Achieved: Negative Temperature For A Quantum Gas!

There exists nothing as negative temperature (in Kelvin scale), at least not in ‘normal’ systems; this is something we learn in physics. This is a scale devised by Lord Kelvin (and hence the name of the unit) and according to this scale, there can be no negative value of temperature. Temperature was thought to be the measure of the energy of the particles in a system. While this isn’t untrue, the modern definition of temperature is broader.

For a system with energy levels, temperature is a measure of the probability of the occupation of an energy level with respect to energy. As we access more and more energetic states, the probability of occupation generally decreases and this leads to a positive temperature state. Now, imagine a system having the reverse configuration, like the higher energy states being more populated than the lower energy states. This kind of system will then have a negative temperature.

Try and note that negative temperature states are extremely rare and do not occur in our day-to-day lives. Particles will always like to occupy the lower energy states first and then go for the higher energy ones. In a room of air, you’ll always find more molecules with very low energies than molecules with very high energies. This is because the energy has a lower limit, viz E=0. The lowest energy possible is if the molecule were completely static. However, there is no upper limit.

Interesting systems

But if you did have an upper limit, things would be interesting! Say there is an upper limit of the energy spectrum, meaning that no particle can have any energy beyond this limit (just like no particle could go below the lower limit). Now, under certain conditions, the system would occupy the upper energy levels more than the lower ones! This causes an inversion of the sign of temperature, according to the modern definition. Thus, we have negative temperature!

The temperature on the right half is negative. We do not live in that half, but some systems do! (taken from the Nature paper – link given below)

So what’s the big deal, you ask? Negative temperatures have been known for magnetic systems (which have an upper and a lower limit), but we haven’t known of any system with motional degrees of freedom (like an atom free to move in 3 dimensions) to have such an energy spectrum.

The Experiment

Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany and his team created an ultra-cold quantum gas made up of potassium atoms and they confined these atoms to a lattice (i.e. a crystal like arrangement). At positive temperatures, the atoms repelled each other, but the team was able to flip the magnetic field fast enough for the atoms to start attracting each other. This also flips the sign of the temperature. Explains Prof. Schneider:


The temperature measured was a billionths of a degree below absolute zero! Wolfgang Ketterle, Nobel Laureate, called this an ‘experimental Tour de Force’. It truly is!

Link to paper in Naturedoi:10.1038/nature.2013.12146

Scientists Create First Light Controlled Nano-Switch



Light Switches!



How they did it


And that’s it!



The paper appears in Nature Nanoscience:

Scientists Split The Electron, Create an ‘Orbiton’ For The First Time Ever

Condensed matter physicists are known for creating miracles and they haven’t disappointed! They have just split the electron into two, creating a hitherto unobserved ‘orbiton’ in the process. While this has immediate consequences in theoretical condensed matter physics, like figuring out how high temperature superconductivity occurs (more later), the very idea of this is just too cool.

An explanation for superconductivity?

The ‘pieces’ of the electron

Condensed matter physicists have long identified that in a chain of atoms (called a ‘spin chain’), aligned in a particular direction, especially in the presence of a magnetic field, electrons can be thought of as particles being made up of three components. One component represents the charge(a ‘holon’), another the spin (a ‘spinon’) and a third one should store the orbital location information (an ‘orbiton’). Do note, however, that these three components exist independently only inside the material, not outside it. Outside the material, the electron is just the elementary particle – unbreakable into other particles – just like we know it to be.

History revisited

Fifteen years ago, a team of scientists, led by C. Kim of Stanford University, split the electron into its holon and spinon components. The material they used was ‘one-dimensional’ Strontium Cuprate. Now, another team, led by J. van den Brink, have split the electron into a spinon and an orbiton, making it the first ever spectroscopic observation of a free orbiton. The material is another version of Strontium Cuprate.

Performing a miracle with a laser

The team fired a beam of X-ray photons into the one-dimensional material. The electrons in the outer orbitals were excited to a higher orbital. In this process, the electron can separate out into a spinon and an orbiton. And this is exactly what the scientists got.

When the electron got excited to a higher orbital, the laser light lost some energy. The scattered beam’s energy and momentum were plotted and compared with various computer simulations. The plot matched perfectly if one assumes that the electron has ‘split’ into an orbiton and a spinon. These two quasi-particles would be moving in opposite directions through the medium.

Van der Brink is more ambitious:

The next step will be to produce the holon, spinon and the orbiton at the same time

Problem in superconductivity

So what theoretical problem in superconductivity does it really solve?

The long standing problem in superconductivity (the phenomenon of flow of electric current through a material with zero resistance) has been the problem of high temperature superconductivity. No one know how some materials manage to superconduct at temperatures such as -196 degrees Celsius, which is much higher than the previously known -268 to -263 degree Celsius. No one knows what conducts the current through the material. There is a theory that orbitons might be the key.

To have the power to create your own materials and rediscover one of the oldest discoveries of ‘modern’ science is to be able to do modern day alchemy. It’s a miracle, indeed.

The paper appears here:

Evidences of Majorana Particles Seen In Nanowires


A computer image of the nanowire created

Condensed Matter physicists join in…


Device and Methodology




The work appears here:

Scientists Unleash “Designer Electrons”; Synthesize Graphene Atom-By Atom

Stanford University researchers have come up with ‘designer electrons’  – electrons whose properties can be controlled and fine-tuned. Leading the research is Hari Manoharan, associate professor at the Stanford Physics department. He reports that his group has created graphene-like electrons and then tweaked them!

The honeycomb potential

Why is this important? Let Prof. Manoharan answer that question:

The behavior of electrons in materials is at the heart of essentially all of today’s technologies. We’re now able to tune the fundamental properties of electrons so they behave in ways rarely seen in ordinary materials.

