Poster Presentation
Coherent control of symmetry protected excitations of magnetic clusters
Lorenzo Amato (PSI)
In this poster, I will present some ideas on how to characterize and coherently control special excitedstates living on symmetric clusters of rare-earth ions (embedded in a non-magnetic crystal host).
These states carry non-trivial cluster symmetry representations, hence can be proven to be well
protected from the environment. The preparation of these states could be useful in the future forquantum sensing and quantum technologies.

Polarization superlattices for controlling the electronic structure in graphene/h-BN
multilayers
Marta Brzezinska (EPFL)
Moiré superlattice systems based on twisted heterostructures of two-dimensional materials represent
an emerging design principle for realizing novel physical phenomena. Motivated by the recent
discovery of polarization superlattices in twisted multilayers of hexagonal boron nitride (h-BN), we
investigate the possibility of using these systems for controlling the properties of multilayer grapheneby means of the polarization proximity effect. In particular, by using first-principles and tight-binding
model calculations, we address the possibility of creating topological flat bands in the multilayer
graphene subsystem.

From hyperbolic drum towards hyperbolic topological insulators
Tomáš Bzdušek (PSI)
Hyperbolic lattices correspond to regular tessellations of the sheet of constant negative curvature,
known as the hyperbolic plane. Over the past few years, the study of classical and quantum dynamics
on hyperbolic lattices has witnessed a fascinating progress: On the experimental side, hyperbolic
heptagon-kagome lattice has been realized with coupled waveguide resonators [1], while on thetheory side, characterization of eigenstates using a hyperbolic extension of band theory has beenachieved [2]. Curiously, the momentum space associated with two-dimensional hyperbolic lattices isinevitably four- (or higher-)dimensional. In this talk, I will discuss our simulation of a negatively curved“hyperbolic drum” in an electric-circuit network [3], and show how fingerprints of the emergent
curvature enter both static and dynamical experiments on the set-up. Subsequently, after shedding
light on the key theoretical concepts, I will demonstrate how the hyperbolic band theory can beapplied to characterize topological insulators [4] and flat bands [5] on hyperbolic lattices.
[1] A. J. Kollár, M. Fitzpatrick, and A. A. Houck, Hyperbolic lattices in circuit quantum electrodynamics, Nature 571, 45—50(2019).
[2] J. Maciejko and S. Rayan, Hyperbolic band theory, Sci. Adv. 7, abe9170 (2021); J. Maciejko and S. Rayan, Automorphic
Bloch theorem for hyperbolic lattices, Proc. Natl. Acad. Sci. U.S.A. 119, e2116869119 (2022).
[3] P. M. Lenggenhager, A. Stegmaier, L. K. Upreti, T. Hofmann, T. Helbig, A. Vollhardt, M. Greiter, C. H. Lee, S. Imhof, H.
Brand, T. Kießling, I. Boettcher, T. Neupert, T. Thomale, and T. Bzdušek, Simulating hyperbolic space on a circuit board, Nat.
Commun. 13, 4373 (2022).
[4] D. M. Urwyler, P. M. Lenggenhager, I. Boettcher, R. Thomale, T. Neupert, and T. Bzdušek, Hyperbolic topological band
insulators, arXiv:2203.07292 (2022).
[5] T. Bzdušek and J. Maciejko, Flat bands and band touching from real-space topology in hyperbolic lattices, arXiv:
2205.11571 (2022).

Mixed state quantum random walk and the entanglement phase transition
Christian Carisch (ETHZ)

Inhomogeneous nonequilibrium DMFT with kernel memory truncation
Jiyu Chen (University of Fribourg)
We introduce the formalism of the nonequilibrium cluster DMFT for inhomogeneous systems. With
this scheme, we study a realistic multi-layer material 1$T$-TaS$_2$ and benchmark the reliability of a
recently proposed memory truncation method of the Kadanoff-Baym equations (KBE).

GW+EDMFT investigation of Pr1-xSrxNiO2 under pressure
Viktor Christiansson (University of Fribourg)
Motivated by the recent experimental observation of a large pressure effect on Tc in Pr1-xSrxNiO2, westudy the electronic properties of this compound as a function of pressure for x=0 and 0.2 doping
using self-consistent GW+EDMFT. Our results demonstrate a non-trivial interplay between physicalpressure and chemical doping in this material, and small but systematic changes with increasingpressure. The pressure dependent changes in the electronic structure of the undoped compoundsuggest an increasingly single-band-like behavior in the high-pressure regime, while a qualitatively
different behavior is found in the doped system. We also point out that fluctuations in the orbital
occupations and spin states are not consistent with a single-band picture, and that at least a two-bandmodel is necessary to reproduce the full result. This multi-orbital nature manifests itself most clearly inthe doped compound.

