arXiv subjects

D. S. Dessau

Publications and source records attributed to D. S. Dessau.

At least 37 records · Page 2Linked to original sources

arXiv2013

Pair Breaking Caused by Magnetic Impurities in the High-T$_\text{C}$ Superconductor Bi$_{2.1}$Sr$_{1.9}$Ca(Cu$_{1-x}$Fe$_{x}$)$_{2}$O$_{y}$

Conventional superconductivity is robust against the addition of impurities unless the impurities are magnetic in which case superconductivity is quickly suppressed. Here we present a study of the cuprate superconductor Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_{8+δ}$ that is intentionally doped with the magnetic impurity, Fe. Through the use of our Tomographic Density of States (TDoS) technique, we find that while the superconducting gap magnitude is essentially unaffected by the inclusion of iron, the onset of superconductivity, T$_{C}$, and the pair-breaking rate are strongly dependent and correlated. These findings suggest that, in the cuprates, the pair-breaking rate is critical to the determination of T$_{C}$ and that magnetic impurities do not disrupt the strength of pairing but rather the lifetime of the pairs.

cond-mat.supr-con↗

arXiv2012

Anisotropic Impurity-States, Quasiparticle Scattering and Nematic Transport in Underdoped Ca(Fe1-xCox)2As2

Iron-based high temperature superconductivity develops when the `parent' antiferromagnetic/orthorhombic phase is suppressed, typically by introduction of dopant atoms. But their impact on atomic-scale electronic structure, while in theory quite complex, is unknown experimentally. What is known is that a strong transport anisotropy with its resistivity maximum along the crystal b-axis, develops with increasing concentration of dopant atoms; this `nematicity' vanishes when the `parent' phase disappears near the maximum superconducting Tc. The interplay between the electronic structure surrounding each dopant atom, quasiparticle scattering therefrom, and the transport nematicity has therefore become a pivotal focus of research into these materials. Here, by directly visualizing the atomic-scale electronic structure, we show that substituting Co for Fe atoms in underdoped Ca(Fe1-xCox)2As2 generates a dense population of identical anisotropic impurity states. Each is ~8 Fe-Fe unit cells in length, and all are distributed randomly but aligned with the antiferromagnetic a-axis. By imaging their surrounding interference patterns, we further demonstrate that these impurity states scatter quasiparticles in a highly anisotropic manner, with the maximum scattering rate concentrated along the b-axis. These data provide direct support for the recent proposals that it is primarily anisotropic scattering by dopant-induced impurity states that generates the transport nematicity; they also yield simple explanations for the enhancement of the nematicity proportional to the dopant density and for the occurrence of the highest resistivity along the b-axis.

cond-mat.supr-con↗

arXiv2012

Coupled Spin-Orbital Texture in a Prototypical Topological Insulator

One of the most important properties of topological insulators (TIs) is the helical spin texture of the Dirac surface states, which has been theoretically and experimentally argued to be left-handed helical above the Dirac point and right handed helical below. However, since the spin is not a good quantum number in these strongly spin-orbit coupled systems, this can not be a complete statement, and we must consider the total angular momentum J = L + S that is a contribution of the spin and orbital terms. Using a combination of orbital and spin-resolved angle-resolved photoemission spectroscopy (ARPES), we show a direct link between the different orbital and spin components, with a "backwards" spin texture directly observed for the in-plane orbital states of Bi2Se3.

cond-mat.str-el↗

arXiv2012

Dimensionality controlled Mott transition and correlation effects in single- and bi-layer perovskite iridates

We studied Sr2IrO4 and Sr3Ir2O7 using angle-resolved photoemission spectroscopy (ARPES), making direct experimental determinations of intra- and inter-cell coupling parameters as well as Mott correlations and gap sizes. The results are generally consistent with LDA+U+Spin-orbit coupling (SOC) calculations, though the calculations missed the momentum positions of the dominant electronic states and neglected the importance of inter-cell coupling on the size of the Mott gap. The calculations also ignore the correlation-induced spectral peak widths, which are critical for making a connection to activation energies determined from transport experiments. The data indicate a dimensionality-controlled Mott transition in these 5d transition-metal oxides (TMOs).

cond-mat.str-el↗

arXiv2011

Electric field-induced quantum interference control in a semiconductor: A new manifestation of the Franz-Keldysh effect

In (100)-oriented GaAs illuminated at normal incidence by a laser and its second harmonic, interference between one- and two-photon absorption results in ballistic current injection, but not modulation of the overall carrier injection rate. Results from a pump-probe experiment on a transversely biased sample show that a constant electric field enables coherent control of the carrier injection rate. We ascribe this to the nonlinear optical Franz-Keldysh effect and calculate it for a two-band parabolic model. The mechanism is relevant to centrosymmetric semiconductors as well.

