Publications

2022

• Two-dimensional Hubbard model at finite temperature: Weak, strong, and long correlation regimes
  
  • Iv Fedor Šimkovic
  • Rossi Riccardo
  • Ferrero Michel
  Physical Review Research, American Physical Society, 2022, 4 (4), pp.043201. We investigate the momentum-resolved spin and charge susceptibilities, as well as the chemical potential and double occupancy in the two-dimensional Hubbard model as functions of doping, temperature and interaction strength. Through these quantities, we identify a weak-coupling regime, a strong-coupling regime with short-range correlations and an intermediate-coupling regime with long magnetic correlation lengths. In the spin channel, we observe an additional crossover from commensurate to incommensurate correlations. In contrast, we find charge correlations to be only short ranged for all studied temperatures, which suggests that the spin and charge responses are decoupled. These findings were obtained by a novel connected determinant diagrammatic Monte Carlo algorithm for the computation of double expansions, which we introduce in this paper. This permits us to obtain numerically exact results at unprecedentedly low temperatures $T\geq 0.067$ for interactions up to $U\leq 8$, while working on arbitrarily large lattices. Our method also allows us to gain physical insights from investigating the analytic structure of perturbative series. We connect to previous work by studying smaller lattice geometries and report substantial finite-size effects. (10.1103/PhysRevResearch.4.043201)
  DOI : 10.1103/PhysRevResearch.4.043201
• Light-induced translation symmetry breaking via nonlinear phononics
  
  • Gómez Pueyo Adrián
  • Subedi Alaska
  Physical Review B, American Physical Society, 2022, 106, pp.214305. Light has a wavelength that is usually longer than the size of the unit cell of crystals. Hence, even intense light pulses are not expected to break the translation symmetry of materials. However, certain materials, including KTaO$_3$, exhibit peaks in their Raman spectra corresponding to their Brillouin zone boundary phonons due to second-order Raman processes, which provide a mechanism to drive these phonons using intense midinfrared lasers. We investigated the possibility of breaking the translation symmetry of KTaO$_3$ by driving its highest-frequency transverse optic mode $Q_{\textrm{HX}}$ at the $X$ $(0,\frac{1}{2},0)$ point. Our first principles calculations show that the energy curve of the transverse acoustic mode $Q_{\textrm{LZ}}$ at $X$ softens and develops a double-well shape as the value of the $Q_{\textrm{HX}}$ coordinate is increased, while that of the other transverse acoustic component $Q_{\textrm{LX}}$ hardens when the value of the $Q_{\textrm{HX}}$ coordinate is similarly varied. We performed similar total energy calculations as a function of the $Q_{\textrm{HX}}$ coordinate and electric field to extract the nonlinear coupling between them. These were then used to construct the coupled equations of motion for the three phonon coordinates in the presence of an external pump term on the $Q_{\textrm{HX}}$ mode, which we numerically solved for a range of pump frequencies and amplitudes. We find that 465 MV/cm is the smallest pump amplitude that leads to an oscillation of the $Q_{\textrm{LZ}}$ mode at a displaced position, hence, breaking the translation symmetry of the material. Such highly intense light pulses cannot be generate by currently available laser sources, and they have the possibility to damage the material. Nevertheless, our work shows that light can in principle be used to break the translation symmetry of a material via nonlinear phononics. (10.1103/PhysRevB.106.214305)
  DOI : 10.1103/PhysRevB.106.214305
• Tuning the Fermi liquid crossover in Sr2RuO4 with uniaxial stress
  
  • Chronister A.
  • Zingl M.
  • Pustogow A.
  • Luo Yongkang
  • Sokolov D.
  • Jerzembeck F.
  • Kikugawa N.
  • Hicks C.
  • Mravlje J.
  • Bauer E.
  • Thompson J.
  • Mackenzie A.
  • Georges A.
  • Brown S.
  Npj Quantum Materials, Nature publishing, 2022, 7 (113), pp.1-6. We perform nuclear magnetic resonance (NMR) measurements of the oxygen-17 Knight shifts for Sr 2 RuO 4 , while subjected to uniaxial stress applied along [100] direction. The resulting strain is associated with a strong variation of the temperature and magnetic field dependence of the inferred magnetic response. A quasiparticle description based on density-functional theory calculations, supplemented by many-body renormalizations, is found to reproduce our experimental results, and highlights the key role of a van-Hove singularity. The Fermi-liquid coherence scale is shown to be tunable by strain, and driven to low values as the associated Lifshitz transition is approached. (10.1038/s41535-022-00519-6)
  DOI : 10.1038/s41535-022-00519-6
• Recovering information in an asymptotically flat spacetime in quantum gravity
  