From chiral squeezing to nonlinear topology in optomechanics
Javier del Pino (ETHZ)
Synthetic gauge fields can be harnessed to engineer unconventional transport and localise bosonicstates by breaking time-reversal symmetry and mimicking electrons' behaviour in electromagnetic
fields. Optomechanical systems address optically mechanical modes via modulated radiationpressure, enabling spring constant tuning and strong mechanical interactions that imprint
nonreciprocal Peierls phases – akin to the Aharonov-Bohm effect for electrons [1].
Here we demonstrate how optomechanical cavities unlock synthetic magnetic fields for many-mode
oscillator networks, offering a route toward acoustic chirality and non-Hermitian topological states [2].
These ideas are tested within state-of-the-art nanobeam photonic crystals that support localised
optical resonances coupled to multiple coherent mechanical overtones. Phase control of intensitymodulated driving in a single cavity then unlocks a versatile, optically-tunable nanomechanicalnetwork featuring arbitrary-range interactions that span a synthetic dimension (Fig. 1a). Our study
analyses the emergence of chiral phononic propagation in single mechanical loops with nonreciprocal
Aharonov-Bohm (AB) link phases. In addition, we demonstrate the interplay of AB interference andgain by inducing parametric interactions through radiation pressure, through control of non-Hermitianphysics, including exceptional points and non-reciprocal phononic amplification (Fig. 1b). We finally
overview our efforts [3] in exploiting optomechanical nonlinearities, natural in our systems, to control
bifurcations into self-oscillating phases via nonreciprocal control phases.

Our findings open new prospects for bosonic transport and non-Hermitian topological phases formechanical modes at the nanoscale. They ultimately illustrate the potential of optomechanicalsystems toward quantum chiral acoustic networks and strongly nonlinear systems with broken
Hermiticity and time-reversal symmetry.
[1] Mathew J. P.* , del Pino, J.* , Verhagen E. (2020). Synthetic gauge fields for phonon transport in a nano-optomechanicalsystem (*equal contribution) - [Nature Nanotechnology volume 15, pages 198 - 202][2] del Pino, J.*, Slim, Jesse J.* and Verhagen, E. (2021). Non-Hermitian chiral phononics through optomechanically-induced
squeezing. (*equal contribution) [Nature volume 606, pages 82–87 (2022)][3] Košata, Jan*, del Pino, J.*, Heugel, Toni L. and Zilberberg, Oded (2022). HarmonicBalance.jl: a
Julia suite for interacting nonlinear dynamics. (*equal contribution) [SciPost Phys. Codebases 6 (2022)]

Magnetic Flux Response of Non-Hermitian Topological Phases
Michael Denner (University of Zurich)
We derive the response of non-Hermitian topological phases with intrinsic point gap topology tolocalized magnetic flux insertions. In two spatial dimensions, we identify the necessary and sufficientconditions for a flux skin effect that localizes an extensive number of in-gap modes at a flux core. In
three dimensions, we furthermore establish the existence of: a flux spectral jump, where flux tube
insertion fills up the entire point gap only at a single parallel crystal momentum; a higher-order flux
skin effect, which occurs at the ends of flux tubes in presence of pseudo-inversion symmetry; and aflux Majorana mode that represents a spectrally isolated mid-gap state in the complex energy plane.
We uniquely associate each non-Hermitian symmetry class with intrinsic point gap topology with oneof these cases or a trivial flux response, and discuss possible experimental realizations.

Linear Flavor-Wave Analysis of SU(4)-Symmetric Tetramer Model
Nobuo Furukawa (Aoyama Gakuin University)
Spin-dimer materials such as TlCuCl3 are prototypical examples for studying interesting phases ofmatter and quantum phase transitions, e.g., non-magnetic state to a canted Néel phase undermagnetic fields. In the area of cold atomic and optical systems, which have high controllability as forthe geometry of lattice, the strength of interaction between atoms, etc. Recently, a great deal of effort
is being made to realize higher-symmetric quantum many-body systems to find novel physicalproperties. For example, alkaline-earth(-like) fermionic atoms are closed-shell in the ground state, andthe nuclear spin I provides 2I + 1 states, e.g., I = 5/2 for 173Yb. In principle, with these atomic species
we can prepare ideal SU(N ≤ 2I + 1)-symmetric systems because the interatomic interaction does notdepend on the nuclear spin to a great approximation.
In this work, we consider a natural extension of the physics of spin-dimer materials under strong
magnetic field to SU(4)-symmetric systems. We study the quantum magnetism of the SU(4) Mott
insulator in an optical tetramerized superlattice, in which atoms with four nuclear-spin components(named “u”, “d”, “c”, and “s”) strongly interact with each other, by using the SU(4) Heisenberg model.
More specifically, we investigate quantum phases induced by the external field by which the
population of {u, d} tends to increase while {c, s} components are disfavored. Using an extended
linear flavor-wave theory (LFWT) based on four-site plaquettes, we observe quantum phasetransitions from fully antisymmetrized tetramer-singlet state (SU(4)-singlet state) to resonatingvalence-bond (RVB) state on each tetramer, connected by an intermediate mixed phase between
these two phases. We also report excitation spectra of these phases using LFWT calculations.
This work has been done by in collaboration with Yuki Miyazaki(1), Giacomo Marmorini(1,2) andDaisuke Yamamoto(2). (1) Aoyama Gakuin University (2) Nihon University.

