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Papers by Emma Minarelli

Bulletin of the American Physical Society, Mar 6, 2020

arXiv (Cornell University), Dec 19, 2022

Rn c : Rn`1σ c Rnσ` RnnRnσ˘H imp´ex``tL0 c : L1σ c L0σ`t ‹ L0 c : L0σ c L1σ`tR0 c : R1σ c R0σ`t ‹... more Rn c : Rn`1σ c Rnσ` RnnRnσ˘H imp´ex``tL0 c : L1σ c L0σ`t ‹ L0 c : L0σ c L1σ`tR0 c : R1σ c R0σ`t ‹ R0 c : R0σ c R1σ˘¸,

Cornell University - arXiv, Sep 2, 2022

Nanoelectronics devices, such as quantum dot systems or single-molecule transistors, consist of a... more Nanoelectronics devices, such as quantum dot systems or single-molecule transistors, consist of a quantum nanostructure coupled to a macroscopic external electronic circuit. Thermoelectric transport between source and drain leads is controlled by the quantum dynamics of the lead-coupled nanostructure, through which a current must pass. Strong electron interactions due to quantum confinement on the nanostructure produce nontrivial conductance signatures such as Coulomb blockade and Kondo effects, which become especially pronounced at low temperatures. In this work we first provide a modern review of standard quantum transport techniques, focusing on the linear response regime, and highlight the strengths and limitations of each. In the second part, we develop an improved numerical scheme for calculation of the ac linear electrical conductance through generic interacting nanostructures, based on the numerical renormalization group (NRG) method, and explicitly demonstrate its utility in terms of accuracy and efficiency. In the third part we derive low-energy effective models valid in various commonly-encountered situations, and from them we obtain simple analytical expressions for the low-temperature conductance. This indirect route via effective models, although approximate, allows certain limitations of conventional methodologies to be overcome, and provides physical insights into transport mechanisms. Finally, we apply and compare the various techniques, taking the two-terminal triple quantum dot and the serial multi-level double dot devices as nontrivial benchmark systems.

Nanomaterials, 2022

Nanoelectronic quantum dot devices exploiting the charge-Kondo paradigm have been established as ... more Nanoelectronic quantum dot devices exploiting the charge-Kondo paradigm have been established as versatile and accurate analogue quantum simulators of fundamental quantum impurity models. In particular, hybrid metal-semiconductor dots connected to two metallic leads realize the two-channel Kondo (2CK) model, in which Kondo screening of the dot charge pseudospin is frustrated. In this article, a two-channel charge-Kondo device made instead from graphene components is considered, realizing a pseudogapped version of the 2CK model. The model is solved using Wilson's Numerical Renormalization Group method, uncovering a rich phase diagram as a function of dot-lead coupling strength, channel asymmetry, and potential scattering. The complex physics of this system is explored through its thermodynamic properties, scattering T-matrix, and experimentally measurable conductance. The strong coupling pseudogap Kondo phase is found to persist in the channel-asymmetric two-channel context, while in the channel-symmetric case, frustration results in a novel quantum phase transition. Remarkably, despite the vanishing density of states in the graphene leads at low energies, a finite linear conductance is found at zero temperature at the frustrated critical point, which is of a non-Fermi liquid type. Our results suggest that the graphene charge-Kondo platform offers a unique possibility to access multichannel pseudogap Kondo physics.

Physical Review B, 2019

Impurities embedded in electronic systems induce bound states which under certain circumstances c... more Impurities embedded in electronic systems induce bound states which under certain circumstances can
hybridize and lead to impurity bands. Doping of insulators with impurities has been identified as a promising
route toward engineering electronic topological states of matter. In this paper we show how to realize
tuneable Chern insulators starting from a three-dimensional topological insulator whose surface is gapped and
intentionally doped with magnetic impurities. The main advantage of the protocol is that it is robust and in
particular not very sensitive to the impurity configuration. We explicitly demonstrate this for a square lattice of
impurities as well as a random lattice. In both cases we show that it is possible to change the Chern number of
the system by one through manipulating its topological state. We also discuss how this can be used to engineer
circuits of edge channels.

Ultrafast magnetisation dynamics is commonly described by the Three Termperature Model. In the st... more Ultrafast magnetisation dynamics is commonly described by the Three
Termperature Model.
In the studied case, we have a system of s-electrons (itinerant) and d-electrons (magnons, i.e. responsible for the total magnetisation of the system). Their interaction, i.e. ultrafast spin dynamics, is analysed in terms of specific temperatures: Tm for magnons and Ts = Tup-Tdown for s-electrons. This allows to obtain a more physical picture of the dynamics of the system, since all the elements involved in the scattering process are fully expressed in terms of their temperature and chemical potential.

