Singular charge fluctuations at a magnetic quantum critical point

Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy–grown thin films of YbRh2Si2, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter.

QUANTUM FLUID MECHANICS AND QUANTUM ELECTRODYNAMICS

The commutation relations of Landau quantum fluid mechanics are compared with those of quantum electrodynamics. In both cases, the operator representation of the commutators require a macroscopic phase, and a wavefunction periodic in that phase. A physical discussion is given for analogous effects in superfluids and superconductors, with regard to quantum coherence on a macroscopic scale. Other applications are then briefly described.

Experimental uniaxial stress and strain derivatives of the Fermi surface of rhenium

The derivatives of the areas of extremal orbits on all the small sheets of the Fermi surface of rhenium, with respect to stress and strain along the hexad axis, have been determined from simultaneous measurements of Landau quantum oscillations in magnetostriction and torque, and also in sound velocity and torque. Strong anisotropy is observed in the stress derivatives of orbits in zones five and six as the direction of the magnetic field defining the normal to the orbit is varied; the anisotropy is most pronounced for orbits which come close to the line of degeneracy AL on the hexagonal Brillouin zone face. The derivatives of the small void in zone eight are found to be very large; this is consistent with the results of band structure calculations which show that this feature of the Fermi surface is very sensitive to small changes in the Fermi energy. Cyclotron effective masses for a number of orbits on the void have also been measured.

Experimental determination of the dilational strain dependence of the Fermi surface of white tin

The derivatives with respect to uniaxial elongational strain of the areas of representative orbits on all sheets of the Fermi surface of tetragonal white tin have been deduced from simultaneous measurements of the Landau quantum oscillations in elastic moduli and in torque. Strain derivatives have been determined for most known extremal cross-sectional areas normal to the [100], [110], and [001] symmetry axes; the anisotropy of the strain derivatives of several area branches, having normal directions in the (010) and (001) planes, has also been studied. Uniaxial and hydrostatic stress derivatives deduced from the strain derivatives have been found to be generally consistent with values obtained by other means.