C. Jozwiak

University of California, Berkeley, Berkeley, CA, United States

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Publications (27)101.84 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A high-efficiency spin- and angle-resolved photoemission spectroscopy (spin-ARPES) spectrometer is coupled with a laboratory-based laser for rapid high-resolution measurements. The spectrometer combines time-of-flight (TOF) energy measurements with low-energy exchange scattering spin polarimetry for high detection efficiencies. Samples are irradiated with fourth harmonic photons generated from a cavity-dumped Ti:sapphire laser that provides high photon flux in a narrow bandwidth, with a pulse timing structure ideally matched to the needs of the TOF spectrometer. The overall efficiency of the combined system results in near-EF spin-resolved ARPES measurements with an unprecedented combination of energy resolution and acquisition speed. This allows high-resolution spin measurements with a large number of data points spanning multiple dimensions of interest (energy, momentum, photon polarization, etc.) and thus enables experiments not otherwise possible. The system is demonstrated with spin-resolved energy and momentum mapping of the L-gap Au(111) surface states, a prototypical Rashba system. The successful integration of the spectrometer with the pulsed laser system demonstrates its potential for simultaneous spin- and time-resolved ARPES with pump-probe based measurements.
    The Review of scientific instruments 09/2013; 84(9):093904. · 1.58 Impact Factor
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    ABSTRACT: Laser-based time- and angle-resolved photoemission spectroscopy (trARPES) is a technique that uses an initial laser pulse to pump a system, and a second pulse to probe it by photoemission. By using trARPES on the high temperature superconductor, Bi2Sr2CaCu2O8+δ, we open a window into its many-body quasiparticle interactions. Here we report on the effect of pumping on the quasiparticle band structure of Bi2Sr2CaCu2O8+δ. We will discuss the dynamics of this effect, and its relation to the superconducting state.
    03/2013;
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    ABSTRACT: We present technical specifications for a high resolution time- and angle-resolved photoemission spectroscopy setup based on a hemispherical electron analyzer and cavity-dumped solid state Ti:sapphire laser used to generate pump and probe beams, respectively, at 1.48 and 5.93 eV. The pulse repetition rate can be tuned from 209 Hz to 54.3 MHz. Under typical operating settings the system has an overall energy resolution of 23 meV, an overall momentum resolution of 0.003 Å(-1), and an overall time resolution of 310 fs. We illustrate the system capabilities with representative data on the cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+δ). The descriptions and analyses presented here will inform new developments in ultrafast electron spectroscopy.
    The Review of scientific instruments 12/2012; 83(12):123904. · 1.58 Impact Factor
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    ABSTRACT: In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We used a femtosecond laser pump pulse to perturb superconducting Bi(2)Sr(2)CaCu(2)O(8+δ) and studied subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics revealed marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap was sensitive to the pump intensity, and Cooper pairs recombined slowly. Far from the nodes, pumping affected the gap only weakly, and recombination processes were faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.
    Science 06/2012; 336(6085):1137-9. · 31.48 Impact Factor
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    ABSTRACT: High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi2Se3 using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.
    Physical review. B, Condensed matter 10/2011; 84(16). · 3.66 Impact Factor
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    ABSTRACT: High-transition-temperature cuprate superconductors are characterized by a strong momentum-dependent anisotropy between the low-energy excitations along the Brillouin zone diagonal (nodal direction) and those along the Brillouin zone face (antinodal direction) - the most striking example of which is the d-wave superconducting gap, with the largest magnitude found in the antinodal direction and no gap in the nodal direction. Furthermore, whereas antinodal quasiparticle excitations occur only below the transition temperature (Tc), superconductivity is thought to be indifferent to nodal excitations that are regarded as robust and insensitive to Tc. Here we reveal an unexpected link between nodal quasiparticles and superconductivity using high-resolution time- and angle-resolved photoemission on optimally doped Bi2Sr2CaCu2O8+δ�. We observe a suppression of the nodal quasiparticle spectral weight following pump laser excitation, and measure its recovery dynamics. This suppression is greatly enhanced in the superconducting state. These results reduce the nodal–antinodal dichotomy and challenge the conventional view of nodal excitation neutrality in superconductivity.
    Nature Physics 07/2011; 7(10):805-809. · 20.60 Impact Factor
