A5085293801- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Quantum many-body systems
- Theoretical and Computational Physics
- Topological Materials and Phenomena
- Quantum and electron transport phenomena
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum Computing Algorithms and Architecture
- Magnetic and transport properties of perovskites and related materials
- Rare-earth and actinide compounds
- Algebraic structures and combinatorial models
- Neural Networks and Applications
- Quantum Information and Cryptography
- Iron-based superconductors research
- Neural Networks and Reservoir Computing
- Atomic and Subatomic Physics Research
- Complex Network Analysis Techniques
- Spectroscopy and Quantum Chemical Studies
- Multiferroics and related materials
- Catalysis and Oxidation Reactions
- Quantum Chromodynamics and Particle Interactions
- Machine Learning in Materials Science
- Stochastic processes and statistical mechanics
- Complex Systems and Time Series Analysis
- 2D Materials and Applications
Instituto de Física Teórica
2024-2025
University of Cologne
2015-2024
Flatiron Health (United States)
2022-2023
Microsoft (United States)
2006-2013
University of California, Santa Barbara
2006-2013
Microsoft Research (United Kingdom)
2009-2011
University of California System
2006-2008
University of Maryland, College Park
2008
ETH Zurich
2004-2007
Board of the Swiss Federal Institutes of Technology
2004-2006
Combining thermodynamic measurements with theoretical calculations we demonstrate that the iridates ${A}_{2}{\mathrm{IrO}}_{3}$ ($A=\mathrm{Na}$, Li) are magnetically ordered Mott insulators where magnetism of effective spin-orbital $S=1/2$ moments can be captured by a Heisenberg-Kitaev (HK) model interactions beyond nearest-neighbor exchange. Experimentally, observe an increase Curie-Weiss temperature from $\ensuremath{\theta}\ensuremath{\approx}\ensuremath{-}125\text{ }\text{ }\mathrm{K}$...
We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries application programs simulation strongly correlated quantum lattice models such as magnets, bosons, fermion systems. The code development is centered on common XML HDF5 data formats, simplify speed up development, evaluation plotting tools, programs. enable non-experts start carrying out serial or parallel numerical simulations by providing basic...
We discuss generalizations of quantum spin Hamiltonians using anyonic degrees freedom. The simplest model for interacting anyons energetically favors neighboring to fuse into the trivial ("identity") channel, similar Heisenberg favoring spins form singlets. Numerical simulations a chain Fibonacci show that is critical with dynamical exponent z=1, and described by two-dimensional (2D) conformal field theory central charge c=7/10. An exact mapping onto 2D tricritical Ising given...
State-of-the-art machine learning techniques promise to become a powerful tool in statistical mechanics via their capacity distinguish different phases of matter an automated way. Here we demonstrate that convolutional neural networks (CNN) can be optimized for quantum many-fermion systems such they correctly identify and locate phase transitions systems. Using auxiliary-field Monte Carlo (QMC) simulations sample the system, show Green's function (but not auxiliary field) holds sufficient...
In transition-metal compounds with partially filled 4d and 5d shells spin–orbit entanglement, electronic correlations, crystal-field effects conspire to give rise a variety of novel forms topological quantum matter. This includes Kitaev materials — family assisted Mott insulators, in which local, entangled j=1/2 moments form that are subject dominant bond-directional Ising exchange interactions. On conceptual level, attract much interest for their potential unconventional magnetism, such as...
Half-integer thermal quantum Hall conductance has recently been reported for the two-dimensional honeycomb material α-RuCl3 We found that half-integer plateau appears even a magnetic field with no out-of-plane components. The measured field-angular variation of quantized same sign structure as topological Chern number pure Kitaev spin liquid. This observation suggests non-Abelian order associated fractionalization local moments persists in presence non-Kitaev interactions α-RuCl3.
In the field of monitored quantum circuits, it has remained an open question whether finite-time protocols for preparing long-range entangled states lead to phases matter that are stable gate imperfections, can convert projective into weak measurements. Here, we show in certain cases, entanglement persists presence measurements, and gives rise novel forms criticality. We demonstrate this explicitly two-dimensional Greenberger-Horne-Zeilinger cat state three-dimensional toric code as minimal...
Abstract For decades, frustrated quantum magnets have been a seed for scientific progress and innovation in condensed matter. As much as the numerical tools low-dimensional magnetism thrived improved recent years due to breakthroughs inspired by information computation, higher-dimensional can be considered final frontier, where strong entanglement, multiple ordering channels, manifold ways of paramagnetism culminate. At same time, efforts crystal synthesis induced significant increase number...
We apply a recently developed adaptive algorithm that systematically improves the efficiency of parallel tempering or replica exchange methods in numerical simulation small proteins. Feedback iterations allow us to identify an optimal set temperatures/replicas which are found concentrate at bottlenecks simulations. A measure convergence for equilibration is discussed. test our by simulating 36-residue villin headpiece sub-domain HP-36 wherewe find lowest-energy configuration with...
