Session K44: Emergent Phenomena of Mixed Valence Kondo Insulators

Quantum Oscillations in Kondo Insulators

In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators. Here, we report a notable exception in an insulator —ytterbium dodecaboride (YbB₁₂). The resistivity of YbB₁₂, which is of a much larger magnitude than the resistivity in metals, exhibits distinct quantum oscillations. These unconventional oscillations arise from the insulating bulk, even though the temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. Quantum oscillations in the magnetic torque are also observed, albeit with a lighter effective mass.   

Fermi surfaces in Kondo insulators

TBD   

A Physical-Chemical Understanding of Samarium Hexaboride

TBD   

Mixed valence insulators with neutral Fermi surfaces

A number of recent experiments have suggested the possibility that the low-temperature insulating bulk of mixed valence systems like SmB6 and YbB12 hosts electrically neutral gapless excitations. I will describe a new phase of matter---composite exciton Fermi liquid--- a mixed valence insulator with a three dimensional fermi-surface of a neutral fermion, that we name the "composite exciton". I will describe the mechanism responsible for the formation of such excitons, discuss the phenomenology of the composite exciton Fermi-liquid and discuss existing and possible future experiments.
  

Quantum Oscillation from in-gap states in Kondo insulators

Recent experiments on quantum oscillation in heavy fermion materials, such as SmB6 and YbB12, has gained great many interests in the community of strongly correlated electrons. Its physical origin has been hotly debated.

In this talk, we present the most direct explanation to this novel phenomenon––quantum oscillation comes from in-gap quasiparticles. The quantum oscillation found in these narrow gap insulators, where the scattering rate controls Lifshitz-Kosevich (LK) factor instead of Dingle factor, is quite the opposite to the case of normal metals, where the scattering rate controls Dingle factor instead of LK factor. This novel result is an important prediction of our theory and differs clearly with other theories. We provide an analytical formula that can be used by experimentalists to fit and interpret their data. Our calculation based on the ARPES data agrees very well with the quantum oscillation experiments.