Fractional excitations in the square lattice quantum antiferromagnet.

Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spins-1/2 is far from complete. The quantum square-lattice Heisenberg antiferromagnet (QSLHAF), for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wave vector (π, 0). We use polarized neutron spectroscopy to fully characterize the magnetic fluctuations in the metal-organic compound CFTD, a known realization of the QSLHAF model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially-extended pairs of fractional S=1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wave vector, these fractional excitations are bound and form conventional magnons. Our results establish the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration.

Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates.

The high-Tc cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin waves--magnons--of the antiferromagnetic insulating parent compounds, suggesting that magnons may survive in damped, broadened form throughout the phase diagram. Here we show by resonant inelastic X-ray scattering on Bi(2)Sr(2)CaCu(2)O(8+δ) (Bi-2212) that the analogy with spin waves is only partial. The magnon-like features collapse along the nodal direction in momentum space and exhibit a photon energy dependence markedly different from the Mott-insulating case. These observations can be naturally described by the continuum of charge and spin excitations of correlated electrons. The persistence of damped magnons could favour scenarios for superconductivity built from quasiparticles coupled to spin fluctuations. However, excitation spectra composed of particle-hole excitations suggest that superconductivity emerges from a coherent treatment of electronic spin and charge in the form of quasiparticles with very strong magnetic correlations.

Spin excitations in a single La2CuO4 layer.

Cuprates and other high-temperature superconductors consist of two-dimensional layers that are crucial to their properties. The dynamics of the quantum spins in these layers lie at the heart of the mystery of the cuprates. In bulk cuprates such as La(2)CuO(4), the presence of a weak coupling between the two-dimensional layers stabilizes a three-dimensional magnetic order up to high temperatures. In a truly two-dimensional system however, thermal spin fluctuations melt long-range order at any finite temperature. Here, we measure the spin response of isolated layers of La(2)CuO(4) that are only one-unit-cell-thick. We show that coherent magnetic excitations, magnons, known from the bulk order, persist even in a single layer of La(2)CuO(4), with no evidence for more complex correlations such as resonating valence bond correlations. These magnons are, therefore, well described by spin-wave theory (SWT). On the other hand, we also observe a high-energy magnetic continuum in the isotropic magnetic response that is not well described by two-magnon SWT, or indeed any existing theories.

Measurement of magnetic excitations in the two-dimensional antiferromagnetic Sr2CuO2Cl2 insulator using resonant x-ray scattering: evidence for extended interactions.

We measured the momentum dependence of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr2CuO2Cl2 (SCOC). We identify a single-spin-wave feature and a multimagnon continuum, with different polarization dependences. The spin waves display a large (70 meV) dispersion between the zone-boundary points (π, 0) and (π/2, π/2). Employing an extended t-t'-t''-U one-band Hubbard model, we find significant electronic hopping beyond nearest-neighbor Cu ions, indicative of extended magnetic interactions. The spectral line shape at (π, 0) indicates sizable quantum effects in SCOC and probably more generally in the cuprates.

Results of conservative treatment (transurethral resection plus adjuvant intravesical chemotherapy) in patients with primary T1, G3 transitional cell carcinoma of the bladder.

OBJECTIVES: To evaluate a selected population of 50 consecutive patients with primary T1, G3 bladder transitional cell carcinoma in the absence of carcinoma in situ (Tis) treated with a bladder-sparing approach. METHODS: Between January 1983 and December 1992, all patients were treated by transurethral resection (TUR) plus adjuvant intravesical chemotherapy over 1 year. In most cases, doxorubicin, epirubicin, and mitomycin were used alone or in combination. RESULTS: At a mean follow-up period of 52 months (range, 18 to 126), 16 of 50 patients (32%) showed a recurrent superficial tumor. The recurrent lesion was of Stage T1 in 11 (22%) cases, but was a T1, G3 tumor only in 5 cases (10%). In 2 additional patients (4%) a Tis developed during the observation period after TUR. The mean interval between TUR and first recurrence was 14.6 months (range, 3 to 38). At a mean time of 17 months after the initial TUR, 3 patients (6%) underwent a radical cystectomy due to a progression in T category and 3 additional patients (6%) developed distant metastases at a mean time of 23 months after TUR. In brief, 84% of the patients are alive and tumor-free. Five patients (10%) died of bladder cancer with a mean follow-up of 52 months. CONCLUSIONS: If no concomitant Tis exist, a conservative approach is a legitimate option as an initial treatment of patients with primary T1, G3 bladder tumors.

