Publications

2024

• Time-dependent Neural Galerkin Method for Quantum Dynamics
  
  • Sinibaldi Alessandro
  • Hendry Douglas
  • Vicentini Filippo
  • Carleo Giuseppe
  , 2024. <div><p>We introduce a classical computational method for quantum dynamics that relies on a globalin-time variational principle. Unlike conventional time-stepping approaches, our scheme computes the entire state trajectory over a finite time window by minimizing a physically motivated loss function that enforces the Schrödinger's equation. The variational state is parametrized with a Galerkin-inspired ansatz based on a time-dependent linear combination of time-independent Neural Quantum States. This structure effectively captures the relevant dynamical frequencies in the time evolution and is particularly well-suited for exploring long-time dynamics. We showcase the method's effectiveness by simulating global quantum quenches in the paradigmatic Transverse-Field Ising model in both 1D and 2D. By extracting the asymptotic long-time evolution, we uncover signatures of ergodicity breaking and absence of thermalization in two dimensions. Overall, the method presented here shows competitive performance compared to state-of-the-art time-dependent variational approaches and highlight the potential to explore previously inaccessible dynamical regimes of strongly interacting quantum systems.</p></div>
• Topological superconductivity in the presence of light-matter coupling and Coulomb interactions
  
  • del Pozo Frederick
  , 2024. This thesis explores the topological phases and critical properties of electrically interacting p-wave superconducting wires. We approximate the low-energy properties of these wires by the well-known Kitaev wire model, which considerably simplifies the description and allows us to test novel paradigms and approaches. We investigate the effects of both static (Coulomb) and dynamic (electromagnetic waves) interactions in one or coupled wire geometries and introduce a novel topological marker that can be extracted entirely from real-space (two-point) correlation functions. This is one of our central results, and we show that it accurately captures the phase transitions in the presence of interactions and disorder and can be used to map the phase diagram of coupled wires as well. To do that, density matrix renormalization group (DMRG) calculations are performed. Another result of this thesis is a novel protocol to directly measure the winding-number, through (momentum-resolved) quasi-particle populations excited by classical light. Lastly, we also investigate the critical phases of two interacting and coupled wires and focus in particular on the doubly critical Ising phase (DCI) discovered in 2016. A combined approach of quantum field theory and numerical results obtained with DMRG show that it is robust against weak disorder, with interactions being the driving force behind the stability in critical chains. The localization dynamics in the presence of inter-wire couplings and fluctuations of the chemical potential is analysed by solving renormalization group (RG) flow equations numerically.Our work emphasizes the positive effects that strong interactions between two wires can have on the physical and topological properties, and additionally raises new questions related to critical modes in open chains. (10.70675/99a9f149z7952z49dez9c56z51cefec0c950)
  DOI : 10.70675/99a9f149z7952z49dez9c56z51cefec0c950
• Luttinger surface dominance and Fermi liquid behaviour of topological Kondo insulators SmB$_6$ and YbB$_{12}$
  
  • Blason Andrea
  • Pasqua Ivan
  • Ferrero Michel
  • Fabrizio Michele
  Physical Review B, American Physical Society, 2024, 110 (23), pp.235115. Defying the traditional classification into metals and insulators, several materials simultaneously display metallic thermal properties and insulating electric behaviour, as if they hosted quasiparticles carrying entropy but not charge. Among them, some materials also possess quantum oscillations in magnetic fields as if they had well-defined Fermi surfaces despite the insulating gap. This remarkable dichotomy has been observed in the topological Kondo insulators SmB$_6$ and YbB$_{12}$. Prompted by the peculiar mixed-valence nature of these compounds, involving $f$ and $d$ electrons of the lanthanide, we propose an explanation of their intriguing properties drawing inspiration from the physics of the pseudogap phase in underdoped cuprates. We argue that the $f$ and $d$ subsystems, when considered separately, act, respectively, as electron- and hole-doped Mott insulators, featuring Fermi pockets coexisting with Luttinger surfaces responsible for the pseudogap. When the two are coupled to each other a hybridisation gap opens up, and the whole turns into a topological insulator endowed with genuine chiral edge states. However, the Luttinger surfaces persist and support neutral quasiparticles. This scenario, supported by numerical simulations within the dynamical cluster approximation, effectively resolves the paradoxical phenomenology of SmB$_6$ and YbB$_{12}$. (10.1103/PhysRevB.110.235115)
  DOI : 10.1103/PhysRevB.110.235115
• High-field ultrasound study of elastic constants and possible magnetic symmetry transformations in UO 2
  