Strong pinning transition with arbitrary defect potentials
Filippo Gaggioli (ETHZ)
Dissipation-free current transport in type II superconductors requires vortices, the topological defectsof the superfluid, to be pinned by defects in the underlying material. The pinning capacity of a defectis quantified by the Labusch parameter κ ∼ fp/ξC, measuring the pinning force fp relative to theelasticity C of the vortex lattice, with ξ denoting the coherence length (or vortex core size) of thesuperconductor. The critical value κ = 1 separates weak from strong pinning, with a strong defect at
κ > 1 able to pin a vortex on its own. The onset of strong pinning at κ = 1+ exhibits a striking
correspondence to the physics of a critical point terminating a thermodynamic first-order transition,with the Labusch parameter κ replacing the scaled temperature T/Tc. So far, this transition has beenstudied for isotropic defect potentials, resulting in a critical exponent μ = 2 for the onset of the strong
pinning force density Fpin ∼ np fp(ξ/a0)2(κ−1)μ, with np denoting the density of defects and a0 theintervortex distance. This result is owed to the special rotational symmetry of the defect producing afinite trapping area Strap ∼ ξ^2 at the strong-pinning onset. The behavior changes dramatically whenstudying anisotropic defects with no special symmetries: the strong pinning then originates out of
isolated points with length scales growing as ξ(κ − 1)1/2, resulting in a different force exponent μ =5/2. Our analysis of the strong pinning onset for arbitrary defect potentials makes heavy use of the
Hessian matrix describing the curvature of the pinning potential and leads us to interestinggeometrical structures: the strong pinning onset is characterized by the appearance of unstable areasof elliptical shape whose boundaries mark the locations where vortices jump. The associatedlocations of asymptotic vortex positions define areas of bistable vortex states; these bistable regions
assume the shape of a crescent with boundaries that correspond to the spinodal lines in a first-ordertransition and cusps corresponding to critical end- points. Both, unstable and bistable areas grow with
κ > 1 and join up into larger domains; for a uniaxially anisotropic defect, they merge into the ringshaped areas previously encountered for isotropic defects. Finally, we extend the analysis to the caseof a random two-dimensional pinning landscape (or short, pinscape) and discuss the topologicalproperties of unstable and bistable regions as expressed through the Euler characteristic.

Creep effects on the Campbell response in type II superconductors
Vadim Geshkenbein (ETHZ)
Applying the strong pinning formalism to the mixed state of a type-II superconductor, we study theeffect of thermal fluctuations (or creep) on the penetration of an ac magnetic field as quantified by theso-called Campbell length λC. Within strong pinning theory, vortices get pinned by individual defects,
with the jumps in the pinning energy and force between bistable pinned and free states quantifying
the pinning process. We find that the evolution of the Campbell length λC(t) as a function of time t is
the result of two competing effects, the change in the force jumps and a change in the trapping areaof vortices; the latter describes the area around the defect where a nearby vortex gets and remains
trapped. Contrary to naive expectation, we find that during the decay of the critical state in a zero-fieldcooled (ZFC) experiment, the Campbell length is usually nonmonotonic, first decreasing with time t
and then increasing for long waiting times. Field cooled (FC) experiments exhibit hysteretic effects in
λC; relaxation then turns out to be predominantly monotonic, but its magnitude and direction dependon the specific phase of the cooling-heating cycle. Furthermore, when approaching equilibrium, theCampbell length relaxes to a finite value, different from the persistent current, which vanishes at longwaiting times t, e.g., above the irreversibility line. Finally, measuring the Campbell length for different
states, zero-field cooled, field cooled, and relaxed, as a function of different waiting times t andtemperatures T , allows to spectroscopyse the pinning potential of the defects.

Floquet ground state in periodically-driven many-body quantum systems
Tatsuhiko Ikeda (ISSP)

Emergent U(1) symmetry in non-particle-conserving 1D models
Zakaria Jouini (EPFL)
Motivated by recent investigations of Rydberg atom chains, we explore the properties of Luttinger
liquid phases that emerge in 1D models with a non-conserved number of particles. We consider achain of spinless fermion where particles are created three by three on adjacent sites. Despite being
irrelevant in the RG sense, the perturbation still affects the observables due to its breaking of U(1)symmetry. In the framework of the flow equation approach, we present an intuitive picture that
accounts for additional terms in the correlations which cannot be captured by standard bosonization
mapping. The obtained results provide insight into the properties of the floating phase in the Z3 symmetric model of hard-core bosons that was introduced as a dual description of the commensurate
melting of period-3 density waves.

