Kevin M. Ryan; Carlos G. Torres-Castanedo; Dominic P. Goronzy; David A. Garcia Wetter; Matthew J Reagor; Mark Field; Cameron J Kopas; Jayss Marshall; Michael J. Bedzyk; Mark C. Hersam; Venkat Chandrasekhar
Characterization of Nb films for superconducting qubits using phase boundary measurements Journal Article
In: Applied Physics Letters, vol. 121, pp. 202601, 2022.
Abstract | Links | BibTeX | Tags: epitaxial, instrumentation, Superconductivity, superconductor
@article{Ryan2022,
title = {Characterization of Nb films for superconducting qubits using phase boundary measurements},
author = {Kevin M. Ryan and Carlos G. Torres-Castanedo and Dominic P. Goronzy and David A. Garcia Wetter and Matthew J Reagor and Mark Field and Cameron J Kopas and Jayss Marshall and Michael J. Bedzyk and Mark C. Hersam and Venkat Chandrasekhar},
url = {https://arxiv.org/abs/2207.13125
https://aip.scitation.org/doi/10.1063/5.0119932},
year = {2022},
date = {2022-07-26},
urldate = {2022-07-26},
journal = {Applied Physics Letters},
volume = {121},
pages = {202601},
abstract = {Continued advances in superconducting qubit performance require more detailed understandings of the many sources of decoherence. Within these devices, two-level systems arise due to defects, interfaces, and grain boundaries, and are thought to be a major source of qubit decoherence at millikelvin temperatures. In addition to Al, Nb is a commonly used metalization layer for superconducting qubits. Consequently, a significant effort is required to develop and qualify processes that mitigate defects in Nb films. As the fabrication of complete superconducting qubits and their characterization at millikelvin temperatures is a time and resource intensive process, it is desirable to have measurement tools that can rapidly characterize the properties of films and evaluate different treatments. Here we show that measurements of the variation of the superconducting critical temperature Tc with an applied external magnetic field H (of the phase boundary Tc−H) performed with very high resolution show features that are directly correlated with the structure of the Nb films. In combination with x-ray diffraction measurements, we show that one can even distinguish variations quality and crystal orientation of the grains in a Nb film by small but reproducible changes in the measured superconducting phase boundary.},
keywords = {epitaxial, instrumentation, Superconductivity, superconductor},
pubstate = {published},
tppubtype = {article}
}
Continued advances in superconducting qubit performance require more detailed understandings of the many sources of decoherence. Within these devices, two-level systems arise due to defects, interfaces, and grain boundaries, and are thought to be a major source of qubit decoherence at millikelvin temperatures. In addition to Al, Nb is a commonly used metalization layer for superconducting qubits. Consequently, a significant effort is required to develop and qualify processes that mitigate defects in Nb films. As the fabrication of complete superconducting qubits and their characterization at millikelvin temperatures is a time and resource intensive process, it is desirable to have measurement tools that can rapidly characterize the properties of films and evaluate different treatments. Here we show that measurements of the variation of the superconducting critical temperature Tc with an applied external magnetic field H (of the phase boundary Tc−H) performed with very high resolution show features that are directly correlated with the structure of the Nb films. In combination with x-ray diffraction measurements, we show that one can even distinguish variations quality and crystal orientation of the grains in a Nb film by small but reproducible changes in the measured superconducting phase boundary.
Varada Vilas Bal
Transport Measurements on (111) Oriented (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 Heterostructures PhD Thesis
Northwestern University, 2018.
Abstract | Links | BibTeX | Tags: epitaxial, Kondo effect, magnetic impurity, Magnetism, perovskite, spin-orbit scattering, Superconductivity, superconductor
@phdthesis{Bal2018b,
title = {Transport Measurements on (111) Oriented (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 Heterostructures},
author = {Varada Vilas Bal},
url = {http://www.nano.northwestern.edu/wp-content/uploads/2018/09/BalVarada_PhD_Thesis.pdf},
year = {2018},
date = {2018-09-01},
address = {Department of Physics},
school = {Northwestern University},
abstract = {At the interface of two dissimilar entities, something novel can emerge. This idea has driven a vast amount of fruitful work on semiconductor interfaces, and given us the digi- tal revolution. In the past decade, remarkable progress has been made in the synthesis and understanding of interfaces between oxides, opening up new avenues to explore fundamen- tal emergent physics at the interface, as well as to provide viable candidates to augment or even surpass the performance of conventional semiconductor electronics. The two- dimensional conducting interface in the (001) LaAlO3/SrTiO3 system is the most studied example of oxide interfaces, showing a wide range of coexisting and competing phenomena such as superconductivity, superconductor-insulator transitions, magnetism, and spin- orbit interactions. The (111) oriented LaAlO3/SrTiO3 system has been recently found to have a few surprises of its own, with intriguing anisotropies in many transport properties along different in-plane crystal directions. This thesis presents the first results on a different SrTiO3 based system: the conducting