  • Chowdhury Chandramouli
  • Papadoulaki Olga
  Classical and Quantum Gravity, IOP Publishing, 2022, 39 (24), pp.245012. Abstract As an extension of Chowdhury et al (2021 SciPost Phys. 10 106) and Laddha et al (2021 SciPost Phys. 10 041) we present a physical protocol that a set of observers can use to detect a pure state in the bulk when they are spread across a small cut near in flat spacetime. The protocol involves the modification of a bulk state using simple unitary operators and measurements of the energy of the state. The states that we study are constructed by acting with low energy operators on a vacuum state such that a perturbative analysis is valid. We restrict ourselves to 3 + 1 dimensional spacetimes and only consider massless excitations. From this analysis, the principle of holography of information becomes manifest in the case of asymptotically flat spacetime. (10.1088/1361-6382/aca192)
  DOI : 10.1088/1361-6382/aca192
• Possible structural quantum criticality tuned by rare-earth ion substitution in infinite-layer nickelates
  
  • Subedi Alaska
  , 2022. I show the infinite-layer rare-earth nickelates are near a structural quantum critical point by mapping the energetics of their structural instabilities using first priniciples calculations. I first confirm previous results that show a phonon instability in the $P4/mmm$ phase leading to the $I4/mcm$ structure for $R$NiO$_2$ with $R$ = Sm--Lu. I then study the non-spin-polarized phonon dispersions of the $I4/mcm$ phase and find that they exhibit rare-earth size dependent instabilities at the $X$ and $M$ points for materials with $R$ = Eu--Lu. Group-theoretical analysis was used to enumerate all the isotropy subroups due to these instablities, and the distorted structures corresponding to their order parameters were generated using the eigenvectors of the unstable phonons. These structures were then fully relaxed by minimizing both the atomic forces and lattice stresses. I was able to stabilize only five out of the twelve possible distortions. The $Pbcn$ isotropy subgroup with the $M_5^+(a,a)$ order parameter shows noticeable energy gain relative to other distortions for the compounds with late rare-earth ions. However, the order parameter of the lowest-energy phase switches first to $X_2^- (0,a) + M_5^+ (b,0)$ and then to $X_2^- (0,a)$ as the size of the rare-earth ion is progressively increased. Additionally, several distorted structures lie close in energy for the early members of this series. These features of the structural energetics persist even when antiferromagnetism is allowed. Such a competition between different order parameters that can be tuned by rare-earth ion substitution suggests that any structural transition that could arise from the phonon instabilities present in these materials can be suppressed to 0 K.
• Snowmass 2021 White Paper: Electron Ion Collider for High Energy Physics
  
  • Khalek R. Abdul
  • d'Alesio U.
  • Arratia M.
  • Bacchetta A.
  • Battaglieri M.
  • Begel M.
  • Boglione M.
  • Boughezal R.
  • Boussarie Renaud
  • Bozzi G.
  • Chekanov S. V.
  • Celiberto F. G.
  • Chirilli G.
  • Cridge T.
  • Cruz-Torres R.
  • Corliss R.
  • Cotton C.
  • Davoudiasl H.
  • Deshpande A.
  • Dong X.
  • Emmert A.
  • Fazio S.
  • Forte S.
  • Furletova Y.
  • Gal C.
  • Gwenlan C.
  • Guzey V.
  • Harland-Lang L. A.
  • Helenius I.
  • Hentschinski M.
  • Hobbs T. J.
  • Hoeche S.
  • Hou T.-J.
  • Ji Y.
  • Jing X.
  • Kelsey M.
  • Klasen M.
  • Kang Z.-B.
  • Kovchegov Y. V.
  • Kumar K. S.
  • Lappi T.
  • Lee K.
  • Lee Y.-J.
  • Li H.-T.
  • Li X.
  • Lin H.-W.
  • Liu H.
  • Liu Z. L.
  • Liuti S.
  • Lorce C.
  • Lunghi E.
  • Marcarelli R.
  • Magill S.
  • Makris Y.
  • Mantry S.
  • Melnitchouk W.
  • Mezrag C.
  • Moch S.
  • Moutarde H.
  • Mukherjee Swagato
  • Murgia F.
  • Nachman B.
  • Nadolsky P. M.
  • Nam J. D.
  • Neill D.
  • Neill E. T.
  • Nocera E.
  • Nycz M.
  • Olness F.
  • Petriello F.
  • Pitonyak D.
  • Platzer S.
  • Prestel S.
  • Prokudin A.
  • Qiu J.
  • Radici M.
  • Radhakrishnan S.
  • Sadofyev A.
  • Rojo J.
  • Ringer F.
  • Salazar F.
  • Sato N.
  • Schenke B.
  • Schlichting S.
  • Schweitzer P.
  • Sekula S. J.
  • Shao D. Y.
  • Sherrill N.
  • Sichtermann E.
  • Signori A.
  • Simsek K.
  • Simonelli A.
  • Sznajder P.
  • Tezgin K.
  • Thorne R. S.
  • Tricoli A.
  • Venugopalan R.
  • Vladimirov A.
  • Vicini A.
  • Vitev I.
  • Wiegand D.
  • Wong C.-P.
  • Xie K.
  • Zaccheddu M.
  • Zhao Y.
  • Zhang J.
  • Zheng X.
  • Zurita P.
  , 2022. Electron Ion Collider (EIC) is a particle accelerator facility planned for construction at Brookhaven National Laboratory on Long Island, New York by the United States Department of Energy. EIC will provide capabilities of colliding beams of polarized electrons with polarized beams of proton and light ions. EIC will be one of the largest and most sophisticated new accelerator facilities worldwide, and the only new large-scale accelerator facility planned for construction in the United States in the next few decades. The versatility, resolving power and intensity of EIC will present many new opportunities to address some of the crucial and fundamental open scientific questions in particle physics. This document provides an overview of the science case of EIC from the perspective of the high energy physics community.
• Causality constraints on nonlinear supersymmetry
  
