Pristupačnost
Dr. Hannes Kühne
Dresden University of Technology, Institute of Solid State Physics, Dresden, Germany
Quantum critical dynamics in the one-dimensional spin chain systems Cu(C4H4N2)(NO3)2 and (phzH)2CuCl4H2O
Vrijeme: srijeda, 14. 9. 2011., 14:15 sati (točno)
Mjesto: Fizički odsjek, Bijenička c. 32, predavaonica F201
I will present a comprehensive NMR study of the magnetic field-driven quantum phase transitions in the S=1/2 spin chain systems Cu(C4H4N2)(NO3)2 and (phzH)2CuCl4H2O.
The first compound, Cu(C4H4N2)(NO3)2, is known to be one of the best realizations of the antiferromagnetic S=1/2 Heisenberg chain model with a low coupling constant J [1]. The zero temperature saturation field Bc =
14.6 T corresponds to a quantum critical point (QCP), where the system is driven from a Luttinger liquid state to ferromagnetic polarization. With an emphasis on the vicinity of the QCP, a comparison of our experimental findings from 13C-NMR with both numerical (quantum Monte Carlo) and analytical (conformal field theory) approaches is made and yields a very good agreement. In particular, a well-defined maximum of 1/T1 (B,T) below Bc is revealed as the signature of essential spin-spin interactions in the Luttinger liquid phase [2,3].
The second compound, (phzH)2CuCl4H2O, is a recently synthesized spin chain system [4]. 1H- and 35Cl-NMR experiments consistently yield a field- and temperature dependent behavior of 1/T1 similar to that of the first compound. But, in contrast, a pronounced second maximum is observed at about ž of the saturation field Bc = 12.2 T. This effect is not found in the local or macroscopic magnetization, suggesting a more complicated magnetic interaction scheme.
[1] P.R. Hammar et al., PRB 59, 1008 (1999).
[2] H. Kühne et al., PRB 80, 045110 (2009).
[3] H. Kühne et al., PRB 83, 100407 (2011).
[4] R. Schneider et al., Polyhedron 26, 1849 (2007).
Voditelj seminara FO
Hrvoje Buljan, hbuljan@phy.hr