Quantum Optics with Giant Artificial Atoms
Johannes Knörzer (ETHZ)
Superconducting circuits coupled to acoustic waveguides have extended the range of phenomena that can beexperimentally studied using tools from quantum optics. In particular giant artificial atoms permit the investigationof systems in which the electric dipole approximation breaks down and pronounced non-Markovian effects
become important. While previous studies of giant atoms focused on the realm of the rotating-wave
approximation, in [1] we go beyond this and perform a numerically exact analysis of giant atoms strongly coupled
to their environment, in regimes where counterrotating terms cannot be neglected. To achieve this, we use a
Lanczos transformation to cast the field Hamiltonian into the form of a one-dimensional chain and employ matrixproduct state simulations. This approach yields access to a wide range of system-bath observables and topreviously unexplored parameter regimes, and is of independent interest for the simulation of strongly coupledsystems.
[1] D. Noachtar, J. Knörzer, and R. H. Jonsson, Non-perturbative treatment of giant atoms using chain transformations, Phys.
Rev. A 106, 013702 (2022).

Marginal quenches and drives in Tomonaga-Luttinger liquids
Bastien Lapierre (University of Zurich)
In this talk I will discuss the physics of Tomonaga-Luttinger liquids (TLLs) thrown out-of-equilibrium by
marginal deformations, i.e., interaction modulations. I will show that the quench dynamics startingfrom generic initial states exhibit rich physics, with periodic exact zeros in the Loschmidt echo time
evolution. I will then discuss the Floquet dynamics of TLLs and show how the su(1,1) structure of theperiodic drive can be used to derive the stroboscopic time evolution of various physical observables,
which is dictated by an exactly derived stability diagram. Finally using the tools developed previously,
I will show that the Renyi divergence between two TLLs can be non-perturbatively obtained as aquench in Euclidean space-time.

Tunable tachyon mass in PT-broken massive Thirring
Benjamin Liegeois (ETHZ)
We investigate the possibility of phase transition and influence of effective gauge fields in a nonHermitian PT-symmetric generalization of the two-dimensional massive Thirring model with particular focus on the PT-broken sector of the model. For this purpose, the functional renormalization-

group is employed. The method predicts a new phase displaying a relevant imaginary mass, corresponding to monstronic excitations displaying exponentially growing amplitudes for timelike intervals and tachyonic (Lieb-Robison-bound breaking, oscillatory) excitations for spacelike intervals.
Furthermore, since the phase manifests itself as an unconventional attractive spinodial fixed point,
which is expected not to be reached in finite real-life systems, we predict that the effective renormalized mass reached can be tuned through the microscopic parameters of the model. While our results
further predict a dramatic change in the renormalization group flows in the presence of an effective
gauge field, the robustness of the new phase is nevertheless shown to hold contrary to the celebrated
BKT transition occurring in the PT-unbroken sector. The effective gauge-field is further predicted toprovide an additional way to tune the renormalized mass, and therefore the growth/oscillation rate of
the corresponding excitations.

Ab initio calculations of electrical magnetochiral anisotropy with Wannierinterpolation
Xiaoxiong Liu (University of Zurich)sign with handedness. An example is electrical magnetochiral anisotropy (eMChA), a linear change inthe resistivity of chiral conductors in a magnetic field. A strong eMChA was recently reported in p
doped tellurium [1,2]. Motivated by these works, we have developed an ab initio methodology forevaluating the eMChA response of chiral crystals. We use the semiclassical Berry-Boltzmann
formalism within the constant relaxation-time approximation to express the Ohmic current at order E2 x
B in terms of the band energies, Berry curvature, and intrinsic orbital moment of the Bloch states,
which we then evaluate numerically using Wannier interpolation. We report preliminary results fortellurium as a function of temperature and doping concentration, and compare with experiment.
[1] G. Rikken and N. Avarvari, Phys. Rev. B 99, 245153 (2019).
[2] F. Calavalle et al. Nat. Mater. 21, 526 (2022).

A homodyne detection scheme for the measurement of quantum geometry andtopological invariants
Markus Lysne (University of Fribourg)
We apply a quantum optical measurement scheme - homodyne detection - to the study of geometricaland topological quantities of condensed matter systems. By a hybrid set-up involving a 2D material
placed within a cavity coupled to input and output ports, we perform correlation measurements on theelectric field generated by the cavity light-matter interaction. By different polarizations of theintracavity field, we are able to measure all components of the quantum geometric tensor,$Q_{\mu\nu}$, for constant energy contours in the Brillouin zone. Applying recent results involving themetric-curvature correspondence, we use the measured quantum metric in order to describe thetopological phase of the material at hand. As an interesting application, we consider a minimal modelfor twisted bilayer graphene at the magic angle, and discuss the feasibility of extracting the Euler
number.

