How can a tunnel diode be used as a memory element?
By providing a resistive load line for a tunnel diode, the memory effect can be exploited.
As a kid, buying a tunnel diode from Lafayette Electronics, I found 100 ohm series resistors provided a STEEP enough load line that I could map out the entire I_V curve
(this from memory, of decades_ago tinkering).
However, high_resistance load lines would have the SNAP between states; a coupling capacitor would inject the charge transient needed to flip between states.
I did not evaluate the state_store behavior.
I did use the Tunnel Diode as an oscillator.
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Andy: from what I recall of the I_V curve(s) for a tunnel/Esaki diode

a HIGH VOLTAGE and a HIGH RESISTANCE provide the snap_memory

I'd draw an I_V curve, but stackX no longer allows my browser that ability.