  • Tereshina-Chitrova E.
  • Pourovskii L.
  • Khmelevskyi S.
  • Gorbunov D.
  • Caciuffo R.
  Physical Review B, American Physical Society, 2024, 110 (22), pp.224417. In this study, we probe the coupling between magnetism and lattice dynamics in UO2, a 3k antiferromagnet that undergoes magnetic ordering below its Néel temperature (TN ) of 30.8 K. Ultrasound measurements provide insights into the interplay between the material's magnetic properties and lattice vibrations in response to the applied high magnetic field. A model analysis based on ab initio calculated superexchange interactions predicts a change in the magnetic structure from 3k to 2k at around 50 T. Although this change is not evident in the magnetization curve, we observe a crossover of ultrasound velocity ∆v/v using a phase-sensitive pulse-echo technique in pulsed magnetic fields of up to 65 T. We show that at Hz &gt; 50 T, the structure remains antiferromagnetic in the (x, y) plane and becomes ferromagnetic in the z direction. A further transition into the 1k structure is theoretically predicted to take place at a magnetic field of ∼104 tesla. (10.1103/PhysRevB.110.224417)
  DOI : 10.1103/PhysRevB.110.224417
• The Fractional Poisson Process and Other Limit Point Processes for Rare Events in Infinite Ergodic Theory
  
  • Bansard-Tresse Dylan
  , 2024. We study the process of suitably normalized successive return times to rare events in the setting of infinite-measure preserving dynamical systems. Specifically, we consider small neighborhoods of points whose measure tends to zero. We obtain two types of results. First, we conduct a detailed study of a class of interval maps with a neutral fixed point and we fully characterize the limit processes for all points, highlighting a trichotomy and the emergence of the fractional (possibly compound) Poisson process. This is the first time that these processes have been explicitly identified in this context. Second, we prove an abstract result that offers an explanation for the emergence of the fractional Poisson process, as the unique fixed point of a functional equation, drawing a parallel with the well-established behavior of the Poisson process in finite-measure preserving dynamical systems.
• Prospective report of the French QCD community to the ESPPU 2025 with respect to the program of the LHC Run 5 and beyond and future colliders at CERN
  
  • Arata Carolina
  • Arleo François
  • Audurier Benjamin
  • Baldisseri Alberto
  • Bastid Nicole
  • Batigne Guillaume
  • Belikov Iouri
  • Bluhm Marcus
  • Bossu Francesco
  • Borel Hervé
  • Castillo Castellanos Javier
  • Caucal Paul
  • Cheshkov Cvetan
  • Conesa Balbastre Gustavo
  • Conesa del Valle Zaida
  • Coquet Maurice
  • Corredoira Fernandez Imanol
  • Crochet Philippe
  • Espagnon Bruno
  • Faivre Julien
  • Ferrero Andrea
  • Francisco Audrey
  • Fleuret Frédéric
  • Flett Chris
  • Furget Christophe
  • Germain Marie
  • Gossiaux Pol Bernard
  • Guernane Rachid
  • Guilbaud Maxime
  • Guittiere Manuel
  • Hadjidakis Cynthia
  • Hippolyte Boris
  • Kuhn Christian
  • Lansberg Jean-Philippe
  • Lopez Xavier
  • Maire Antonin
  • Mallick Dukhishyam
  • Marquet Cyrille
  • Martinez-Garcia Ginés
  • Massacrier Laure
  • Mattioli Kara
  • Maurice Émilie
  • Muñoz Camacho Carlos
  • Nahrgang Marlene
  • Nefedov Maxim
  • Niel Élisabeth
  • Ozcelik Melih A
  • Panebianco Stefano
  • Pillot Philippe
  • Pire Bernard
  • Porteboeuf Houssais Sarah
  • Rakotozafindrabe Andry
  • Ramasubramanian Niveditha
  • Robbe Patrick
  • Sazdjian Hagop
  • Senyukov Serhiy
  • Suire Christophe
  • Uras Antonio
  • Wallon Samuel
  • Winn Michael
  , 2024. This document summarizes the prospective physics plans of the French QCD and Heavy-Ion community, including the experimental programs at the LHC Run 5 and beyond and future colliders at CERN, within the context of the French contribution to the update of the European Strategy in Particle Physics (ESPPU 2025), as discussed in the workshop on European Strategy for Particle Physics Update 2025 organised by the QCD GdR in Oct. 2024.
• Aspects of confinement within non-Abelian gauge theories
  
