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Charge Dynamics across Phase Transition in Strongly Correlated Electron Systems.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Charge Dynamics across Phase Transition in Strongly Correlated Electron Systems./
作者:	Adhikari, Dasharath.
面頁冊數:	1 online resource (137 pages)
附註:	Source: Dissertations Abstracts International, Volume: 83-01, Section: B.
Contained By:	Dissertations Abstracts International83-01B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28498381click for full text (PQDT)
ISBN:	9798516936302

Charge Dynamics across Phase Transition in Strongly Correlated Electron Systems.
Adhikari, Dasharath.

Charge Dynamics across Phase Transition in Strongly Correlated Electron Systems. - 1 online resource (137 pages)

Source: Dissertations Abstracts International, Volume: 83-01, Section: B.

Thesis (Ph.D.)--State University of New York at Buffalo, 2021.

Includes bibliographical references

In condensed matter, phase transition is a phenomenon in which a matter changes its behavior from one form to an another under a suitable thermodynamic condition. Several phase transitions triggered by different external stimuli such as temperature, electric field, magnetic field, etc., are observed in many materials. Transition from a metallic to an insulating behavior and vice versa in response to change in a thermodynamic variable is known as metal-insulator transition (MIT) and electrical resistance is a popular, measurable quantity to trace the changes during the transition. Conventionally, phase transitions are broadly classified into two classes: first and second order transitions. Many decades of research, however, suggests that in real condensed materials more complex transitions occur. Despite several experimental and theoretical efforts in explaining the observed behaviors across the transition, phase transitions are still least understood in condensed matter physics and this could be is partly due to the intrinsic complexity of the phenomena.Materials such as transition-metal oxides compounds, manganites, and spinel sulphides where strong electronic correlation makes them behave in a nontrivial, complex manner leading to unexpected collective responses are known as strongly correlated electron systems (SCES). Subtle interplay of different degrees of freedom such as charge, spin, lattice, and orbital are considered to be responsible for the intrinsiccomplexity in SCES. SCES display a broad range of interesting and subtle emergent phenomena like MIT, multiferroicity, high-temperature superconductivity, and colossal magnetoresistance and these are difficult to rationalize through mere addition of electronic properties of individual atoms. Such observations are of great significance across the sciences and engineering since each distinct phenomenon could provide a new functionality for future technologies. For instance, multiferroic materials, which combine ferroelectricity (the emergence of a permanent electric polarization) and magnetism, could enable devices that couple electric and magnetic effects for information storage and reading in information technologies.Understanding the transition region, which is often complex, is a challenging but rewarding research problem in condensed matter physics. Emergent phenomena like metal-insulator transition (MIT) in SCES are intimately associated with the spontaneous appearance of electronic phase separation (EPS). The competing phases form ordered or random patterns, at length scales ranging from a few nm to several μm, due to a variety of parameters such as lattice distortion, inherent strain, or disorder etc. However, despite great efforts being made to understand EPS and to engineer it, precise understanding of electronic phase nucleation, growth, and their role on the emergent phenomena are still unclear. The understanding of domain density and growth kinetics in response to external perturbation is challenging but crucial to understand the physics of EPS and for understanding the electrical, magnetic, and optical properties of SCES.When a SCES is near a phase transition, one phase could locally dominate over the other and none of the states dominate globally and a subtle interplay transpires leading to an electronic inhomogeneity in the system and an interesting and delicatebalance exists among the various energy scales resulting in the emergence of multiple metastable electronic states where the system can find itself. The information about how long a system spends in an energy configuration, shuttling between the configurations and especially how the electronic inhomogeneity due to phase coexistence affect charge carrier transport are critical to the understanding of phase transitions. An experimental technique that can provide a detailed understanding of how the charge carrier dynamics evolves as we traverse the phase transition and the possible mechanisms triggering the transition are needed.In this work, we employed electrical transport measurements and resistance noise spectroscopy to understand MITs in single crystals of CuIr2S4 and organic charge transfer complex, potassium-7,7,8,8-tetracyanoquinodimethane (K-TCNQ). Electrical transport measurements provide macroscopic information since it measures instantaneous value of a relevant quantity (in our case electrical resistance) which survives statistical averaging. More detailed and microscopic understanding can be gained by focusing on the fluctuations over time since it contains signatures of dynamics which would not be captured in macroscopic transport measurements because such information would not likely survive after the averaging. Therefore, the noise spectroscopy enables accessing dynamics resulting due to stochastic rearrangement of many charge configurations in an electronically phase separated system, which makes the technique an experimentally robust tool to probe phase transitions that display EPS.The MIT in CuIr2S4 occurs around Tc ∼ 231 K upon cooling from room temperature. The notable features of the MIT are an orders-of-magnitude change in resistance accompanied by a lattice structural transition and a magnetic transition. Along with the thermal induced MIT, we observe threshold-like hysteretic resistiveswitching/transition (RS) below Tc.The normalized noise power spectral density (PSD) magnitude enhancement with1/f2 behavior and asymmetric trend captured in PSD emphasize crucial role of electronic domains across the thermal MIT in CuIr2S4. For the thermal-triggered MIT, we observe two features: asymmetric PSD around the transition and a dramatic increase in α value following the PSD trend. This helps in understanding the physical dynamics happening in the system across the transition. The creation and the growth of domains of opposite phase would have distinctly different impact on electrical transport on either side of the transition since on the metallic phase the creation of an insulating domain does not have a significant effect until the charge carriers can avoid high resistive paths. However, on the insulating phase, the creation of a single metallic domain will affect the charge carrier path and hence PSD magnitude. Emergence of multiple metastable states near the transition region and systems' wandering among such states is suggested by the observation of 1/f2 PSD behaviors. Therefore, the 1/f2 behavior around MIT emphasizes crucial role of collective charge dynamics.In the electrically-driven case, by studying both current-voltage (IV) characteristics and noise PSD, we conjecture that at T ≪ Tc, a single jump in IV and smoothly changing PSD points to non-thermal effects as the dominant mechanism. While for T ∼ Tc, multiple jumps in IV and increase in PSD are seen, indicating thermal effects play a synergistic role with the electric field causing non-uniform heating and proliferating electrical inhomogeneity.A theoretical framework, based on Ginzburg-Landau (GL) φ6-theory with nonequilibrium modifications so that both equilibrium (thermal MIT) and nonequilibrium (RS) transitions are described on same footing, is developed. Qualitatively closeagreement between experimental and theoretical results provides a novel way of looking into transitions under a unified picture serving an important role in understanding of emergent phenomena in a range of SCES driven in and out of equilibrium.K-TCNQ is a prototypical quasi 1D SCES, where a threshold-like RS is observed along the stacking a-axis direction. The temperature dependence of threshold field (Eth) is found to increase exponentially with decreasing temperature similar to field induced classical depinning in low-dimensional charge density wave (CDW) materials. Similar to the observation in classical CDW systems, approaching the threshold field noise PSD is found to exhibit 1/f2 behavior with magnitude increased by few orders.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798516936302Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Charge dynamicsIndex Terms--Genre/Form:

