C. R. Rotundu

Photoelectron spin-flipping and texture manipulation in a topological insulator

In a topological insulator, the surface-state electron spins are ‘locked’ to their direction of travel. But when an electron is kicked out by a photon through the photoelectric effect, the spin polarization is not necessarily conserved. In fact, the ejected spins can be completely manipulated in three dimensions by the incident photons.

Widespread spin polarization effects in photoemission from topological insulators

High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi2Se3 using a recently developed high-efficiency spectrometer. The topological surface states helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

High magnetic field phase diagram of PrOs4Sb12

The magnetic phase diagram of PrOs4Sb12 has been investigated by specific heat measurements between 8 and 32 T. A new Schottky anomaly, due to excitations between two lowest crystalline-electric-field (CEF) singlets, has been found for both H parallel (100) and H parallel (110) above the field where the field-induced ordered phase (FIOP) is suppressed. The constructed H-T phase diagram shows weak magnetic anisotropy and implies a crossing of the two CEF levels at about 8-9 T for both field directions. These results provide an unambiguous evidence for the Gamma(1) singlet being the CEF ground state and suggest the level crossing (involving lowest CEF levels) as the driving mechanism of FIOP.

Spin-polarized surface resonances accompanying topological surface state formation

Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator Bi2Se3. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation. Its momentum dependence and spin texture imply an intimate connection with the topological surface state. Calculations show these two distinct states can emerge from trivial Rashba-like states that change topology through the spin-orbit-induced band inversion. This work thus provides a compelling view of the coevolution of surface states through a topological phase transition, enabled by the unique capability of directly measuring the spin-polarized unoccupied band structure.

Anomalous low-temperature state of a possible Kondo semimetal Ce Os 4 Sb 12 : Magnetic field and La impurity study

Specific heat in magnetic fields to

High-pressure resistivity technique for quasi-hydrostatic compression experiments

14\phantom{\rule{0.3em}{0ex}}\mathrm{T}

Tomonaga-Luttinger Liquid in a Quasi-One-Dimensional S 1 Antiferromagnet Observed by Specific Heat Measurements

, magnetic susceptibility and electrical resistivity for single crystalline samples of

X-ray Absorption and Emission Spectroscopy Study of the Effect of Doping on the Low Energy Electronic Structure of PrFeAsO1-δ

{\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}

Exotic Kondo-hole band resistivity and magnetoresistance of Ce 1 − x La x Os 4 Sb 12 alloys

(x=0,0.02,0.1)