A. Damascelli

Publications and source records attributed to A. Damascelli.

At least 91 records · Page 5Linked to original sources

arXiv2003

Effect of chemical inhomogeneity in the bismuth-based copper oxide superconductors

We examine the effect on the superconducting transition temperature (Tc) of chemical inhomogeneities in Bi2201 and Bi2212 single crystals. Cation disorder at the Sr crystallographic site is inherent in these materials and strongly affects the value of Tc. Partial substitution of Sr by Ln (Ln = La, Pr, Nd, Sm, Eu, Gd, and Bi) in Bi_{2}Sr_{1.6}Ln_{0.4}CuO_{6} results in a monotonic decrease of Tc with increasing ionic radius mismatch. By minimizing Sr site disorder at the expense of Ca site disorder, we demonstrate that the Tc of Bi2212 can be increased to 96 K. Based on these results we discuss the effects of chemical inhomogeneity in other bulk high-temperature superconductors.

cond-mat.supr-con↗

arXiv2003

Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates

The low-energy excitations of the lightly doped cuprates were studied by angle-resolved photoemission spectroscopy. A finite gap was measured over the entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This effect was observed to be generic to the normal states of numerous cuprates, including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to close with increasing carrier doping. We consider various scenarios to explain our results, including the possible effects of chemical disorder, electronic inhomogeneity, and a competing phase.

cond-mat.supr-con↗

arXiv2003

Powerlaw optical conductivity with a constant phase angle in high Tc superconductors

In certain materials with strong electron correlations a quantum phase transition (QPT) at zero temperature can occur, in the proximity of which a quantum critical state of matter has been anticipated. This possibility has recently attracted much attention because the response of such a state of matter is expected to follow universal patterns defined by the quantum mechanical nature of the fluctuations. Forementioned universality manifests itself through power-law behaviours of the response functions. Candidates are found both in heavy fermion systems and in the cuprate high Tc superconductors. Although there are indications for quantum criticality in the cuprate superconductors, the reality and the physical nature of such a QPT are still under debate. Here we identify a universal behaviour of the phase angle of the frequency dependent conductivity that is characteristic of the quantum critical region. We demonstrate that the experimentally measured phase angle agrees precisely with the exponent of the optical conductivity. This points towards a QPT in the cuprates close to optimal doping, although of an unconventional kind.

cond-mat.str-el↗

arXiv2003

An angle-resolved photoemission spectral function analysis of the electron doped cuprate Nd_1.85Ce_0.15CuO_4

Using methods made possible by recent advances in photoemission technology, we perform an indepth line-shape analysis of the angle-resolved photoemission spectra of the electron doped (n-type) cuprate superconductor Nd_1.85Ce_0.15CuO_4. Unlike for the p-type materials, we only observe weak mass renormalizations near 50-70 meV. This may be indicative of smaller electron-phonon coupling or due to the masking effects of other interactions that make the electron-phonon coupling harder to detect. This latter scenario may suggest limitations of the spectral function analysis in extracting electronic self-energies when some of the interactions are highly momentum dependent.

cond-mat.supr-con↗

arXiv2003

Evolution of a Metal to Insulator Transition in Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$, as seen by ARPES

We present angle resolved photoemission (ARPES) data on Na-doped Ca$_2$CuO$_2$Cl$_2$. We demonstrate that the chemical potential shifts upon doping the system across the insulator to metal transition. The resulting low energy spectra reveal a gap structure which appears to deviate from the canonical $d_{x2-y2} ~ |cos(k_x a)-cos(k_y a)|$ form. To reconcile the measured gap structure with d-wave superconductivity one can understand the data in terms of two gaps, a very small one contributing to the nodal region and a very large one dominating the anti-nodal region. The latter is a result of the electronic structure observed in the undoped antiferromagnetic insulator. Furthermore, the low energy electronic structure of the metallic sample contains a two component structure in the nodal direction, and a change in velocity of the dispersion in the nodal direction at roughly 50 meV. We discuss these results in connection with photoemission data on other cuprate systems.

