Atomic and Electronic Structure of a Rashba pp-nn Junction at the BiTeI Surface

The non-centrosymmetric semiconductor BiTeI exhibits two distinct surface terminations that support spin-split Rashba surface states. Their ambipolarity can be exploited for creating spin-polarized $p$-$n$ junctions at the boundaries between domains with different surface terminations. We use scanning tunneling microscopy/spectroscopy (STM/STS) to locate such junctions and investigate their atomic and electronic properties. The Te- and I-terminated surfaces are identified owing to their distinct chemical reactivity, and an apparent height mismatch of electronic origin. The Rashba surface states are revealed in the STS spectra by the onset of a van Hove singularity at the band edge. Eventually, an electronic depletion is found on interfacial Te atoms, consistent with the formation of a space charge area in typical $p$-$n$ junctions.Comment: 5 pages, 4 figure

Ultrafast Optical Control of the Electronic Properties of ZrTe5ZrTe_5

We report on the temperature dependence of the $ZrTe_5$ electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure across the Fermi energy on the sample temperature. This finding is regarded as the dominant mechanism responsible for the anomalous resistivity observed at T* $\sim$ 160 K along with the change of the charge carrier character from holelike to electronlike. Having addressed these long-lasting questions, we prove the possibility to control, at the ultrashort time scale, both the binding energy and the quasiparticle lifetime of the valence band. These experimental evidences pave the way for optically controlling the thermoelectric and magnetoelectric transport properties of $ZrTe_5$

Non-Fermi liquid angle resolved photoemission lineshapes of Li0.9Mo6O17

A recent letter by Xue et al. (PRL v.83, 1235 ('99)) reports a Fermi-Liquid (FL) angle resolved photoemission (ARPES) lineshape for quasi one-dimensional Li0.9Mo6O17, contradicting our report (PRL v.82, 2540 ('99)) of a non-FL lineshape in this material. Xue et al. attributed the difference to the improved angle resolution. In this comment, we point out that this reasoning is flawed. Rather, we find that their data have fundamental differences from other ARPES results and also band theory.Comment: To be published as a PRL Commen

An ASP-based Solution to the Chemotherapy Treatment Scheduling problem

The problem of scheduling chemotherapy treatments in oncology clinics is a complex problem, given that the solution has to satisfy (as much as possible) several requirements such as the cyclic nature of chemotherapy treatment plans, maintaining a constant number of patients, and the availability of resources, for example, treatment time, nurses, and drugs. At the same time, realizing a satisfying schedule is of upmost importance for obtaining the best health outcomes. In this paper we first consider a specific instance of the problem which is employed in the San Martino Hospital in Genova, Italy, and present a solution to the problem based on Answer Set Programming (ASP). Then, we enrich the problem and the related ASP encoding considering further features often employed in other hospitals, desirable also in S. Martino, and/or considered in related papers. Results of an experimental analysis, conducted on the real data provided by the San Martino Hospital, show that ASP is an effective solving methodology also for this important scheduling problem

Electronic Instability in a Zero-Gap Semiconductor: The Charge-DensityWave in (TaSe4)(2)I

We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)(2)I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the nondistorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the charge-density wave formation below T-CDW = 263 K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T-CDW.open114sciescopu

Evidence for core-hole-mediated inelastic x-ray scattering from metallic Fe1.087_{1.087}Te

We present a detailed analysis of resonant inelastic scattering (RIXS) from Fe$_{1.087}$Te with unprecedented energy resolution. In contrast to the sharp peaks typically seen in insulating systems at the transition metal $L_3$ edge, we observe spectra which show different characteristic features. For low energy transfer, we experimentally observe theoretically predicted many-body effects of resonant Raman scattering from a non-interacting gas of fermions. Furthermore, we find that limitations to this many-body electron-only theory are realized at high Raman shift, where an exponential lineshape reveals an energy scale not present in these considerations. This regime, identified as emission, requires considerations of lattice degrees of freedom to understand the lineshape. We argue that both observations are intrinsic general features of many-body physics of metals.Comment: 4 pages, 4 figure

Nodal Landau Fermi-Liquid Quasiparticles in Overdoped La1.77_{1.77}Sr0.23_{0.23}CuO4_4

Nodal angle resolved photoemission spectra taken on overdoped La$_{1.77}$Sr$_{0.23}$CuO$_4$ are presented and analyzed. It is proven that the low-energy excitations are true Landau Fermi-liquid quasiparticles. We show that momentum and energy distribution curves can be analyzed self-consistently without quantitative knowledge of the bare band dispersion. Finally, by imposing Kramers-Kronig consistency on the self-energy $\Sigma$, insight into the quasiparticle residue is gained. We conclude by comparing our results to quasiparticle properties extracted from thermodynamic, magneto-resistance, and high-field quantum oscillation experiments on overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$.Comment: Accepted for publication in Phys. Rev.

Promjene spektralnih svojstava kuprata visokog Tc izazvane defektima

Superconductivity in high-Tc cuprates is particularly sensitive to disorder due to the unconventional d-wave pairing symmetry. We investigated effects of disorder on the spectral properties of Bi2Sr2CaCu2O8+x high-Tc superconductor. We found that already small defect densities suppress the characteristic spectral signature of the superconducting state. The spectral line shape clearly reflects new excitations within the gap, as expected for defect-induced pair breaking. At the lowest defect concentrations the normal state remains unaffected, while increased disorder leads to suppression of the normal quasiparticle peaks.Zbog nekonvencionalne d-valne simetrije, supravodljivost u visokotemperaturnim kupratima je posebno osjetljiva na neuređenost. Ispitivali smo utjecaj neuređenosti na spektralna svojstva Bi2Sr2CaCu2O8+x supravodiča primjenom ARPES metode. Već mala gustoća defekata smanjuje karakteristični spektralni odziv supravodljivog stanja. Oblik spektralne linije očito reflektira nova pobuđenja unutar zabranjene vrpce, kako se i očekuje u slučaju razbijanja Cooperovih parova izazvanog defektima. Za male koncentracije defekata, normalno stanje ostaje nepromijenjeno, dok viši stupanj neuređenosti smanjuje intenzitet spektralnih linija kvazičestica