A one-atom laser shares similar features with an optical laser. However, the distinct characteris... more A one-atom laser shares similar features with an optical laser. However, the distinct characteristic
concerns its output: it is a coherent matter wave, a coherent beam of atoms which can be
focused to a spot or can be collimated to travel large distances without spreading. This is
the reason why, calling the device one-atom laser, is a deceptive definition. The laser cooling and evaporative cooling techniques are exploited to obtain a Bose-
Einstein Condensate; the BEC itself stands for the gain mediumthrough which an atom beam
accumulates in a single-mode of the trap and, once it is extracted, it propagates from the trap.

Thesis Chapters by Emma Minarelli

The enormous interest in industrial application of semiconductor components has led to the develo... more The enormous interest in industrial application of semiconductor components has led to the development of unprecedented control over the manufacture of electronic devices on the nanometer scale. This allows to perform highly controllable and fine-tuned experiments in the quantum regime where exotic effects can nowadays be measured. Among those, breakthrough measurements of electrical conductance experimentally confirmed the Kondo effect - a many-body quantum effect involving macroscopic entanglement. In quantum dot devices, enhanced conductance below a characteristic energy scale is the signature of Kondo singlet formation. Precise predictions of quantum transport properties in similar nanoelectronics devices is therefore desired to design optimal functionality and control. Standard mesoscopic transport methods suffer from limitations in nanostructure specifics, set-up design, energy, temperature and voltage regime of applicability. To overcome these issues, such that we obtain modelling flexibility and accurate conductance predictions, in this thesis we analytically derive alternative and improved quantum transport formulations having as their starting point scattering theory in the Landauer-Buettiker formula, linear response theory in the Kubo formula, nonequilibrium Keldysh theory in the Meir-Wingreen formula and Fermi liquid theory in the Oguri formula. We perform a systematic benchmark of our exact expressions, comparing with the standard approaches using a state-of-the-art numerical renormalization group techniques (NRG). The new formulations not only reproduce literature results, but also show higher accuracy and computational efficiency, as well as a wider applicability under regimes and conditions out of reach by existing methods. We also derive generalized effective models for multi-orbital two-lead interacting nanostructures in both Coulomb blockade and mixed-valence regime, which yield reusable conductance predictions directly in terms of the effective model parameters. We conclude by applying our novel formulations to complex nanoelectronics systems, including a single-molecule benzene transistor, a charge-Kondo quantum dot made from graphene and a semiconductor triple quantum dot.

Bulletin of the American Physical Society, Mar 6, 2020

arXiv (Cornell University), Dec 19, 2022

Rn c : Rn`1σ c Rnσ` RnnRnσ˘H imp´ex``tL0 c : L1σ c L0σ`t ‹ L0 c : L0σ c L1σ`tR0 c : R1σ c R0σ`t ‹... more Rn c : Rn`1σ c Rnσ` RnnRnσ˘H imp´ex``tL0 c : L1σ c L0σ`t ‹ L0 c : L0σ c L1σ`tR0 c : R1σ c R0σ`t ‹ R0 c : R0σ c R1σ˘¸,

Cornell University - arXiv, Sep 2, 2022

Nanoelectronics devices, such as quantum dot systems or single-molecule transistors, consist of a... more Nanoelectronics devices, such as quantum dot systems or single-molecule transistors, consist of a quantum nanostructure coupled to a macroscopic external electronic circuit. Thermoelectric transport between source and drain leads is controlled by the quantum dynamics of the lead-coupled nanostructure, through which a current must pass. Strong electron interactions due to quantum confinement on the nanostructure produce nontrivial conductance signatures such as Coulomb blockade and Kondo effects, which become especially pronounced at low temperatures. In this work we first provide a modern review of standard quantum transport techniques, focusing on the linear response regime, and highlight the strengths and limitations of each. In the second part, we develop an improved numerical scheme for calculation of the ac linear electrical conductance through generic interacting nanostructures, based on the numerical renormalization group (NRG) method, and explicitly demonstrate its utility in terms of accuracy and efficiency. In the third part we derive low-energy effective models valid in various commonly-encountered situations, and from them we obtain simple analytical expressions for the low-temperature conductance. This indirect route via effective models, although approximate, allows certain limitations of conventional methodologies to be overcome, and provides physical insights into transport mechanisms. Finally, we apply and compare the various techniques, taking the two-terminal triple quantum dot and the serial multi-level double dot devices as nontrivial benchmark systems.