  • Reinosa Urko
  , 2024. These lectures cover two aspects: first, irrespectively of the particular approach followed to tackle the QCD phase diagram, we introduce some tools that help discussing the confinement/deconfinement transition in the continuum; second, within one particular continuum approach, based on the Curci-Ferrari model, we illustrate the use of these various notions in order the describe to the confinement/deconfinement transition. (10.48550/arXiv.2404.06118)
  DOI : 10.48550/arXiv.2404.06118
• Three lectures on the Curci-Ferrari model
  
  • Reinosa Urko
  , 2024. In these lectures, we review the status of the Curci-Ferrari model as a phenomenological approach to Landau gauge-fixed YM theories in the infrared. More precisely, after discussing some of the general properties of the model, we explain in full detail the evaluation of the one-loop two-point correlators that allowed for a successful comparison to the corresponding Landau-gauge lattice data. We also review the renormalization group flow of the model which controls its fate at high and low momentum scales. (10.48550/arXiv.2403.10702)
  DOI : 10.48550/arXiv.2403.10702
• Testing the instanton approach to the large amplification limit of a diffraction–amplification problem
  
  • Mounaix Philippe
  Journal of Physics A: Mathematical and Theoretical, IOP Publishing, 2024, 57 (48), pp.485003. Abstract The validity of the instanton analysis approach is tested numerically in the case of the diffraction–amplification problem ∂ z ψ − i 2 m ∂ x 2 2 ψ = g | S | 2 ψ for ln ⁡ U ≫ 1 , where U = | ψ ( 0 , L ) | 2 . Here, S ( x , z ) is a complex Gaussian random field, z and x respectively are the axial and transverse coordinates, with 0 ⩽ z ⩽ L , and both m ≠ 0 and g &gt; 0 are real parameters. We consider a class of S , called the ‘one-max class’, for which we devise a specific biased sampling procedure. As an application, p ( U ), the probability distribution of U , is obtained down to values less than 10 −2270 in the far right tail. We find that the agreement of our numerical results with the instanton analysis predictions in Mounaix (2023 J. Phys. A: Math. Theor. 56 305001) is remarkable. Both the predicted algebraic tail of p ( U ) and concentration of the realizations of S onto the leading instanton are clearly confirmed, which validates the instanton analysis numerically in the large ln ⁡ U limit for S in the one-max class. (10.1088/1751-8121/ad8f08)
  DOI : 10.1088/1751-8121/ad8f08
• Modeling and simulations of hydrodynamic shocks in a plasma flowing across randomized ICF scale laser beams
  
