Emergent symmetry in TbTerevealed by ultrafast reflectivity under anisotropic strain.

We report ultrafast reflectivity measurements of the dynamics of the order parameter of the charge density wave (CDW) in TbTeunder anisotropic strain. We observe an increase in the frequency of the amplitude mode with increasing tensile strain along the-axis (which drives the lattice into > , withandthe lattice constants), and similar behavior for tensile strain along( > ). This suggests that both strains stabilize the corresponding CDW order and further support the near equivalence of the CDW phases oriented in- and-axis, in spite of the orthorhombic space group.

Anomalous Superfluid Density in a Disordered Charge-Density-Wave Material: Pd-Intercalated ErTe_{3}.

We image local superfluid density in single crystals of Pd-intercalated ErTe_{3} below the superconducting critical temperature T_{c}, well below the onset temperature T_{CDW} of (disordered) charge-density-wave order. We find no detectable inhomogeneities on micron scales. We observe a rapid increase of the superfluid density below T_{c}, deviating from the behavior expected in a conventional Bardeen-Cooper-Schrieffer superconductor, and show that the temperature dependence is qualitatively consistent with a combination of quantum and thermal phase fluctuations.

Emergent tetragonality in a fundamentally orthorhombic material.

Symmetry plays a key role in determining the physical properties of materials. By Neumann's principle, the properties of a material remain invariant under the symmetry operations of the space group to which the material belongs. Continuous phase transitions are associated with a spontaneous reduction in symmetry.

Light-Induced Currents at Domain Walls in Multiferroic BiFeO.

Multiferroic BiFeO (BFO) films with spontaneously formed periodic stripe domains can generate above-gap open circuit voltages under visible light illumination; nevertheless the underlying mechanism behind this intriguing optoelectronic response has not been understood to date. Here, we make contact-free measurements of light-induced currents in epitaxial BFO films via detecting terahertz radiation emanated by these currents, enabling a direct probe of the intrinsic charge separation mechanisms along with quantitative measurements of the current amplitudes and their directions. In the periodic stripe samples, we find that the net photocurrent is dominated by the charge separation across the domain walls, whereas in the monodomain samples the photovoltaic response arises from a bulk shift current associated with the non-centrosymmetry of the crystal.