| NSF Org: |
DMR Division Of Materials Research |
| Recipient: |
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| Initial Amendment Date: | August 17, 2022 |
| Latest Amendment Date: | August 17, 2022 |
| Award Number: | 2233111 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Birgit Schwenzer
bschwenz@nsf.gov (703)292-4771 DMR Division Of Materials Research MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | September 1, 2022 |
| End Date: | August 31, 2024 (Estimated) |
| Total Intended Award Amount: | $297,189.00 |
| Total Awarded Amount to Date: | $297,189.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
110 8TH ST TROY NY US 12180-3590 (518)276-6000 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
110 8TH ST Troy NY US 12180-3522 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
DMR SHORT TERM SUPPORT, SOLID STATE & MATERIALS CHEMIS |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
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.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The main goal of this research program is to enable cooling to low temperatures less than 1 K, required in particular for quantum information technologies, without the reliance of current refrigeration techniques on extremely rare elements/isotopes such as 3He. Specifically, we proposed a refrigeration cycle that relied on the large changes in the entropy of electron spins upon application of electric fields in semiconductors with induced Rashba spin-orbit coupling in materials.
We developed a detailed theoretical model of the spin entropy in such Rashba materials as a function of temperature and electric field. We used this model to estimate the achievable cooling rates in materials as a function of the Rashba coefficient, which determines the energy difference of different spin states as a function of momentum and is related both to the strength of spin-orbit coupling and extent of symmetry breaking of the material. We evaluated semiconductors with different classes of spin-orbit coupling, including cubic semiconductors such as gallium arsenide that exhibit a Dresselhaus spin texture, and hexagonal ones such as gallium nitrides that exhibit a Rashba spin texture. We showed that the cubic semiconductors which develop a Rashba spin texture only upon applying an electric field are much more promising for refrigeration because of the much greater sensitivity of the spin entropy to the applied electric fields. We used first-principles quantum-mechanical calculations of the electronic structure of several such candidate materials to quantify the electric fields required for cooling power at various temperatures, finding that materials like gallium arsenide require fields ~ 200 MV/m for cooling starting at 1 K temperatures, which could potentially be lowered in materials with higher spin-orbit coupling.
To experimentally test the prospect for electrically-tuned refrigeration using spin-orbit coupling in materials, we designed and fabricated test structures combining gallium arsenide with aluminum oxide insulators in order to apply strong electric fields. We optimized the structure of the device by examining gate dielectric area, geometry and thickness of source drains and metal contacts, developed and optimized ohmic contact electrode of NiGeTiAu on n-type doped gallium arsenide. We further evaluated the working characteristics of the 2D electron gas transistor under various source/drain current densities and gate voltages. We applied the circular photo galvanic effect on characterizing the spin texture of the gallium arsenide-based system. We conducted Shubnikov-de Haas quantum oscillation measurement on gallium arsenide system through which the lattice temperature could be estimated. We showed that at the Schottky interface with a built-in electric field, spin splitting occurs and thus electronic entropy increases.
Last Modified: 10/29/2024
Modified by: Ravishankar Sundararaman
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