Daniel S. Dessau

Professor, Ph.D. Stanford University, 1993.
Dessau@Colorado.edu
Duane Physics room F625
303-492-1607 (office)       303-492-3308 (lab)       303-492-2998 (fax)

Professor  Dessau's research interests center around using femtosecond optics and electron spectroscopic tools for the study of the electronic structure, magnetic structure, and phase transitions of novel materials systems such as high temperature superconductors (HTSCs or cuprates) and colossal magnetoresistive oxides (CMRs or manganites).  A couple of examples of our work is highlighted below.

Some of our work has been In the News Recently.

 

First Demonstration of  true Laser-ARPES

We have recently made the first demonstration of true Laser-ARPES (Angle Resolved Photoemission Spectroscopy) at our home lab in Colorado.  The data below shows the measured dispersion (Energy vs. momentum) for electronic states from the high transition temperature superconductor Bi2Sr2CaCu2O8 along the "nodal" direction of the Brillouin zone.  The two right panels were taken at the synchrotron (Advanced Light Source, Berkeley) using their most powerful undulator beamlines.  The left panel was taken using our laser-ARPES system and shows dramatically sharper spectral peaks.  This increase in the spectral resolution is due to improvements in the energy and momentum resolution of the experiment, but also may be due to other issues such as a decrease in the final-state electron broadening effects and an improved bulk sensitivity.  The increase in the spectral resolution can give a much greater window into the inherent electronic physics of these exotic materials, allowing us to measure the details of the "quantum dance" that the electrons are undergoing in these materials.  Ultimately we hope this kind of information will enable us to uncover the interactions responsible for the superconductivity in these amazing materials.  Click here for a reprint of this work published in Physical Review Letters recently.  A news article highlighting this data also recently appeared in Science.

ARPES data from the "nodal" line of the high temperature superconductor Bi2Sr2CaCu2O8. (Left) laser-ARPES data compared to data we measured at the Advanced Light Source (middle and right). From Science 310, 1271 (2005)

 

AntiNodal "kinks" in Cuprate Superconductors

We used high resolution ARPES to make the first clear observation of dispersion "kinks" in the antinodal region (where the superconducting pairing is strongest) of a high Tc superconductor.  This kink is only present in the superconducting state and indicates significantly stronger coupling and a lower energy scale than the "nodal kink" previously observed in the cuprates, where the superconducting pairing is absent.  We argue that the origin of this effect is likely the magnetic resonance mode observed by inelastic neutron scattering, greatly increasing the possibility that this mode helps mediate the pairing.  If so, this would be in opposition to the case of conventional superconductivity, where the superconducting pairing is mediated by phonons (quantized sound waves).  Shown below is a figure from our article in Nature.  An other paper describing this in more detail is available here.

 

 

Fermi Surface and Pseudogaps in CMR Oxides

 

We used high resolution ARPES to make the first measurements of the Fermi Surface of a CMR oxide (panel A, below).  Even though these measurements show a clear Fermi Surface the electronic spectral weight at the Fermi level is very small, which is surprising since these measurements were made in the metallic state.  This very small weight at EF is termed a pseudogap, and has become one of the central topics of modern condensed matter research.  Shown below is a figure from our paper  published in Science.