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    ABSTRACT: We have studied Bi2Sr1.6Nd0.4CuO6+δ using angle-resolved photoemission spectroscopy in the optimal and overdoped regions of the phase diagram. We identify a narrow crossover region in the electronic structure between nodal and antinodal regions associated with the deviation from a pure d-wave gap function, an abrupt increase in the quasiparticle lifetime, the formation of Fermi arcs above Tc, and a sudden shift of the bosonic mode energy from higher energy, ∼60 meV, near the nodal direction, to lower energy, ∼20 meV, near the antinodal direction. Our work underscores the importance of a unique crossover region in the momentum space near EF for the single-layered cuprates, between nodal and antinodal points, that is independent of the antiferromagnetic zone boundary.
    Physical review. B, Condensed matter 05/2010; 81(18). · 3.66 Impact Factor
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    ABSTRACT: We have studied Bi$_{2}$Sr$_{1.6}$Nd$_{0.4}$CuO$_{6+\delta}$ using Angle Resolved Photoemission Spectroscopy in the optimal and overdoped regions of the phase diagram. We identify a narrow crossover region in the electronic structure between the nodal and antinodal regions associated with the deviation from a pure d-wave gap function, an abrupt increase of the quasiparticle lifetime, the formation of Fermi arcs above T$_c$, and a sudden shift of the bosonic mode energy from higher energy, $\sim${60meV}, near the nodal direction, to lower energy, $\sim${20meV}, near the antinodal direction. Our work underscores the importance of a unique crossover region in the momentum space near E$_F$ for the single layered cuprates, between the nodal and antinodal points, that is independent of the antiferromagnetic zone boundary. Comment: 5 pages, 4 figures, Accepted for publication in Physical Review B
    05/2010;
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    ABSTRACT: We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90 degrees bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.
    The Review of scientific instruments 05/2010; 81(5):053904. · 1.58 Impact Factor
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    ABSTRACT: We used ultra high resolution laser based angle resolved photoemission (ARPES) to study the temperature dependence of the electronic structure of double layer Bi2Sr2CaCuO8+delta at optimal doping (Tc=91K) along the nodal direction. Our study reveals fine details of the nodal quasiparticle spectral function as a function of temperature. The results are discussed in terms the electron-lattice and electron-electron interaction in these materials.
    03/2010;
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    ABSTRACT: Laser-based technology has opened the field of angle-resolved photoemission to a variety of new techniques. Compared to synchrotron facilities, laser experiments typically benefit from higher flux, greater resolution and bulk sensitivity, and a system that is more readily modified for specialized experiments. We demonstrate the results of using this system to probe bosonic renormalization and electron-electron effects at varied dopings and temperatures in the double-layered cuprate Bi-2212.
    03/2010;
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    ABSTRACT: We report a systematic measurement of the space charge effect observed in the few-picosecond laser pulse regime in laser-based solid-state photoemission spectroscopy experiments. The broadening and the shift of a gold Fermi edge as a function of spot size, laser power, and emission angle are characterized for pulse lengths of 6 ps and 6 eV photon energy. The results are used as a benchmark for an N-body numerical simulation and are compared to different regimes used in photoemission spectroscopy. These results provide an important reference for the design of time- and angle-resolved photoemission spectroscopy setups and next-generation light sources.
    Journal of Applied Physics 01/2010; 107:014912. · 2.19 Impact Factor
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    ABSTRACT: We study the stability of various kinds of graphene samples under soft x-ray irradiation. Our results show that in single-layer exfoliated graphene (a closer analog to two-dimensional material), the in-plane carbon-carbon bonds are unstable under x-ray irradiation, resulting in nanocrystalline structures. As the interaction along the third dimension increases by increasing the number of graphene layers or through the interaction with the substrate (epitaxial graphene), the effect of x-ray irradiation decreases and eventually becomes negligible for graphite and epitaxial graphene. Our results demonstrate the importance of the interaction along the third dimension in stabilizing the long range in-plane carbon-carbon bonding, and suggest the possibility of using x-ray to pattern graphene nanostructures in exfoliated graphene.
    Physical Review B - PHYS REV B. 01/2010;
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    ABSTRACT: Using angle-integrated photoemission spectroscopy we have probed the novel LaFeAsO0.9F0.1 superconductor over a wide range of photon energies and temperatures. We have provided a full characterization of the orbital character of the valence-band (VB) density of states (DOS) and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90 K where a pseudogap-like feature appears to close and 120 K where a sudden change in the DOS near EF occurs. We associate these phenomena with the spin density wave magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics, and structural distortion in the physics of Fe-based superconductors.
