Supporting Image
Feb 24, 2016 0    
Magnets and superconductors
Going With the FFLO

What follows is adapted from materials originally published on the Brown University website. A link to the original article can be found below.

Superconductors and magnetic fields do not usually get along. However, a research team led by a Brown University physicist has produced new evidence for an exotic superconducting state, first predicted a half-century ago, that can indeed arise when a superconductor is subject to a strong magnetic field.

Superconductivity—the ability to conduct electric current without resistance—depends on the formation of electron twosomes known as Cooper pairs. In a normal conductor, electrons rattle around in the structure of the material, which creates resistance. But Cooper pairs move in concert in a way that keeps them from rattling around, enabling them to travel without resistance.

Magnetic fields are the enemy of Cooper pairs. In order to form a pair, electrons must be opposites in a property that physicists refer to as spin. Normally, a superconducting material has a roughly equal number of electrons with each spin, so nearly all electrons have a dance partner. But strong magnetic fields can flip “spin-down” electrons to “spin-up,” making the spin population in the material unequal.

So what happens when we have more electrons with one spin than the other–that is, what happens with the ones that don’t have pairs? Can we actually form superconducting states that way, and if so, what would this state look like?

In 1964, physicists predicted that superconductivity could indeed exist in certain kinds of materials exposed to a magnetic field. They theorized that the unpaired electrons would gather together in discrete bands or stripes across the superconducting material. Those bands would conduct normally, while the rest of the material would be superconducting. This modulated superconductive state is known as the FFLO phase, named for physicists Peter Fulde, Richard Ferrell, Anatoly Larkin, and Yuri Ovchinniko, who predicted its existence.

Physicists have been trying for years to demonstrate that the FFLO state exists, but without success. To investigate the phenomenon, we used a superconductor with the catchy name κ-(BEDT-TTF)2Cu(NCS)2. The material consists of ultra-thin sheets stacked on top of each other and is exactly the kind of material predicted to exhibit the FFLO state. After applying an intense magnetic field to the material, we investigated its properties and found there were regions across the material where unpaired, spin-up electrons had congregated. These electrons behave like little particles constrained in a box, as illustrated in the figure. Since superconductors usually require very cold temperatures to limit the random motion of particles, one surprising finding was that the material we studied exhibited the FFLO state at a much higher temperature than expected.

This new understanding of what happens when electron spin populations become unequal could have implications for other situations in which superconductors coexist with magnetic fields. It might help astrophysicists to understand pulsars—densely packed neutron stars believed to harbor both superconductivity and strong magnetic fields. It could also be relevant to the field of spintronics, in which devices made of layered magnetic and superconducting structures store information based on electron spin rather than charge.

Fig. 1 (Click to enlarge). Artist's rendering of the Mitrovic lab at Brown University, where very cold temperatures are used to maintain and study highly ordered states of matter, like those found in superconductors. (Jelena Berenc)
Fig. 1 (Click to enlarge). Artist's rendering of the Mitrovic lab at Brown University, where very cold temperatures are used to maintain and study highly ordered states of matter, like those found in superconductors. (Jelena Berenc)
Fig. 2 (Click to enlarge). Sometimes physicists make jokes. (Jelena Berenc)
Fig. 2 (Click to enlarge). Sometimes physicists make jokes. (Jelena Berenc)
TAGS: #Electrons    #magnetism    #spin    #spintronics    #superconductors    
 
SHARE THIS POST:

Related Posts

11/30
Supporting Image
Supporting Image
Domains and Disks
by Shireen Adenwalla, Xiaoshan Xu

Magnets curve themselves into beautiful patterns called domains, which cannot be seen with the naked eye. Now that magnetic paint and nail polish are easily available, we can use magnets to create all kinds of magnetic patterns which we can see, photograph, erase and rewrite! Click to find out how YOU can paint with magnets!

