Electrons are the most basic constituents of matter all around us as an integral part of every atom. Individually, electrons are known to exist as an electron gas independently or within matter. Electron gas is a well known concept in science while explaining the physical and chemical properties of pure metals which are supposed to contain electron gas according to free electron theory or Drude’s model. Drude (Free electron) Model is a model to predict some physical phenomena in solid state materials.

It considers electrons involved metallic bonds as free that wanders in Brownian motion, hence called as electron gas. One the other hand, in conventional electronic devices, electricity requires the movement of electrons and their positive counterparts, called holes, which behave much like the gas molecules in our atmosphere. Although they move rapidly and collide infrequently in the gas phase, electrons and holes can condense into liquid droplets akin to liquid water in devices composed of ultrathin materials. Cooling the electron-hole liquid to ultra-low temperatures could cause it to transform into a "quantum fluid" with exotic physical properties that could reveal new fundamental principles of matter.

Formation of electron liquid: By bombarding an ultrathin semiconductor sandwich with powerful laser pulses, physicists at the University of California, Riverside, have created the first "electron liquid" at room temperature. In their experiments, researchers constructed an ultrathin sandwich of the semiconductor molybdenum ditelluride between layers of graphene. The layered structure was just slightly thicker than the width of a single DNA molecule. The researchers then bombarded the material with superfast laser pulses, measured in quadrillionths of a second. Normally, with such semiconductors as silicon, laser excitation creates electrons and their positively charged holes that diffuse and drift around in the material, which is how we define a gas. However, the team detected evidence of condensation into the equivalent of a liquid. Such a liquid would have properties resembling common liquids such as water, except that it would consist, not of molecules, but of electrons and holes within the semiconductor.

Possible applications: The achievement opens a pathway for development of the first practical and efficient devices to generate and detect light at terahertz wavelengths - between infrared light and microwaves. The electronic properties of such droplets would enable development of optoelectronic devices that operate with unprecedented efficiency in the terahertz region of the spectrum. Such devices could be used in applications as diverse as communications in outer space, cancer detection, and scanning for concealed weapons. Terahertz transmitters and receivers could also be used for faster communication systems in outer space. And, the electron-hole liquid could be the basis for quantum computers, which offer the potential to be far smaller than silicon-based circuitry now in use. The research could also enable exploration of the basic physics of matter at infinitesimally small scales and help usher in an era of quantum metamaterials, whose structures are engineered at atomic dimensions.