Super conducting voltage controlled switch??

Skip to first unread message

Jan Panteltje

Jan 31, 2023, 12:46:20 AMJan 31
Superconductivity switches on and off in 'magic-angle' graphene
A quick electric pulse completely flips the material's electronic properties:

Super conducting voltage controlled switch??

Anthony William Sloman

Jan 31, 2023, 1:17:14 AMJan 31
Of course, while it is turning off, there will be current flowing through the two atom thick layer of graphene while it's resistance is finite.

It wouldn't take much current to blow up the switch.

You'd have to use it rather carefully.

Bill Sloman, Sydney

John Larkin

Jan 31, 2023, 4:21:07 PMJan 31
On Tue, 31 Jan 2023 05:41:50 GMT, Jan Panteltje <al...@comet.invalid>
2-state superconducting switches, switched by various mechanisms, have
been around for decades. They were for the computers of the future
when I was in high school.

Phil Hobbs

Jan 31, 2023, 6:30:44 PMJan 31
Yup. Originally it was cryotrons (not to be confused with krytrons),
which switched between normal and superconducting when a magnetic field
was applied. Dudley Buck and his collaborators got fairly far down that
road before his untimely death in 1959.
(The writer doesn't know the difference between a cryotron and a
Josephson junction, which are about as alike as chalk and cheese, but
never mind.)

Then IBM spent many years and a whole bunch of money on trying to make
Josephson junction computers. Their first try was a Pb overlap junction
technology, which failed because iirc it wouldn't survive much
temperature cycling and was too slow anyway. Their second try (which a
couple of my pals worked on BITD) was based on niobium edge junctions,
which worked pretty well but never overcame the power and cost
disadvantages of a LHe technology.


The program had been closed down well before I arrived in 1987, but I
heard lots of stories.


Phil Hobbs

Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

John Walliker

Feb 1, 2023, 5:46:29 AMFeb 1
I got to make my own Josephson junctions and demonstrate the microwave
induced voltage steps in a physics practical. The junction was a niobium
cat's whisker pressing against a niobium plate. The tricky bit was grinding
the point in just the right way to get a suitably thick oxide layer on the tip.


Phil Hobbs

Feb 1, 2023, 11:43:10 AMFeb 1
Cool. I'm surprised they let undergrads handle liquid helium. I had
an NSERC summer grant after third year to work on a nuclear orientation
experiment with a dilution fridge (which I was not allowed to touch).

John Larkin

Feb 1, 2023, 12:27:51 PMFeb 1
I had a high school summer job at LSUNO, designing electronics for
Stark effect microwave spectroscopy at 85 cents per hour. I was
kneeling near a dewar and somebody spilled a bunch of liquid nitrogen.
Froze my knee.

We did have dry ice and liquid helium too. Lots of cool stuff like
gamma sources for mossbauer spectroscopy.

My high school had little radiation sources, alpha and beta and gamma.
I took one home in my pants pocket.

The Tulane physics dept had an open-pool subcritical nuclear reactor
and we passed uranium rods around by hand. And some giant xray source
that was protected by pieces of yellow tape on the floor.

Reply all
Reply to author
0 new messages