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Biomedical subjects

A Furrer

Publications and source records attributed to A Furrer.

At least 19 recordsLinked to original sources
PubMed2005

Quantum statistics of interacting dimer spin systems.

The compound TlCuCl(3) represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Würtz [Phys. Rev. B 50, 13 515 (1994)10.1103/Phys. Rev. B 50, 13515] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important.

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PubMed2004

Pressure-induced quantum phase transition in the spin-liquid TlCuCl3.

The condensation of magnetic quasiparticles into the nonmagnetic ground state has been used to explain novel magnetic ordering phenomena observed in quantum spin systems. We present neutron scattering results across the pressure-induced quantum phase transition and for the novel ordered phase of the magnetic insulator TlCuCl3, which are consistent with the theoretically predicted two degenerate gapless Goldstone modes, similar to the low-energy spin excitations in the field-induced case. These novel experimental findings complete the field-induced Bose-Einstein condensate picture and support the recently proposed field-pressure phase diagram common for quantum spin systems with an energy gap of singlet-triplet nature.

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PubMed2004

Neutron scattering study of the field-dependent ground state and the spin dynamics in spin-one-half NH4CuCl3.

Elastic and inelastic neutron scattering experiments have been performed on the dimer spin system NH4CuCl3, which shows plateaus in the magnetization curve at m=1/4 and m=3/4 of the saturation value. Two structural phase transitions at T1 approximately 156 K and at T(2)=70 K lead to a doubling of the crystallographic unit cell along the b direction and as a consequence a segregation into different dimer subsystems. Long-range magnetic ordering is reported below T(N)=1.3 K. The magnetic field dependence of the excitation spectrum identifies successive quantum phase transitions of the dimer subsystems as the driving mechanism for the unconventional magnetization process in agreement with a recent theoretical model.

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PubMed2004

Origin of higher order magnetic exchange: evidence for local dimer exchange striction in CsMn0.28Mg0.72Br3 probed by inelastic neutron scattering.

The origin of higher-order exchange interactions in localized S-state systems has been the subject of intensive investigations in the past. In particular, it has been suggested that a biquadratic exchange term may arise from the magnetoelastic energy. Here we report on the pressure and temperature dependence of the excitation spectra of magnetic Mn2+ dimers in CsMn0.28Mg0.72Br3 probed by inelastic neutron scattering. Biquadratic exchange and a strong distance dependence of the bilinear exchange are observed. It is shown that the mechanism of local exchange striction may explain the occurrence of biquadratic exchange in accordance with the elastic properties of the compound.

Journal Article↗
PubMed2003

Bose-Einstein condensation of the triplet states in the magnetic insulator TlCuCl3.

Bose-Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled to form a dimer in a crystalline network: the dimer ground state is a spin singlet (total spin zero), separated by an energy gap from the excited triplet state (total spin one). In these dimer compounds, Bose-Einstein condensation becomes theoretically possible. At a critical external magnetic field, the energy of one of the Zeeman split triplet components (a type of boson) intersects the ground-state singlet, resulting in long-range magnetic order; this transition represents a quantum critical point at which Bose-Einstein condensation occurs. Here we report an experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals. We verify unambiguously the theoretically predicted gapless Goldstone mode characteristic of the Bose-Einstein condensation of the triplet states.

Journal Article↗
PubMed1991

[Organ-preserving surgery of renal cell carcinoma. The surgical technic, results and complications].

Operative method, course and complications were analysed retrospectively in 120 patients in whom a kidney tumour had been resected without nephrectomy. In 49 patients (18 women and 31 men, mean age 59 [38-77] years; 45 renal-cell carcinomas, 4 benign renal tumours) there was an "imperative indication" for an organ-preserving operation, because nephrectomy would have made dialysis obligatory. In 74 patients with a healthy contralateral kidney (25 women, 49 men, mean age 55 [31-74] years; 61 renal-cell carcinomas, 13 benign tumours) the tumour was enucleated by choice; 55 of these patients were symptom-free. 36 of 49 patients with an imperative indication are without sign of tumour progression after a mean follow-up period of 4.5 years. In two there was a recurrence after 4 and 5 years, respectively, requiring a second organ-preserving operation. Known metastases were present in 3 of 6 patients who died of their tumours. 68 of 74 patients operated on electively are without signs of tumour progression after a mean follow-up period of 3.3 years. One patient died from tumour metastases. Two patients had tumour recurrence, requiring nephrectomy and enucleation, respectively.

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