542853
Electronic books.

Charge Dynamics across Phase Transition in Strongly Correlated Electron Systems.
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504 $a Includes bibliographical references
520 $a In condensed matter, phase transition is a phenomenon in which a matter changes its behavior from one form to an another under a suitable thermodynamic condition. Several phase transitions triggered by different external stimuli such as temperature, electric field, magnetic field, etc., are observed in many materials. Transition from a metallic to an insulating behavior and vice versa in response to change in a thermodynamic variable is known as metal-insulator transition (MIT) and electrical resistance is a popular, measurable quantity to trace the changes during the transition. Conventionally, phase transitions are broadly classified into two classes: first and second order transitions. Many decades of research, however, suggests that in real condensed materials more complex transitions occur. Despite several experimental and theoretical efforts in explaining the observed behaviors across the transition, phase transitions are still least understood in condensed matter physics and this could be is partly due to the intrinsic complexity of the phenomena.Materials such as transition-metal oxides compounds, manganites, and spinel sulphides where strong electronic correlation makes them behave in a nontrivial, complex manner leading to unexpected collective responses are known as strongly correlated electron systems (SCES). Subtle interplay of different degrees of freedom such as charge, spin, lattice, and orbital are considered to be responsible for the intrinsiccomplexity in SCES. SCES display a broad range of interesting and subtle emergent phenomena like MIT, multiferroicity, high-temperature superconductivity, and colossal magnetoresistance and these are difficult to rationalize through mere addition of electronic properties of individual atoms. Such observations are of great significance across the sciences and engineering since each distinct phenomenon could provide a new functionality for future technologies. For instance, multiferroic materials, which combine ferroelectricity (the emergence of a permanent electric polarization) and magnetism, could enable devices that couple electric and magnetic effects for information storage and reading in information technologies.Understanding the transition region, which is often complex, is a challenging but rewarding research problem in condensed matter physics. Emergent phenomena like metal-insulator transition (MIT) in SCES are intimately associated with the spontaneous appearance of electronic phase separation (EPS). The competing phases form ordered or random patterns, at length scales ranging from a few nm to several μm, due to a variety of parameters such as lattice distortion, inherent strain, or disorder etc. However, despite great efforts being made to understand EPS and to engineer it, precise understanding of electronic phase nucleation, growth, and their role on the emergent phenomena are still unclear. The understanding of domain density and growth kinetics in response to external perturbation is challenging but crucial to understand the physics of EPS and for understanding the electrical, magnetic, and optical properties of SCES.When a SCES is near a phase transition, one phase could locally dominate over the other and none of the states dominate globally and a subtle interplay transpires leading to an electronic inhomogeneity in the system and an interesting and delicatebalance exists among the various energy scales resulting in the emergence of multiple metastable electronic states where the system can find itself. The information about how long a system spends in an energy configuration, shuttling between the configurations and especially how the electronic inhomogeneity due to phase coexistence affect charge carrier transport are critical to the understanding of phase transitions. An experimental technique that can provide a detailed understanding of how the charge carrier dynamics evolves as we traverse the phase transition and the possible mechanisms triggering the transition are needed.In this work, we employed electrical transport measurements and resistance noise spectroscopy to understand MITs in single crystals of CuIr2S4 and organic charge transfer complex, potassium-7,7,8,8-tetracyanoquinodimethane (K-TCNQ). Electrical transport measurements provide macroscopic information since it measures instantaneous value of a relevant quantity (in our case electrical resistance) which survives statistical averaging. More detailed and microscopic understanding can be gained by focusing on the fluctuations over time since it contains