Dyson-Maleev representation of nonlinear sigma models

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Background: The increasingly common applications of machine-learning schemes to atomic-scale simulations have triggered efforts to better understand the mathematical properties of the mapping between the Cartesian coordinates of the atoms and the variety o ...

Theoretical and computational approaches to the study of materials and molecules have, over the last few decades, progressed at an exponential rate. Yet, the possibility of producing numerical predictions that are on par with experimental measurements is t ...

The corner transfer matrix renormalization group (CTMRG) algorithm has been extensively used to investigate both classical and quantum two-dimensional (2D) lattice models. The convergence of the algorithm can strongly vary from model to model depending on ...

This thesis presents a combined experimental and theoretical study of the classical and quantum magnetization dynamics in single magnetic adatoms and molecules, and on the classical and quantum coherent control thereof. First, a detailed description of t ...

In solid-state NMR, homonuclear dipolar couplings contribute greatly to the broadening of 1H spectral line shapes. Even at the fastest magic-angle spinning rates (MAS) available today [100-150kHz], the linewidths still extend over several hundred Hertz, li ...

Quantum Field Theories (QFTs) in Anti-de Sitter (AdS) spacetime are often strongly coupled when the radius of AdS is large, and few methods are available to study them. In this work, we develop a Hamiltonian truncation method to compute the energy spectrum ...

Bound-states of particles are an interesting problem in quantum mechanics dating back to 1931 Bethe's solution of spin-1/2 Heisenberg chain. These exotic composite states are realized in quantum magnets and are detectable in inelastic neutron scattering (I ...

We consider the phase diagram of the most general SU(4)-symmetric two-site Hamiltonian for a system of two fermions per site (i.e., self-conjugate 6 representation) on the square lattice. It is known that this model hosts magnetic phases breaking SU(4) sym ...

This thesis explores the application of semiclassical methods in the study of states with large quantum numbers for theories invariant under internal symmetries. In the first part of the thesis, we study zero-temperature superfluids. These provide a gener ...

In an idealized infinite crystal, the material properties are constrained by the symmetries of the unit cell. The point-group symmetry is broken by the sample shape of any finite crystal, but this is commonly unobservable in macroscopic metals. To sense th ...

Symmetry and topology are fundamental properties of nature. Mathematics provides us with a general framework to understand these concepts. On one side, symmetry describes the invariance properties of an object for specific transformations. On the other sid ...

The concept of quasi-symmetry-a perturbatively small deviation from exact symmetry-is introduced and leads to topological materials with strong resilience to perturbations. ...

We study the zero-temperature phase diagram of the spin-1/2 Heisenberg model with breathing anisotropy (i.e., with different coupling strength on the upward and downward triangles) on the kagome lattice. Our study relies on large scale tensor network simul ...

Collective tunneling is a ubiquitous phenomenon in finite-size spin clusters that shows up in systems as diverse as molecular magnets or spin clusters adsorbed at surfaces. The basic problem we explore is to understand how small flipping terms can cooperat ...

We develop a reduced model for hard-magnetic, thin, linear-elastic shells that can be actuated through an external magnetic field, with geometrically exact strain measures. Assuming a reduced kinematics based on the Kirchhoff-Love assumption, we derive a r ...

Parity-time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. So far, all of the experimentally identified topologically nontrivial Dirac semimetals (DSMs) possess both parity and time reversal symmetry. The realizatio ...

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 i ...

Conformal Field Theories (CFTs) are crucial for our understanding of Quantum Field Theory (QFT). Because of their powerful symmetry properties, they play the role of signposts in the space of QFTs. Any method that gives us information about their structure ...

Building on the mapping of large-S spin chains onto the O(3) nonlinear sigma model with coupling constant 2/S, and on general properties of that model (asymptotic freedom, implying that perturbation theory is valid at high energy, and Elitzur's conjecture ...

Motivated by the lack of direct evidence with inelastic neutron scattering of the well documented bound state of Heisenberg ferromagnets, we use the time-dependent thermal density matrix renormalization group algorithm to study the temperature dependence o ...

Dyson-Maleev representation of nonlinear sigma models

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Local invertibility and sensitivity of atomic structure-feature mappings

Physics-enhanced machine learning with symmetry-adapted and long-range representations

Critical line of the triangular Ising antiferromagnet in a field from a C3-symmetric corner transfer matrix algorithm

Quantum dynamics in individual surface spins

Development of strategies to improve 1H resolution in NMR of solids at 100 kHz magic-angle spinning

Hamiltonian truncation in Anti-de Sitter spacetime

Numerical investigation of bound states in quantum magnets

Quantum spin liquid phases in the bilinear-biquadratic two-SU(4)-fermion Hamiltonian on the square lattice

Large charge, semiclassics and superfluids : from broken symmetries to conformal field theories

Directional ballistic transport in the two-dimensional metal PdCoO2

Experimental studies of the equilibrium and out-of-equilibrium electronic structure of non-symmorphic topological materials

Quasi-symmetry-protected topology in a semi-metal

Spin-1/2 kagome Heisenberg antiferromagnet with strong breathing anisotropy

Perturbative approach to tunneling and quantum interferences in spin clusters

A geometrically exact model for thin magneto-elastic shells

Emergence of Nontrivial Low-Energy Dirac Fermions in Antiferromagnetic EuCd2As2

Two-dimensional Hubbard model at finite temperature: Weak, strong, and long correlation regimes

Semiclassical methods in conformal field theories scrutinized by the epsilon-expansion

Asymptotic Freedom and Large Spin Antiferromagnetic Chains

Possibility to detect the bound state of the Heisenberg ferromagnetic chain at intermediate temperature