  • Bonnefoy Quentin
  • Casagrande Gabriele
  • Dudas Emilian
  Journal of High Energy Physics, Springer, 2022, 2022 (11), pp.113. It is well-known that gravitino propagation in standard supergravities is free of any causality problems. However, two issues related to gravitino propagation were recently uncovered in specific supergravities with nonlinear supersymmetry. One of them concerns potential acausality/superluminality, whereas the second one arises from the vanishing of the sound speed at specific points during inflation. The former is famously related to positivity constraints on specific EFT operators, derived from dispersion relations on the energy-growing part of scattering amplitudes, and indeed we show that subluminality constraints for the gravitino are related via the equivalence theorem to positivity bounds in low-energy goldstino actions. However, the former are stronger, in the sense that they apply to functions of the scalar fields not only in the ground state, but for any field values such as those scanned by time-dependent solutions, unlike bounds derived from 2 → 2 scattering amplitudes in the vacuum. We also argue that nontrivial causality constraints arise only in the case where nonlinear supersymmetry in the matter sector is encoded into superfield constraints which do not seem to arise from microscopic two-derivative lagrangians, in particular for the orthogonal constraint used to build minimal models of inflation in supergravity. This allows us to propose simple alternatives which maintain the minimality of the spectra and are causal in all points of the theory parameter space. We also discuss minimal supergravity models of inflation along these lines. (10.1007/JHEP11(2022)113)
  DOI : 10.1007/JHEP11(2022)113
• Magnetic and optical properties of correlated rare-earth compounds from first principles
  
  • Boust James
  , 2022. This thesis focuses on magnetic and optical properties of various rare-earth-based materials from an ab initio perspective. Rare-earth (R) elements usually exhibit a partially filled 4f shell which is very localized around the nucleus; the resulting strong Coulomb interaction between 4f electrons gives rise to electronic correlation effects. These compounds hence fall into the category of so-called "strongly correlated" materials.In the first part of this thesis, we describe the quantum many-body problem which governs the physics of materials. Well established since the 1920s, it remains in general insoluble. However, a remarkable progress in the treatment of this problem has since been achieved by approximate approaches.The first chapter deals with one of them, developed in the 1960s: the exact Density Functional Theory (DFT) combined with the Local Density Approximation (LDA) for exchange and correlation effects. While DFT has now become the standard method for electronic structure calculation of real materials, it fails at treating strong electronic correlations such as those at play in the rare-earth compounds.In the second chapter, we describe the Dynamical Mean-Field Theory (DMFT) which was designed in the 1990s to study correlation effects in the Hubbard model (a simplified version of the full quantum many-body problem in a solid). DMFT is based on the mapping of the Hubbard model onto a quantum impurity problem of an atom exchanging electrons with a bath, which is easier to solve.The third chapter reviews the DFT+DMFT method which combines the applicability to real materials of DFT and the proper treatment of strong correlations by DMFT. It is now widely applied to correlated materials, in particular rare-earth compounds. The present thesis is based on this DFT+DMFT scheme in conjunction with a quasi-atomic approximation for the quantum impurity problem involved in DMFT. This so-called Hubbard-I (HI) approximation is relevant for the rare-earth 4f shell which is in the strong (Coulomb) coupling regime.In the second part of this thesis, we focus on magnetic properties of rare-earth transition metal intermetallics.The fourth chapter details our treatment of these systems, which is based on DFT+HI. We focus in particular on the crystal field effects which, combined with the strong 4f spin-orbit coupling, are at the origin of significant magnetic anisotropy in many of them.In the fifth chapter, we apply our DFT+HI-based approach to the RCo5 family. We notably show that a large value of a rank-6 crystal field parameter in RCo5 predicted by our calculations explains a puzzling reduction of the zero-temperature Nd moment in NdCo5.In the sixth chapter, we use the same technique to study partial substitution of Nd by Ce or Dy in Nd2Fe14B, the most widely used high-performance permanent magnet in the industry. We predict that optimizing the Ce (Dy) occupancy on one precise crystallographic site yields enhanced magnetic anisotropy.In the third part (seventh chapter), we focus on spectral and optical properties of rare-earth semiconductors. In order to address the systematic DFT underestimation of non-correlated gaps, we combine the DMFT approach to strongly-correlated 4f electrons with the modified Becke-Johnson exchange potential. We then apply this method to study optical properties of rare-earth sesquioxides R2O3 and fluorosulfides RSF. We notably explain the characteristic onset of the measured optical conductivity in R2O3 compounds and determine the nature of the optical gap in the light RSF series.In the fourth part (eighth chapter), to go beyond the Hubbard-I approximation, we explore a new approach to solve the DMFT quantum impurity problem in the strong coupling limit. This method is based on an equation of motion formalism preserving the analytical properties of the impurity Green's function. (10.70675/75364766zf48bz4812za4e7z57b7bceec2f2)
  DOI : 10.70675/75364766zf48bz4812za4e7z57b7bceec2f2
• Shafranov shift correction to the Furth-Yoshikawa scaling of tokamak adiabatic compression
  