Anomalous magneto-transport at low-density in a quasi 1d conductor
Giacomo Morpurgo (University of Geneva)
Among the various 2D magnetic semiconductors that have been recently discovered and investigated, CrSBr has shown unexpected transport properties under field-effect doping. In particular,
the absence of Hall effect and a large anisotropy of the conductivity indicate quasi- 1D behavior andpossibly strong disorder [1]. Here, we study the field- and temperature- dependent longitudinal andtransverse conductivities in a 2D anisotropic tight-binding model (t⊥ ≤ t∥), where the dissipation is
described by a local (i.e., momentum-independent) self- energy Σ. Using the Kubo formalism, we
calculate numerically the conductivity tensor up to second order in the field. This model allows one todescribe the crossover from a regime of coherent anisotropic transport when Σ < t⊥ to a quasi-1D
regime with incoherent transport along one direction when t⊥ < Σ < t∥. Furthermore, it allows us to
explore a low-density regime that has not been much studied so far, where the chemical potential lies
below the band and, when kB T < Σ, the metallicity stems from spectral-weight broadening due to theself-energy rather than thermal excitation of carriers.
[1] W. Fan et al., Adv. Mater. 2022, 2109759 (2022)

Ultrafast control of spin-orbital separation probed with time-resolved RIXS
Aaron Müller (ETHZ – PHYS)
Quasi-one-dimensional systems exhibit many-body effects elusive in higher dimensions. A primeexample is spin-orbital separation, which has been measured by resonant inelastic X-ray scattering(RIXS) in Sr2CuO3. Here, we theoretically analyze the time-resolved RIXS spectrum of Sr2CuO3 under
the action of a time-dependent electric field. We show that the external field can reversibly modify theparameters in the effective t−J model used to describe spinon and orbiton dynamics in the material.
For strong driving amplitudes, we find that the spectrum changes qualitatively as a result of reversing
the relative spinon to orbiton velocity. The analysis shows that in general, the spin-orbital dynamics inMott insulators in combination with time-resolved RIXS should provide a suitable platform to explore
the reversible control of many-body physics in the solid with strong laser fields.

Effect of eletrostatic interaction on domain structures of thin film hexagonal
manganites
Aaron Müller (ETHZ – MATL)

Signature of two-triplet bound states condensation in the INS spectrum of SrCu2(BO3)2 at high magnetic field
Mithilesh Nayak (EPFL)
Inelastic Neutron Scattering experiments have been conducted on SrCu2 (BO3)2 in high external
magnetic field up to 26 T. The INS energy transfer shows a rich set of excitations whose energies andspectral intensities have been measured as a function of magnetic field. The dynamics of theunderlying Shastry-Sutherland model with Dzyaloshinskii–Moriya interactions has been simulated with
Time-dependent Variational Principle and the numerical dynamical structure factor agrees
qualitatively with the experiments. The ground state develops a uniform magnetization that increases
linearly with the magnetic field in the regime 20-26 T. Our numerics indicate that this is due to thecondensation of S=2, Sz=2 bound state of triplets [1, 2] and not to the condensation of single triplets.
These bound states eventually crystallize to give the known structure of the magnetization plateau at
1/8 beyond 26 T [3]. Our analysis considers two possible scenarios, (a) single triplet condensation, (b)bound state condensation, and it compares the Shastry-Sutherland model’s excitations on therespective states with the numerical estimates. A component-wise analysis shows that the series ofenergies at which excitations occur are only consistently explained by the condensation of boundstates.
[1] T. Momoi and K. Totsuka, Magnetization plateaus of the Shastry-Sutherland model for SrCu2(BO3)2 : Spin-density wave,
supersolid, and bound states, Phys. Rev B, 62, 15067(2000)[2] H. Nojiri, H. Kageyama, Y. Ueda and M. Motokawa, ESR Study on the Excited State Energy Spectrum of SrCu2(BO3)2 –A
Central Role of Multiple-Triplet Bound States, J. Phys. Soc. Jpn. 72, pp. 3243-3253 (2003)[3] P. Corboz and F. Mila, Crystals of Bound States in the Magnetization Plateaus of the Shastry Sutherland Model, Phys. Rev.
Lett. 112, 147203 (2014)