cond-mat.other↗

arXiv2009

Non-monotonic Fermi surface evolution and its correlation with stripe ordering in bilayer manganites

In correlated electron systems such as cuprate superconductors and colossal magnetoresistive (CMR) oxides there is often a tendency for a nanoscale self-organization of electrons that can give rise to exotic properties and to extreme non-linear responses. The driving mechanisms for this self-organization are highly debated, especially in the CMR oxides in which two types of self-organized stripes of charge and orbital order coexist with each other. By utilizing angle-resolved photoemission spectroscopy measurements over a wide doping range, we show that one type of stripe is exclusively linked to long flat portions of nested Fermi surface, while the other type prefers to be commensurate with the real space lattice but also may be driven away from this by the Fermi surface. Complementarily, the Fermi surface also appears to be driven away from its non-interacting value at certain doping levels, giving rise to a host of unusual electronic properties.

cond-mat.str-el↗

arXiv2009

Dynamics of bi-stripes and a colossal metal-insulator transition in the bi-layer manganite La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x~0.59)

In correlated electron materials, electrons often self-organize and form a variety of patterns with potential ordering of charges, spins, and orbitals, which are believed to be closely connected to many novel properties of these materials including superconductivity, metal-insulator transitions, and the CMR effect. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. Moreover, although the presence of static stripes is indisputable, the existence (and potential impacts) of fluctuating stripes in such compounds is a subject of great debate. Here we present the electronic excitations of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x ~ 0.59) probed by angle-resolved photoemission (ARPES), from which we demonstrate that a novel type of ordering, termed bi-stripes, can exhibit either static or fluctuating order as a function of temperature. We found that the static bi-stripe order is especially damaging to electrical conductivity, completely localizing the electrons in the bi-stripe regions, while the fluctuating stripes can coexist with mobile carriers. This physics drives a novel phase transition with colossal conductivity changes as a function of temperature. Our finding suggests that quantum stripes can give rise to electronic properties significantly different from their static counterparts. Inducing transition between them can turn on remarkable electronic phenomena, enriching our understanding of correlated electron systems as well as opening a window for potential applications in electronic devices.

cond-mat.str-el↗

arXiv2009

Energy-dependent scaling of incoherent spectral weight and the origin of the waterfalls in high-Tc cuprates

The exotic physics in condensed matter systems, such as high-Tc superconductivity in cuprates, is due to the properties of the elementary excitations and their interactions. The dispersion of the electronic states revealed by angle-resolved photoemission spectroscopy (ARPES) provides a chance to understand these excitations. Recently, a "high energy anomaly" or "waterfall-like" feature in cuprates' dispersion has been reported and studied theoretically. Most of the current views argue that it is the result of some many-body effect at a specific high energy scale (e.g. ~ 0.3eV), though there are other arguments that this is an artificial effect. Here, we report a systematic ARPES study on the "high energy anomaly" in Bi2212 samples over multiple Brillouin zones and with a large variety of ARPES matrix elements. We find that the incoherent weight of the electron spectral function at high binding energy is intimately linked to the energy of the dispersive coherent weight through an unexpected but simple relationship with no special energy scales. This behavior in concert with strong k-dependent matrix element effects gives rise to the heavily studied "waterfall" behavior.

cond-mat.supr-con↗

arXiv2009

Low-energy (< 10 meV) feature in the nodal electron self-energy and strong temperature dependence of the Fermi velocity in Bi(2)Sr(2)CaCu(2)O(8+delta)

Using low-photon energy angle-resolved photoemission (ARPES), we study the low-energy dispersion along the nodal (pi, pi) direction in Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) as a function of temperature. Less than 10 meV below the Fermi energy, the high-resolution data reveals a novel "kink"-like feature in the real part of the electron self-energy that is distinct from the larger well-known kink roughly 70 meV below E_F. This new kink is strongest below the superconducting critical temperature and weakens substantially as the temperature is raised. A corollary of this finding is that the Fermi velocity, as measured over this energy range, varies rapidly with temperature - increasing by almost 30% from 70 to 110 K.

cond-mat.supr-con↗

arXiv2008

An Isotopic Fingerprint of Electron-Phonon Coupling in High-Tc Cuprates

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi2Sr2CaCu2O8+delta reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, which are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.

