Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

We demonstrate methods to synthesize reliably single crystals of uranium ditelluride that either superconductor do not, which is crucial to studying exotic spin-triplet superconductivity. Following this vapor transport recipe, we'll reliably yield uranium ditelluride samples that exhibit bulk superconductivity. This is not achieved using other methods.

This method impacts research on spin-triplet and topological superconductivity, as well as correlated electrons. All these areas fall in the field of quantum materials. Demonstrating the procedure will be Sheng Ran, an assistant professor in Washington University in St.Louis who is a postdoctoral researcher in my group.

Begin by weighing the appropriate amount of elemental tellurium depending on the amount of cleaned uranium at the atomic ratio of uranium to tellurium of two to three. Weigh an appropriate amount of iodine to be used during synthesis. Select the tube lengths so that the tube spans the furnace and each end is sitting in one of the temperature zones, ensuring that the diameter fits well in the furnace.

Close one end of a fused quartz tube using a hydrogen torch or any torch that produces enough heat to soften the fused quartz. Once the tube is cold enough, place all the materials into the quartz tube. Neck the tube and use a vacuum pump to evacuate the tube and seal the tube with the torch.

Insert the tube into a two-zone horizontal tube furnace, ensuring all the raw materials slide to the hot side of the tube. Over 12 hours, heat the hot side of the tube to 1, 060 degrees Celsius, the other side at 1, 000 degrees Celsius and hold the temperature for one week. Then turn off the furnace to allow the tube to cool slowly to reach room temperature.

Weigh the uranium and tellurium according to the atomic ratio of one to three. Place all the materials in a two millimeter alumina crucible. Once the tube is cold enough, place the two crucibles into a quartz tube having an inner diameter of 14 millimeters.

Close one end of a fused quartz tube using a torch. After necking the tube, use a dry vacuum pump to evacuate the tube and then seal the tube with the torch. Put the sealed quartz tube into a 50 milliliter alumina crucible to be used as an exterior container for stability.

Place the crucible containing the quartz tube in a box furnace, then heat and cool the furnace as described in the text manuscript. Prepare a centrifuge with a swing out rotor and metal buckets. Use the furnace tongs to take the quartz tube out of the furnace, invert the tube, and spin the tube at 2, 500 times G for 10 to 20 seconds for separating the extra liquid tellurium from the uranium ditelluride crystals.

Let the tube cool to room temperature. The crystals obtained using the chemical vapor transport and the flux grown crystals looked similar and were not easily distinguishable by visual inspection. The x-ray diffraction measurements were performed on crushed single crystals obtained from both techniques to confirm the crystal structure.

The crystal structure was similar using both techniques with no sign of impurity phases. The residual resistance ratio of the flux grown crystal is 15 times smaller than the residual resistance ratio of the chemical vapor transport crystal, indicating more crystallographic impurities or defects in the flux grown sample and responsible for the stronger scattering of the conduction electrons and higher residual resistance. The magnetic susceptibility of the crystals grown using both techniques was similar.

The magnetic susceptibility increased sharply at low temperatures and showed a slight slope change at approximately 10K due to the condo coherence. The most important part of both process is to seal the quartz tube properly. A bad seal of the quartz tube can lead to a unwanted reaction with air which can be a safety hazard.