Identifying the Huse-Fisher universality class of the three-state chiral Potts model
Samuel Nyckees (EPFL)
Using the corner-transfer matrix renormalization group approach, we revisit the three-state chiralPotts model on the square lattice, a model proposed in the eighties to describe commensurateincommensurate transitions at surfaces, and with direct relevance to recent experiments on chains of
Rydberg atoms. This model was suggested by Huse and Fisher to have a chiral transition in thevicinity of the Potts point, a possibility that turned out to be very difficult to definitely establish or refutenumerically. Our results confirm that the transition changes character at a Lifshitz point that separates
a line of Pokrovsky-Talapov transition far enough from the Potts point from a line of direct continuous
order-disorder transition close to it. Thanks to the accuracy of the numerical results, we have beenable to base the analysis entirely on effective exponents to deal with thecrossovers that have hampered previous numerical investigations. The emerging picture is that of a
new universality class with exponents that do not change between the Potts point and the Lifshitz
point, and that are consistent with those of a self-dual version of the model, namely correlation
lengths exponents nx = 2/3 in the direction of the asymmetry and ny = 1 perpendicular to it, an
incommensurability exponent b = 2/3, a specific heat exponent that keeps the value a = 1/3 of thethree-state Potts model, and a dynamical exponent z = 3/2. These results are in excellent agreementwith experimental results obtained on reconstructed surfaces in the nineties, and shed light on recent
Kibble-Zurek experiments on the period-3 phase of chains of Rydberg atoms.

Weak ergodicity breaking in Hubbard, t-J-U and related models
Kiryl Pakrouski (ETHZ)
Many-body scars are states that do not obey the eigenstate thermalization hypothesis and thus leadto weak ergodicity breaking. Time evolution starting from a mix of such states exhibits "revivals" - thesystem returns to the exact initial state after equal periods of time. It has been shown[arXiv:2007.00845] that three families of highly symmetric states are many-body scars for any spin1/2 fermionic Hamiltonian of the form H0+OT, where T is a generator of an appropriate Lie group. Oneof these families consists of the well-known eta-pairing states while all such states have advantages
for storing and processing quantum information. We show that a number of well-known couplingterms, such as the Hubbard and the Heisenberg interactions, and the Hamiltonians containing them(including topological ones), are of the required form and support these states as scars without finetuning. To facilitate possible experimental implementations, we discuss the conditions for the lowenergy subspace of these models to be comprised solely of scars. We expand this framework to thenon-Hermitian open systems and demonstrate that for them the scar subspace continues to undergocoherent time evolution and exhibit "revivals".
Based on: arXiv:2106.10300 and arXiv:2007.00845.

Quasiparticle conductance oscillations and snake states in domain walls of a chiral pwave superconductor
Tudor Pahomi (ETHZ)
In a nonuniform perpendicular magnetic field, classical charged particles exhibit open, meandering,snake-like trajectories, for instance at the boundary between two regions with opposite field
directions. We present in this poster the analogous quantum snake states expected to appear ininhomogeneous chiral p-wave superconductors. At the domain wall separating two superconducting
phases with opposite chiralities, we prove such localized in-gap modes originate from the overlapping
Andreev bound states belonging to the respective domains and sharing the propagation direction.
Consequently, their properties depend on certain features of the effective Josephson junction whose
control might be experimentally feasible, for example, the inter-domain tunneling strength or the
relative global superconducting phase. The periodic spatial structure of the snake states is found toplay a particularly important role in the transport of Bogoliubov quasiparticles. We explain theoscillations of the quasiparticle (energy) transmission probability are owed to a commensurability
condition of the snake-state period and thus represent a hallmark of the chiral domain wall.

Electron slush and Mott criticality in TMD moirés
Louk Rademaker (University of Geneva)
Though the recent revolution in moiré materials started with the discovery of correlated insulatorsand superconductivity in twisted bilayer graphene, I will argue that much strong electron correlations
are present in bilayers of transition-metal dichalcogenides (TMDs). I will introduce the origins of flatbands in TMD moirés, including surprising ARPES results on twisted bilayer WSe2. Moving on toheterobilayers, I will discuss theoretical results on the exotic phases one might expect in the regimeof Wigner-Mott phases, including the possibility of an amorphous conducting electron “slush”.
Finally, the TMD bilayers realize the unique opportunity to study continuous Mott metal-insulatortransitions. I will compare results between TMDs, organic compounds and dilute 2DEGs to set thestage for a theoretical pursuit of Mott criticality.

Non-thermal superconducting order in multi-orbital systems
Sujay Ray (University of Fribourg)
Non-thermal order in out of equilibrium systems has recently become an active field. There have been
predictions of eta pairing in the photo-doped single band Hubbard model and enhanced triplet pairingin a two orbital Hubbard model. We study the photo-doped two orbital Hubbard model using
nonequilibrium dynamical mean field simulation to search for non-thermal orders. Our calculations
show that, at half filling, there is an emerging eta pairing in case of complete population inversion in
the lower and upper Hubbard bands. The population inversion corresponds to the creation of triplonsand singlons in the half filled two orbital Hubbard model. The triplon-singlon subspace can be studied
by a generalized Schrieffer-Wolff transformation which projects out the doublon states. Our analytical
study indicates that, unlike in the single band model, there are potential instabilities to magnetic,
orbital and charge ordering along with eta pairing, leading to a rich phase diagram in the triplonsinglon subspace of the multi orbital systems.