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arXiv2007

Accurate theoretical fits to laser ARPES EDCs in the normal phase of cuprate superconductors

Anderson has recently proposed a theory of the strange metal state above Tc in the high Tc superconductors. [arXiv:cond-mat/0512471] It is based on the idea that the unusual transport properties and spectral functions are caused by the strong Mott- Hubbard interactions and can be computed by using the formal apparatus of Gutzwiller projection. In ref. 1 Anderson computed only the tunneling spectrum and the power-law exponent of the infrared conductivity. He had calculated the energy distribution curves (EDCs) in angle resolved photoemission spectroscopy (ARPES) but was discouraged when these differed radically from the best ARPES measurements available at the time, and did not include them. In this letter we compare the spectral functions computed within this model to the novel laser-ARPES data of the Dessau group.These are found to capture the shape of the experimental EDCs with unprecedented accuracy and in principle have only one free parameter.

cond-mat.str-el↗

arXiv2007

Experimental setup for low-energy laser-based angle resolved photoemission spectroscopy

A laser-based angle resolved photoemission (APRES) system utilizing 6 eV photons from the fourth harmonic of a mode-locked Ti:sapphire oscillator is described. This light source greatly increases the momentum resolution and photoelectron count rate, while reducing extrinsic background and surface sensitivity relative to higher energy light sources. In this review, the optical system is described, and special experimental considerations for low-energy ARPES are discussed. The calibration of the hemispherical electron analyzer for good low-energy angle-mode performance is also described. Finally, data from the heavily studied high T_c superconductor Bi2Sr2CaCu2O8+δ(Bi2212) is compared to the results from higher photon energies.

cond-mat.other↗

arXiv2006

A local metallic state in globally insulating $La_{1.24}Sr_{1.76}Mn_2O_7$ well above the metal-insulator transition

Angle-resolved photoemission spectroscopy was used to investigate the evolution of the electronic structure across the metal-insulator transition in bi-layer manganite $La_{1.24}Sr_{1.76}Mn_2O_7$. We found that this system is a metal for $T T^*$. These results indicate the critical role of electronic phase separation and percolation effects for the metal-insulator transition in $La_{1.24}Sr_{1.76}Mn_2O_7$.

cond-mat.str-el↗

arXiv2005

Quasiparticle-like peaks, kinks, and electron-phonon coupling at the ($π$,0) regions in the CMR oxide La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$

Using Angle-Resolved Photoemission (ARPES), we present the first observation of sharp quasiparticle-like peaks in a CMR manganite. We focus on the ($π$,0) regions of k-space and study their electronic scattering rates and dispersion kinks, uncovering the critical energy scales, momentum scales, and strengths of the interactions that renormalize the electrons. To identify these bosons we measured phonon dispersions in the energy range of the kink by inelastic neutron scattering (INS), finding a good match in both energy and momentum to the oxygen bond-stretching phonons.

cond-mat.str-el↗

arXiv2005

Laser ARPES, the sudden approximation, and quasiparticle-like peaks in Bi2Sr2CaCu2O8+delta

A new low photon energy regime of angle resolved photoemission spectroscopy is accessed with lasers and used to study the superconductor Bi2Sr2CaCu2O8+delta. The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy - the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink and associated weight transfer are robust to a possible breakdown of the sudden approximation.

cond-mat.supr-con↗

arXiv2004

Persistence of an Energy Scale in Over-Doped High-Tc Superconductors

Citing the disappearance of a sharp peak in the electron self-energy, extracted from optics and angle-resolved photoemission spectroscopy (ARPES) experiments in deeply over-doped copper-oxide superconductors with Tc of 55-60K, Hwang, Timusk et al. argue that sharp modes, be they phononic or magnetic in origin, are not important for superconductivity in the cuprates. If true, this would have been an important progress. We show, however, their conclusions are unfounded because of the insensitivity of the optics experiment in studying strongly anisotropic material like the cuprates, and a misrepresentation of existing ARPES data. In an added note, we refute the claim by Valla, Timusk et. al. that the doping level of the data presented in the first part of this comment is lower than reported.

cond-mat.supr-con↗

arXiv2002

An intrinsic peak-dip-hump and strong coupling effects in $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$ ARPES data near $(π,0)$

A well-known peak-dip-hump structure exists near $(π, 0)$ in superconducting state ARPES spectra of $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$ (Bi2212). Here we report results on optimal and overdoped Bi2212 samples indicating the traditional peak-dip-hump structure observed near $(π,0)$ is largely due to bilayer splitting. However a separate, much weaker peak-dip hump (PDH) structure distinct from bilayer splitting can be detected near $(π, 0)$. This new PDH structure is consistent with electronic coupling to the magnetic resonance mode in Bi2212. Both the dispersion and line shape signatures indicate strong coupling to this mode.

cond-mat.supr-con↗

arXiv2002

Mass-renormalized electronic excitations at ($π$, 0) in the superconducting state of $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$

Using high-resolution angle-resolved photoemission spectroscopy on $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$, we have made the first observation of a mass renormalization or "kink" in the E vs. $\vec k$ dispersion relation localized near $(π, 0)$. Compared to the kink observed along the nodal direction, this new effect is clearly stronger, appears at a lower energy near 40 meV, and is only present in the superconducting state. The kink energy scale defines a cutoff below which well-defined quasiparticle excitations occur. This effect is likely due to coupling to a bosonic excitation, with the most plausible candidate being the magnetic resonance mode observed in inelastic neutron scattering.

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