The overall goal of the following experiment is to determine the low energy electronic structure of solids at ultra-low temperatures using angle resolved photo emission spectroscopy or arrp pez with synchrotron radiation. In the synchrotron radiation facilities, ultra high vacuum chamber attached to the beam line, a single crystal of the studied material is cleaved, exposing an atomically clean surface as a second step. The sample is cooled below one Kelvin, which ensures minimal temperature broadening and proximity to the ground state of the material.
Next, the photo emission intensity is recorded as a function of tilt, angle and energy and static geometry. By rotating the sample information can be collected from a large portion of momentum energy space needed to obtain the firming surface map and dispersions close to the firm level Results are obtained that show that low energy electronic structure of complex materials can be determined with unprecedented clarity and resolution. Using the helium three cryo manipulator and synchrotron based arrp e Angle result for the emission spectroscopy is a technique based on a simple photoelectric effect, which has been discovered and explained more than a century ago.
We use this technique today in order to determine the electronic structure of solids with a very high precision. In our approach. We use three latest achievements in the fields of synchrotron radiation, surface science, and cryogenics.
We use tuneable exudation photo images, which contributed in certainty of one milli electron Walt. We detect the kinetic energy of our photo electrons with uncertainty of one milli electron Walt, and what is more important? We use helium three cryostat, which allows to keep the temperature of our samples below one column.
Because of these three ones we call our system one cube, We use a specially designed helium three cryostat, which provides a free access for the incoming light and outgoing electrons. The design of our system makes it the most powerful in the world.Actually. With this system, it is possible to see a surface at one column through the room temperature window.
With this technique and this setup, we can answer key questions in the field of electronic systems. In particular for superconductivity, we can determine the structure of the other parameter to find out what drives the phenomenon. This experiment uses the synchrotron radiation produced by the Bessie storage ring of the helm, Holt Centrum Berlin.
The photons travel a beamline to our end station where a sample is mounted. Begin with a single crystal of the material to be investigated here. STR urinate use silver based epoxy to glue the sample to the sample holder.
The silver based epoxy ensures good thermal and electrical contact glue. An aluminum top post to the surface of the single crystal. The top post will be used to cleave the sample in ultra high vacuum to expose an anatomically clean surface mount, the sample holder in the load lock begin evacuating the load lock to minimize contamination of the ultra high vacuum chamber.
Monitor the pressure. Once a pressure of about 10 to the minus eight millibar has been achieved, transfer the assembly to the preparation chamber and subsequently to the main chamber. The cold finger and sample holder have been specially designed to guarantee the best possible thermal contact with the helium pot.
These demonstration versions show how this is achieved by using conical surfaces to increase the area of contact. The conical surfaces are pressed against one another, and the sample holder and cold finger are firmly fixed in place using a titanium nut and bolt. The transfer system has been designed to minimize thermal contact with the assembly as seen in this demonstration unit.
This is accomplished by using a thin titanium tube with multiple openings as the main carrying element of the assembly. At the end of the transfer arm, a spring activated screwdriver inside the assembly is used to adjust the angular position of the sample. The next step is to orient the sample within the cold finger along the asmuth using the transfer arm.
Fix the position of the sample by tightening the nut while applying a counterforce with the supporting arm attached to the opposite side of the chamber. Clea the sample by moving the manipulator upward so that the top post is removed by interaction with the supporting arm. With the beam shutter closed, move the sample into position in the beam line using the manipulator.
Once the sample is in place, make sure the cryo shields are closed properly. Start pumping on the one kelvin pot and circulate the helium three gas in order to cool the sample to the base temperature. Open the beam shutter of the beam line.
Use the micrometer screws on the apparatus to adjust the position of the sample so that it is at the focus of the analyzer lens. This adjustment is crucial. Once the setup is ready, switch to the angle resolved mode of the analyzer and record the spectrum in swept mode.
This will generate data for two dimensional energy angle plots. Conduct a fury surface map using the data. Select polar angles that correspond to firmly level crossings.
For study of the superconducting gap of stratum urinate record high resolution spectra at the chosen polar angles above and below the superconducting transition temperature of the stratum urinate to investigate the behavior of the superconducting gap. Shown here is the photo electron intensity as a function of tilt angle and energy. For a sample of zirconium three Telluride.
Compare this with the theoretical band structure calculation for the same material. A standard test for energy resolution is to measure the full width at half maximum of the Gaussian, which when convoluted with the step function describes the firm edge. The Gaussian full width at half maximum used fit.
This data for freshly evaporated indium is of order, two milli electron vols. Here is a plot of the energy distribution curve in a superconducting sample of lithium ion arsenide taken with the system. As another example of the resolution that can be achieved here is the momentum distribution curve at the firming level of zirconium three Telluride.
The anticipated overall energy resolution of the system is expressed by the formula shown here. The actual performance is very close to this goal. On the left is a typical spectrum taken to study the superconducting gap of stratum brunate for T equals 970 millikelvin.
The arrow indicates momentum corresponding to the energy distribution curve on the right. The image on the right shows the shift of the leading edge of the integrated energy distribution curve for a sample of str and urinate above and below the superconducting transition temperature. The spectrum used for the calculation is shown on the left.
The momentum window is indicated by the width of the red arrow. The gap corresponds to a firming surface point on the band near the Brill wall zone diagonal as another example. Here is the shift of the energy distribution curve as a function of temperature from another point on the firmi surface of strate.
Finally, the system allows measurement of the typical temperature behavior of the binding energy of the leading edge in the vicinity of the crossing of two fury surfaces. Once mastered, this technique can be done within eight hours if everything is performed properly. That is within one shift of a typical syn zone operation.
While attempting this procedure, it is very important to follow all the describable steps with high degree of precautions, luing the sample during the sample transfer. Unsuccessful cleavage because of bad sample preparation or just poor adjustments, all could lead to failure of the whole experiment. This technique provides the information about the electronic structure of a solid or inana objects.
With the new level of precision, we have access to the firm surface maps, bend dispersion and comparison with this data, with the EB bend structure calculations allows us to determine the bandwidth randomization or velocity normalization. Thus, we can judge about the complexity of the materials in terms of the correlations. Defined structures near the firm level allow to detect the fingerprints of the interaction between the electrons and other degrees of freedom like phonons, plasmin, or magnets.
Using the systematic momentum dependent study, one can see the dependence of the superconducting gap as a function of momentum. Thus getting the information about the all the parameter, its symmetry and structure. This experiment can provide the ultimate test for the existing theories as well as stimulate new paths of inquiry.
