More Like this

1. Acceptor-Induced Bulk Dielectric Loss in Superconducting Circuits on Silicon

   https://doi.org/10.1103/PhysRevX.14.041022  

   Zhang, Zi-Huai; Godeneli, Kadircan; He, Justin; Odeh, Mutasem; Zhou, Haoxin; Meesala, Srujan; Sipahigil, Alp (October 2024, Physical Review X)

   The performance of superconducting quantum circuits is primarily limited by dielectric loss due to interactions with two-level systems (TLSs). State-of-the-art circuits with engineered material interfaces are approaching a limit where dielectric loss from bulk substrates plays an important role. However, a microscopic understanding of dielectric loss in crystalline substrates is still lacking. In this work, we show that boron acceptors in silicon constitute a TLS bath that leads to an energy dissipation channel for superconducting circuits. We discuss how the electronic structure of boron acceptors leads to an effective TLS response in silicon. We sweep the boron concentration in silicon and demonstrate the bulk dielectric loss limit from boron acceptors. We show that boron-induced dielectric loss can be reduced in a magnetic field due to the spin-orbit structure of boron. This work provides the first detailed microscopic description of a TLS bath for superconducting circuits and demonstrates the need for ultrahigh-purity substrates for next-generation superconducting quantum processors. Published by the American Physical Society2024 

   more » « less
2. X-ray Diffraction and Equation of State of the C-S-H Room-Temperature Superconductor

   Lamichhane, A.; Kumar, R.; Ahart, M.; Salke, N.; Dasenbrock-Gammon, N; Meng, Y.; Lavina, B.; Chariton, S.; Prakapenka, V. B.; Somayazulu, M.; et al (September 2021, Journal of chemical physics)

   null (Ed.)

   X-ray diffraction indicates that the structure of the recently discovered carbonaceous sulfur hydride (C-S-H) room temperature superconductor is derived from previously established van der Waals compounds found in the H2S-H2 and CH4-H2 systems. Crystals of the superconducting phase were produced by a photochemical synthesis technique leading to the superconducting critical temperature Tc of 288 K at 267 GPa. X-ray diffraction patterns measured from 124 to 178 GPa, within the pressure range of the superconducting phase, are consistent with an orthorhombic structure derived from the Al2Cu-type determined for (H2S)2H2 and (CH4)2H2 that differs from those predicted and observed for the S-H system to these pressures. The formation and stability of the C-S-H compound can be understood in terms of the close similarity in effective volumes of the H2S and CH4 components, and denser carbon-bearing S-H phases may form at higher pressures. The results are crucial for understanding the very high superconducting Tc found in the C-S-H system at megabar pressures. 

   more » « less
3. Pressure-induced superconductivity in a novel germanium allotrope

   https://doi.org/10.1016/j.mtphys.2024.101338  

   Deng, Liangzi; Zhang, Jianbo; Sakai, Yuki; Tang, Zhongjia; Adnani, Moein; Dahal, Rabin; Litvinchuk, Alexander P.; Chelikowsky, James R.; Cohen, Marvin L.; Hemley, Russell J.; et al (February 2024, Materials Today Physics)

   - (Ed.)

   High-pressure studies on elements play an essential role in superconductivity research, with implications for both fundamental science and applications. Here we report the experimental discovery of surprisingly low pressure driving a novel germanium allotrope into a superconducting state in comparison to that for α-Ge. Raman measurements revealed structural phase transitions and possible electronic topological transitions under pressure up to 58 GPa. Based on pressure-dependent resistivity measurements, superconductivity was induced above 2 GPa and the maximum Tc of 6.8 K was observed under 4.6 GPa. Interestingly, a superconductivity enhancement was discovered during decompression, indicating the possibility of maintaining pressure-induced superconductivity at ambient pressure with better superconducting performance. Density functional theory analysis further suggested that the electronic structure of Ge (oP32) is sensitive to its detailed geometry and revealed that disorder in the β-tin structure leads to a higher Tc in comparison to the perfect β-tin Ge. 

   more » « less
4. Spectrally-selective Photovoltaics via Photonic Band Engineering in Absorbing Media

   https://doi.org/10.1109/PVSC40753.2019.8980467  

   Chiu, Arlene; Qiu, Botong; Lin, Yida; Arinze, Ebuka S.; Li, Lulin; Thon, Susanna M. (June 2019, Spectrally-selective Photovoltaics via Photonic Band Engineering in Absorbing Media)

   Spectral selectivity is of interest for many photovoltaic applications, such as in multijunction and transparent solar cells, where wavelength-selectivity of the photoactive material is necessary. We investigate using artificial photonic band engineering as a method for achieving spectral selectivity in an absorbing material such as PbS CQD thin films. Using FDTD simulations, we find that a CQD-based photonic crystal (CQD-PC) is able to maintain its photonic band structure, including the existence of a reduced photonic density of states, in the presence of weak material absorption. This shows that CQD-PCs are a promising material for photovoltaic applications that require spectral selectivity. 

   more » « less
5. The Microscopic Diamond Anvil Cell: Stabilization of Superhard, Superconducting Carbon Allotropes at Ambient Pressure

   https://doi.org/10.1002/anie.202205129  

   Wang, Xiaoyu; Proserpio, Davide M.; Oses, Corey; Toher, Cormac; Curtarolo, Stefano; Zurek, Eva (June 2022, Angewandte Chemie International Edition)

   Abstract A metallic, covalently bonded carbon allotrope is predicted via first principles calculations. It is composed of ansp³carbon framework that acts as a diamond anvil cell by constraining the distance between parallelcis‐polyacetylene chains. The distance between thesesp²carbon atoms renders the phase metallic, and yields two well‐nested nearly parallel bands that cross the Fermi level. Calculations show this phase is a conventional superconductor, with the motions of thesp²carbons being key contributors to the electron–phonon coupling. Thesp³carbon atoms impart superior mechanical properties, with a predicted Vickers hardness of 48 GPa. This phase, metastable at ambient conditions, could be made by on‐surface polymerization of graphene nanoribbons, followed by pressurization of the resulting 2D sheets. A family of multifunctional materials with tunable superconducting and mechanical properties could be derived from this phase by varying thesp²versussp³carbon content, and by doping. 

   more » « less