  • Hüller Stefan
  • Ludwig J D
  • Rose H A
  • Bruulsema C
  • Farmer W
  • Michel P
  • Milder A L
  • Rozmus W
  • Swadling George F.
  Comptes Rendus. Physique, Académie des sciences (Paris), 2024, 25, pp.353-365. High-energy laser beams interacting with flowing plasmas can produce a plasma response that leads to deflection of the beam, beam bending. Such beams have usually a speckle structure generated by optical smoothing techniques that reduce the spatial and temporal coherence in the laser f ield pattern. The cumulative plasma response from laser speckles slows down the velocity of the incoming flow by momentum conservation. For slightly super-sonic flow the cumulative plasma response to the ponderomotive force exerted by the beam speckle ensemble is the strongest, such that slowing down the flow to subsonic velocities leads eventually to the generation of a shock around the cross section of the beam. This scenario has been predicted theoretically and is confirmed here by our hydrodynamic simulations in two dimensions with speckled beams and in one dimension with a reduced model. The conditions of shock generation are given in terms of the ponderomotive pressure, speckle size and the flow velocity. The nonlinear properties of the shocks are analyzed using Rankine-Hugoniot relations. According to linear theory, temporally smoothed laser beams exhibit a higher threshold for shock generation. Numerical simulations with beams that are smoothed by spectral dispersion compare well with the linear theory results, diverging from those produced by beams with only a random phase plates in the nonlinear regime. The conditions necessary for shock generation and their effects on the laser plasma coupling in inertial confinement fusion (ICF) experiments are also discussed. (10.5802/crphys.200)
  DOI : 10.5802/crphys.200
• High-quality poor man's Majorana bound states from cavity embedding
  
  • Gómez-León Álvaro
  • Schiro Marco
  • Dmytruk Olesia
  , 2024. <div><p>Poor man's Majorana Bound States (MBS) arise in minimal Kitaev chains when the parameters are fine-tuned to a sweet spot. We consider an interacting two-site Kitaev chain coupled to a singlemode cavity and show that the sweet spot condition can be controlled with the cavity frequency and the hopping between sites. Furthermore, we demonstrate that photon-mediated effective interactions can be used to screen intrinsic interactions, improving the original quality of the MBS. We describe experimental signatures in the cavity transmission to detect their presence and quality. Our work proposes a new way to tune poor man's MBS in a quantum dot array coupled to a cavity.</p></div>
• Fast Scrambling at the Boundary
  
  • Larzul Ancel
  • Sengupta Anirvan M
  • Georges Antoine
  • Schirò Marco
  , 2024. Many-body systems which saturate the quantum bound on chaos are attracting interest across a wide range of fields. Notable examples include the Sachdev-Ye-Kitaev model and its variations, all characterised by some form or randomness and all to all couplings. Here we study many-body quantum chaos in a quantum impurity model showing Non-Fermi-Liquid physics, the overscreened multichannel $SU(N)$ Kondo model. We compute exactly the low-temperature behavior of the out-of time order correlator in the limit of large $N$ and large number of channels $K$, at fixed ratio $\gamma=K/N$. Due to strong correlations at the impurity site the spin fractionalizes in auxiliary fermions and bosons. We show that all the degrees of freedom of our theory acquire a Lyapunov exponent which is linear in temperature as $T\rightarrow 0$, with a prefactor that depends on $\gamma$. Remarkably, for $N=K$ the impurity spin displays maximal chaos, while bosons and fermions only get up to half of the maximal Lyapunov exponent. Our results highlights two new features: a non-disordered model which is maximally chaotic due to strong correlations at its boundary and a fractionalization of quantum chaos.
• The Ubiquity of Twisted Flux Ropes in the Quiet Sun
  
  • Amari Tahar
  • Canou Aurélien
  • Velli Marco
  • Mikic Zoran
  • Alauzet Frederic
  • Buchlin Eric
  • Luciani Jean-François
  • Aly Jean-Jacques
  • Tarr Lucas A.
  , 2024. Models and observations have demonstrated that Twisted Flux Ropes (TFRs) play a significant role in the structure and eruptive dynamics of active regions. Their role in the dynamics of the quiet Sun atmosphere on has remained elusive, their fundamental relevance emerging mainly from theoretical models (Amari et al. 2015), showing that they form and erupt as a result of flux cancellation. Here HINODE high-resolution photospheric vector magnetic field measurements are integrated with advanced environment reconstruction models: TFRs develop on various scales and are associated with the appearance of mesospots. The developing TFRs contain sufficient free magnetic energy to match the requirements of the recently observed "campfires" discovered by Solar Orbiter in the quiet Sun. The free magnetic energy is found to be large enough to trigger eruptions while the magnetic twist large enough to trigger confined eruptions, heating the atmosphere. TFRs are also connected to larger scale magnetic fields such as supergranulation loops, allowing the generation of Alfv\'en waves at the top of the chromosphere that can propagate along them. High-resolution magnetohydrodynamic simulations, incorporating subsurface dynamo activity at an unprecedented 30 km spatial resolution, confirm that TFRs are ubiquitous products of the permanent small scale dynamo engine that feeds their formation, destabilization, eruption via flux emergence, submergence and cancellation of their chromospheric feet, similar to the dynamics driving large scale eruptive events. Future investigations, especially with the Daniel K. Inouye Solar Telescope (DKIST) and Solar Orbiter will deepen our understanding of TFRs in the context of atmospheric heating.
• Twisted Orientifold planes and S-duality without supersymmetry
  
