EAGER: CRYO: Refrigeration across temperature scales with electrically-tunable spin-orbit materials

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

Non-technical summary Quantum computing and communication technologies, which will become increasingly critical for competitiveness and security in the next phase of the information age, require ultralow temperatures that are hundreds to thousands of times smaller than room temperature. Currently the predominant approach to reach such temperatures relies on repeatedly mixing and separating two isotopes of helium, He-3 and He-4, in a dilution refrigerator. However, helium in general, and He-3 in particular, are rare and increasingly expensive. This poses a severe challenge to the widespread adoption of quantum technologies. With this high risk/high reward project, supported by the Division of Materials Research, researchers at the Rensselaer Polytechnic Institute investigate a new approach for achieving ultralow temperatures without relying on rare elements. Specifically, they leverage the unique interactions of the spin of electrons in a class of materials called Rashba materials with electric fields. Preliminary simulations show that switching a voltage applied to these materials on and off in a specific pattern and direction may allow reaching low temperatures efficiently, making these potentially promising materials to compete with dilution refrigerators. In addition to enabling the widespread adoption of quantum technologies, the success of this new approach to reach very low temperatures could make a wide range of low-temperature phenomena, such as superconductors, more scientifically and technologically accessible. To educate the next generation of STEM workforce, the researchers integrate the underlying theory and experimental demonstrations of ultralow temperature refrigeration into undergraduate and graduate curricula as well as high-school outreach programs. This helps introduce future scientists and engineers to the technological challenges on the path to the age of quantum information. Technical summary With support from the Division of Materials Research, the researchers leverage Rashba spin-orbit coupling in materials as a new platform for enabling new approaches to reach ultralow temperatures down to 0.01 K, breaking the current dependency on the extremely rare He-3 isotope required by dilution refrigerators. They study new thermodynamic cycles that take advantage of the dependence of the electronic entropy on electric fields, due to the change of the spin-orbit splitting with electric field strength in Rashba materials. In particular, they investigate the possibility for refrigeration by adiabatic electrification of Rashba materials and determine if this can provide sufficient cooling power that matches or even exceeds that of typical dilution refrigerators. Research objectives include exploring a wide class of Rashba materials with different spin-orbit coupling strengths, synthesize structures capable of electric field cycling in these materials and quantify the field- and temperature-dependent thermodynamic parameters of these materials relevant for refrigeration. If successful, this approach may be extensible to a wide temperature range due to the broad range of Rashba energy splits, potentially opening up a pathway to cool from liquid nitrogen to millikelvin temperatures in a single material platform. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.