Posted: May 27, 2009 
Major breakthrough in the study of lowdimensional quantum systems 
(Nanowerk News) Scientists at the London Centre for Nanotechnology report a major breakthrough in the study of lowdimensional quantum systems.

Quantum effects in lowdimensional magnets have been the subject of intense research for many decades dating right back to the birth of quantum mechanics itself. This is due to the fact that magnetic systems are particularly amenable to theoretical description and experimentation, allowing the testing of fundamental concepts, and from the fact that the properties of lowdimensional magnets are exploited in a raft of technologies.

Of particular interest are the intriguing properties of onedimensional (1D) systems such as magnetic ladders – literally a magnetic analogue of a step ladder – in which the magnetic moments carried by individual atoms are coupled together through rungs and legs. In 1D, longrange magnetic order is destroyed by quantum fluctuations, and theory predicts that instead a particular kind of exotic magnetic quantum liquid forms, known as a Luttinger liquid (LL). When a magnetic field is applied, this fascinating state of quantum matter becomes a key component of the extraordinary rich phase diagram of the ladder and can be studied using extremely sensitive magnetometers in the laboratory and highresolution neutron spectroscopy. In the presence of weak magnetic links between ladders, the system can even display BoseEinstein condensation, which underpins the remarkable properties of superfluids and superconductors.

In two recent publications in Physical Review Letters, and one in Physical Review: Rapid Communications, an international research team led by Dr. Christian Ruegg from the LCN has reported the first comprehensive study of a magnetic quantum ladder over its entire phase diagram.

This work provides an unprecedented insight into quantum effects and their microscopic control in low dimensional magnets, and was enabled by recent progress in instrumentation, synthetic chemists supplying samples of the highest quality, and most advanced theoretical methods. In the words of Dr. Ruegg, “For many years the arrangement of spins on a ladderlike structure has been the prototypical system for theoretical studies in quantum magnetism, but suitable model materials were lacking, in particular for experiments in a magnetic fields. Well, I love it when a plan comes together”.


Copies of the original articles can be accessed via the links below:

Direct observation of magnon fractionalization in the quantum spin ladder.
B. Thielemann, Ch. Rüegg, H.M. Ronnow, A.M. Läuchli, J.S. Caux, B. Normand, D. Biner, K.W. Krämer, H.U. Güdel, J. Stahn, K. Habicht, K. Kiefer, M. Boehm, D.F. McMorrow, and J. Mesot. Phys. Rev. Lett. 102, 107204 (2009).
http://link.aps.org/doi/10.1103/PhysRevLett.102.107204

Fieldcontrolled magnetic order in the quantum spinladder system (Hpip)2CuBr4.
B. Thielemann, Ch. Rüegg, K. Kiefer, H.M. Ronnow, B. Normand, P. Bouillot, C. Kollath, E. Orignac, R. Citro, T. Giamarchi, A.M. Läuchli, D. Biner, K.W. Krämer, F. WolffFabris, V.S. Zapf, M. Jaime, J. Stahn, N.B. Christensen, B. Grenier, D.F. McMorrow, and J. Mesot. Phys. Rev. B 79, 020408(R) (2009).
http://link.aps.org/doi/10.1103/PhysRevB.79.020408

Thermodynamics of the spin Luttingerliquid in a model ladder material.
Ch. Rüegg, K. Kiefer, B. Thielemann, D.F. McMorrow, V.S. Zapf, B. Normand, M.B. Zvonarev, P. Bouillot, C. Kollath, T. Giamarchi, S. Capponi, D. Poilblanc, D. Biner, and K.W. Krämer. Phys. Rev. Lett. 101, 247202 (2008).
http://link.aps.org/doi/10.1103/PhysRevLett.101.247202
