• Séminaire nano-électronique quantique
• Personne à contacter : Alexandre Assouline ()
• Lieu : Salle Rémy Lemaire K223, Institut Néel

Résumé : The massive number of spectra required for high-resolution quasiparticle interference of low-dimensional quantum materials motivates the development of faster point spectroscopies. While the advent of parallel spectroscopy and compressive sensing enhancements has provided welcome speed boosts, these come at a cost. The application of a sinusoidal voltage on the nonlinearities in the current-voltage characteristics of a tunneling junction generates a frequency comb of higher order current-harmonics. While their parallel measurement enables faster tunneling spectroscopy, it unfortunately averages longest where the currents are largest, leading to poor signal-to-noise ratios for smaller signals associated with features close to the Fermi level. After examining the key concepts of QPI, parallel spectroscopy, and compressive sensing, we introduce a multifrequency excitation mode that increases the averaging time for small currents, enabling fast and high-resolution spectroscopy. Additionally, the AC excitation of our method can be used to dramatically increase the dynamical current range by exactly and deliberately suppressing the large amplitude, low order harmonics that would otherwise saturate the preamplifier stage.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Léonie Canet ()
• Lieu : Salle Roger Maynard G-421

Résumé : My PhD thesis is concerned with Functional Renormalization Group (FRG) approach to turbulence. In this talk I will cover the results that we obtained for the Burgers equation, which was introduced as a simplified model of turbulence (it has same nonlinear term as the Navier-Stokes equation). It maps exactly to the Kardar-Parisi-Zhang (KPZ) equation (which describes completely different physics – randomly growing surfaces) and is a very famous model of non-equilibrium statistical physics. Within the FRG approach, we can obtain a “coarse-grained” effective description in order to access statistical properties of the model, such as scaling regimes, distinguished by a dynamical exponent z, which tells how the correlation time t is related to momentum k, t~k^(-z). In fact, different scaling regimes correspond to different fixed points of the FRG equation. The motivation of our study was that a new scaling regime characterized by a z=1 dynamical critical exponent has been reported in several numerical simulations of the one-dimensional KPZ and noisy Burgers equations \[1-2\]. This scaling was found to emerge in the tensionless limit for the interface (KPZ) and in the inviscid limit for the fluid (Burgers). Based on FRG, the origin of this scaling has been elucidated \[3\]. It was shown to be controlled by a yet unpredicted fixed point of the one-dimensional Burgers-KPZ equation, termed inviscid Burgers fixed point. The associated universal properties, including the scaling function, were calculated. In this talk, I will show how this analysis can be generalized to the multi-dimensional Burgers-KPZ equation \[4\]. I will show that the inviscid Burgers fixed point exists in all dimensions d, and that it controls the large momentum behavior of the correlation functions in the inviscid limit. It turns out that it yields in all d the same super-universal value z=1 for the dynamical exponent.

References

• \[1\] C. Cartes, E. Tirapegui, R. Pandit, M. Brachet, The Galerkin-truncated Burgers equation: crossover from inviscid-thermalized to Kardar-Parisi-Zhang scaling, Phil. Trans. Roy. Soc. A 380, 20210090 (2022)
• \[2\] E. Rodriguez-Fernandez, S. N. Santalla, M. Castro, R. Cuerno, Anomalous ballistic scaling in the tensionless or inviscid Kardar-Parisi-Zhang equation, Phys. Rev. E 106, 024802 (2022)
• \[3\] C. Fontaine, F. Vercesi, M. Brachet, L. Canet, Unpredicted scaling of the one-dimensional Kardar-Parisi-Zhang equation, Phys. Rev. Lett. 131, 247101 (2023)
• \[4\] L. Gosteva, M. Tarpin, N. Wschebor, L. Canet, Inviscid fixed point of the multidimensional Burgers–Kardar-Parisi-Zhang equation, Phys. Rev. E 110, 054118 (2024)

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Résumé : A chaotic light source is characterized by the fact that many independent emitters radiate photons with a random optical phase. This is similar compared to a tunnel junction where many independent channels are able to emit photons due to a coupling to an electromagnetic environment. However, in a recent experiment it has been observed that a tunnel junction can deviate from the expectation of chaotic light and is able to emit strongly correlated, superbunched photons. Motivated by this, we study the correlation of the radiation and show that the superbunching originates from the emission of multiple photons which is possible due to the quantization of charge.

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Résumé : With only a few exactly solvable models in two dimensions, computer simulations play a vital role in addressing the physics of high-Tc​ superconductors and frustrated magnets. Yet, modeling such strongly correlated systems is, in general, NP-hard. This challenge has been driving the development of cutting-edge numerical methods. In this talk, I will introduce the rapidly emerging tensor network approach, based on projected entangled-pair states (PEPS), which possesses a genuine two-dimensional structure. I will discuss the application of PEPS to both the ground states and excited states of frustrated magnets, with the latter providing valuable feedback between effective models and inelastic neutron scattering experiments, here exemplified in recent investigation of K2Co(SeO3)2, a frustrated triangular lattice antiferromagnet.

Liens :

• Séminaire LPMMC
• Personne à contacter : Anna Minguzzi ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire LPMMC
• Personne à contacter : Sergey Skipetrov ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire maths-physique
• Personne à contacter : Loïc Herviou ()
• Lieu : Salle Roger Maynard G-421 (CNRS, polygone scientifique)

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire QuantAlps
• Personne à contacter : Michele Filippone ()
• Lieu : PARAMS

Liens :