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TT: Fachverband Tiefe Temperaturen

TT 2: Quantum-Critical Phenomena

TT 2.5: Vortrag

Montag, 26. März 2007, 10:30–10:45, H19

High pressure quantum phase transition in the weakly coupled spin cluster system Cu₂Te₂O₅Br₂ — •Hans-Henning Klauss¹, Christopher Mennerich¹, Hemke Maeter¹, Hannes Kühne¹, Peter Lemmens¹, Jochen Litterst¹, Hubertus Luetkens², Alex Amato², Rie Takagi³, and Mats Johnsson³ — ¹IPKM, TU Braunschweig, Braunschweig, Germany — ²Paul-Scherrer-Institut, Villigen, Switzerland — ³Dept. of Inorganic Chem., Stockholm Univ., Stockholm, Sweden

Tetragonal Cu₂Te₂O₅Br₂ contains clusters of four Cu²⁺ (S = 1/2) in a planar coordination. These tetrahedra form weakly coupled sheets within the crystallographic a-b plane. Therefore, this system is ideal to study the interplay between the spin frustration on a tetrahedron with localized low-energy excitations and collective magnetism induced by inter-tetrahedra couplings. In this material a strongly reduced magnetic transition temperature T_N = 11.4 K in comparison with a dominant magnetic exchange of 40 K is found.

We examined the quantum critical behaviour of polycrystalline Cu₂Te₂O₅Br₂ in ZF muSR experiments under external pressures. We observed a continuous decrease of the magnetic phase volume and of the sublattice magnetization, studied via the spontaneous muon spin precession frequency, with increasing pressure. The measurements at 6 kbar did not show any sign of static magnetic correlations down to 0.3 Kelvin. We conclude that this system shows a quantum critical point at 6 kbar where the magnetic ordered phase disappears and a spin liquid ground state is formed.