# Colloquium

## Many-body delocalisation as symmetry breaking

12 November in 11:30

In the second part of the talk I will discuss minimal models for quantum chaos and many-body localisation. The models are Floquet quantum circuits for lattice spin systems, in which time evolution is generated by unitary gates that couple neighbouring sites. In particular, I will examine the circumstances in which a version of the so-called diagonal approximation (originally developed for the semiclassical limit in low-dimensional chaotic systems) can be applied to these systems. Within this framework I will show that the many-body delocalisation transition can be seen as a form of symmetry breaking transition, having many of the features generally associated with conventional phase transitions in classical statistical mechanical models.

Joint work with Sam Garratt: Phys. Rev. X 11, 021051 (2021) and Phys. Rev. Lett. 127, 026802 (2021)

## Limit shape phase transitions. A merger of Arctic circles

29 October, the day after tomorrow in 15:30

[1] V. L. Pokrovsky and A. L. Talapov, Phys. Rev. Lett. 42, 65 (1979). "Ground State, Spectrum, and Phase Diagram of Two-Dimensional Incommensurate Crystals."

[2] D. J. Gross and E. Witten, Phys. Rev. D, 21 (2): 446, (1980). "Possible third-order phase transition in the large-n lattice gauge theory"; S. R. Wadia, Phys. Lett. B 93, 403 (1980). "$N=\infty$ phase transition in a class of exactly soluble model lattice gauge theories."

[3] M. R. Douglas and V. A. Kazakov. Phys. Lett. B, 319 (1-3): 219–230, 1993. "Large n phase transition in continuum QCD2."

## The Riemann Hypothesis and Quantum Physics

1 October in 11:30

## Tetraquarks in the spotlight of recent LHCb data

17 September in 11:30

## Topology protection–unprotection transition: Example from multiterminal superconducting nanostructures

21 May in 11:30

__Yuli V. Nazarov (TU Delft)__

## The hydrodynamics of many-body integrable systems

19 March in 11:30

## Probabilistic Liouville Theory

19 February in 11:30

I will review a probabilistic construction of LCFT developed together with David, Rhodes and Vargas and recent proofs concerning the integrability of LCFT.

References

Francois David, Antti Kupiainen, Remi Rhodes, Vincent Vargas, Liouville quantum gravity on the Riemann sphere, Commun. Math. Phys. 342 (3), 869-907 (2016)

Antti Kupiainen, Remi Rhodes, Vincent Vargas, The DOZZ formula from the path integral, Journal of High Energy Physics May 2018, 2018:94

Antti Kupiainen, Remi Rhodes, Vincent Vargas, Integrability of Liouville Theory: Proof of the DOZZ Formula, Annals of Mathematics 191, 81-166, (2020)

Colin Guillarmou, Antti Kupiainen, Remi Rhodes, Vincent Vargas, Conformal bootstrap in Liouville Theory, arXiv:2005.11530

## First principle models of human memory

15 January in 11:30

## Photon-assisted tunneling at the atomic scale: Probing resonant Andreev reflections from Yu-Shiba-Rusinov states

4 December 2020 in 16:00

References

[1] M. Ruby, F. Pientka, Y. Peng, F. von Oppen, B.W. Heinrich, and K.J. Franke, "Tunneling Processes into Localized Subgap States in Superconductors", Phys. Rev. Lett. 115, 087001 (2015).

[2] O. Peters, N. Bogdanoff, S. Acero González, L. Melischek, J. Rika Simon, Gaël Reecht, C.B. Winkelmann, Felix von Oppen & K.J. Franke, "Resonant Andreev reflections probed by photon-assisted tunnelling at the atomic scale", Nat. Phys. (2020). https://doi.org/10.1038/s41567-020-0972-z; arXiv:2001.09534

## Mòire Samples: The twisted bilayer graphene scenario

20 November 2020 in 16:00

## Higher-order topological insulators and superconductors

15 May 2020 in 11:30

## Towards an analytic description of periodic anomalous waves in nature via the focusing NLS model (joint work with P. G. Grinevich)

7 May 2020 in 11:30

## Charge and entropy transport in strontium titanate

17 April 2020 in 11:30

The temperature dependence of the resistivity of this dilute metal at low-temperature implies that electron-electron scattering can generate a T-square resistivity even in absence of Umklapp scattering with a single Fermi pocket. The magnitude of resistivity at a low temperature would imply a mean-free-path too short to be physically plausible. Combined with the temperature dependence of the Seebeck coefficient, this implies that non-degenerate electrons become heavier with warming. We will see that these observations cannot be explained by available polaronic theories. There is a whole family of dilute metals emerging from doped quantum paraelectrics with similar properties.

## Effective function theory on Riemann surfaces and applications.

21 February 2020 in 11:30

## Electric dipole moment searches using storage rings

24 January 2020 in 11:30

## Non-ergodic delocalized states for efficient population transfer within a narrow band of the energy landscape

20 December 2019 in 15:00

## Ordered fluctuations: about vestigial order in quantum materials

20 December 2019 in 11:30

We demonstrate that this concept naturally explains the nematic state in iron-based superconductors and nematic superconductivity in doped topological insulators. In addition we propose a natural mechanism for charge 4e superconductivity with half flux quanta. We present a formalism that provides a framework to understand the complexity of quantum materials based on symmetry, largely without resorting to microscopic models.

## Physics at the Edge of a QHE setting

25 October 2019 in 11:30

## Dynamical Glass - en route from KAM and FPUT to MBL

6 September 2019 in 11:30

## Two-fluid phenomena in one-dimensional quantum liquids

21 June 2019 in 11:30

## Minimal excitations states: From time resolved single particle fermionic states for Electron Quantum Optics to Digital communication and music.

