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Why Study Noise due to Two Level Systems: A Suggestion for Experimentalists
Noise is often considered to be a nuisance. Here we argue that it can be a
useful probe of fluctuating two level systems in glasses. It can be used to:
(1) shed light on whether the fluctuations are correlated or independent
events; (2) determine if there is a low temperature glass or phase transition
among interacting two level systems, and if the hierarchical or droplet model
can be used to describe the glassy phase; and (3) find the lower bound of the
two level system relaxation rate without going to ultralow temperatures.
Finally we point out that understanding noise due to two level systems is
important for technological applications such as quantum qubits that use
Josephson junctions.Comment: 15 pages, 4 figures, Latex, to be published in J. Low Temp. Phys.
issue in honor of S. Hunklinge
Critical behavior of quasi-two-dimensional semiconducting ferromagnet CrGeTe
The critical properties of the single-crystalline semiconducting ferromagnet
CrGeTe were investigated by bulk dc magnetization around the paramagnetic
to ferromagnetic phase transition. Critical exponents
with critical temperature K and
with K are obtained by the Kouvel-Fisher method whereas
is obtained by the critical isotherm analysis at K. These critical exponents obey the Widom scaling relation , indicating self-consistency of the obtained values. With these
critical exponents the isotherm curves below and above the critical
temperatures collapse into two independent universal branches, obeying the
single scaling equation , where and are renormalized
magnetization and field, respectively. The determined exponents match well with
those calculated from the results of renormalization group approach for a
two-dimensional Ising system coupled with long-range interaction between spins
decaying as with
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