DCMPMS Seminars

How do we discover Majorana particles in nanowires?

by Prof. Sergey Frolov (University of Pittsburgh)

Monday, September 27, 2021 from to (Asia/Kolkata)
at Zoom seminar ( https://zoom.us/j/92926081538 Meeting ID: 929 2608 1538 Passcode: 050857 )
https://zoom.us/j/92926081538 Meeting ID: 929 2608 1538 Passcode: 050857
Description
I have been on a ten year journey to gather evidence of Majorana
particles, a quarter of my life. For me personally this came from
theorists: frist Carlo Beenakker and his students who presented at our
group meetings, and then - during a 30 second conversation with Roman
Lutchyn at the 2010 March meeting, when I realized that we could try
this in semiconductor nanowires which I was working with in the Delft
lab as a postdoc. (Wires came from Sebastien Plissard and Erik Bakkers
in Eindhoven).
I fleshed out ideas for how we would do it and ghost-written a grant
proposal with my advisor Leo Kouwenhoven. It gave us money to hire two
amazing PhD students: Kun Zuo and Vincent Mourik. With my faculty job in
Pittsburgh secure by that time, there was no risk in trying to hunt for
Majorana, and we went for it with force. By 2012 we found promising
Majorana signatures: zero-bias peaks in conductance that were sticky:
did not move from zero voltage bias when we changed electric or magnetic
fields. A lot of work lay ahead to verify, improve and find additional
evidence. Yet we - and lots of other people - had little doubt that we
were on track to demonstrate Majorana.
But nature prepared a surprise for us: in subsequent years other
researchers, Eduardo Lee and Silvano de Franceschi from Grenoble,
demonstrated that sticky zero-bias peaks can also come from Andreev
states, not only Majorana. It is very rare that a phenomenon so
carefully mapped out can also have another compelling explanation. At
that time my old team in Delft, and my new team in Pittsburgh were
struggling to find further Majorana signatures. It took time for us to
embrace the fact that Majorana have not been discovered: some are still
working through that.
Yet in a decade we have learned a lot. First, we learned how to tell
Andreev from Majorana. Even if all we measured so far is Andreev, we are
sure that we will know Majorana when we see it. Second, we improved our
nanowire materials by deploying advanced growth and nanofabrication
techniques. We developed elaborate computational models that capture
many subtleties of nanowire devices, with superconducting shells. The
future is bright: because Majorana is based on a solid theoretical
foundation, we should be able to make the discovery. If society still
has the patience to let us pursue it. What of quantum computing
applications? That will have to wait until we figure out the basic
physics.