[seminar] Seminar FO , Kühne

[hbuljan at phy.hr]

Poštovani kolege,

podsjećam na današnji seminar.

Srdačan pozdrav
Hrvoje Buljan


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SEMINAR FIZIČKOG ODSJEKA
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Vrijeme:   srijeda, 14. 9. 2011., 14:15 sati (točno)
Mjesto:     Fizički odsjek, Bijenička c. 32, predavaonica F201

 Quantum critical dynamics in the one-dimensional
spin chain systems Cu(C4H4N2)(NO3)2 and (phzH)2CuCl4H2O

      Hannes Kühne
 Dresden University of Technology,
 Institute of Solid State Physics,
 Dresden, Germany

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 at phy.hr
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