2 2    
05/12
Supporting Image
Supporting Image
Laser memory

Instead of pencil, paper, and eraser, we can use combinations of lasers and magnetic materials to write, read, and and erase information by varying the temperature and magnetic field. Here we apply our laser "pencil" to magnetic "paper" to write the letter “N” (Go Huskers!!). This technique allows us write, erase, and rewrite tiny magnetic memories like those found in your computer hard drive and other devices. Click to learn how it works!

0 0    
04/20
Supporting Image
Supporting Image
Thermalizing nanowires

It’s a hot summer day. You desperately want something cold to drink, but unfortunately, your bottle of root beer has been sitting in a hot car all day. You put it into a bucket full of ice to cool it down. But it’s taking forever! How, you wonder, could you speed the process up? The same question is important for understanding how electronic devices work, and how we can make them work better by controlling the temperature of the electrons that power them. Read on to find out what a bottle of root beer in a cooler full of ice and a nanowire in a vat of liquid helium have in common!

0 0    

More Funsize Research

11/21
Supporting Image
Supporting Image
Nanoscale fluid mechanics

We think we're pretty familiar with how ordinary liquids behave, but it turns out that some of the basic things we know are no longer true when we look at these liquids on short enough length scales and fast enough time scales. The liquids start to behave more like solids, pushing back when you push on them, and slipping across solid surfaces instead of being dragged along. Click to ride the tiny-but-mighty new wave of nanofluidics!

0 0    
09/22
Supporting Image
Supporting Image
Funsize Lasers

Soap bubbles are marvelously playful. A cascade of bubbles blown into the air can send children running in circles to pop them before they hit the ground. And if you know how to look, soap bubbles are just as playful on much smaller scales, sending scientists running in circles to understand their fascinating physics. Read on to learn more!

0 0    
07/25
Supporting Image
Supporting Image
Ferroelectric hafnia

Ferroelectric materials generate electric fields that move charges around, just as a bar magnet produces a magnetic field that moves magnets around. Ferroelectric materials can be used for data storage to make electronics more energy efficient, but they don’t always play well with the silicon technology used in devices like phones and computers. HAFNIA TO THE RESCUE! Click to learn more.

0 0    
04/20
Supporting Image
Supporting Image
Fluids and filling

You take a pristine-looking Oreo from a package of seemingly identical sandwich cookies, and you decide to open it up to eat the creme filling first. You gently twist the cookie apart without breaking the chocolate wafers, but the creme sticks to one side only. Why? Happily, the physics of fluids helped two MIT students solve this delicious mystery. Read on to find out what they learned, and how you can test their results at home.

0 0    
05/12
Supporting Image
Supporting Image
Laser memory

Instead of pencil, paper, and eraser, we can use combinations of lasers and magnetic materials to write, read, and and erase information by varying the temperature and magnetic field. Here we apply our laser "pencil" to magnetic "paper" to write the letter “N” (Go Huskers!!). This technique allows us write, erase, and rewrite tiny magnetic memories like those found in your computer hard drive and other devices. Click to learn how it works!

0 0    
04/20
Supporting Image
Supporting Image
Thermalizing nanowires

It’s a hot summer day. You desperately want something cold to drink, but unfortunately, your bottle of root beer has been sitting in a hot car all day. You put it into a bucket full of ice to cool it down. But it’s taking forever! How, you wonder, could you speed the process up? The same question is important for understanding how electronic devices work, and how we can make them work better by controlling the temperature of the electrons that power them. Read on to find out what a bottle of root beer in a cooler full of ice and a nanowire in a vat of liquid helium have in common!

0 0    
02/23
Supporting Image
Supporting Image
World's smallest diode

Diodes, also known as rectifiers, are a basic component of modern electronics. As we work to create smaller, more powerful and more energy-efficient electronic devices, reducing the size of diodes is a major objective. Recently, a research team from the University of Georgia developed the world's smallest diode using a single DNA molecule. This diode is so small that it cannot be seen by conventional microscopes.

0 0    
02/01
Supporting Image
Supporting Image
Liquid magnetism
by Robert Streubel, Scott Schrage

You may have heard that there are three main phases of matter: solids, liquids, and gases (plus plasma if you want to get fancy). Liquids can take virtually any shape and deform instantly. Solid materials possess interesting electronic and magnetic properties essential to our daily life. But how about designing rigid liquids with magnetic properties? Impossible? Not anymore. Click to learn more!