  • Nicolas T
  • Lütjens H
  • Sauter O
  • Garbet X
  , 2022. In 1970, Furth and Yoshikawa[1] introduced the scalings of adiabatic plasma compression. Basically, if the shape of the external plasma boundary and the aspect ratio are preserved during the compression, then the density, kinetic pressure, beta and current scale respectively as n ∼ C$^3$ , p ∼ C$^5$ , B ∼ C$^2$ , β ∼ C, I$_t$ ∼ C, where C is the linear compression ratio, that is, the ratio between initial and final major radii. In this work, we show analytically, by expanding the Grad-Shafranov equation in terms of C, that the deviation to the Furth-Yoshikawa scaling is related to the Shafranov shift that arises when beta increases at large compression ratios. There is an obvious effect of the Shafranov shift because the axis is moved to a region with larger volume element, and an indirect effect, associated to the relation between flux and radius. The latter effect adds to the first, and is of the same order of magnitude. The result is that the pressure increases less than the C$^5$ scaling, which can have a significant impact on the fusion power achieved at maximum compression. The analytical results are backed up by equilibrium simulations carried out with the CHEASE code. Equilibria are obtained for different values of C, with conservation of the total fluxes, q profile, and entropy of the plasma. The agreement of the theory and simulations is very good when the boundary of the plasma is circular and the aspect ratio small. When the aspect ratio is close to 1, and/or the boundary not circular, the analytical result gives the gist of the reduction of compression. Finally, a pressure anisotropy ($p_⊥$ − p$_\|$)/p approximately equal to the increase in normalized Shafranov shift is predicted.
• Two-loop three-gluon vertex from the Curci-Ferrari model and its leading infrared behavior to all loop orders
  
  • Barrios Nahuel
  • Peláez Marcela
  • Reinosa Urko
  , 2022. We evaluate the three-gluon vertex with one vanishing external momentum within the Curci-Ferrari (CF) model at two-loop order and compare our results to Landau-gauge lattice simulations of the same vertex function for the SU(2) and SU(3) gauge groups in four dimensions. The parameters of the model being adjusted by fitting the two-point functions to lattice data, our evaluation of the three-gluon vertex arises as a pure prediction. We find that two-loop corrections systematically improve the agreement between the model and the lattice data as compared to earlier one-loop calculations, with a better agreement in the SU(3) case, as already seen in previous studies [1,2]. We also analyze the renormalization scheme dependence of our calculation. In all cases, this dependence diminishes when two-loop corrections are included, which is consistent with the perturbative CF paradigm. In addition, we study the low momentum regime of the three-gluon vertex in relation with the possibility of zero-crossing. Within the CF model, we show that the leading infrared behavior of the exact vertex is given by the same linear logarithm that arises at one-loop order, multiplied by the all orders cubic ghost dressing function at zero-momentum (we provide similar exact results for other vertex functions). We argue that this property remains true within the FP framework under the assumption that the resummed gluon propagator features a decoupling behavior. This shows that the zero-crossing is a property of the exact three-gluon vertex function. Within the CF model, we find however that the scale of the zero-crossing is considerably reduced when going from one- to two-loop order. This seems consistent with some recent lattice simulations [3]. Our analysis also allows us to support recent claims about the dominance of the tree-level tensor component [4].
• Holographic Lorentz and Carroll Frames
  
  • Campoleoni Andrea
  • Ciambelli Luca
  • Delfante Arnaud
  • Marteau Charles
  • Petropoulos P. Marios
  • Ruzziconi Romain
  , 2022. Relaxing the Bondi gauge, the solution space of three-dimensional gravity in the metric formulation has been shown to contain an additional free function that promotes the boundary metric to a Lorentz or Carroll frame, in asymptotically AdS or flat spacetimes. We pursue this analysis and show that the solution space also admits a finite symplectic structure, obtained taking advantage of the built-in ambiguities. The smoothness of the flat limit of the AdS symplectic structure selects a prescription in which the holographic anomaly appears in the boundary Lorentz symmetry, that rotates the frame. This anomaly turns out to be cohomologically equivalent to the standard holographic Weyl anomaly and survives in the flat limit, thus predicting the existence of quantum anomalies in conformal Carrollian field theories. We also revisit these results in the Chern--Simons formulation, where the prescription for the symplectic structure admitting a smooth flat limit follows from the variational principle, and we compute the charge algebra in the boundary conformal gauge.
• Kinematical higher-twist corrections in $\gamma^* \gamma \to M \bar M $
  
