Phase Transitions and Electron Correlation in: Depleted Spin Ladders, Itinerant Electrons on Triangular Lattices and Unconventional Iron Based Superconductors
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Author
Date
2018Type
- Doctoral Thesis
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Abstract
Condensed matter physics is perhaps the largest branch of physics currently studied. Al-
though progress in this field promises potential applications technological breakthroughs,
there is a much more fundamental reason for such interest in this field. Part of the
explanation lies in the inherently many-body nature of condensed matter. Properties and
laws governing single particles become far more complex when a large number of objects
begins to interact with one another. Such aggregates often exhibit new emergent properties
that cannot be easily inferred from the basic law governing their constituents. This is the
reason underlying the richness of different possible states of condensed matter.
The past years were witness of a rapid development in both experimental and theoreti-
cal techniques giving us the tools to understand condensed matter at an unprecedented
level. However in many sub-fields the experimental and theoretical understanding did not
progress in parallel.
One such example is the discovery of high temperature superconductivity. Since their
discovery in 1986 experimentalists have collected overwhelming amount of data which
to a large extent still remains mysterious. At the same time theoretical studies of one
dimensional systems reached maturity, with current work often focusing on clarifying fine
details of the existing theories. Interestingly until recently these works have been largely
unconfirmed experimentally due to the lack of appropriate experimental realizations of the
proposed models.This thesis explores problems in both ends of the spectrum.
The rst part of this work focuses on exploratory study of two new and relatively poorly
understood materials: SmFeAs(O, F) and Na x CoO 2 .
In the study of SmFeAs(O, F) a novel multi-band high temperature superconductor a
series of thermodynamic and transport measurements was performed to uncover to what
extent conductivity and specific heat in this new material can be described using the simple
Lowest Landau Level scaling relations. In addition this study was a practice ring for the
development and testing of a setup allowing specific heat measurements of nano-gram
samples.
For Na x CoO 2 the calorimetry setup was used in combination with x-ray diffraction to
uncover the relation between different high temperature Na ordering patterns and the low
temperature magnetic states they induces. Rapid quenching of the sample, due to the
extremely short relaxation times of the calorimeter allowed to establish the two key roles
sodium intercalation plays in the formation of the magnetic ground state: supplying the
proper electron count and providing an inter-plane anti-ferromagnetic exchange path.
The second part of this thesis focuses on both experimental and numerical investigation of
the physics of depleted spin ladders.
In the first study the emergence of spin islands in the Haldane phase of the spin ladders
is studied. Through a combination of magnetic measurements and neutron spectroscopy
it is shown that disorder-induced degrees of freedom lead to a specific magnetic response,
described in terms of new emergent - spin islands. The structure and dynamics of these
objects is studied by high-resolution inelastic neutron scattering both in the limit of diluted
and strongly interacting spin islands
The study of spin islands is followed by the investigation of the role of spin depletion in the
magnetized - Luttinger phase of the ladder. Here a combination of Quantum Monte Carlo
simulations and extensive low temperature specific heat measurements is used to uncover
whether introduction of non-magnetic impurities to a spin ladder leads to its effective
segmentation and emergence of LT scaling.
The materials and methods used throughout this work are briefy explained chapter 1. As
most of the methods used in this work is extensively covered in a selection of excellent
textbooks only the basic information necessary for understanding the subsequent chapters
is introduces. Show more
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https://doi.org/10.3929/ethz-b-000314212Publication status
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Publisher
ETH ZurichSubject
Quantum magnetism; Electron correlation; Superconductivity; Luttinger liquid; SuperstructuresOrganisational unit
03855 - Zheludev, Andrey / Zheludev, Andrey
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ETH Bibliography
yes
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