HOME | WHAT WE DO | WHO WE ARE | WHAT'S GOING ON | HOW TO JOIN
While the universe is ultimately described by quantum mechanics, in many materials the impact of quantum effects is largely about numerical factors. For example, the picture of a metal as a classical fluid of electrons gives a reasonable starting point for transport phenomena, even though it misses the magnitudes of many quantities by orders of magnitude.
There are other solids and situations where quantum mechanics has more dramatic consequences. An example is superconductivity: in a superconductor, electrons suddenly begin to flow without measurable resistance below some nonzero temperature (Fig. 1). The term “quantum materials” has become a useful shorthand for solids whose properties cannot be captured even qualitatively without a quantum-mechanical description.
Figure 1: (left) 1911 data from Leiden showing the vanishing of resistivity in a superconductor. (right) The Meissner effect, which is the expulsion of magnetic field from a superconductor, can be used to levitate all sorts of things.
Topological phases of matter are another class of quantum materials and a major focus of our group. Topological insulators and semimetals (Fig. 2) are the simplest examples of this class: these can be understood via the standard one-electron description of bands in crystals as long as it is supplemented by the ideas of Thouless, Haldane and others about the geometry of electronic wavefunctions.
Fractional topological phases, such as the fractional quantum Hall effect and certain complex magnets known as spin liquids, host new kinds of particles as the electron breaks up into pieces. In many two-dimensional materials, these particles are neither bosons nor fermions but rather have more complicated behavior under particle exchange. These states have potential applications to quantum information and can sometimes be observed through their effects on quantum dynamics
Our group works on many other kinds of quantum materials as well, and seeks to find signatures of novel phenomena in collaboration with experiments at Berkeley and elsewhere. An introductory review to the physics of quantum materials is here