  • Bossard Guillaume
  • Casagrande Gabriele
  • Dudas Emilian
  • Dudas Emilian
  , 2024. We construct a novel orientifold of type IIB string theory that breaks all supersymmetries. It is a closed string theory without open sector and it can be understood as a Scherk-Schwarz deformation in which supersymmetry is restored at infinite radius. We conjecture that it is realised in F-theory as a compactification on a freely acting orbifold that acts as the reflection on the elliptic fibre. The SL(2,Z) selfduality is manifest in the F-theory formulation. We construct explicitly the D-branes in this model and find that stable D-branes match the geometric prediction in M-theory. This theory has the salient feature that the O-planes couple only to the massive twisted states of the theory. We call them twisted O-planes. We describe supersymmetric examples of such twisted O-planes and argue that they are similar in nature to combinations of O+ and O- planes with vanishing total charge.
• Twisted Orientifold planes and S-duality without supersymmetry
  
  • Bossard Guillaume
  • Casagrande Gabriele
  • Dudas Emilian
  , 2024. We construct a novel orientifold of type IIB string theory that breaks all supersymmetries. It is a closed string theory without open sector and it can be understood as a Scherk-Schwarz deformation in which supersymmetry is restored at infinite radius. We conjecture that it is realised in F-theory as a compactification on a freely acting orbifold that acts as the reflection on the elliptic fibre. The SL(2,Z) selfduality is manifest in the F-theory formulation. We construct explicitly the D-branes in this model and find that stable D-branes match the geometric prediction in M-theory. This theory has the salient feature that the O-planes couple only to the massive twisted states of the theory. We call them twisted O-planes. We describe supersymmetric examples of such twisted O-planes and argue that they are similar in nature to combinations of O+ and O- planes with vanishing total charge.
• Respective Roles of Electron-Phonon and Electron-Electron Interactions in the Transport and Quasiparticle Properties of SrVO 3
  
  • Abramovitch David
  • Mravlje Jernej
  • Zhou Jin-Jian
  • Georges Antoine
  • Bernardi Marco
  Physical Review Letters, American Physical Society, 2024, 133 (18), pp.186501. (10.1103/PhysRevLett.133.186501)
  DOI : 10.1103/PhysRevLett.133.186501
• Constraints on the action of effective theories in quantum gravity
  
