Kitchen temperature supercurrents from stacked 2D materials

Date:
October 21, 2020
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
A 'stack' of 2D materials could allow for supercurrents at ground-
breakingly warm temperatures, easily achievable in the household
kitchen.

An international study opens a new route to high-temperature
supercurrents -- at temperatures, as 'warm' as inside your kitchen
fridge. (Previously, superconductivity has been difficult even
at temperatures as low as -170DEGC, making superconductivity
impractical for many of its most exciting applications.)


FULL STORY ========================================================================== Could a stack of 2D materials allow for supercurrents at ground-breakingly
warm temperatures, easily achievable in the household kitchen?

==========================================================================
An international study published in August opens a new route to high- temperature supercurrents at temperatures as 'warm' as inside a kitchen
fridge.

The ultimate aim is to achieve superconductivity (ie, electrical current without any energy loss to resistance) at a reasonable temperature.

TOWARDS ROOM-TEMPERATURE SUPERCONDUCTIVITY Previously, superconductivity
has only been possible at impractically low temperatures, less than
-170DEGC below zero -- even the Antarctic would be far too warm!
For this reason, the cooling costs of superconductors have been high,
requiring expensive and energy-intensive cooling systems.



========================================================================== Superconductivity at everyday temperatures is the ultimate goal of
researchers in the field.

This new semiconductor superlattice device could form the basis of a
radically new class of ultra-low energy electronics with vastly lower
energy consumption per computation than conventional, silicon-based
(CMOS) electronics.

Such electronics, based on new types of conduction in which solid-state transistors switch between zero and one (ie, binary switching) without resistance at room temperature, is the aim of the FLEET Centre of
Excellence.

EXCITON SUPERCURRENTS IN ENERGY-EFFICIENT ELECTRONICS Because oppositely-charged electrons and holes in semiconductors are strongly
attracted to each other electrically, they can form tightly-bound
pairs. These composite particles are called excitons, and they open up
new paths towards conduction without resistance at room temperature.



========================================================================== Excitons can in principle form a quantum, 'superfluid' state, in which
they move together without resistance. With such tightly bound excitons,
the superfluidity should exist at high temperatures -- even as high as
room temperature.

But unfortunately, because the electron and hole are so close together,
in practice excitons have extremely short lifetimes -- just a few
nanoseconds, not enough time to form a superfluid.

As a workaround, the electron and hole can be kept completely apart
in two, separated atomically-thin conducting layers, creating so-called 'spatially indirect' excitons. The electrons and holes move along separate
but very close conducting layers. This makes the excitons long-lived,
and indeed superfluidity has recently been observed in such systems.

Counterflow in the exciton superfluid, in which the oppositely charged electrons and holes move together in their separate layers, allows
so-called 'supercurrents' (dissipationless electrical currents) to flow
with zero resistance and zero wasted energy. As such, it is clearly an
exciting prospect for future, ultra-low-energy electronics.

STACKED LAYERS OVERCOME 2D LIMITATIONS Sara Conti who is a co-author
on the study, notes another problem however: atomically-thin conducting
layers are two-dimensional, and in 2D systems there are rigid topological quantum restrictions discovered by David Thouless and Michael Kosterlitz
(2016 Nobel prize), that eliminate the superfluidity at very low
temperatures, above about -170DEGC.

The key difference with the new proposed system of stacked atomically-thin layers of transition metal dichalcogenide (TMD) semiconducting materials,
is that it is three dimensional.

The topological limitations of 2D are overcome by using this 3D
`superlattice' of thin layers. Alternate layers are doped with excess
electrons (n-doped) and excess holes (p-doped) and these form the 3D
excitons.

The study predicts exciton supercurrents will flow in this system at temperatures as warm as -3DEGC.

David Neilson, who has worked for many years on exciton superfluidity
and 2D systems, says "The proposed 3D superlattice breaks out from the topological limitations of 2D systems, allowing for supercurrents at
-3DEGC. Because the electrons and holes are so strongly coupled, further
design improvements should carry this right up to room temperature." "Amazingly, it is becoming routine today to produce stacks of these
atomically- thin layers, lining them up atomically, and holding them
together with the weak van der Waals atomic attraction," explains Prof
Neilson. "And while our new study is a theoretical proposal, it is
carefully designed to be feasible with present technology."

========================================================================== Story Source: Materials provided by ARC_Centre_of_Excellence_in_Future_Low-Energy_Electronics
Technologies. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. M. Van der Donck, S. Conti, A. Perali, A. R. Hamilton, B. Partoens,
F. M.

Peeters, D. Neilson. Three-dimensional electron-hole superfluidity
in a superlattice close to room temperature. Physical Review B,
2020; 102 (6) DOI: 10.1103/PhysRevB.102.060503 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201021112406.htm

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