Origin of the Magnetic Exciton in the van der Waals Antiferromagnet NiPS_{3}.

An ultrasharp photoluminescence line intimately related to antiferromagnetic order has been found in NiPS_{3}, a correlated van der Waals material, opening prospects for magneto-optical coupling schemes and spintronic applications. Here we unambiguously clarify the singlet origin of this excitation, confirming its roots in the spin structure. Based on a comprehensive investigation of the electronic structure using angle-resolved photoemission and q-dependent electron energy loss spectroscopy as experimental tools we develop, in a first step, an adequate theoretical understanding using density functional theory (DFT). In a second step the DFT is used as input for a dedicated multiplet theory by which we achieve excellent agreement with available multiplet spectroscopy. Our Letter connects the understanding of the electronic structure and of optical processes in NiPS_{3} and related materials as a prerequisite for further progress of the field.

A new approach to time-dependent transport through an interacting quantum dot within the Keldysh formalism.

The time-dependent transport through a nanoscale device consisting of a single spin-degenerate orbital with on-site Coulomb interaction, coupled to two leads, is investigated. Various gate and bias voltage time dependences are considered. The key and new point lies in the proposed way to avoid the difficulties of the usual heavy computation when dealing with two-time Green's functions within the Keldysh formalism. The time-dependent retarded dot Green's functions are evaluated, in an efficient manner within a non-canonical Hubbard I approximation. Calculations of the time-dependent current are then presented in the wide-band limit for different parameter sets. A comparison between the method and the Hartree-Fock approximation is performed as well. It is shown that the latter cannot account reliably for dynamical aspects of transport phenomena.

Ligand field parameters and the ground state of Fe(II) phthalocyanine.

A judicious analysis of previously published experimental data leads one to conclude that the ground state of iron(II) phthalocyanine is an orbitally degenerate spin triplet a(1g)(2) e(g)(↑↓↑) b(2g)(↑) ((3)Eg). The ligand field parameters, in relation to Racah's C, are approximately as follows: B20∕C = 0.84, B40∕C = 0.0074. The uniqueness of this result is demonstrated by means of a special diagram in the B20∕C - B40∕C plane (under additional conditions that B44∕B40 = 35∕3 and B∕C = 0.227). The system is in a strong-ligand-field regime, which enables the use of single-determinant techniques corrected for correlations within the 3d shell of Fe.

Electronic structure and Jahn-Teller effect in GaN:Mn and ZnS:Cr.

We present an ab initio and analytical study of the Jahn-Teller effect in two diluted magnetic semiconductors with d(4) impurities, namely Mn-doped GaN and Cr-doped ZnS. We show that the correct insulating electronic structure may be obtained by a proper treatment of the strong electron correlation in the 3d shell in combination with the Jahn-Teller distortion which breaks the local symmetry. Using the LSDA + U approach, we treat the zinc-blende and the wurtzite crystal structures of GaN:Mn, as well as zinc-blende ZnS:Cr. We show that the trigonal distortion due to the wurtzite structure is less important than the Jahn-Teller deformation. This observation allows us to construct a simplified phenomenological ligand field theory (trigonal influence is neglected) which completes the ab initio part. Our work corrects previous studies and the obtained energy gain due to the Jahn-Teller effect (from both the LSDA + U calculation and the ligand field theory) is in good agreement with the experimental data. The same is true for the complete set of crystal field parameters obtained from the phenomenological model which agrees well with previous optical measurements.

CeFePO: f-d hybridization and quenching of superconductivity.

As a homologue to the new, Fe-based type of high-temperature superconductors, the electronic structure of the heavy-fermion compound CeFePO was studied by means of angle-resolved resonant photoemission. It was experimentally found-and later on confirmed by local-density approximation (LDA) as well as dynamical mean-field theory (DMFT) calculations-that the Ce 4f states hybridize to the Fe 3d states of d{3z{2}-r{2}} symmetry near the Fermi level that discloses their participation in the occurring electron-correlation phenomena and provides insight into mechanism of superconductivity in oxopnictides.

Magnetic state around cation vacancies in II-VI semiconductors.

The magnetic properties of neutral cation vacancies in II-VI semiconductors are examined using first principles calculations and group theory. A molecular cluster model of a single vacancy in II-VI semiconductors is developed to explain the observed chemical trend. We show that a single Zn vacancy in ZnO yields a total spin ST=1 in agreement with experiments. But for the other less ionic Zn-based II-VI semiconductors ZnA (A=S, Se, Te) this spin triplet state is nearly degenerate with a nonmagnetic spin singlet state.

Magnetic anisotropy of Co2+ as signature of intrinsic ferromagnetism in ZnO:Co.

We report on the magnetic properties of thoroughly characterized Zn(1-x)Co(x)O epitaxial thin films, with low Co concentration, x = 0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials.

Evidence for two types of low-energy charge transfer excitations in Sr2CuO3.

A comparative analysis of electron energy-loss spectroscopy (EELS) spectra for the 1D insulating cuprate Sr2CuO3 with transferred momentum q--> axially and radially to the chain axis allows one to elucidate the structure of the charge transfer gap in in-chain response. It is determined by the superposition of two types of excitations with different magnitudes of dispersion. The low-energy response with q--> radially to the chain direction, but yet within the plane of CuO4 plaquettes, exhibits also a dispersionless peak near 2 eV. The theoretical simulation of the EELS data using exact diagonalizations of an appropriate extended Hubbard Hamiltonian for relevant clusters requires the explicit consideration of low-lying oxygen 2p pi states within the CuO4 plaquette plane beyond the standard pd sigma extended Hubbard model widely used for cuprates with corner-shared CuO4 plaquettes.

Paclitaxel for platinum-refractory ovarian cancer: results from the first 1,000 patients registered to National Cancer Institute Treatment Referral Center 9103.

PURPOSE: To provide an investigational drug, paclitaxel, now commercially available, to women with refractory ovarian cancer and to evaluate response and toxicity in these patients. PATIENTS AND METHODS: Patients with platinum-refractory ovarian cancer, Eastern Cooperative Oncology Group (ECOG) performance status 0 to 3, at least three prior chemotherapy regimens, adequate hepatic and renal function, and no significant cardiac history were eligible. Patients were treated with paclitaxel 135 mg/m2 administered by 24-hour continuous intravenous infusion every 3 weeks. RESULTS: Leukopenia was the most frequent toxicity, with 78% of patients experiencing grade 3 or 4 toxicity. Other grade 3 and 4 toxicities were less common: fever (33%), infection (12%), thrombocytopenia (8%), vomiting (7%), cardiac (2%), neurologic (2%), and mucositis (1%). Fifteen treatment-related deaths (1.5%) were reported. The objective response rate was 22% (4% complete response [CR], 18% partial response; 95% confidence interval [CI] for overall response, 19% to 25%). The median time to progression from treatment initiation was 7.1 months in responding patients and 4.5 months for all patients. The median survival duration was 8.8 months. CONCLUSION: Paclitaxel has shown activity in women with platinum-refractory ovarian cancer, and it can be administered with an acceptable safety profile. Further research is needed to determine the optimal role of paclitaxel in the primary and salvage treatment of ovarian cancer.