  • Lorcé Cédric
  • Pire Bernard
  • Song Qin-Tao
  Physical Review D, American Physical Society, 2022, 106 (9), pp.094030. We estimate kinematical higher-twist (up to twist 4) corrections to the $\gamma^*(q_1) \gamma(q_2) \to M(p_1) \bar{M}(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$, where $M$ is a scalar or pseudoscalar meson. This process is known to factorize at leading twist into a perturbatively calculable coefficient function and generalized distribution amplitudes (GDAs). The kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ turn out to be important in the cross section, considering the kinematics accessible at Belle and Belle II. We present numerical estimates for the cross section for $\gamma^* \gamma \to \pi^0 \pi^0$ with the $\pi \pi$ GDA extracted from Belle measurements and with the asymptotic $\pi \pi$ GDA as inputs to study the magnitude of the kinematical corrections. To see how the target mass corrections of order $m^2/Q^2$ affect the cross section, we also perform the calculation for $\gamma^* \gamma \to \eta \eta$ by using a model $\eta \eta$ GDA.In the range $s> 1$ GeV$^2$, the kinematical higher-twist corrections account for $\sim 15 \%$ of the total cross section, an effect which is not negligible. Since $\pi \pi$ GDAs are the best way to access the pion energy-momentum tensor (EMT), our study demonstrates that an accurate evaluation of EMT form factors requires the inclusion of kinematical higher-twist contributions.
• Consistent Kaluza-Klein Truncations and Two-Dimensional Gauged Supergravity
  
  • Bossard Guillaume
  • Ciceri Franz
  • Inverso Gianluca
  • Kleinschmidt Axel
  Physical Review Letters, American Physical Society, 2022, 129 (20), pp.201602. (10.1103/PhysRevLett.129.201602)
  DOI : 10.1103/PhysRevLett.129.201602
• Reverse wavefront engineering for remote generation of a near-infrared femtosecond Bessel beam filament in air
  
  • Zou Long
  • Sun Chen
  • Rao Yunfei
  • Sun Tianyang
  • Yu Jin
  • Couairon Arnaud
  Physical Review Research, American Physical Society, 2022, 4 (4), pp.043025. Precise control of the filamentation of an ultrashort and intense near-infrared laser pulse in air is crucial for many applications but remains challenging. By combining inverse design for shaping of a pulse at the output of a laser with simulation of the nonlinear propagation of the pulse in air, we numerically investigate the way to simultaneously control the length and position of a plasma filament at an arbitrary remote distance for the first time. An intermediate state, with a Bessel-Gauss beam profile, is introduced between the laser output and the filament. Through forward and backward propagations of the intermediate state, an end-to-end design of the initial laser pulse is achieved to match the desired filament characteristics. Our calculations show that a properly engineered torus pulse can project such a Bessel-Gauss beam at remote distance and generate a long plasma filament without requiring any feedback loop. We also proposed an experimental arrangement to project such an intermediate state and generate the corresponding filament remotely. The method can be further extended to other types of filaments or targets that may be reached from different intermediate states. (10.1103/PhysRevResearch.4.043025)
  DOI : 10.1103/PhysRevResearch.4.043025
• Mesoscopic fluctuating domains in strontium titanate
  
  • Fauqué Benoît
  • Bourges Philippe
  • Subedi Alaska
  • Behnia Kamran
  • Baptiste Benoît
  • Roessli Bertrand
  • Fennell Tom
  • Raymond Stéphane
  • Steffens Paul
  Physical Review B, American Physical Society, 2022, 106 (14), pp.L140301. Spatial correlations between atoms can generate a depletion in the energy dispersion of acoustic phonons. Two well-known examples are rotons in superfluid helium and the Kohn anomaly in metals. Here we report on the observation of a large softening of the transverse acoustic mode in quantum paraelectric SrTiO3 by means of inelastic neutron scattering. In contrast to other known cases, this softening occurs at a tiny wave vector implying spatial correlation extending over a distance as long as 40 lattice parameters. We attribute this to the formation of mesoscopic fluctuating domains due to the coupling between local strain and ferroelectric fluctuations. Thus, a hallmark of the ground state of insulating SrTiO3 is the emergence of hybridized optical-acoustic phonons. Mesoscopic fluctuating domains may play a role in quantum tunneling, which impedes the emergence of a finite macroscopic polarization. (10.1103/PhysRevB.106.L140301)
  DOI : 10.1103/PhysRevB.106.L140301
• Tunable stripe order and weak superconductivity in the Moiré Hubbard model
  