  • Loty Adrien
  , 2024. String theory constitutes one of the most popular and studied framework to approach quantum gravity. It is well known that the low energy limit of string theory gives a wide range of effective field theories. One recent and promising way to extract information about quantum gravity from this string landscape has been the swampland program. The string lamppost principle postulates that the quantum gravity landscape and the string landscape coincide. In this thesis we propose to study this claim for the case of higher order Wilson couplings in the very restricted case of maximal supersymmetry.We first study the low energy limit of genus 0, 1 and 2 string amplitudes for type II string theory compactified on a torus and compare them to tree level, 1-loop and 2-loop maximal supergravity amplitudes respectively. This allows us to compute the perturbative contributions to the leading Wilson coefficients of maximally supersymmetric string theory. We also show that in dimension 8 logarithmic divergences of the supergravity amplitudes can be linked to divergences of Wilson couplings. We give a prescription to properly regularise the divergence by using the finite string amplitude.We then use the differential equations entailed by the supersymmetric Ward identities as well as the constraints imposed by U-duality to derive the full non perturbative Wilson coefficients for maximally supersymmetric string theory in dimensions higher or equal to 6. These are given for the leading and next to leading Wilson coefficients by Eisenstein and Epstein series for the relevant U-duality group. The parabolic Fourier expansions of these series can then be used to check the different degeneration limits of the Wilson coefficients.Finally we study the minima of these functions on moduli space to give lower bounds on Wilson coefficients coming from maximally supersymmetric string theory. This implies finding the minima of Epstein series for special values of the s parameter. We first extend Grenier's recursive construction of a fundamental domain to almost any simple Lie group which allows us to properly define the domain of study of our functions. We then show that symmetric points are necessarily extrema of automorphic forms and give precise criteria for them to be minima. We also identify these symmetric points as corners of fundamental domains. We study relevant symmetric points for the case of SL(n) and SO(n,n) groups and give additional density arguments regarding the global minima for large s parameter. We then checked our conjecture numerically for the cases n=5 relevant for dimensions 7 and 6.These lower bounds should then be compared to lower bounds coming from unitarity constraints using S-matrix bootstrap methods. As far as we know this analysis still needs to be performed in dimensions lower or equal to 8. We have shown that in dimension 6 factorisation properties of maximally supersymmetric amplitudes imply that the unitarity properties of superamplitudes reduce to the unitarity properties of scalar amplitudes. These kind of factorisations also exist in other dimensions but do not always lead to such drastic simplifications. However one can always restrict to elastic scattering to make the numerics bearable. This kind of analysis, if successful, would be a strong argument for the validity of the string lamppost principle in the case of maximal supersymmetry. (10.70675/876f90d7z89e3z4157z978dz1049d26bac09)
  DOI : 10.70675/876f90d7z89e3z4157z978dz1049d26bac09
• Testing the Instanton Approach to the Large Amplification Limit of a Diffraction-Amplification Problem
  
  • Mounaix Philippe
  , 2024. <div><p>The validity of the instanton analysis approach is tested numerically in the case of the diffraction-</p><p>Here, S(x, z) is a complex Gaussian random field, z and x respectively are the axial and transverse coordinates, with 0  z  L, and both m 6 = 0 and g &gt; 0 are real parameters. We consider a class of S, called the 'one-max class', for which we devise a specific biased sampling procedure. As an application, p(U ), the probability distribution of U , is obtained down to values less than 10 2270 in the far right tail. We find that the agreement of our numerical results with the instanton analysis predictions in Mounaix (2023 J. Phys. A: Math. Theor. 56 305001) is remarkable. Both the predicted algebraic tail of p(U ) and concentration of the realizations of S onto the leading instanton are clearly confirmed, which validates the instanton analysis numerically in the large ln U limit for S in the one-max class.</p></div>
• Interconnected Renormalization of Hubbard Bands and Green's Function Zeros in Mott Insulators Induced by Strong Magnetic Fluctuations
  
  • Stepanov Evgeny
  • Chatzieleftheriou Maria
  • Wagner Niklas
  • Sangiovanni Giorgio
  Physical Review B, American Physical Society, 2024, 110 (16), pp.L161106. We analyze the role of spatial electronic correlations and, in particular, of the magnetic fluctuations in Mott insulators. A half-filled Hubbard model is solved at large strength of the repulsion U on a two-dimensional square lattice using an advanced diagrammatic non-perturbative approach capable of going beyond Hartree-Fock and single-site dynamical mean-field theories. We show that at high temperatures the magnetic fluctuations are weak, and the electronic self-energy of the system is mainly local and is well reproduced by the atomic (Hubbard-I) approximation. Lowering the temperature toward the low-temperature magnetically ordered phase, the non-locality of the self-energy becomes crucial in determining the momentum-dispersion of the Hubbard bands and the Green's function zeros. We therefore establish a precise link between Luttinger surface, non-local correlations and spectral properties of the Hubbard bands. (10.1103/PhysRevB.110.L161106)
  DOI : 10.1103/PhysRevB.110.L161106
• Laser-driven ion acceleration in presence of increasing heating of relativistic electrons at steep overdense plasma interfaces
  
