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The Joy of Condensed Matter Physics

The Joy of Condensed Matter Physics

The Joy Of Condensed Matter Physics 8/15/22, 8:05 PM

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The Joy Of Condensed Matter Physics

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Aug 11, 2016, 01:50pm EDT

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Why is condensed matter physics interesting? originally

appeared on Quora - the knowledge sharing network where

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The Joy Of Condensed Matter Physics 8/15/22, 8:05 PM

compelling questions are answered by people with unique

insights .

Answer by Inna Vishik, Assistant Professor of Physics at

UC Davis, on Quora:

I am drawn to condensed matter physics because it is

simultaneously useful and fundamental, simultaneously

mundane and fantastical, simultaneously large and small, and

most of all, some of the phenomena that are observed in

condensed matter systems are just flipping cool.

First, a definition of condensed matter. This field studies many
atom systems that are condensed (i.e. not a gas) but not too

condensed (i.e. not the inside of a neutron star). Condensed

matter physics in its broadest definition encompasses many

different subfields (cold atoms, biophysics, soft matter, solid
state physics, etc.). For this piece, I will focus on solid-state

physics (the study of crystalline solids; also called hard

condensed matter) with which I am most familiar.

With that disclaimer out of the way, back to our scheduled

programming …

Condensed matter physics is both useful and fundamental .

Many people who know a little bit about solid state physics know

that it gave us microscopic understanding of silicon and its native

oxide, which gave us solid-state transistors, which gave us every

computer and smartphone on the planet. But those same

semiconducting materials, when stacked on top of each other in a

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specific way, can produce a very pure 2-dimensional metal at the

interface. When this specially-prepared material is cooled down

to very low temperature (<4K, i.e. not useful) and subjected to a

large magnetic field (several Tesla, not useful), it exhibits

quantized conductance comprising the integer and fractional

quantum Hall effect, both of which garnered Nobel prizes in

physics. The former is used as a standard for electrical resistance

(useful after all), and the latter exhibits electron-like

quasiparticles that behave as if they have fractional charge

(whaa??).

On that note, condensed matter systems manifest other

quasiparticles (objects that behave like particles inside the solid

but don’t exist outside the solid) which are predicted in particle

physics but never observed in free space, such as majorana

fermions [1] and magnetic monopoles [2]. The quantum hall

effect is the intellectual predecessor to a subfield of solid-state

physics that is currently very trendy—topological materials,

including topological insulators, Dirac semimetals and Weyl

semimetals. These also connect to particle physics via

quasiparticles that behave like massless Dirac and Weyl fermions

(fundamental), and if they can be made superconducting in the

proper way, it is predicted that they will also manifest majorana

fermions which may be used for quantum computation [3]

(potentially useful).

Condensed matter physics is simultaneously mundane and

fantastical . I am typing this answer at my dining room table,

and I can use condensed matter physics to explain why various

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objects in my vicinity behave the way they do: why my ceramic

coffee mug is good for handling hot liquids and would break if I

dropped it, why my stainless steel fork does not attract a paper

clip right now but would if I held it up to a big honking magnet,

why my diamond is so flawless (when at a loss for a third item on

a list, quote Beyoncé).

These same materials can be implicated in my personal favorite

phenomenon in condensed matter physics—superconductivity—

in which a material suddenly loses its resistivity at low enough

temperature and can conduct a dissipationless current (basically,

a perpetual motion machine, if you can keep it cold enough).

Some of the highest temperature superconductors out there are

ceramic materials [4]. Iron (the main elemental constituent of

steel) can be compressed (but not nearly as much as a neutron

star) and become a superconductor [5]; or it can be alloyed with,

say, arsenic and barium to make a different type of high
temperature superconductor [6]. And diamond becomes

superconducting [7] if you dope it with an ample amount of

boron.