Is there a role for recombinant tumor necrosis factor alpha in the intravesical treatment of superficial bladder tumors?--a phase II study.

Clinical use of recombinant tumor necrosis factor-alpha is strongly limited by its severe toxicity, mainly cardiovascular, when systemically administered. Recent studies suggest that topical (intrapleural, intraperitoneal, intratumoral) administration is free of significant toxicity. Human recombinant tumor necrosis factor-alpha was administered intravesically, at a dose of 500 mg dissolved in 30 ml of phosphate buffer (pH 7.6-7.8) plus 0.25% human albumin, weekly for two months to 18 patients with papillary transitional cell carcinoma of the bladder. Of the 15 evaluable patients, four (26%) achieved a complete response. Systemic and local tolerability were excellent.

Idarubicin in the intravesical treatment of superficial transitional-cell carcinoma of the bladder (ta-t1) - a phase I-ii study.

Local recurrences of superficial transitional cell carcinoma of the bladder (TCCB) can be significantly reduced by intravesical treatment following transurethral resection (TUR) but they are not fully abolished. There is a need to gain experience with new agents. Anthracyclines, such as doxorubicin and epirubicin, have been clearly demonstrated to be active against superficial TCCB by intravesical route. Idarubicin is an anthracycline, much more lipophilic than doxorubicin, inhibiting tumour cell growth at lower concentrations. The aim of this study was to evaluate the tolerability and the ablative efficacy on a marker lesion of weekly intravesical instillations of idarubicin given at different doses and concentrations. Seventeen patients, affected by superficial TCCB, Ta-T1 G1-G2, after TUR of all tumours except one, that was used as a 'marker lesion', were treated intravesically with idarubicin weekly for two months. The drug, in the first 4 patients, was administered at the dose of 15 mg diluted in 30 mi of normal saline solution and maintained in the bladder for one hour. Because of severe chemical cystitis, the dose was reduced to 10 mg in 40 mi in the following 13 patients. The study was closed because of the severe local toxicity. In eight (47%) patients the treatment was interrupted for local toxicity between the first and sixth week and in 5 more patients pharmacological therapy was required because of severe chemical cystitis. No systemic toxicity was evident. Three patients achieved a complete response. Our experience shows that idarubicin is not indicated in the intravesical therapy of superficial TCCB because of severe chemical cystitis limiting the administration of doses able to explicate a relevant antitumoral action.

Correlation between clinical response and urinary interleukin levels using different doses and intravesical administration schedules of interferon-alpha-2b combined with epirubicin: a pilot study.

A total of 62 patients at high risk for recurrence of superficial bladder cancer were selected for a study designed to compare the prophylactic efficacy of different doses and schedules of sequential intravesical instillations of epirubicin and interferon-alpha-2b and to evaluate which sequence could enhance the release of cytokines in the urine. Our investigations showed a significant increase in urinary concentrations of interleukins in patients who received the sequential intravesical administration of epirubicin and interferon-alpha-2b. Higher urinary concentrations of interleukins and a lower recurrence rate were detected in patients who received interferon-alpha-2b 24h after epirubicin instillation.

Intravesical therapy of superficial bladder transitional cell carcinoma with tumor necrosis factor-alpha: preliminary report of a phase I-II study.

A phase I-II trial of intravesical immunotherapy with tumor necrosis factor (TNF)-alpha in 24 patients affected by superficial bladder tumors is herein presented. Of these, 11 patients were submitted, at weekly intervals, after complete TUR, to 8 instillations of TNF-alpha at increasing doses from 50 to 600 micrograms. Tolerability was excellent, even at the highest dose. In a second group of 13 patients with a histologically proved papillary marker lesion, TNF-alpha was instilled at weekly intervals at the dose of 500 micrograms for 8 weeks. Three complete responses (23%) were obtained.