  • Hüller Stefan
  • Porzio Anna
  • Héron Anne
  • Mora Patrick
  Physics of Plasmas, American Institute of Physics, 2024, 31, pp.103103. (10.1063/5.0222378)
  DOI : 10.1063/5.0222378
• Superconductivity and Mott Physics in Organic Charge Transfer Materials
  
  • Menke Henri
  • Klett Marcel
  • Kanoda Kazushi
  • Georges Antoine
  • Ferrero Michel
  • Schäfer Thomas
  Physical Review Letters, American Physical Society, 2024, 133 (13), pp.136501. (10.1103/PhysRevLett.133.136501)
  DOI : 10.1103/PhysRevLett.133.136501
• Adventures in (thermal) Wonderland
  
  • Vilatte Matthieu
  , 2024. The work we present in this thesis is structured around the concepts of field theories and geometry, which are applied to gravity and thermalisation.On the gravity side, our work aims at shedding new light on the asymptotic structure of the gravitational field in the context of asymptotically flat spacetimes, using information encoded on the conformal boundary. The latter is a null hypersurface on which Carrollian physics instead of relativistic physics is at work. A Carroll structure on a manifold is a degenerate metric and a vector field spanning the kernel of the latter. This vector selects a particular direction which can be the starting point for describing Carroll structures in a split frame. We first elaborate on the geometry one can construct on such a manifold in this frame, including a comprehensive study of connections and (conformal isometries). Effective actions can be defined on a Carrollian background. Canonical momenta conjugate to the geometry or the connection are introduced, and the variation of the action shall give their conservation equations, upon which isometric charges can be reached.Carrollian physics is also known to emerge as the vanishing speed of light of relativistic physics. This limit usually exhibits more Carrollian descendants than what might be expected from a naive intrinsic analysis, as shown in the explicit examples of Carrollian fluids, Carrollian scalar fields (for which two actions, electric and magnetic arise in the limit) and the Carrollian Chern-Simons action. The richness of the limiting procedure is due to this versatility in describing a palette of degrees of freedom. This turns out to be an awesome tool in studying the relationship between asymptotically anti de Sitter (AdS) and flat spacetimes.Metrics on asymptotically flat spacetimes can be expressed as an infinite expansion in a gauge, covariant with respect to their null boundaries. This slight extension of the Newman-Unti gauge is shown to be valid also in AdS, which allows to take the flat limit in the bulk i.e. the Carrollian limit on the boundary, while preserving this covariance feature. We demonstrate that the infinite solution space of Ricci-flat spacetimes actually arises from the Laurent expansion of the AdS boundary energy-momentum tensor. These replicas obey at each order Carrollian dynamics (flux/balance laws). Focusing our attention to Petrov algebraically special spacetimes (for which the infinite expansion resums), we use the Carrollian flux/balance laws together with the conservation of the energy-momentum and Cotton tensors to build two dual towers of bulk charges from a purely boundary perspective. Among them we recover the mass and angular momentum mutipolar moments for the Kerr-Taub-NUT family. The covariant gauge is also the appropriate framework to unveil the action of hidden symmetries of gravity on the null boundary. In this thesis we study exhaustively the case of Ehlers' L(2,mathbb{R}) symmetry.On the side of thermal field theory we see that while at infinite temperature a CFT is described by its spectrum and the OPE coefficients, additional data is needed in the thermal case. These are the average values of primary operators, completely determined up to a constant coefficient. Numerical simulations, duality with black-hole states in AdS or spectral analyses are the methods usually employed to uncover the latter. Our work features a new breadth. Starting from two coupled harmonic oscillators, we show that they are related to conformal ladder graphs of fishnet theories. This observation is the first step for setting a new correspondence between thermal partition functions and graphs. (10.70675/a1ce6c73zef06z4234z8bc8z21a8f3f64001)
  DOI : 10.70675/a1ce6c73zef06z4234z8bc8z21a8f3f64001
• Origin and fate of the pseudogap in the doped Hubbard model
  