  • Wietek Alexander
  • Wang Jie
  • Zang Jiawei
  • Cano Jennifer
  • Georges Antoine
  • Millis Andrew
  Physical Review Research, American Physical Society, 2022, 4 (4), pp.043048. The moiré Hubbard model describes correlations in certain homobilayer twisted transition metal dichalcogenides. Using exact diagonalization and density matrix renormalization group methods, we find magnetic Mott insulating and metallic phases which, upon doping, exhibit intertwined charge and spin ordering and, in some regimes, pair binding of holes. The phases are highly tunable via an interlayer potential difference. Remarkably, the hole-binding energy is found to be highly tunable, revealing an experimentally accessible regime where holes become attractive. In this attractive regime, we study the superconducting correlation function and point out the possibility of weak superconductivity. (10.1103/PhysRevResearch.4.043048)
  DOI : 10.1103/PhysRevResearch.4.043048
• Far-from-equilibrium dynamics and entanglement in long-range quantum systems
  
  • Schneider Jan
  , 2022. Long-range interacting quantum systems have attracted considerable attention in recent years both from an experimental and theoretical perspective.The class of long-range systems considers the all-to-all interaction of any two constituents whereas the interaction strength falls off algebraically with distance R between them as R^{-alpha}.Latest experimental and technological progress made it possible to realise long-ranged systems on several quantum simulation platforms, including artificial ion crystals and dipolar quantum gases.In the theoretical framework of quantum many-body systems, long-range interactions break various fundamental concepts and theorems with far-reaching consequences.Among those are Lieb--Robinson bounds which guarantee the emergence of causality in short-ranged nonrelativistic lattice systems.In this thesis, we study the effects of long-range interactions on out-of-equilibrium and in-equilibrium features of lattice spin models by employing complementary analytical calculations and state-of-the-art tensor-network simulations while particularly focusing on the central and unique quantum feature of entanglement.First, in the long-range transverse-field Ising model, we show the emergence of a weak form of causality characterised by non-universal dynamical exponents. On the one hand, local magnetisation and correlations have an emergent sub-ballistic causal cone while the marked features in the interior of it propagate super-ballistic or ballistic, respectively. On the other hand, the emergent causal cone for all entanglement entropies is shown to be ballistic irrespective of the interaction range and the interior is without marked features.Second, we determine the equilibrium quantum phase diagram of the long-range XXZ model in terms of the anisotropic coupling and the long-range interaction exponent through studying a representation of the spectrum of the reduced density matrix following a half-chain bipartition, the so-called entanglement spectrum.We show it exhibits a remarkable self-similarity within the critical phase where the system is described by a Luttinger liquid while the self-similarity extends to the geometric entanglement and the Luttinger parameter.The transition away from a Luttinger liquid is consistent with the breakdown of self-similarity and a renormalisation group analysis. The synergetic combination of the two latter allows us to locate the corresponding phase transitions which we corroborate by numerical simulations.Furthermore, we show the entanglement Hamiltonian, the Hermitian operator whose spectrum is the entanglement spectrum, follows the form of the Bisognano--Wichmann theorem in large regions of the phases which include the short-range limit, while such a form can be excluded in the phase where genuinely long-ranged effects are relevant.Our results shed new light through the lens of quantum entanglement on the out-of-equilibrium as well as ground state features of long-range interacting spin chains and pave the way for further experimental and theoretical studies. (10.70675/19a4dfcdz202bz4e3aza76fz49b15523ccca)
  DOI : 10.70675/19a4dfcdz202bz4e3aza76fz49b15523ccca
• Perturbative renormalization of ϕ44 theory on the half space R+×R3 with flow equations
  
  • Borji Majdouline
  • Kopper Christoph
  Journal of Mathematical Physics, American Institute of Physics (AIP), 2022, 63 (9), pp.092304. In this paper, we give a rigorous proof of the renormalizability of the massive $\phi_4^4$ theory on a half-space, using the renormalization group flow equations. We find that five counter-terms are needed to make the theory finite, namely $\phi^2$, $\phi\partial_z\phi$, $\phi\partial_z^2\phi$, $\phi\Delta_x\phi$ and $\phi^4$ for $(z,x)\in\mathbb{R}^+\times\mathbb{R}^3$. The amputated correlation functions are distributions in position space. We consider a suitable class of test functions and prove inductive bounds for the correlation functions folded with these test functions. The bounds are uniform in the cutoff and thus directly lead to renormalizability. (10.1063/5.0097164)
  DOI : 10.1063/5.0097164
• Signature of Accidental Symmetry Breaking in Two-particle Correlations within the CGC
  
  • Kohara Anderson Kendi
  • Marquet Cyrille
  • Vila Víctor
  , 2022. (10.5506/APhysPolBSupp.16.5-A25)
  DOI : 10.5506/APhysPolBSupp.16.5-A25
• Magnetosphere‐Ionosphere‐Thermosphere Coupling study at Jupiter Based on Juno’s First 30 Orbits and Modeling Tools
  