    Physical review. B, Condensed matter 12/2008; 78(24). · 3.66 Impact Factor
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    ABSTRACT: Using angle-integrated photoemission spectroscopy we have probed the novel LaO$_{0.9}$F$_{0.1}$FeAs superconductor over a wide range of photon energies and temperatures. We have provided the first full characterization of the orbital character of the VB DOS and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90K where a pseudogap-like feature appears to close and 120K where a sudden change in the DOS near E$_F$ occurs. We associate these phenomena with the SDW magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics and structural distortion in the physics of Fe-based superconductors.
    11/2008;
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    ABSTRACT: By performing angle-resolved photoemission spectroscopy of the bilayer colossal magnetoresistive (CMR) manganite, $La_{2-2x}Sr_{1+2x}Mn_{2}O_{7}$, we provide the complete mapping of the Fermi level spectral weight topology. Clear and unambiguous bilayer splitting of the in-plane 3d$_{x^2-y^2}$ band, mapped throughout the Brillouin zone, and the full mapping of the 3d$_{3z^2-r^2}$ band are reported. Peculiar doping and temperature dependencies of these bands imply that as transition from the ferromagnetic metallic phase approaches, either as a function of doping or temperature, coherence along the c-axis between planes within the bilayer is lost, resulting in reduced interplane coupling. These results suggest that interplane coupling plays a large role in the CMR transition. Comment: 8 pages, 6 figures
    Physical review. B, Condensed matter 06/2008; · 3.66 Impact Factor
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    ABSTRACT: We report the first measurement of the Cu-O bond stretching phonon dispersion in optimally doped Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a softening of this phonon at q=( approximately 0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A comparison with angle-resolved photoemission data on the same sample revealed an excellent agreement in terms of energy and momentum between the angle-resolved photoemission nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63+/-5 meV kink is observed can be connected with a vector q=(xi,0,0) with xi > or =0.22, corresponding exactly to the soft part of the bond stretching phonon.
    Physical Review Letters 06/2008; 100(22):227002. · 7.73 Impact Factor
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    ABSTRACT: We report the first measurement of the optical phonon dispersion in optimally doped single layer Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a strong softening of the Cu-O bond stretching phonon at about q=(0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A direct comparison with angle-resolved photoemission spectroscopy measurements taken on the same sample, revealed an excellent agreement in terms of energy and momentum between the ARPES nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63 meV kink is observed can be connected with a vector q=(xi,0,0) with xi~0.22, which corresponds exactly to the soft part of the bond stretching phonon mode. This result supports an interpretation of the ARPES kink in terms of electron-phonon coupling.
    05/2008;
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    ABSTRACT: We report the first measurement of the Cu-O bond stretching phonon dispersion in optimally doped BiSr{sub 1.6}La{sub 0.4}CuO{sub 6+} using inelastic x-ray scattering. We found a softening of this phonon at q = ( 0.25, 0, 0) from 76 to 60 meV, similar to the one reported in other cuprates. A comparison with angle-resolved photoemission data on the same sample revealed an excellent agreement in terms of energy and momentum between the angle-resolved photoemission nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63 {+-} 5 meV kink is observed can be connected with a vector q = (, 0, 0) with 0.22, corresponding exactly to the soft part of the bond stretching phonon.
    Physical Review Letters 01/2008; 100(22):227002-4. · 7.73 Impact Factor
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    ABSTRACT: This paper reports on the development of a high resolution electron/photon/ion imaging system which detects events with a timing accuracy of <160 ps FWHM and a two-dimensional spatial accuracy of ∼50 μm FWHM. The event counting detector uses microchannel plates for signal amplification and can sustain counting rates exceeding 1.5 MHz for evenly distributed events (0.4 MHz with 10% dead time for randomly distributed events). The detector combined with a time-of-flight angular resolved photoelectron energy analyzer was tested at a synchrotron beamline. The results of these measurements illustrate the unique capabilities of the analytical system, allowing simultaneous imaging of photoelectrons in momentum space and measurement of the energy spectrum, as well as filtering the data in user defined temporal and/or spatial windows.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2007; · 1.32 Impact Factor

Publication Stats

283 Citations
101.84 Total Impact Points

Institutions

  • 2004–2013
    • University of California, Berkeley
      • Department of Physics
      Berkeley, CA, United States
  • 2007–2012
    • Lawrence Berkeley National Laboratory
      • • Advanced Light Source Facility
      • • Materials Sciences Division
      Berkeley, CA, United States
  • 2010
    • CSU Mentor
      Long Beach, California, United States