cond-mat.str-el↗

arXiv2002

Universality of the Electronic Structure from a Half Filled CuO_2 Plane

We present angle resolved photoemission (ARPES) data from insulating A_2CuO_2X_2 (A=Sr, Ca; X=Cl, Br), Sr_2Cu_3O_4Cl_2, and Bi_2Sr_2MCu_2O_8 (M=Er, Dy) single crystals which illustrate that the low energy electronic structure of the half-filled cuprates are independent of the apical atom. By performing a photon energy dependent study on Ca_2CuO_2Cl_2 we are able to distinguish between features which are intrinsic and those which are a result of the photoemission matrix elements. We find that the dispersion is independent of photon energy, while an asymmetry in the electron occupation probability across the antiferromagnetic zone boundary is robust to variations in photon energy. Finally, we show that the d-wave-like dispersion which exists in the insulator along the antiferromagnetic zone boundary does not precisely fit the simple d-wave functional form near the nodal direction.

cond-mat.str-el↗

arXiv2002

Doping dependence of an n-type cuprate superconductor investigated by ARPES

We present an angle resolved photoemission (ARPES) doping dependence study of the n-type cuprate superconductor Nd_2-xCe_xCuO_4, from the half-filled Mott-insulator to the T_c=24K superconductor. In Nd2CuO4, we reveal the charge-transfer band (CTB) for the first time. As electrons are doped into the system, this feature's intensity decreases with the concomitant formation of near-E_F spectral weight. At low doping, the Fermi surface is an electron-pocket (with volume ~ x) centered at (pi,0). Further doping leads to the creation of a new hole-like Fermi surface (volume ~ 1+x) centered at (pi,pi). These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the n-type cuprates.

cond-mat.str-el↗

arXiv2001

Electronic structure of MgB$_2$ from angle-resolved photoemission spectroscopy

The first angle-resolved photoemission spectroscopy results from MgB$_2$ single crystals are reported. Close to the $Γ$K and $Γ$M directions, three distinct dispersions are observed approaching the Fermi energy, as can be assigned to the theoretically predicted $σ$ (B $2p_{x,y}$) and $π$ (B $2p_z$) bands. In addition, we also observed a small parabolic-like band centered around $Γ$, and attributed it to a surface-derived state. Good agreement between our results and the band calculations suggests that the electronic structure of MgB$_2$ is of a conventional nature, thus implying that electron correlations are weak, and may be of little importance to the superconductivity in this system.

cond-mat.supr-con↗

arXiv2001

Electronic structure of the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$

The low-energy electronic structure of the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ near optimal doping is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface, and the superconducting d-wave gap and coherence peak are observed and compared with those of single and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with $T_c$ for various optimally doped materials. This suggests that the higher $T_c$ of the trilayer system should be attributed to parameters that simultaneously enhance phase stiffness and pairing strength.

cond-mat.supr-con↗

arXiv2001

Anomalous electronic structure and pseudogap effects in Nd_1.85Ce_0.15CuO_4

We report a high-resolution angle-resolved photoemission spectroscopic (ARPES) study of the electron-doped (n-type) cuprate superconductor Nd_1.85Ce_0.15CuO_4. We observe regions along the Fermi surface where the near-E_F intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy ``pseudogap'' in the underdoped p-type (hole doped) cuprates. However, instead of occurring near the (pi, 0) region, as in the p-type materials, this pseudogap falls near the intersection of the underlying Fermi surface with the antiferromagnetic Brillouin zone boundary.

cond-mat.supr-con↗

arXiv2001

Nature of the Electronic Excitations near the Brillouin Zone Boundary of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Based on angle resolved photoemission spectra measured on different systems at different dopings, momenta and photon energies, we show that the anomalously large spectral linewidth in the $(π,0)$ region of optimal doped and underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ has significant contributions from the bilayer splitting, and that the scattering rate in this region is considerably smaller than previously estimated. This new picture of the electronic excitation near $(π,0)$ puts additional experimental constraints on various microscopic theories and data analysis.

cond-mat.supr-con↗

arXiv2001

From Mott insulator to overdoped superconductor: Evolution of the electronic structure of cuprates studied by ARPES