Working with individual molecules

So, this is what they did. They placed carbon monoxide molecules on an atomically smooth copper substrate using a Scanning Tunneling Microscope (STM), which then created the potential mimicking that of the carbon atoms in graphene, forcing the electrons to behave like those of graphene. The peculiarity of graphene electrons is that, within graphene, they act as if they have no mass. They thus move at the maximum speed possible within the substrate. Manoharan calls this ‘molecular graphene’, built from scratch atom-by-atom.

Making electrons go crazy – at will

Manoharan’s group could then tweak the potential properties by changing the positions of the Carbon Monoxide molecules and then the electrons suddenly gained mass! More than that, they could make the electrons behave as if they were in an electric or magnetic field. Says Manoharan:


The team is now looking to synthesize more semiconductor substances and also replicate certain properties of graphene. The team promises that more ‘Dirac materials’ are on the way! We live in exciting times.

The work is featured in Nature and it appeared yesterday. Here is the link:

More info from Stanford news:

Also, do watch the video below, where the group explains their work. You do NOT want to miss this.

Novel New Material Graphyne Can Be A Serious Competitor To Graphene


An artist's impression of graphene


Graphene and Graphyne



6,6,12- Graphyne

Simulations and predictions




More about the mechanical properties of graphyne:

Created: A One-Atom Transistor!



Quantum Mechanics and Choices!



Moore’s Law









Fabricated: The World’s First Two-Dimensional Glass



Making Graphene… err Glass



A pleasant surprise


The scientists have published this finding in Nano Letters.

Size Of A Byte : Less Than 100 Atoms, Courtesy IBM!

Data storage units, as thin as a few strands of hair, may soon be on the cards. IBM and the German Center for Free-Electron Laser Science (CFEL) have come up with a new size of the byte and it’s the world’s smallest data storage unit. The storage unit – one bit – comprises just 12 atoms! The byte – or 8 bits – thus comprises just 96 atoms, far less than the 500 million atoms that normal hard drives of today take!

A bit! Two arrays of anti-ferromagnetic ordered iron atoms, as seen by spin-polarized imaging techniques using a Scanning Tunneling Microscope (Courtesy: DESY/ Helmholtz Research Association)


This amazing fabrication comes from the IBM Almaden research Center in San Jose, California. They made up two rows of iron atoms, each row being six atoms long. Each atom was placed carefully on the substrate using a Scanning Tunnelling Microscope (STM). This formed one byte. The team then made 8 such structures. Each byte covers just 4 nm x 16 nm area (nm = nanometer; 1 nm = One billionths of a meter).

Using Spin States

The storage is done using the spin states of the ferromagnetic iron atoms. The two states – 0 and 1 – representing on and off respectively, are simulated by the spin being either parallel or anti-parallel to a certain direction. The state can be changed using the STM, employing a tiny electric pulse. Thus data can be written into and also read out of these tiny atomic magnetic units. The electric pulse, only a few nano amperes strong, can only be stable at very low temperatures like 5 Kelvin or minus 268 degrees Celsius.

The revolutionary idea, as compared to the conventional storage devices, is the use of anti-ferromagnetic order of the adjacent iron atoms. This means that two neighboring toms will have two different states of spin – one will be ‘up’ and the other ‘down’. This will make the bulk material non-magnetic.

Building bottoms-up starting from single atoms is by no mean task! Only a very few research facilities in the world have been able to master the wizardry. But, why 12 atoms? Sebastian Loth, who migrated from IBM to CFEL and is the lead of the study explains it:

Beneath this threshold quantum effects blur the stored information.

There is a long way to go for these atomic devices to be made available for public use.

The paper highlighting this new fabrication appeared on Science (link) on 13th January, 2012.

Info obtained from:

“Time Cloak” Makes A Hole In Time; Makes Events Invisible

Time has finally been punched through, even though for a very short period of time. Scientists, using the technology for making invisibility cloaks’, have bent light in a tight circle, creating a time cloak. The effect lasts for 40 trillionths of a second.

The art of invisibility

This is the basic idea: If you can make sure that light doesn’t scatter off or reflect of a certain object, that object is invisible. Now, assume that an event occurs, but the lights are switched off at that precise point of time. You don’t register that event. What researchers mean to do is to create this gap in the continuum of light, which then becomes akin to making a small hole in time itself.

Cornell physicist and study co-author Alex Gaeta explains better:

Imagine that you could divert light in time slow it down, speed it up so that you create a gap in the light beam in time. In this case, any event that occurs at that instant of time won’t lead to scattering of light. It appears as if the event never occurred.

He goes on splendidly:

If a device would perhaps speed up a portion of the beam and slow down another portion of it so that there is an instant of time with no beam. You could pass through, and then [on the other side of the event] the device would do the oppositeâ€”speed up the part that had been slowed and slow the part that had been sped up. That would put the beam of light back together, so to speak, so that the detector never recognizes that anything has happened.


Bending light in the temporal dimension

Gaeta and colleagues have used a device called a time lens’. It bends light, not in spatial directions, but in temporal direction. It uses the trick described above, only with higher sophistication and precision to create gaps in the continuum.

Tweaking time with light might be more than just a gimmick in terms of technological value. It might be used in cryptography, using the time lens to create gaps in codes, passed through optical fibres and then reverse them using a second laser source. The information can be sent and received perfectly, but during the transit, it will be highly coded.

Making the hole in space and time a bit bigger and more stable is the current focus. Also, the team is looking to make a three dimensional hole in space (along with the one in time) and this will require great synchronization from six different lasers, rather than just the two used for the one-dimensional case.