Quantum phases in small spin J1-J2 chains
Aman Sharma (EPFL)As Mermin-Wagner theorem indicates there is no order possible for a one-dimensional chain with
Heisenberg interactions due to very high quantum fluctuations. In such cases, Quantum spin liquid isobtained, which as the name suggests has no long range order, on the other hand this phase isinteresting because there exists a long range entanglement, and the system is described by, what
was first suggested by Phil Anderson, Valence Bond state (VBS). In a VBS spin-1/2s which arepresent on each site form singlet entangled pairs with the spin-1/2s present on the other sites. It is tobe remembered that entanglement obeys what is known as monogamy, that is, once a spin-1/2 ispaired with one of the spin-1/2s on another site it cannot be paired with any other spin-1/2. Also, thispicture works even for the higher spins because each spin can be thought to be composed of spin1/2s, this is true because the spin at the metal ions fundamentally arise from the orbital picture of thefilling of electrons, with each unpaired spin in the d or f orbital of a transition metal ion, or rare earth
metal ion respectively providing an overall spin to the ion. However, VBS picture only fails in the waythat the VBS ground states are non-orthogonal, the problem is solved though using projector
methods. The rotational symmetry (SU(2)) possessed by the QSL state, due to the lack of ordering,can be broken if we activate next nearest neighbor coupling, or that is also a way of realising the spinladder, so that in the system we have nearest neighbor AFM couplings with J1 strength and next
nearest neighbor AFM couplings with J2 strength. Adding J2 coupling causes frustration in the system,
however, if J2 is large enough it causes a Quantum phase transition into an ordered phase. We havefound in our simulations performed by DMRG techniques if we keep increasing J2 the system
traverses through several phases, namely, starting from Heisenberg critical phase, it goes into a
dimerised phase, then again into the critical phase with no long range order but at the same time no
fixed q vector of the classical helical phase of the J1-J2 model. J1-J2 model studied for smaller spins isparticularly interesting because they show higher quantum behavior which cannot be expected bystudying the classical model. Spin-1/2 is fully quantum mechanical, but spins like 3/2 or 5/2 still havereminiscents of the quantum behavior .In my poster presentation, I would like to discuss about thesedifferent quantum phases in J1-J2 model for various small spin chains.

Strain modulation effects on the topological properties of a chiral p-wave
superconductor
Yuto Shibata (ETHZ)
Motivated by recent developments in sample fabrication techniques, we study strain modulation
effects on electronic structures of a two-dimensional single-band chiral p-wave superconductor within
the BCS mean-field scheme. We employ a lattice model and solve the Bogolyubov-de Gennes
equations numerically. Implementing strain modulations through spatially varying hopping matrix
elements, we observe the appearance of spontaneous supercurrents due to the resulting spatial
modulation of order parameter amplitudes. Moreover, we show from analyses of spectral functions
and local Chern markers that sufficiently strong strain modulation induces the formation of
topologically distinct domains within the system and, thus, chiral edge modes at their boundaries [2].
[1] M. D. Bachmann et al., Science 366, 221 (2019).
[2] Y. Shibata and M. Sigrist arXiv:2205.13918.

Quantum quench in non-Hermitian systems
Karin Sim (ETHZ)
Non-Hermiticity leads to non-unitary evolution and possibly complex energy eigenvalues. We employ
a consistent framework to address these issues by considering the non-trivial dynamics of the Hilbert
space metric. Our study of a linearly-quenched non-Hermitian system reveals defect freezing in the
adiabatic limit, and that no Kibble-Zurek scaling regime exists in our model. In particular, we compare
this to the approach of simply normalising quantities by the norm of the time-evolved state. We findthat the normalisation approach fails to capture the essential physics of defect freezing and thecorrect symmetry of physical observables.

Kondo physics in structured mesoscopic impurities
Lidia Stocker (ETHZ)
The characterisation of strongly-correlated effects in quantum impurity systems (QIS) is particularly
challenging due to the infinite size of the environment and the inability of local correlators to capture
the build-up of long-ranged
entanglement in the system. Here, we devise an entanglement-based observable – the purity of the
impurity – as a witness for the formation of strong correlations. In combination with the Numerical
Renormalisation Group (NRG) and Variational Matrix Product States (VMPS) method for QIS, weshowcase the utility of our scheme when exactly solving (i) all-electronic dots–cavity and (ii) graphene
quantum dots devices. In (i), we identify how the conducting dot-lead Kondo singlet is quenched by an
insulating intra-impurity singlet formation. In (iii), we identify SU(2), SU(4) dot-leads Kondo effects,
and valley-valley intradot singlet formation. With the generalisation of the NRG-VMPS method to outof-equilibrium scenarios, we advance an extensive framework for the study of many-body effects in
QIS.

