High pressure studies of superconductivity and anomalous normal states in novel quantum materials
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Authors
Worasaran, Puthipong
Advisors
Grosche, Friedrich
Date
2021-08-20Awarding Institution
University of Cambridge
Qualification
Doctor of Philosophy (PhD)
Type
Thesis
Metadata
Show full item recordCitation
Worasaran, P. (2021). High pressure studies of superconductivity and anomalous normal states in novel quantum materials (Doctoral thesis). https://doi.org/10.17863/CAM.80342
Abstract
This dissertation contains a wide range of studies of many intriguing physical systems,
including a novel incommensurate host-guest structure, strange metal, low-dimensional
system, iron-based superconductivity, and a geometrically frustrated magnetic system. We
used pressure as the primary tool in our studies, not only as one of the tuning parameters for
accessing or tuning away from the quantum critical point but also to enter novel phases that
cannot usually be found in any materials at ambient conditions.
Sb (Chapter 4): High-pressure phase Sb-II exhibits a novel incommensurate host-guest
structure, giving rise to exotic sliding mode between host and guest chain. In principle,
this sliding mode has a very flat dispersion relation perpendicular to the chain, enhancing
electron-phonon coupling greatly. This unusual phonon spectrum causes the normal-state
resistivity at low temperature to be linear, as previously observed in Bi-III phase. However,
it is not the case in Sb-II as it shows a quadratic Fermi liquid-like relation, suggesting the
pinning of the phason mode. The phason-pinning is supported by the estimation of electron-
phason coupling parameter λ~0.18, which is surprisingly small. Furthermore, we observed
an anomalous first-order transition at a high temperature in resistivity. Combining our results
with the experiments from other literature that the interaction between host and guest chain is
very strong in Sb-II, we propose that Sb-II may be the first material ever to exhibit Aubry’s
transition.
Ca$_2$RuO$_4$ (Chapter 5): Calcium ruthenate has a long history of studies due to its similarity
in structure to cuprates. There are series of transitions in the crystal structure and magnetic
ground state under pressure, going from an antiferromagnetic Mott insulator, itinerant ferro-
magnetic, to unconventional superconductivity. Our experiment has revealed a possibility of
a new phase in Ca$_2$RuO$_4$ . The most prominent features that we observed are (i) a cross-over
from the power-law exponent n = 4/3 to n = 1 in resistivity from below and above 100 kbar
(ii) a coexistence between a magnetic ordering and superconductivity. We interpret this to be a cross-over between itinerant ferromagnetic state and itinerant antiferromagnetic state, or
more general, a spin texture state.
YFe$_2$Ge$_2$ (Chapter 6): The anomaly in the low-temperature resistivity power-law exponent
of the iron-based superconductor YFe$_2$Ge$_2$ has posed a question since its discovery. This
work aims to answer this question. We found that the application of pressure can completely
suppress superconductivity in YFe$_2$Ge$_2$. Moreover, the power-law study demonstrates the
recovery of Fermi-liquid behaviour at high pressure. Our results support the picture that
the exponent 3/2 in the resistivity power-law temperature dependence emerges from its
proximity to the quantum critical regime.
PdCrO$_2$ (Chapter 6): This work aims to explore any possible quantum critical point that
may arise in the geometrically frustrated magnet
PdCrO$_2$. It is shown that the transition
temperature of antiferromagnetic ordering that arises in this system is very much pressure
independent. However, resistivity measurement suggests that there may be a structural phase
transition to some unknown phase above 80 kbar. The physics of the high-pressure phase are
unknown and requires further studies.
Keywords
Superconductivity, Incommensurate Host-Guest Structure, High-Pressure, Unconventional Superconductivity, Quantum Criticality
Identifiers
This record's DOI: https://doi.org/10.17863/CAM.80342
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