Search

We demonstrate quantum critical scaling for an S = 1/2 Heisenberg antiferromagnetic chain compound Cu(C4H4N2)(NO3)(2) in a magnetic field around saturation, by analyzing previously reported magnetization [Y. Kono et al., Phys. Rev. Lett. 114, 037202 (2015)], thermal expansion [J. Rohrkamp et al., J. Phys.: Conf. Ser. 200, 012169 (2010)], and NMR relaxation data [H. Kuhne et al., Phys. Rev. B 80, 045110 (2009)]. The scaling of magnetization is demonstrated through collapsing the data for a range of both temperature and field onto a single curve without making any assumption for a theoretical form. The data collapse is subsequently shown to closely follow the theoretically predicted scaling function without any adjustable parameters. Experimental boundaries for the quantum critical region could be drawn from the variable range beyond which the scaled data deviate from the theoretical function. Similarly to the magnetization, quantum critical scaling of the thermal expansion is also demonstrated. Further, the spin dynamics probed via NMR relaxation rate 1/T-1 close to the saturation is shown to follow the theoretically predicted quantum critical behavior as 1/T-1 proportional to T-0.5 persisting up to temperatures as high as k(B)T similar or equal to J, where J is the exchange coupling constant.

During this project we studied cavities as an alternative method to stripline resonators, to create an oscillating magnetic field. We were able to simulate different cavity designs and reproduce theoretical results as a numerical simulation and experimentally. Thus getting familiar with cavities and studying how their design influences the TE011 mode in which we lay our interest. It was shown that with cavities one could reach a higher quality factor than with stripline resonators. We also found out that in order to make a cavity small enough to be useful it is indispensable to use dielectric materials and studied the behavior of a few possible cavity designs.

The study of quantum matter has become a great part of modern physics research. Quantum criticality appears in the vicinity of a quantum critical point where there is an interplay between quantum and thermal fluctuations. In the quantum critical region, ’exotic’ phases therefore appear which might be the origin of unconventional superconductivity, for example. The study of quantum phase transitions has also many potential technological applications such as in memory storage devices or in processors for future quantum simulations. Technologies may be fabricated with materials showing interesting behaviour of charge, spin and current at cryogenic temperatures. In this report, a Graphic User Interface will be presented which helps to visualize quantum critical scaling. Then, the GUI will be used to determine the critical scaling of the magnetization and thermal expansion of Cu(C4H4N2)(NO3)2 as already done in [1]. A critical scaling of the susceptibility of LiErF4 is found. Finally, there seems to be a critical scaling for the dielectric constant of Ba2CoGe2O7 but stronger evidence is needed to confirm this hypothesis.