Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 16: Correlated Electrons: Low-dimensional Systems - Materials 1

TT 16.5: Talk

Tuesday, March 24, 2009, 10:30–10:45, HSZ 304

Magnetocaloric effect near a B induced quantum critical point in an S = 1/2 antiferromagnetic Heisenberg chain — •Deepshikha Jaiswal-Nagar¹, Georg Hofmann¹, Yeekin Tsui¹, Katarina Remović-Langer¹, Ulrich Tutsch¹, Bernd Wolf¹, Andrey Profofiev^1,2, Wolf Assmus¹, Andreas Honecker³, and Michael Lang¹ — ¹Phys. Institut, Goethe-Universität, D-60438 Frankfurt(M), SFB/TR49, Germany — ²Inst. f. Festkörperphys., TU Wien, 1040-Wien, Austria — ³2 Inst. f. Theor. Physik, Georg-August-Universität at Göttingen, 37077, Göttimgen, Germany

The magnetocaloric effect (MCE), i.e., heating or cooling of a system under adiabatic conditions in response to an external magnetic field, is an important tool for exploring quantum critical points (QCP's), as it is expected to diverge at the QCP. The competition between different ground states at a QCP leads to an accumulation of entropy at the QCP at finite temperature and hence to a variety of interesting properties in thermodynamic quantities like the MCE. A one-dimensional spin S = 1/2 antiferromagnetic Heisenberg chain (AfHC) is quantum critical in magnetic fields up to the saturation field Bs, above which it undergoes a transition to a ferromagnetically polarized state. In this talk, we present MCE data on a metal-organic polymer system built from Cu2+ (S = 1/2) ions, which is shown to be a very good realization of an AfHC. We obtain field-induced temperature changes which are an order of magnitude larger than those of paramagnetic salts! Our data compare favorably with theoretical results based on exact diagonalization of finite systems.