This juxtaposition between the mundane and the fantastical

also encompasses the ability of condensed matter physics to not

only to describe nature, but also to manipulate nature. We live in

one universe, but crystalline solids allow us to create or discover

another universe with different properties. Do you want a

universe where magnets only have a north pole, but no south

pole? This was realized inside so-called Pyrochlore materials,

which were synthesized in a lab and whose peculiar magnetic

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structure gives rise to quasiparticles, which behave like magnetic

monopoles [8]. Do you want a two-dimensional universe? Maybe

one with a slower speed of light—a slower cosmic speed limit?

Both are realized in graphene, a fantastical material which is

usually produced in the most mundane way possible: by taking a

piece of scotch tape to a hunk of graphite rock mined out of the

ground [9].

Condensed matter physics is simultaneously large and small . I

mean this both in terms of the experiments (and calculations)

that can be done and the science itself. Many experiments in

condensed matter physics can be performed on a tabletop by a

single student in a lab at a relatively low cost. Other experiments,

however, are performed at large user facilities such as

synchrotrons, neutron scattering research reactors and free

electron-lasers, which require a full time support team and can

cost more than a billion dollars to build (the good news is they

can be used for many different experiments, not only in

condensed matter physics, but in chemistry and biology too). On

the theoretical side of the field, some people do pencil and paper

calculations, while others apply for time on a supercomputer to

numerically study systems of many-interacting particles. The

science of condensed matter has a small number of tiny

constituents: electrons, protons, and neutrons. But when many,

many of them are put together, emergent properties can appear

that encompass a macroscopic material and are often quite

different from the sum of their parts.

And that brings me to the amazing phenomena that appear in

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condensed matter systems [10]. It should be noted that

oftentimes these phenomena are discovered by surprise, not

predicted beforehand. Previously, I discussed fractional charges

in the fractional quantum hall effect and superconductivity (fun

fact: the theory of the Higgs’ Boson originates from the theory

explaining why certain metals become superconductors at low

temperature; all of physics is connected). Other cool phenomena

include super-obese electrons in some rare-earth compounds who

behave as if they have a mass 1,000 times that of a free electron

[11], materials in which the resistance suddenly increases by a

factor of 100,000 when subjected to a magnetic field [12], highly

radioactive elements that undergo five different structural phase

transitions in their solid state [13], fractal behavior (Hofstadter's

butterfly) in graphene/boron nitride heterostructures, novel types

of magnetic order such as skyrmions (the name alone…), just to

name a few. And we are not limited to the phenomena we know

about today: the smallest speck of crystalline solid contains over a

septillian mutually interacting electrons and ions, which can be

arranged in nearly limitless ways, so there is no shortage of

astounding phenomena (some of which might be useful, too)

waiting to be discovered/invented. It goes down in the CM, for

sure.

A big thank you to Prof. Alexander F. Kemper, Dr. George

Burkhard, and Noah Raman for helpful suggestions,

improvements, and discussion on this piece.

Footnotes

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[1] Observation of Majorana fermions in ferromagnetic atomic

chains on a superconductor

[2] http://www.nature.com/nature/jou...

[3] http://www.nature.com/nphys/jour...

[4] High-temperature superconductivity

[5] http://www.nature.com/nature/jou...

[6] Iron Exposed as High-Temperature Superconductor

[7] https://arxiv.org/ftp/cond-mat/p...

[8] Dirac Strings and Magnetic Monopoles in the Spin Ice

Dy2Ti2O7

[9] Minerals | Graphite

[10] The Theory of Everything

[11] Heavy fermion

[12] Thousandfold Change in Resistivity in Magnetoresistive La-

Ca-Mn-O Films

[13] Allotropes of plutonium

[14] http://www.nature.com/nature/jou...

This question originally appeared on Quora - the knowledge

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Condensed Matter Physics: What is condensed matter?

Physics of Everyday Life: How do flames burn upward

while gravity pulls them down?

Science: What do chemists know that physicists don't?

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