Low-dimensional quantum spin systems

-> our publications in this field.

In systems with low dimensional magnetic interactions, geometrical frustration and small spins the macoscopic properties are strongly affected by quantum fluctuations. We aim to unveil novel ground states and effects in this class of materials and to establish new model systems. The objective is to achieve a broad understanding of the important physical parameters and to find common features in mechanisms that drive the formation of these states in strongly correlated electron system

  • Telephone number compounds (Sr,Ca,La)12Cu24O41
  • S=1 spin ladders in Na2Ni2(C2O4)3(H2O)2
  • Frustrated edge sharing spin chains: FM vs. helical spin structures: Li2CuO2, LiZrCuO4, NaCu2O2

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Frustrated Magnets

Due to their complex structure, geometrically frustrated magnets can not satisfy all magnetic exchange interactions between their spins concommitantly. A simple example is the triangular arrangement of Ising-spins, in which antiferromagnetic exchange yields spin frustration. Geometrically frustration hence competes with spin ordering, thereby suppressing ordered phases and giving rise to novel phenomena such as macroscopic degeneracy of the ground state, quantum criticallity and anomalous energy scales. E.g., in structurally disordered magnets one often observes a spin-glas, whereas, in structurally ordered but geometrically frustated systems spin-liquid or spin-ice phases are realized.

Another realisation of a geometrically frustrated magnet are CuO2 spin chains in which the ferromagnetic nearest neighbor ecxchange competes with antiferromagnetic next nearest neighbor interactions. In this case, a quantum critical point appears for a certain frustration ratio of nearest to next nearest neigbor coupling, which generates peculiar properties of compounds with similar frustation ratio.

Investigation of geometrically frustrated magnets is not only valuable for basic research, but there are also very promising perspectives for technologically innovative applications. One example are novel magnetic refrigerators, multiferroics or ultrafast optical devices. Both the potential applications and the spectacular physical effects give rise to an increasing international interest on this topic.

 
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