  • Al Saati S.
  • Clément N.
  • Louis C.
  • Blanc M.
  • Wang Y.
  • André N.
  • Lamy L.
  • Bonfond B.
  • Collet B.
  • Allegrini F.
  • Bolton S.
  • Clark G.
  • Connerney J.
  • Gérard J.‐c.
  • Gladstone G.
  • Kotsiaros S.
  • Kurth W.
  • Mauk B.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2022. • We analyze the first 30 orbits of Juno to retrieve the properties of current systems and plasma flows associated with Jovian main auroras. • Southern hemisphere results are consistent with ionospheric plasma sub-corotation. • The two opposite patterns, sub-corotation and super-corotation, are observed in the northern hemisphere. (10.1029/2022JA030586)
  DOI : 10.1029/2022JA030586
• Spectral and magnetic properties of copper oxides : towards a theoretical description from first principles
  
  • Bacq Benjamin
  , 2022. The oxidation of copper does not only lead to an unusable saucepan, but also toone of the most fascinating family of materials: the cuprates. Their largesuperconducting critical temperature first attracted the scientific community’sattention, which led to the discovery of a rich and complex phase diagram.Although it is known that the two-dimensional CuO2 planes are responsible formost of the observed low-energy properties, a complete theoretical understandingis still missing. It is indeed immensely difficult to build an efficient theory of thecuprates, for they are strongly correlated systems: the kinetic energy and theCoulomb interaction are of the same order, thus preventing the use of perturbation theory or weak/strong-coupling approximations. In this thesis, weinvestigate the spectral and magnetic properties of two copper oxide systems: Ca2-xNaxCuO2Cl2 (Na-CCOC) and tetragonal CuO (t-CuO).We study the pseudogap phase of the hole-doped Na-CCOC, which has a simple crystal structure and is notsuperconducting in the low doping region (x<0.1). By a combination of densityfunctional theory (DFT), cellular dynamical mean-field theory (CDMFT) and angle-resolved photoemission spectroscopy (ARPES) we find that the antiferromagneticfluctuations play a predominant role in the opening of the pseudogap, in line with the literature. Performing self-consistent Born approximation calculations for an effective spin model, we interpret the “waterfall” feature of the spectral function as stemming from a cross-over between a spin-polaron close to the Fermi energy and a Hubbard band at higher energy, which is well captured by an atomic limit approximation.t-CuO has an even simpler crystal structure than Na-CCOC: it is composed of two-dimensional CuO planes with a tetragonal symmetry, stacked above a SrTiO3 (STO) substrate. An interesting particularity of t-CuO is the experimentally observed decoupling of each of its CuO planes into two weakly-coupled CuO2 sublattices. Performing CDMFT calculations both at zero and finite temperature, using different impurity solvers, we rationalize this behavior as being driven by the strong on-site Coulomb interaction. Indeed, the suppression of the nearest-neighbor self-energy leads to an effective renormalisation of the hopping parameters inducing the strong decoupling. Finally, this translates upon doping into an unusual superconducting order parameter symmetry of type dxy instead of the usual dx2-y2 found in cuprates.Recently, abnormal paramagnetic spin and pinned orbitals moments were observedexperimentally in t-CuO, a surprising finding in regard of all the previous results in the literature. By performing DFT calculations on large unit cells, we show that the insertion of oxygen vacancies at the t-CuO/STO can induce both types of moments. Indeed, a vacancy in the TiO2 leads to the emergence of a 2D electron gas in the CuO interface layer, which can explain the paramagnetic spin moment. The defect also induces large distortions in the CuO layer, leading to a pinning of the orbital moment in-plane, in excellent agreement with the experimental observations. (10.70675/38e90407zc771z4704zb07bzc5eafcb67003)
  DOI : 10.70675/38e90407zc771z4704zb07bzc5eafcb67003
• Yang-Mills and Quantum Chromodynamics correlation functions from the Curci-Ferrari model at two-loop accuracy
  
