Abstract:To cool a high mobility two-dimensional electron gas (2DEG) at a GaAs-AlGaAs heterojunction to milliKelvin temperatures, we have fabricated low resistance ohmic contacts based on alloys of Au, Ni and Ge. The ohmic contacts have a typical contact resistance of R C ≈ 0.8 Ω at 4.2 K, which drops to 0.2 Ω below 0.9 K. Scanning electron microscope images establish that the contacts have the same inhomogeneous microstructure that has been observed in previous studies. Measurements of the contact resistance R C , the… Show more
“…These transport measurements were performed down to 1 mK with no discernible heating using conventional room temperature electronics without a screened room; this demonstrates the effectiveness of the filtering. A change in the resistance was observed between 0.4 and 0.8 K, that has been identified in similar samples 44 to be a superconducting transition in the ohmic contacts. Fig.…”
Section: Resultssupporting
confidence: 67%
“…The WF law predicts that , where R NT to IV = 27 Ω (6 Ω) is the electrical resistance from the NT ohmic contact to I± and V± connected in parallel, measured before (after) illumination, where is the Lorenz number 47 . Figure 3b shows that after illumination, a clear violation of the WF law that we attribute to superconductivity 53 in the ohmic contacts 44 . To the leading order the change in G Σ due to illumination is Δ G Σ = Δ G e ∝ T ; to explain this observation we propose a model of partially-superconducting ohmic contacts, see Fig.…”
Section: Resultsmentioning
confidence: 89%
“…The 4 mm × 4 mm sample shown in Fig. 1b was fabricated using wafer W476; details of its MBE growth and the subsequent fabrication of AuNiGe ohmic contacts are given elsewhere 44 , together with the critical field measurements of the superconducting state below 1 K. The as-grown 2D carrier density and mobility are n 2D ≈ 2 × 10 11 cm −2 and μ ≈ 1 × 10 6 cm 2 /Vs giving a calculated sheet resistance of R □ ≈ 31 Ω. After illumination these quantities are 3.3 × 10 11 cm −2 , 3 × 10 6 cm 2 /Vs and 6 Ω. Illumination was performed at 1.5 K with the immersion cell evacuated.…”
Two-dimensional electron gases (2DEGs) with high mobility, engineered in semiconductor heterostructures host a variety of ordered phases arising from strong correlations, which emerge at sufficiently low temperatures. The 2DEG can be further controlled by surface gates to create quasi-one dimensional systems, with potential spintronic applications. Here we address the long-standing challenge of cooling such electrons to below 1 mK, potentially important for identification of topological phases and spin correlated states. The 2DEG device was immersed in liquid 3He, cooled by the nuclear adiabatic demagnetization of copper. The temperature of the 2D electrons was inferred from the electronic noise in a gold wire, connected to the 2DEG by a metallic ohmic contact. With effective screening and filtering, we demonstrate a temperature of 0.9 ± 0.1 mK, with scope for significant further improvement. This platform is a key technological step, paving the way to observing new quantum phenomena, and developing new generations of nanoelectronic devices exploiting correlated electron states.
“…These transport measurements were performed down to 1 mK with no discernible heating using conventional room temperature electronics without a screened room; this demonstrates the effectiveness of the filtering. A change in the resistance was observed between 0.4 and 0.8 K, that has been identified in similar samples 44 to be a superconducting transition in the ohmic contacts. Fig.…”
Section: Resultssupporting
confidence: 67%
“…The WF law predicts that , where R NT to IV = 27 Ω (6 Ω) is the electrical resistance from the NT ohmic contact to I± and V± connected in parallel, measured before (after) illumination, where is the Lorenz number 47 . Figure 3b shows that after illumination, a clear violation of the WF law that we attribute to superconductivity 53 in the ohmic contacts 44 . To the leading order the change in G Σ due to illumination is Δ G Σ = Δ G e ∝ T ; to explain this observation we propose a model of partially-superconducting ohmic contacts, see Fig.…”
Section: Resultsmentioning
confidence: 89%
“…The 4 mm × 4 mm sample shown in Fig. 1b was fabricated using wafer W476; details of its MBE growth and the subsequent fabrication of AuNiGe ohmic contacts are given elsewhere 44 , together with the critical field measurements of the superconducting state below 1 K. The as-grown 2D carrier density and mobility are n 2D ≈ 2 × 10 11 cm −2 and μ ≈ 1 × 10 6 cm 2 /Vs giving a calculated sheet resistance of R □ ≈ 31 Ω. After illumination these quantities are 3.3 × 10 11 cm −2 , 3 × 10 6 cm 2 /Vs and 6 Ω. Illumination was performed at 1.5 K with the immersion cell evacuated.…”
Two-dimensional electron gases (2DEGs) with high mobility, engineered in semiconductor heterostructures host a variety of ordered phases arising from strong correlations, which emerge at sufficiently low temperatures. The 2DEG can be further controlled by surface gates to create quasi-one dimensional systems, with potential spintronic applications. Here we address the long-standing challenge of cooling such electrons to below 1 mK, potentially important for identification of topological phases and spin correlated states. The 2DEG device was immersed in liquid 3He, cooled by the nuclear adiabatic demagnetization of copper. The temperature of the 2D electrons was inferred from the electronic noise in a gold wire, connected to the 2DEG by a metallic ohmic contact. With effective screening and filtering, we demonstrate a temperature of 0.9 ± 0.1 mK, with scope for significant further improvement. This platform is a key technological step, paving the way to observing new quantum phenomena, and developing new generations of nanoelectronic devices exploiting correlated electron states.
“…These transport measurements were performed down to 1 mK with no discernible heating using conventional room temperature electronics without a screened room; this demonstrates the effectiveness of the filtering. A change in the resistance was observed between 0.4 and 0.8 K, that has been identified in similar samples [46] to be a superconducting transition in the ohmic contacts.…”
“…The challenge is to transfer the cold while ensuring the device and leads are electrically isolated from the demag stage. Royal Holloway researchers employ these methods to cool 2D electron gases [4].…”
Section: How Do We Do It and Where Are We Now?mentioning
In labs across Europe physicists are pushing the boundaries of how far we can cool the electrons in nano-fabricated circuits and quantum-enhanced devices. The cryogen-free revolution in dilution refrigeration has liberated researchers from a reliance on helium, a costly and non-renewable resource, and hugely expanded the numbers of cooling machines available for new science and quantum technology applications which exploit the properties of materials at kelvin and millikelvin temperatures.
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