24 May 2019 in 11:30

At the root of the minimal excitation property is a specific single side band modulation of the electron wave by the Lorentzian voltage pulse. This property can be applied to classical electromagnetic or acoustic waves for applications in digital communication [8] or in music sound synthesis.

[1] G. B. Lesovik, JETP Letters, 49 (9), 592-594 (1989).

[2] L.S. Levitov, G.B. Lesovik, Charge-transport statistics in quantum conductors, JETP Lett., 55 (9), 555-559 (1992).

[3] A. Ivanov, H.W. Lee, L.S. Levitov, Coherent states of alternating current, Phys. Rev. B 56(11), 6839-6850 (1997); cond-mat/9501040

[4] L.S. Levitov, H. Lee, G.B. Lesovik, Electron Counting Statistics and Coherent States of Electric Current, J. Math. Phys., 37(10), 4845-4866 (1996); cond-mat/9607137.

[5] J. Keeling, I. Klich, and L. S. Levitov, Minimal Excitation States of Electrons in One-Dimensional Wires, Phys. Rev. Lett. 97, 116403 (2006).

[6] Minimal-excitation states for electron quantum optics using levitons, J. Dubois, T. Jullien, F. Portier, P. Roche, A. Cavanna, Y. Jin, W. Wegscheider, P. Roulleau & D. C. Glattli, Nature, 502, 659–663 (2013).

[7] Quantum tomography of an electron, T. Jullien, P. Roulleau, B. Roche, A. Cavanna, Y. Jin & D. C. Glattli, Nature, 514, 603–607 (2014).

[8] Power Spectrum Density of Single Side Band CPM Using Lorenztian Frequency Pulses, Haïfa Farès, D. Christian Glattli, Yves Louet, Jacques Palicot, Preden Roulleau, and Christophe Moy, IEEE Wireless Communications Letters, 6 (6), 786-789, (2017).

## Hydrodynamic approach to electronic transport

26 April 2019 in 11:30

Видео (в связи с ошибкой видео записано не до конца)

## On reconstructing nonlinearly encrypted signals corrupted by noise.

12 April 2019 in 11:30

## Correlation-induced localization

5 April 2019 in 11:30

We suggest a new class of random matrix models (Toeplitz RMT) with translation-invariant hopping integrals and identify the character of eigenfunction and eigenvalue statistics in them. We formulate the principles of level statistics if the type of eigenfunction statistics is known both in the coordinate and in the momentum basis and demonstrate that for the Toeplitz RMT the ergodic delocalization in the coordinate space may coexist with the Poisson level statistics.

Finally, we suggest a matrix-inversion trick that allows to identify uniquely the type of eigenfunction statistics and prove the absence of delocalized states in the bulk of spectrum of long-range Hamiltonians with deterministic (fully correlated) hopping.

## Recent theoretical developments in the integer quantum Hall effects

22 February 2019 in 11:30

Notwithstanding this status, the last ten years have seen considerable progress in understanding basic properties of scaling near localization-delocalization transitions that have implications also for the quantum Hall transition. These concern, e.g., the important topic of corrections to scaling, the wavefunction statistics and higher-order multifractality. A brief review of these developments will be offered in the first part of the talk.

The second part of the talk will be devoted to the spin quantum Hall effect, which is a variant of the integer quantum Hall effect (class A) taking place in the Altland-Zirnbauer class C. For this transition several critical exponents are known analytically and can serve as reference points. Therefore, this transition provides an ideal testbed for the qualitative predictions made by analytical theories. Analytical predictions will be confronted with most recent numerical results.

## Noisy quantum measurements: just a nuisance or fundamental physics?

7 December 2018 in 11:30

## Wonders of viscous electronics

19 October 2018 in 11:30

## Quantum electrodynamics of heavy ions and atoms

5 October 2018 in 11:30

## Superconductivity that breaks time-reversal symmetry and its experimental manifestations

28 September 2018 in 11:30

References:

- [1] X. Gong, M. Kargarian, A. Stern, D. Yue, H. Zhou, X. Jin, V. M. Galitski, V. M. Yakovenko, and J. Xia, Science Advances 3, e1602579 (2017), arXiv:1609.08538
- [2] P. M. R. Brydon, D. S. L. Abergel, D. F. Agterberg, and V. M. Yakovenko, arXiv:1802.02280

## Quantum Many-Body Physics of Qubits

22 June 2018 in 11:30

## Eukaryotic cell polarity and protein sorting

27 April 2018 in 11:30

## Chiral magnetic crystals

23 March 2018 in 11:30

References:

- [1] M. Janoschek et al. Phys. Rev. B 87, 134407 (2013).
- [2] A. Bauer, M. Garst and C. Pfleiderer, Phys. Rev. Lett. 110, 177207 (2013).
- [3] M. Kugler et al. Phys. Rev. Lett. 115, 097203 (2015)
- [4] T. Weber et al. arXiv:1708.02098
- [5] C. Schütte and M. Garst, Phys. Rev. B 90, 094423 (2014).
- [6] T. Schwarze, J. Waizner, M. Garst, A. Bauer, I. Stasinopoulos, H. Berger, C. Pfleiderer, and D. Grundler, Nat. Mater. 14, 478 (2015).
- [7] M. Garst J. Waizner, and D. Grundler, J. Phys. D: Appl. Phys. 50, 293002 (2017)
- [8] P. Schoenherr et al. Nat. Phys. in press, arXiv:1704.06288

Video