Nanomaterials, 2022

Nanoelectronic quantum dot devices exploiting the charge-Kondo paradigm have been established as ... more Nanoelectronic quantum dot devices exploiting the charge-Kondo paradigm have been established as versatile and accurate analogue quantum simulators of fundamental quantum impurity models. In particular, hybrid metal-semiconductor dots connected to two metallic leads realize the two-channel Kondo (2CK) model, in which Kondo screening of the dot charge pseudospin is frustrated. In this article, a two-channel charge-Kondo device made instead from graphene components is considered, realizing a pseudogapped version of the 2CK model. The model is solved using Wilson's Numerical Renormalization Group method, uncovering a rich phase diagram as a function of dot-lead coupling strength, channel asymmetry, and potential scattering. The complex physics of this system is explored through its thermodynamic properties, scattering T-matrix, and experimentally measurable conductance. The strong coupling pseudogap Kondo phase is found to persist in the channel-asymmetric two-channel context, while in the channel-symmetric case, frustration results in a novel quantum phase transition. Remarkably, despite the vanishing density of states in the graphene leads at low energies, a finite linear conductance is found at zero temperature at the frustrated critical point, which is of a non-Fermi liquid type. Our results suggest that the graphene charge-Kondo platform offers a unique possibility to access multichannel pseudogap Kondo physics.

Physical Review B, 2019

Impurities embedded in electronic systems induce bound states which under certain circumstances c... more Impurities embedded in electronic systems induce bound states which under certain circumstances can
hybridize and lead to impurity bands. Doping of insulators with impurities has been identified as a promising
route toward engineering electronic topological states of matter. In this paper we show how to realize
tuneable Chern insulators starting from a three-dimensional topological insulator whose surface is gapped and
intentionally doped with magnetic impurities. The main advantage of the protocol is that it is robust and in
particular not very sensitive to the impurity configuration. We explicitly demonstrate this for a square lattice of
impurities as well as a random lattice. In both cases we show that it is possible to change the Chern number of
the system by one through manipulating its topological state. We also discuss how this can be used to engineer
circuits of edge channels.

Ultrafast magnetisation dynamics is commonly described by the Three Termperature Model. In the st... more Ultrafast magnetisation dynamics is commonly described by the Three
Termperature Model.
In the studied case, we have a system of s-electrons (itinerant) and d-electrons (magnons, i.e. responsible for the total magnetisation of the system). Their interaction, i.e. ultrafast spin dynamics, is analysed in terms of specific temperatures: Tm for magnons and Ts = Tup-Tdown for s-electrons. This allows to obtain a more physical picture of the dynamics of the system, since all the elements involved in the scattering process are fully expressed in terms of their temperature and chemical potential.

A one-atom laser shares similar features with an optical laser. However, the distinct characteris... more A one-atom laser shares similar features with an optical laser. However, the distinct characteristic
concerns its output: it is a coherent matter wave, a coherent beam of atoms which can be
focused to a spot or can be collimated to travel large distances without spreading. This is
the reason why, calling the device one-atom laser, is a deceptive definition. The laser cooling and evaporative cooling techniques are exploited to obtain a Bose-
Einstein Condensate; the BEC itself stands for the gain mediumthrough which an atom beam
accumulates in a single-mode of the trap and, once it is extracted, it propagates from the trap.

The enormous interest in industrial application of semiconductor components has led to the develo... more The enormous interest in industrial application of semiconductor components has led to the development of unprecedented control over the manufacture of electronic devices on the nanometer scale. This allows to perform highly controllable and fine-tuned experiments in the quantum regime where exotic effects can nowadays be measured. Among those, breakthrough measurements of electrical conductance experimentally confirmed the Kondo effect - a many-body quantum effect involving macroscopic entanglement. In quantum dot devices, enhanced conductance below a characteristic energy scale is the signature of Kondo singlet formation. Precise predictions of quantum transport properties in similar nanoelectronics devices is therefore desired to design optimal functionality and control. Standard mesoscopic transport methods suffer from limitations in nanostructure specifics, set-up design, energy, temperature and voltage regime of applicability. To overcome these issues, such that we obtain modelling flexibility and accurate conductance predictions, in this thesis we analytically derive alternative and improved quantum transport formulations having as their starting point scattering theory in the Landauer-Buettiker formula, linear response theory in the Kubo formula, nonequilibrium Keldysh theory in the Meir-Wingreen formula and Fermi liquid theory in the Oguri formula. We perform a systematic benchmark of our exact expressions, comparing with the standard approaches using a state-of-the-art numerical renormalization group techniques (NRG). The new formulations not only reproduce literature results, but also show higher accuracy and computational efficiency, as well as a wider applicability under regimes and conditions out of reach by existing methods. We also derive generalized effective models for multi-orbital two-lead interacting nanostructures in both Coulomb blockade and mixed-valence regime, which yield reusable conductance predictions directly in terms of the effective model parameters. We conclude by applying our novel formulations to complex nanoelectronics systems, including a single-molecule benzene transistor, a charge-Kondo quantum dot made from graphene and a semiconductor triple quantum dot.