BENSC: Enhanced access to the Berlin neutron scattering center

• Forschungsstelle: EU FRP
• Projektnummer: 02.0048-1
• Projekttitel Englisch: BENSC: Enhanced access to the Berlin neutron scattering center

Schlüsselwörter (Englisch)

Quantum spin systems; quantum phase transitions; neutron scattering

Alternative Projektnummern (Englisch)

EU project number: HPRI-CT-2001-00138

Forschungsprogramme (Englisch)

EU-programme: 5. Frame Research Programme - 4.2 Agriculture and agroindustry

Kurzbeschreibung (Englisch)

See abstract

Abstract (Englisch)

Quantum spin systems exhibit unique magnetic properties which bear no classical analogies. An example of actual relevance is the realization of magnetic quantum phase transitions driven by zero-point spin fluctuations. At a magnetic quantum phase transition the ground-state switches from disorder to order at fixed temperature 'T=0'. The experimental investigation of the above allows to test fundamental models of quantum mechanics.
Our recent efforts have concentrated on the quantum spin system TlCuCl3 and its magnetic quantum phase transition at Hc~6T. An energy gap separates in TlCuCl3 the spin singlet ground-state from spin triplet excitations at zero-field. The Zeeman-split spin triplet excitations reduce and eventually overcome the energy gap at finite fields. By means of neutron scattering investigations on single crystals, the ground-state and the magnetic excitations were investigated below, across and above Hc. The investigations at H>Hc up to H=14T and fixed T=50mK were performed at the Hahn-Meitner-Institut, Berlin, and established that:

A) the magnetic excitations consist of quantum-like modes at high energies and a classic-like mode at low energies;
B) the quantum-like modes are the remains of the Zeeman-split triplet excitations, according to a pertubative dimer scheme;
C) the classic-like mode emerges from the field-induced magnetic Bragg reflections and has no perturbative counterpart.

Points A), B) and C) constitute experimental highlights from a rarely accessible parameter range. They not only allow the complete description of the magnetic quantum phase transition realized in TlCuCl3, but also provide a reference of general interest for models of quantum mechanics. A first account along this line is given in N.Cavadini et al., Phys. Rev. B 65, 132415 (2002).

Datenbankreferenzen (Englisch)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 02.0048-1