signatures of dynamics which would not be captured in macroscopic transport measurements because such information would not likely survive after the averaging. Therefore, the noise spectroscopy enables accessing dynamics resulting due to stochastic rearrangement of many charge configurations in an electronically phase separated system, which makes the technique an experimentally robust tool to probe phase transitions that display EPS.The MIT in CuIr2S4 occurs around Tc ∼ 231 K upon cooling from room temperature. The notable features of the MIT are an orders-of-magnitude change in resistance accompanied by a lattice structural transition and a magnetic transition. Along with the thermal induced MIT, we observe threshold-like hysteretic resistiveswitching/transition (RS) below Tc.The normalized noise power spectral density (PSD) magnitude enhancement with1/f2 behavior and asymmetric trend captured in PSD emphasize crucial role of electronic domains across the thermal MIT in CuIr2S4. For the thermal-triggered MIT, we observe two features: asymmetric PSD around the transition and a dramatic increase in α value following the PSD trend. This helps in understanding the physical dynamics happening in the system across the transition. The creation and the growth of domains of opposite phase would have distinctly different impact on electrical transport on either side of the transition since on the metallic phase the creation of an insulating domain does not have a significant effect until the charge carriers can avoid high resistive paths. However, on the insulating phase, the creation of a single metallic domain will affect the charge carrier path and hence PSD magnitude. Emergence of multiple metastable states near the transition region and systems' wandering among such states is suggested by the observation of 1/f2 PSD behaviors. Therefore, the 1/f2 behavior around MIT emphasizes crucial role of collective charge dynamics.In the electrically-driven case, by studying both current-voltage (IV) characteristics and noise PSD, we conjecture that at T ≪ Tc, a single jump in IV and smoothly changing PSD points to non-thermal effects as the dominant mechanism. While for T ∼ Tc, multiple jumps in IV and increase in PSD are seen, indicating thermal effects play a synergistic role with the electric field causing non-uniform heating and proliferating electrical inhomogeneity.A theoretical framework, based on Ginzburg-Landau (GL) φ6-theory with nonequilibrium modifications so that both equilibrium (thermal MIT) and nonequilibrium (RS) transitions are described on same footing, is developed. Qualitatively closeagreement between experimental and theoretical results provides a novel way of looking into transitions under a unified picture serving an important role in understanding of emergent phenomena in a range of SCES driven in and out of equilibrium.K-TCNQ is a prototypical quasi 1D SCES, where a threshold-like RS is observed along the stacking a-axis direction. The temperature dependence of threshold field (Eth) is found to increase exponentially with decreasing temperature similar to field induced classical depinning in low-dimensional charge density wave (CDW) materials. Similar to the observation in classical CDW systems, approaching the threshold field noise PSD is found to exhibit 1/f2 behavior with magnitude increased by few orders.
520 $a Moreover, the observation of two threshold fields in electrical transport measurements and fluctuation spectroscopy further suggests to study K-TCNQ material system under framework of charge density wave.Finally, in K-TCNQ we observe a dynamic and cooperative reversible stable insulating-conducting phase transition driven by pulsed electromagnetic irradiation. We hypothesize laser-pulse driven stable conducting phase can be realized if the relaxation path can be altered by dynamic lattice perturbation at a characteristic timescale of electron-phonon decoupling. Electromagnetic excitation of ultrafast and intense laser pulses provides a pathway to access both photoexcitation and high strain-rate effects and their synergetic interplay made it possible to realize stable hidden, not accessible via thermodynamic path such as changing temperature or pressure. The strong cooperativity among electronic and lattice degrees leads the system towards a hidden state, which exhibits distinct electronic and magnetic properties that remain stable for over 400 days, significantly extending the lifetime of photoinduced transient state. Noise spectroscopy study performed across the transition suggest thelow-resistivity state is an electrically inhomogeneous phase.
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653 $a Charge dynamics
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