  • Barrios Nahuel
  , 2022. Quantum Chromodynamics (QCD) is a well established gauge theory which describes the dynamics of quarks and gluons. At the analytical level, physical observables can be computed only after the gauge is fixed. The textbook procedure to do so is the Faddeev-Popov (FP) method, which introduces, as a byproduct, auxiliary non-physical fields known as ghosts. Moreover, the QCD gauge coupling becomes small at very high momenta, making of perturbation theory (PT) a suitable calculation tool within that region of momenta. The combination of the FP theory and PT has turned out to be extremely useful and has been tested experimentally in many occasions. However, in the opposite momentum range, the FP method is no longer fully valid due to the presence of Gribov copies. Consequently, in order to access QCD in the infrared, new approaches are needed.This thesis is devoted to one of such approaches: the Curci-Ferrari (CF) model in Landau gauge. It consists in a simple gluon mass extension of the FP theory. Its main motivation comes from the lattice simulations for correlation functions in the Landau gauge, which clearly indicate that the gluon acquire a mass in the deep infrared. In addition to this striking phenomenon, the lattice simulations feature a gauge coupling compatible with a perturbative analysis for the whole range of momenta, at least in the pure gauge - or Yang-Mills (YM) - sector. Thus, with the purpose of testing the model, several two- and three-point correlation functions have been perturbatively evaluated at one-loop order. In general terms, the results show a very good agreement with the lattice data. More recently, the two-point functions from the pure YM theory were evaluated at two-loop order, improving the agreement to lattice data. The goal of this thesis is to extend the two-loop calculations to other correlation functions. This is a way of further testing the perturbative use of the model as well as to clarify its limits.In the case of pure YM theory, we evaluate the ghost-antighost-gluon vertex and the three-gluon vertex in a particular kinematical configuration in four dimensions, for the SU(2) and SU(3) gauge groups. Both quantities emerge as a pure prediction of the CF model, since its two free parameters are determined by fitting the two-point functions. Broadly speaking, the predicted vertices are able to improve the agreement with their numerical counterparts in comparison with the one-loop correction. We also investigate the renormalization scheme dependence of our results, which shows consistency with the perturbative approach. As for the three-gluon vertex, the calculation allows us in particular to gain insight on the zero-crossing as well as to test an exact prediction for the leading behavior in the infrared.We end this investigation by computing the ghost, gluon and quark two-point functions in QCD, with two degenerate quark flavors. We fit them to available lattice data. Our evaluation is consistent with such data in all the cases, except for the quark mass function for light quarks. The result is particularly relevant for the quark dressing function, since the CF model is unable to reproduce the lattice data at one-loop order. This discrepancy is corrected by the two-loop evaluation, which agrees with the data both at a qualitative and quantitative level. (10.70675/c68ebce5zb13bz40bcza342ze76fc9b6ed91)
  DOI : 10.70675/c68ebce5zb13bz40bcza342ze76fc9b6ed91
• Topological phases, light response and kagome lattice
  
  • Legendre Julian
  , 2022. We theoretically study topological lattice models relevant to current experimental solidstate and artificial systems. We develop an explicit analytical computation of the Chern number in the systems we study and we compare it with other computation methods of this topological invariant. We propose a protocol, based on the local response to a light input, to probe the topological properties of a Haldane boson model in a photonic system. On the kagome lattice, we investigate (i) a magnetic and topological phase transition for a two-channel model, in relation with recently discovered quantum materials, and (ii) a timereversal topological model with flux, Rashba spin-orbit coupling and Hubbard interactions, relevant for realization in cold-atom gases. (10.70675/eb9c2eb3z8013z4673zadf6zc5836e83738d)
  DOI : 10.70675/eb9c2eb3z8013z4673zadf6zc5836e83738d
• Infinite horizon for symetric strategy population game
  
  • Privat Meziane
  , 2022. To predict the behavior of a population game when time becomes very long, the process that characterizes the evolution of our game dynamics must be reversible. Known games satisfying this are 2 strategy games as well as potential games with an exponential protocol. We will try to extend the study of infinite horizons for what are called symetric strategy games.
• JRJC 2021- Journées de Rencontres Jeunes Chercheurs. Book of Proceedings
  
  • Chambery Pauline
  • de Bony de Lavergne Mathieu
  • Pracchia Matteo
  • Vernet Kinson
  • Chiche Simon
  • Strebler Thomas
  • Kanafani Mohamad
  • Daumas-Tschopp Sacha
  • de Dominicis Claudia
  • Dedu Vlad
  • Guo Linghua
  • Vaslin Louis
  • Boudon Alexis
  • Juste Vincent
  • Maleubre Sara
  • Nitoglia Elisa
  • Ding Yanchun
  • Migliorin Lucrezia Camilla
  • Bigot Alexandre
  • Tork Theraa
  • Jafarpour Mahbobeh
  • Hojeij Fatima
  • Jahan Johannes
  • Chiedde Nemer
  • de Martino Bianca
  • Jacquet Maxime
  • Portier Alexandre
  • Sayah Sihem
  • Laatu Lauri
  • Martel Lucas
  • Wang Pu-Kai
  • Aguerre Xalbat
  • Cecchini Vincent
  • Hoballah Malak
  • Mellet Lucile
  • Lebrin Victor
  • Kunze Pablo
  • Beloeuvre Arthur
  • Dinh Thi Hoa
  • Wang Yizheng
  • Kamalakannan Keerthana
  • Demane Yasmine
  • Maury Arnaud
  • He Yajun
  • Li Ang
  • Perrin Oceane
  • Sazak Halime
  • Tafoya Vargas Juan Salvador
  • Selem Luka
  • Sessini Mario
  • Borji Majdouline
  • Kriewald Jonathan
  • Bousserja Mohamed Amine
  • Palmiotto Marco
  • Pinsard Emanuelle
  • Zheng Zechuan
  • Li Zhen
  • Costa Philippe Da
  • Caroff Sami
  • Ruppin Florian
  • Uras Antonio
  • Guilbaud Maxime
  • Khandoga Mykola
  • Sacerdoti Sabrina
  • Quilain Benjamin
  • Darmé Luc
  • Gruyer Diego D.
  , 2022.