interface between (La0.3Sr0.7)(Al0.65Ta0.35) and (111) oriented SrTiO3, which has a smaller strain as compared to the LaAlO3/SrTiO3 system. Electrical transport measurements at cryogenic temperatures reveal that no systematic anisotropy is seen in transport properties, unlike in the case of (111) oriented LaAlO3/SrTiO3. High-field magnetotransport shows the presence of high-mobility carri- ers at high electron densities, and exhibits multiband behavior, tunable in situ using an electrical back-gate, similar to the LaAlO3/SrTiO3 system. The data allow us to draw specific conclusions about band ordering in the system, and point to possible differences between the band ordering in (111) (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 and (001) as well as (111) oriented LaAlO3/SrTiO3. Low-field magnetotransport reveals that a strong spin- orbit interaction emerges in the regime of low electron density, when the high-mobility carriers are depleted from the system, a trend which is opposite to that observed in (001) oriented LaAlO3/SrTiO3. The most striking feature is that at millikelvin temperatures, in the regime of low electron densities, concomitant with the development of strong spin- orbit interaction, magnetic order emerges.},
keywords = {epitaxial, Kondo effect, magnetic impurity, Magnetism, perovskite, spin-orbit scattering, Superconductivity, superconductor},
pubstate = {published},
tppubtype = {phdthesis}
}
At the interface of two dissimilar entities, something novel can emerge. This idea has driven a vast amount of fruitful work on semiconductor interfaces, and given us the digi- tal revolution. In the past decade, remarkable progress has been made in the synthesis and understanding of interfaces between oxides, opening up new avenues to explore fundamen- tal emergent physics at the interface, as well as to provide viable candidates to augment or even surpass the performance of conventional semiconductor electronics. The two- dimensional conducting interface in the (001) LaAlO3/SrTiO3 system is the most studied example of oxide interfaces, showing a wide range of coexisting and competing phenomena such as superconductivity, superconductor-insulator transitions, magnetism, and spin- orbit interactions. The (111) oriented LaAlO3/SrTiO3 system has been recently found to have a few surprises of its own, with intriguing anisotropies in many transport properties along different in-plane crystal directions. This thesis presents the first results on a different SrTiO3 based system: the conducting interface between (La0.3Sr0.7)(Al0.65Ta0.35) and (111) oriented SrTiO3, which has a smaller strain as compared to the LaAlO3/SrTiO3 system. Electrical transport measurements at cryogenic temperatures reveal that no systematic anisotropy is seen in transport properties, unlike in the case of (111) oriented LaAlO3/SrTiO3. High-field magnetotransport shows the presence of high-mobility carri- ers at high electron densities, and exhibits multiband behavior, tunable in situ using an electrical back-gate, similar to the LaAlO3/SrTiO3 system. The data allow us to draw specific conclusions about band ordering in the system, and point to possible differences between the band ordering in (111) (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 and (001) as well as (111) oriented LaAlO3/SrTiO3. Low-field magnetotransport reveals that a strong spin- orbit interaction emerges in the regime of low electron density, when the high-mobility carriers are depleted from the system, a trend which is opposite to that observed in (001) oriented LaAlO3/SrTiO3. The most striking feature is that at millikelvin temperatures, in the regime of low electron densities, concomitant with the development of strong spin- orbit interaction, magnetic order emerges.
M. M. Mehta; D. A. Dikin; C. W. Bark; S. Ryu; C. M. Folkman; C. B. Eom; V. Chandrasekhar
Magnetic field tuned superconductor-to-insulator transition at the LaAlO 3 / SrTiO 3 interface Journal Article
In: Physical Review B, vol. 90, no. 10, 2014, ISSN: 1098-0121, 1550-235X.
Links | BibTeX | Tags: epitaxial, insulator, Magnetism, perovskite, superconductor
@article{mehta_magnetic_2014,
title = {Magnetic field tuned superconductor-to-insulator transition at the LaAlO 3 / SrTiO 3 interface},
author = { M. M. Mehta and D. A. Dikin and C. W. Bark and S. Ryu and C. M. Folkman and C. B. Eom and V. Chandrasekhar},
url = {http://link.aps.org/doi/10.1103/PhysRevB.90.100506},
doi = {10.1103/PhysRevB.90.100506},
issn = {1098-0121, 1550-235X},
year = {2014},
date = {2014-01-01},
urldate = {2015-10-23},
journal = {Physical Review B},
volume = {90},
number = {10},
keywords = {epitaxial, insulator, Magnetism, perovskite, superconductor},
pubstate = {published},
tppubtype = {article}
}
P Cadden-Zimansky; J Wei; V Chandrasekhar
Coherent nonlocal correlations in Andreev interferometers Journal Article
In: New Journal of Physics, vol. 14, no. 4, pp. 043004, 2012, ISSN: 1367-2630.
Links | BibTeX | Tags: Andreev reflection, Proximity effect, superconductor
@article{cadden-zimansky_coherent_2012,
title = {Coherent nonlocal correlations in Andreev interferometers},
author = { P Cadden-Zimansky and J Wei and V Chandrasekhar},
url = {http://stacks.iop.org/1367-2630/14/i=4/a=043004?key=crossref.f07cad531c95baf1d401aa858682bf05},
doi = {10.1088/1367-2630/14/4/043004},
issn = {1367-2630},
year = {2012},
date = {2012-01-01},
urldate = {2016-12-28},
journal = {New Journal of Physics},
volume = {14},
number = {4},
pages = {043004},
keywords = {Andreev reflection, Proximity effect, superconductor},
pubstate = {published},
tppubtype = {article}
}