  • Šimkovic Fedor
  • Rossi Riccardo
  • Georges Antoine
  • Ferrero Michel
  Science, American Association for the Advancement of Science (AAAS), 2024, 385 (6715), pp.eade9194. We investigate the doped two-dimensional Hubbard model at finite temperature using controlled diagrammatic Monte Carlo calculations allowing for the computation of spectral properties in the infinite-size limit and, crucially, with arbitrary momentum resolution. We show that three distinct regimes are found as a function of doping and interaction strength, corresponding to a weakly correlated metal with properties close to those of the non-interacting system, a correlated metal with strong interaction effects including a reshaping of the Fermi surface, and a pseudogap regime at low doping in which quasiparticle excitations are selectively destroyed near the antinodal regions of momentum space. We study the physical mechanism leading to the pseudogap and show that it forms both at weak coupling when the magnetic correlation length is large and at strong coupling when it is shorter. In both cases, we show that spin-fluctuation theory can be modified in order to account for the behavior of the non-local component of the self-energy. We discuss the fate of the pseudogap as temperature goes to zero and show that, remarkably, this regime extrapolates precisely to the ordered stripe phase found by ground-state methods. This handshake between finite temperature and ground-state results significantly advances the elaboration of a comprehensive picture of the physics of the doped Hubbard model. (10.1126/science.ade9194)
  DOI : 10.1126/science.ade9194
• Mott Transition for a Lieb-Liniger Gas in a Shallow Quasiperiodic Potential: Delocalization Induced by Disorder
  
  • Yao Hepeng
  • Tanzi Luca
  • Sanchez-Palencia Laurent
  • Giamarchi Thierry
  • Modugno Giovanni
  • D’errico Chiara
  Physical Review Letters, American Physical Society, 2024, 133 (12), pp.123401. (10.1103/PhysRevLett.133.123401)
  DOI : 10.1103/PhysRevLett.133.123401
• Dynamical Correlations and Order in Magic-Angle Twisted Bilayer Graphene
  
  • Rai Gautam
  • Crippa Lorenzo
  • Călugăru Dumitru
  • Hu Haoyu
  • Paoletti Francesca
  • De’ Medici Luca
  • Georges Antoine
  • Bernevig B. Andrei
  • Valentí Roser
  • Sangiovanni Giorgio
  • Wehling Tim
  Physical Review X, American Physical Society, 2024, 14 (3), pp.031045. The interplay of dynamical correlations and electronic ordering is pivotal in shaping phase diagrams of correlated quantum materials. In magic-angle twisted bilayer graphene, transport, thermodynamic, and spectroscopic experiments pinpoint a competition between distinct low-energy states with and without electronic order, as well as between localized and delocalized charge carriers. In this study, we utilize dynamical mean-field theory on the topological heavy fermion model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We contrast moment formation, Kondo screening, and ordering on a temperature basis and explain the nature of emergent correlated states based on three central phenomena: (i) the formation of local spin and valley isospin moments around 100 K, (ii) the ordering of the local isospin moments around 10 K preempting Kondo screening, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low-energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a “bad metal” above the ordering temperature, where scattering off the disordered local moments suppresses electronic coherence, and a “good metal” in the ordered states with coherence of quasiparticles facilitated by isospin order. This finding reveals coherence from order as the microscopic mechanism behind the Pomeranchuk effect observed experimentally by Rozen [] and by Saito []. Upon doping, there is a periodic charge reshuffling between localized and delocalized electronic orbitals leading to cascades of doping-induced Lifshitz transitions, local spectral weight redistributions, and periodic variations of the electronic compressibility ranging from nearly incompressible to negative. Our findings highlight the essential role of charge transfer, hybridization, and ordering in shaping the electronic excitations and thermodynamic properties in twisted bilayer graphene and provide a unified understanding of the most puzzling aspects of scanning tunneling spectroscopy, transport, and compressibility experiments. Published by the American Physical Society 2024 (10.1103/PhysRevX.14.031045)
  DOI : 10.1103/PhysRevX.14.031045