Isospin phase transitions and superconductivity in Bernal bilayer and rhombohedral
trilayer graphene
Andras Szabo (ETHZ)
Of the zoo of graphene-based layered systems, my presentation touches on Bernal bilayer andrhombohedral trilayer graphene, where the low-energy continuum theory is described by four-fold(valley and spin) degenerate gapless electronic bands, exhibiting quadratic and cubic band touching,respectively. Recent experiments shed light on a cascade of degeneracy lifting phase transitions inboth systems, when subjected to chemical doping and external electric displacement field. I propose a
simple explanation for these isospin phase transitions, based on the interplay between theexperimentally tunable chemical doping and electric field, and interaction induced competing phases.
Besides the emergent metallic phases, these systems also give rise to multiple distinct
superconducting orders. I propose that the prominent pairing arising proximal to a spin-polarized halfmetal (with valley degeneracy) is spin-triplet f-wave in nature, which I support via a leading-orderrenormalization group calculation. Moreover, I argue that the valley- and spin-polarized quarter-metal
phase in graphene-like systems is conducive for pair-density-wave ordering, which is yet to beobserved. The spatial and momentum space properties of this exotic pairing will also be highlighted.

Modelling magnetic order in the multiferroic hexagonal manganites
Tara Tosic (ETHZ)
Multiferroic hexagonal manganites (R-MnO3) are prototype systems for studying highly frustrated
magnetism, the suppressed order giving rise to exotic phases such as spin liquids or extended criticalregimes in this family of materials. However, their exact magnetic ground state varies with no obvious
trend from compound to compound. Despite conclusive experimental measurements of their magnetic
orders, the theory leading to a distinct magnetic symmetry is to date unclear. Using a combination ofsymmetry analysis, first-principles density functional theory and phenomenological modelling, we
explore a zone-boudary breathing mode (K1) and show it sits at the junction between magnetic andstructural changes. We propose a phase diagram to describe the magnetic structure as a function of
the anisotropy and exchange interactions. This in turn allows us to explain the dependence of themagnetic ground state on the identity of the rare-earth ion and on the K1 mode. By controlling
structural changes within zone-boundary modes through external stimuli, modes such as K1 could act
as knobs that effectively tune the magnetic ground state.

Hidden magnetic octupoles and second-order magnetoelectric effectAndrea Urru (ETHZ)
We discuss how magnetic octupoles provide a basis for interpreting the second-order magnetoelectriceffect, in which a bilinear electric field induces a linear magnetization, or the product of magnetic andelectric fields induces a polarization. Magnetic octupoles are the next order terms, beyond the wellestablished magnetoelectric multipoles responsible for the linear magnetoelectric effect, in themultipole expansion of a non-uniform magnetization density, m(r) . They are represented by the rank3 tensor
Z

Mijk =µi (r)rj rk d3 r,
which we begin by decomposing into its irreducible spherical components. We then use Cr2O3 as acase study and show that, in addition to the linear magnetoelectric effect caused by its
magnetoelectric multipoles, it has a hidden second-order local magnetic response caused by the antiferroic ordering of its magnetic octupoles.

Symmetry breaking and spectral structure of the interacting Hatano-Nelson model
Songbo Zhang (University of Zurich)
We study the Hatano-Nelson model, i.e., a one-dimensional non-Hermitian chain of spinless fermions
with nearest-neighbor nonreciprocal hopping, in the presence of repulsive nearest-neighborinteractions. At half-filling, we find two transitions, as the interaction strength increases. The firsttransition is marked by an exceptional point between the first and the second excited state in a finitesize system and is a first-order symmetry-breaking transition into a charge density wave regime.
Persistent currents characteristic of the Hatano-Nelson model abruptly vanish at the transition. The
second transition happens at a critical interaction strength that scales with the system size and canthus only be observed in finite-size systems. It is characterized by a collapse of all energy eigenvalues onto the real axis. We further show that in a strong interaction regime, but away from halffilling, the many-body spectrum shows point gaps with nontrivial winding numbers, akin to the
topological properties of the single-particle spectrum of the Hatano-Nelson chain. Our results
contribute to an understanding of fermionic many-body systems with non-Hermitian Hamiltonians.

Electron Optics in an Inverted-Band pn Junction
Yuhao Zhao (ETHZ)
Electron optics offers a promising condensed matter platform for manipulating and guiding electron
beams with high efficiency and robustness. This field commonly relies on the spatial confinement of
the electrons into 1D channels. Recently, electron optics using 2D Dirac materials were proposed,such as graphene-based transistors. In this work, we demonstrate the potential for electron optics
applications using a band-inverted system resulting from particle-hole hybridization. We develop thetheory of the interface scattering in the inverted-band $pn$ junction using a scattering matrix
approach and provide a comprehensive protocol for constructing electron optic components, such as
focusing lens, bifurcating lens, polarizers, and mirrors. The feasibility of the experimental realization
under disorder and finite temperate is confirmed using numeric simulations.