0 0    
11/05
Supporting Image
Supporting Image
Building a better computer
by Peter Dowben, Jocelyn Bosley

Scientists are working to develop electronic devices that store and process information by manipulating a property of electrons called spin—a research area aptly known as spintronics. The semiconductors we are developing will not only be faster and cheaper than those used in conventional devices, but will also have more functionality.

1 1    
11/05
Supporting Image
Supporting Image
Good vibrations

Materials that are absolutely perfect—in other words, materials that contain no defect of any kind—are usually not very interesting. Imagine being married to a saint: you would quickly be bored out of your mind! Defects and impurities can considerably change many properties of materials in ways that allow a wide range of applications.

0 0    
11/05
Supporting Image
Supporting Image
Secrets of semiconductors

Semiconductors are materials with properties intermediate between metals and non-conducting insulators, defined by the amount of energy needed to make an electron conductive in the material. The non-conducting electrons occupy a continuum of energy states, but two of these states (the “heavy hole” and “light hole”) are nearly identical in energy. The heavy hole is easy to observe and study, but the light hole eludes most observers.

0 0    
11/05
Supporting Image
Supporting Image
Locking up electrons

Solids are generally divided into metals, which conduct electricity, and insulators, which do not. Some oxides straddle this boundary, however: a material's structure and properties suggest it should be a metal, but it sometimes behaves as an insulator. Researchers at the University of California, Santa Barbara are digging into the mechanisms of this transformation and are aiming to harness it for use in novel electronic devices.

0 0    
11/05
Supporting Image
Supporting Image
Nanomagnetism

You may know that the media used in magnetic recording technologies, such as computer hard drives, are made of millions of tiny nanomagnets. Each nanomagnet can be switched up or down to record bits of information as ones and zeros. These media are constantly subjected to magnetic fields in order to write, read, and erase information. If you have ever placed a magnet too close to your laptop or cell phone, you know that exposure to an external magnetic field can disrupt information stored this way. Did you know that it is possible for the nanomagnets to "remember" their previous state, if carefully manipulated under specific magnetic field and temperature conditions? Using a kind of memory called topological magnetic memory, scientists have found out how to imprint memory into magnetic thin films by cooling the material under the right conditions.

0 0    
11/05
Supporting Image
Supporting Image
Slow reflection

Inside solids, the properties of photons can be altered in ways that create a kind of "artificial gravity" that affects light. Researchers at the University of Pittsburgh tracked photons with a streak camera and found that whey they enter a solid-state structure, they act just like a ball being thrown in the air: they slow down as they move up, come to a momentary stop, and fall back the other way. Studying this "slow reflection" will allow us to manipulate light's behavior, including its speed and direction, with potential applications in telecommunications and quantum computing technologies.

0 0    
11/05
Supporting Image
Supporting Image
Superfluid helium droplets

In a unique state of matter called a superfluid, tiny "tornadoes" form that may play an important role in nanotechnology, superconductivity, and other applications. Just as tornadoes are invisible air currents that become visible when they suck debris into their cores, the quantum vortices in superfluids attract atoms that make the vortices visible. Quantum vortices are so small they can only be imaged using very short-wavelength x-rays, however.

0 0    
11/05
Supporting Image
Supporting Image
Magnetic anisotropy

Would you rather have data storage that is compact or reliable? Both, of course! Digital electronic devices like hard drives rely on magnetic memory to store data, encoding information as “0”s and “1”s that correspond to the direction of the magnetic moment, or spin, of atoms in individual bits of material. For magnetic memory to work, the magnetization should not change until the data is erased or rewritten. Unfortunately, some magnetic materials that are promising for high density storage have low data stability, which can be improved by squeezing or stretching the crystal structures of magnetic memory materials, enhancing a material property called magnetic anisotropy.

0 0    

WRITE COMMENT

Go to Top