Isoelectronic perturbations to --electron hybridization and the enhancement of hidden order in URuSi.

Electrical resistivity measurements were performed on single crystals of URu Os Si up to = 0.28 under hydrostatic pressure up to = 2 GPa. As the Os concentration, , is increased, 1) the lattice expands, creating an effective negative chemical pressure (); 2) the hidden-order (HO) phase is enhanced and the system is driven toward a large-moment antiferromagnetic (LMAFM) phase; and 3) less external pressure is required to induce the HO→LMAFM phase transition.

Electrical Control of Structural and Physical Properties via Strong Spin-Orbit Interactions in Sr_{2}IrO_{4}.

Electrical control of structural and physical properties is a long-sought, but elusive goal of contemporary science and technology. We demonstrate that a combination of strong spin-orbit interactions (SOI) and a canted antiferromagnetic Mott state is sufficient to attain that goal. The antiferromagnetic insulator Sr_{2}IrO_{4} provides a model system in which strong SOI lock canted Ir magnetic moments to IrO_{6} octahedra, causing them to rigidly rotate together.

Phase diagram and thermal expansion measurements on the system URu2-xFexSi2.

Thermal expansion, electrical resistivity, magnetization, and specific heat measurements were performed on URuFeSi single crystals for various values of Fe concentration x in both the hidden-order (HO) and large-moment antiferromagnetic (LMAFM) regions of the phase diagram. Our results show that the paramagnetic (PM) to HO and LMAFM phase transitions are manifested differently in the thermal expansion coefficient. The uniaxial pressure derivatives of the HO/LMAFM transition temperature T change dramatically when crossing from the HO to the LMAFM phase.

Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy.

A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain.

Imaging the three-dimensional Fermi-surface pairing near the hidden-order transition in URu2Si2 using angle-resolved photoemission spectroscopy.

We report angle-resolved photoemission spectroscopy experiments probing deep into the hidden-order state of URu(2)Si(2), utilizing tunable photon energies with sufficient energy and momentum resolution to detect the near Fermi-surface (FS) behavior. Our results reveal (i) the full itinerancy of the 5f electrons, (ii) the crucial three-dimensional k-space nature of the FS and its critical nesting vectors, in good comparison with density-functional theory calculations, and (iii) the existence of hot-spot lines and pairing of states at the FS, leading to FS gapping in the hidden-order phase.

Quantized breather excitations of Fermi-Pasta-Ulam lattices.

We have calculated the lowest energy quantized breather excitations of both the β and the α Fermi-Pasta-Ulam monoatomic lattices and the diatomic β lattice within the ladder approximation. While the classical breather excitations form continua, the quantized breather excitations form a discrete hierarchy labeled by a quantum number n. Although the number of phonons is not conserved, the breather excitations correspond to multiple bound states of phonons.

Temperature dependence of hybridization gaps in metallic heavy-fermion systems.

There is evidence that a number of heavy-fermion/mixed-valence materials show hybridization gaps either at the Fermi energy or close to it. In the former case, a heavy-fermion semiconducting state ensues, and in the latter case, the system remains metallic at low temperatures. In either case, there are significant indications that the electronic structure is extremely temperature dependent.