Ilaria Maccari - Academia.edu (original) (raw)
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University of Southern California
Centre National de la Recherche Scientifique / French National Centre for Scientific Research
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Papers by Ilaria Maccari
European Physical Journal B, May 1, 2016
Physical review, Feb 7, 2023
Physical review, Jun 24, 2022
Physical review, Mar 11, 2019
Physical review, Aug 28, 2017
Condensed matter, May 14, 2020
arXiv (Cornell University), Apr 14, 2023
arXiv (Cornell University), Feb 27, 2023
Materials that break multiple symmetries allow, under certain conditions, the formation of four-f... more Materials that break multiple symmetries allow, under certain conditions, the formation of four-fermion condensates above the superconducting critical temperature (Tc). Such states can be stabilized by phase fluctuations. Recently a fermionic quadrupling condensate that breaks the Z2 time-reversal symmetry was reported in Ba1-xKxFe2As2 [V. Grinenko et al., Nat. Phys. 17, 1254 (2021)]. However, the related anomaly was not resolved in the specific heat measurements. Resolving two anomalies at Tc and the Z2 transition temperature (TcZ2 > Tc) is key evidence for the existence of two distinct electronic phases. In a broader context, the lack of an additional anomaly in the specific heat at TcZ2 is a common unsolved problem for most superconductors with broken time-reversal symmetry, even in the conventional case where TcZ2 < Tc. Here, we report on detecting two anomalies in the specific heat of Ba1-xKxFe2As2 at zero magnetic field. The anomaly at the higher temperature is accompani...
arXiv (Cornell University), Jun 6, 2022
arXiv (Cornell University), Dec 27, 2022
The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes universal vortex unbinding in many ... more The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes universal vortex unbinding in many two-dimensional systems, including the paradigmatic XY model. However, most of these systems present a complex interplay between excitations at different length scales that complicates theoretical calculations of nonuniversal thermodynamic quantities. These difficulties may be overcome by suitably modifying the initial conditions of the BKT flow equations to account for noncritical fluctuations at small length scales. In this work, we perform a systematic study of the validity and limits of this two-step approach by constructing optimised initial conditions for the BKT flow. We find that the two-step approach can accurately reproduce the results of Monte-Carlo simulations of the traditional XY model. In order to systematically study the interplay between vortices and spin-wave excitations, we introduce a modified XY model with increased vortex fugacity. We present large-scale Monte-Carlo...
Nanomaterials, 2021
Two-dimensional superconductors with disorder at the nanoscale can host a variety of intriguing p... more Two-dimensional superconductors with disorder at the nanoscale can host a variety of intriguing phenomena. The superconducting transition is marked by a broad percolative transition with a long tail of the resistivity as function of the temperature. The fragile filamentary superconducting clusters, forming at low temperature, can be strengthened further by proximity effect with the surrounding metallic background, leading to an enhancement of the superfluid stiffness well below the percolative transition. Finite-frequency dissipation effects, e.g., related to the appearance of thermally excited vortices, can also significantly contribute to the resulting physics. Here, we propose a random impedance model to investigate the role of dissipation effects in the formation and strengthening of fragile superconducting clusters, discussing the solution within the effective medium theory.
Bosonic Z2 metal: Spontaneous breaking of time-reversal symmetry due to Cooper pairing in the res... more Bosonic Z2 metal: Spontaneous breaking of time-reversal symmetry due to Cooper pairing in the resistive state of Ba1−xKxFe2As2
Condensed Matter, 2021
In superconducting films, the role of intrinsic disorder is typically to compete with superconduc... more In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the presence of disorder can actually strengthen the superconducting state against thermal fluctuations. By means of Monte Carlo simulations on the uniformly frustrated XY model in two dimensions, we show that while for weak pinning the superconducting critical temperature Tc increases with the applied field H, for strong enough pinning, the experimental decreasing dependence between Tc and H is recovered with a resulting more robust vortex lattice.
European Physical Journal B, May 1, 2016
Physical review, Feb 7, 2023
Physical review, Jun 24, 2022
Physical review, Mar 11, 2019
Physical review, Aug 28, 2017
Condensed matter, May 14, 2020
arXiv (Cornell University), Apr 14, 2023
arXiv (Cornell University), Feb 27, 2023
Materials that break multiple symmetries allow, under certain conditions, the formation of four-f... more Materials that break multiple symmetries allow, under certain conditions, the formation of four-fermion condensates above the superconducting critical temperature (Tc). Such states can be stabilized by phase fluctuations. Recently a fermionic quadrupling condensate that breaks the Z2 time-reversal symmetry was reported in Ba1-xKxFe2As2 [V. Grinenko et al., Nat. Phys. 17, 1254 (2021)]. However, the related anomaly was not resolved in the specific heat measurements. Resolving two anomalies at Tc and the Z2 transition temperature (TcZ2 > Tc) is key evidence for the existence of two distinct electronic phases. In a broader context, the lack of an additional anomaly in the specific heat at TcZ2 is a common unsolved problem for most superconductors with broken time-reversal symmetry, even in the conventional case where TcZ2 < Tc. Here, we report on detecting two anomalies in the specific heat of Ba1-xKxFe2As2 at zero magnetic field. The anomaly at the higher temperature is accompani...
arXiv (Cornell University), Jun 6, 2022
arXiv (Cornell University), Dec 27, 2022
The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes universal vortex unbinding in many ... more The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes universal vortex unbinding in many two-dimensional systems, including the paradigmatic XY model. However, most of these systems present a complex interplay between excitations at different length scales that complicates theoretical calculations of nonuniversal thermodynamic quantities. These difficulties may be overcome by suitably modifying the initial conditions of the BKT flow equations to account for noncritical fluctuations at small length scales. In this work, we perform a systematic study of the validity and limits of this two-step approach by constructing optimised initial conditions for the BKT flow. We find that the two-step approach can accurately reproduce the results of Monte-Carlo simulations of the traditional XY model. In order to systematically study the interplay between vortices and spin-wave excitations, we introduce a modified XY model with increased vortex fugacity. We present large-scale Monte-Carlo...
Nanomaterials, 2021
Two-dimensional superconductors with disorder at the nanoscale can host a variety of intriguing p... more Two-dimensional superconductors with disorder at the nanoscale can host a variety of intriguing phenomena. The superconducting transition is marked by a broad percolative transition with a long tail of the resistivity as function of the temperature. The fragile filamentary superconducting clusters, forming at low temperature, can be strengthened further by proximity effect with the surrounding metallic background, leading to an enhancement of the superfluid stiffness well below the percolative transition. Finite-frequency dissipation effects, e.g., related to the appearance of thermally excited vortices, can also significantly contribute to the resulting physics. Here, we propose a random impedance model to investigate the role of dissipation effects in the formation and strengthening of fragile superconducting clusters, discussing the solution within the effective medium theory.
Bosonic Z2 metal: Spontaneous breaking of time-reversal symmetry due to Cooper pairing in the res... more Bosonic Z2 metal: Spontaneous breaking of time-reversal symmetry due to Cooper pairing in the resistive state of Ba1−xKxFe2As2
Condensed Matter, 2021
In superconducting films, the role of intrinsic disorder is typically to compete with superconduc... more In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the presence of disorder can actually strengthen the superconducting state against thermal fluctuations. By means of Monte Carlo simulations on the uniformly frustrated XY model in two dimensions, we show that while for weak pinning the superconducting critical temperature Tc increases with the applied field H, for strong enough pinning, the experimental decreasing dependence between Tc and H is recovered with a resulting more robust vortex lattice.