A state of matter is a description of the properties of a substance or material. There are four classical states of matter, solid, liquid, gas and plasma. Solids have definite shape and volume, liquids have a definite volume but change their shape according to the container, and gases have no definite shape or volume. A gas will fill all available space in a container. Plasma, like gas, has no fixed shape or volume, and is electrically conductive. It is produced by phenomena such as lightning and some kinds of fires. These are the states of matter that humans are likely to come across on an everyday basis. However, in extreme environments, or under special conditions, exotic states of matter are known to exist. There are over 30 known states of matter, and those listed below are only the newest to be identified.
There is a lot of subatomic space. A hydrogen atom is made up of just one proton and one electron. If your fist is the electron, then the dome of a cathedral or the Gol Gumbaz is the size of the entire atom. The electron is a tiny moth within this vast space. There is no reason that a sufficiently large atom cannot house other atoms between the electron and the nucleus. In February 2018, an international team of researchers from Austria and the USA proved that this new state of matter, called “Rydberg polarons” can exist. The process involved freezing strontium atoms close to absolute zero temperatures, creating another state of matter known as a Bose-Einstein condensate. Now, one of these strontium atoms was fired at with a laser, providing it with energy. The single strontium atom expanded to thousand times the size of a hydrogen atom, with the other strontium atoms enclosed within the path of the electron of that atom, known as the Rydberg electron. The other strontium atoms exert a very slight force on the Rydberg electron, barely deflecting it from its path. At higher temperatures, this bond would break, so Rydberg polarons can only be observed at extremely low temperatures.
Quantum Spin Liquid
Quantum spin liquid is a state of matter that is naturally found on the Earth. In regular magnetic materials, the spins of electrons interact with each other and settle in an orderly fashion. When these magnets are cooled to near zero temperatures, the spins of electrons freeze. In frustrated magnets, the electron spins never settle, even at close to sub zero temperatures. They perpetually interact with each other in a liquid like state, which lends the name to the state – quantum spin liquid. The existence of quantum spin liquids was first proposed in the 1970s by Nobel laureate Philip Warren Anderson. There was evidence to suggest that the quantum spin liquid state existed in some minerals, including Herbertsmithite. However, finding direct evidence for the same in a lab environment proved difficult. It was only in 2016, using a particle accelerator, that the existence of a special variant of a quantum spin liquid was found. Quantum spin liquids come in many forms with peculiar characteristics that can be of use in future quantum computers.
3D quantum liquid crystals
Liquid crystals are themselves an exotic state of matter. The material shares characteristics with both solid crystals as well as liquids. The molecules in the liquid flow like any other regular liquid, but are all oriented in the same direction, similar to crystals. The liquid crystal state can be found in nature, including in membranes of cells. Most of us encounter liquid crystals on an everyday basis in liquid crystal displays. 3D quantum liquid crystals are quantum analogues of liquid crystals. In a quantum liquid crystal, the electrons behave like the molecules in a liquid crystal. The electrons move freely, but prefer a particular direction to flow in. A Caltech researcher came across the first observed 3D quantum liquid crystals while using lasers to study the atomic structure of rhenium compounds. The patterns observed matched with theoretical predictions of quantum liquid crystals. The find was only the first in a new class of quantum liquid crystals, and just like quantum spin liquids, this discovery could have future implications for quantum computing.
Ordinary crystals have repeated patterns in space, but are constant in time. Time crystals form repeated patterns in space as well as time, and may just be the first form to be identified in a whole new category of non equilibrium materials. A time crystal cannot exist in thermal equilibrium. Nobel laureate Frank Wilczek first proposed the existence of non equilibrium matter in 2012. It was in 2016 that researchers proved that a time crystal could be created in lab environments. In 2017, Norman Yao, an assistant professor in the University of California, Berkeley published a paper containing the details of creating such a crystal, and observing its properties. Two different setups by the University of Maryland and Harvard University were used to prove the viability of his approach. Under different conditions induced using magnetic fields or lasers, the time crystals could shift to different phases, such as solids, liquids or gases. The time crystal was created using a chain of 10 ytterbium ions. Lasers were used to create magnetic fields and partially flip the spins of some atoms. The atoms in the chain interacted in a repetitive manner into a regular pattern that repeated in time, forming the time crystal. Think of it as a chunk of jelly that jiggles at its own period no matter how it is disturbed.
This is a state of matter that have seemingly contradictory characteristics. A supersolid has a definite a shape, or a rigid structure, just like any other solid. Like a superfluid, it can also flow without viscosity. Superfluids have strange characteristics. A superfluid can escape from its container by crawling up the sides. A cup of superfluid, when stirred, would continue to spin forever. Using laser beams and vacuum chambers, researchers created the first supersolid from a superfluid in 2017. A team led by Wolfgang Ketterle successfully demonstrated the creation of a supersolid at MIT. Ketterle had won the 2001 Nobel prize in physics for co-discovering the Bose-Einstein condensate. A team led by Ketterle worked towards creating a supersolid, by manipulating the superfluid Bose-Einstein condensate through a system of lasers. Around the same time, another group from Switzerland used a system of mirrors to create a supersolid. At the present, supersolids can only exist in the vacuum chambers at extremely low temperatures. However, the team is continuing to study the properties of the new state of matter.
Glass is another example of an everyday material having extraordinary properties. Under a microscope, crystals have regular grid of repeated cells. Glass however, is a disordered, amorphous material, appearing like random grains of sand, or like the grid of cells has been warped and twisted. The properties of crystals can be calculated easily, and researchers can predict how they absorb heat or what happens when they break. The same cannot be done for glass. Researchers have long suspected that a mysterious phase transition exists in glass. Using just a pen and paper, a postdoctoral fellow of Duke University, Sho Yaida, solved the problem. His calculations showed that at low temperatures, glass may exist at a new state of matter. Once the glass is assumed to exist in a universe with infinite dimensions, calculating the properties become as easy as calculating the properties of crystals in three dimensions. The discovery has applications in material sciences.
In the 1960s, BI Halperin and TM Rice theorised that a new state of matter could exist under certain conditions in semiconductors. For over 50 years, researchers have tried to find or demonstrate the existence of the state of matter known as excitonium. In 2017, a team of researchers from the University of Illinois used a technique they developed called momentum-resolved electron energy-loss spectroscopy to demonstrate the existence of excitonium. Excitonium is a condensate that exhibits behavior similar to a superconductors, superfluid or an insulating electronic crystal. The state of matter is formed by a combination of escaped electrons, and the holes they leave behind. In areas of semiconductors crowded with electrons, the electrons jump out. The holes they leave behind behave like particles due to a crowd of escaped electrons around them. The holes have a positive charge, and attract the electrons, which jump in and form a particle, known an exciton. At this point, the discovery of excitonium is fundamental research, with no known practical applications.