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Rob Kiefl

My research interests are in  condensed matter physics and in particular the area of so called quantum materials and their interfaces.  In general the properties of an interface (or surface region) are different that the properties of the two constituent materials in the same way a molecule has different properties than its constituent atoms.  Our goals are to discover exactly how these differences arise near surfaces and interfaces . Our group has been developing a  new technique called low energy beta- detected NMR,  in which a spin polarized beam of radioactive nuclei produced at the TRIUMF ISAC facility is used a  probe of local magentic and electronic properties   of quantum materials and their interfaces.

Much of condensed matter physics is concerned with the collective state of electrons in a crystals or solid.  Many solids (e.g. semiconductors and simple metals) can be understood primarily within models where the effective interactions between electrons can be neglected or treated as a perturbation. However there are a growing number of materials being discovered with remarkable properties where the effective interactions are strong and new theoretical approaches are required. One prominent example is the High Tc superconductors.  Our understanding of such materials is far less advanced and is guided by an ongoing interplay between experiment and theory. The low temperature properties of such materials are particularly interesting since that is where we expect effects due to quantum coherence to be largest. Materials which exhibit interesting quantum  phenomena at low temperatures (e.g. superconductivity) are called “quantum materials”. A Heisenberg coupled spin   chain  is an  example of a quantum magnetic material which is particularly important  since it can be treated  precisely from a theory point of view. One striking quantum effect is that a Heisenberg spin chain has a  gapless excitations spectrum whereas the spin 1 chain has a   Haldane gap [1].  Another example is a geometrically frustrated Heisenberg antiferromagnet where the dominant near neighbor interaction is frustrated by the spatial arrangement of the magnetic ions. This  leads to a ground state with a macroscopic degeneracy  called a cooperative paramagnet.  

 

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