We review our angle-resolved photoemission spectroscopy (ARPES) results on different layered oxide superconductors, and on their insulating parent compounds. The low energy excitations are discussed with emphasis on some of the most recent issues, such as the Fermi surface and remnant Fermi surface, the pseudogap and d-wave-like dispersion, and lastly the signatures in the ARPES spectra of multiple electronic components, many body effects, and the superfluid density. We will focus on systematic changes in the electronic structure which may be relevant to the development of a comprehensive picture for the evolution from Mott insulators to overdoped superconductors.

cond-mat.str-el↗

arXiv2001

Surface electronic structure of Sr2RuO4

We have addressed the possibility of surface ferromagnetism in Sr2RuO4 by investigating its surface electronic states by angle-resolved photoemission spectroscopy (ARPES). By cleaving samples under different conditions and using various photon energies, we have isolated the surface from the bulk states. A comparison with band structure calculations indicates that the ARPES data are most readily explained by a nonmagnetic surface reconstruction.

cond-mat.supr-con↗

arXiv2001

Superconducting Gap and Strong In-Plane Anisotropy in Untwinned YBa2Cu3O7-d

With significantly improved sample quality and instrumental resolution, we clearly identify in the (pi,0) ARPES spectra from YBa2Cu3O6.993, in the superconducting state, the long-sought `peak-dip-hump' structure. This advance allows us to investigate the large a-b anisotropy of the in-plane electronic structure including, in particular, a 50% difference in the magnitude of the superconducting gap that scales with the energy position of the hump feature. This anisotropy, likely induced by the presence of the CuO chains, raises serious questions about attempts to quantitatively explain the YBa2Cu3O7-d data from various experiments using models based on a perfectly square lattice.

cond-mat.supr-con↗

arXiv2001

Bilayer Splitting in the Electronic Structure of Heavily Overdoped Bi2Sr2CaCu2O8+d

The electronic structure of heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88 meV for the normal state feature, while it is only about 20 meV for the superconducting peak. This anomalous behavior cannot be reconciled with the quasiparticle picture.

cond-mat.supr-con↗

arXiv2000

Fermi surface of Sr2RuO4 from angle resolved photoemission

We investigated the low-energy electronic structure of Sr2RuO4 by angle-resolved photoemission spectroscopy (ARPES) focusing, in particular, on the controversial issues of the Fermi surface (FS) topology and of the extended van Hove singularity (evHs). A detailed study of temperature and photon energy dependence demonstrates the surface-state nature of the electronic band responsible for the evHs, and may suggest the presence of ferromagnetic correlations at the surface. In addition, we detected a replica of the primary FS that indicates a (sqrt2 x sqrt2) surface reconstruction, as confirmed by LEED. In light of these findings, the FS determined by ARPES is consistent with LDA and de Haas-van Alphen (dHvA) results, and it provides additional information on the detailed shape of the alpha, beta and gamma sheets. Also, at this stage, because of the strong sensitivity of the cleaved surface, we could not find any robust signature of the crossover from 2D to 3D Fermi liquid behavior in our ARPES measurements for T<130 K.

cond-mat.str-el↗

arXiv2000

Superconducting Gap Anisotropy in Nd$_{1.85}$Ce$_{0.15}$CuO$_4$: Results from Photoemission

We have performed angle resolved photoelectron spectroscopy on the electron doped cuprate superconductor Nd$_{1.85}$Ce$_{0.15}$CuO$_4$. A comparison of the leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5-2 meV near the ($π$,0) position, but no observable shift along the zone diagonal near ($π$/2,$π$/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order in this cuprate superconductor.

cond-mat.supr-con↗

arXiv2000

Fermi Surface, Surface States, and Surface Reconstruction in Sr2RuO4

The electronic structure of Sr2RuO4 is investigated by high angular resolution ARPES at several incident photon energies. We address the controversial issues of the Fermi surface (FS) topology and of the van Hove singularity at the M point, showing that a surface state and the replica of the primary FS due to (sqrt2 x sqrt2) surface reconstruction are responsible for previous conflicting interpretations. The FS thus determined by ARPES is consistent with the de Haas-van Alphen results, and it provides additional information on the detailed shape of the alpha, beta and gamma sheets.

cond-mat.str-el↗