We study the stability of topological order against local perturbations by considering effect a magnetic field on spin model---the toric code---which is in phase. The model can be mapped onto quantum loop gas where perturbation introduces bare tension. When tension small, survives. it large, drives continuous phase transition into state. understood as condensation ``magnetic'' vortices, leading to confinement elementary ``charge'' excitations. also show how breaks down when system coupled an...
Motivated by the recent experimental observation of a Mott insulating state for layered iridate Na${}_{2}$IrO${}_{3}$, we discuss possible ordering states effective iridium moments in presence strong spin-orbit coupling and magnetic field. For field pointing $\ensuremath{\langle}111\ensuremath{\rangle}$ direction---perpendicular to hexagonal lattice formed moments---we find that combination Heisenberg Kitaev exchange interactions gives rise rich phase diagram with both symmetry breaking...
We introduce an algorithm for systematically improving the efficiency of parallel tempering Monte Carlo simulations by optimizing simulated temperature set. Our approach is closely related to a recently introduced adaptive that optimizes statistical ensemble in generalized broad-histogram simulations. Conventionally, set chosen such way acceptance rates replica swaps between adjacent temperatures are independent and large enough ensure frequent swaps. In this paper, we show choosing with...
We discuss the finite-temperature phase diagram of Heisenberg-Kitaev model on hexagonal lattice, which has been suggested to describe spin-orbital exchange in Mott-insulating iridate Na${}_{2}$IrO${}_{3}$. The exhibits magnetically ordered ground states well beyond isotropic Heisenberg limit as a gapless spin-liquid around anisotropic Kitaev limit. Using pseudofermion functional renormalization group (RG) approach we extract both Curie-Weiss scale and critical ordering from RG flow magnetic...
We present an extensive numerical study of spin quadrupolar correlations in single and coupled bilinear-biquadratic one chains, using several methods such as Exact Diagonalization, Density Matrix Renormalization Group strong coupling series expansions. For the chain we clarify dominant correlation function enigmatic gapless period-three phase for theta (pi/4,pi/2), which is nature with a period three spatial structure. Then revisit open problem possible existence ferroquadrupolar between...
In quantum magnetism, Kitaev's honeycomb model is well known for its gapped and gapless spin liquid ground states in which the elementary degrees of freedom fractionalize into Majorana fermions a ${\mathbb{Z}}_{2}$ gauge field. this paper, authors discuss liquids arising three-dimensional Kitaev models show that form metallic which, depending on underlying lattice structure, exhibit Fermi surfaces, nodal lines, or Weyl points.
Metallic quantum critical phenomena are believed to play a key role in many strongly correlated materials, including high-temperature superconductors. Theoretically, the problem of criticality presence Fermi surface has proven be highly challenging. However, it recently been realized that models used describe such systems amenable numerically exact solution by Monte Carlo (QMC) techniques, without suffering from fermion sign problem. In this review, we examine status understanding metallic...
Recently, the twist angle between adjacent sheets of stacked van der Waals materials emerged as a new knob to engineer correlated states matter in two-dimensional heterostructures controlled manner, giving rise emergent phenomena such superconductivity or insulating states. Here, we use an ab initio based approach characterize electronic properties twisted bilayer MoS2. We report that, marked contrast graphene, slightly hole-doped MoS2 realizes strongly asymmetric px-py Hubbard model on...
The fractionalization of quantum numbers in interacting many-body systems is a central motif condensed-matter physics with prominent examples including the electron Hall liquids or emergence magnetic monopoles spin-ice materials. Here, we discuss moments three-dimensional Kitaev models into Majorana fermions (and Z_{2} gauge field) and their emergent collective behavior. We analytically demonstrate that form Weyl superconductor for model on recently synthesized hyperhoneycomb structure...
Motivated by the recent synthesis of spin-1 A-site spinel NiRh_{2}O_{4}, we investigate classical to quantum crossover a frustrated J_{1}-J_{2} Heisenberg model on diamond lattice upon varying spin length S. Applying recently developed pseudospin functional renormalization group approach for arbitrary spin-S magnets, find that systems with S≥3/2 reside in regime, where low-temperature physics is dominated formation coplanar spirals and thermal (order-by-disorder) transition. For smaller...
Abstract From the perspective of many-body physics, transmon qubit architectures currently developed for quantum computing are systems coupled nonlinear resonators. A certain amount intentional frequency detuning (‘disorder’) is crucially required to protect individual states against destabilizing effects resonator coupling. Here we investigate stability this variant a localized phase system parameters relevant current processors by IBM, Delft, and Google consortia, considering cases natural...
Renormalization group methods are well-established tools for the (numerical) investigation of low-energy properties correlated quantum many-body systems, allowing to capture their scale-dependent nature. The functional renormalization (FRG) allows continuously evolve a microscopic model action an effective as function decreasing energy scales via exact flow equation, which is then approximated by some truncation scheme facilitate computation. Here, we report on our transcription recently...
Pinch point singularities, associated with flat band magnetic excitations, are tell-tale signatures of Coulomb spin liquids. While their properties in the presence quantum fluctuations have been widely studied, fate complementary non-analytic features -- shaped as half-moons and stars arising from adjacent shallow dispersive bands has remained unexplored. Here, we address this question for $S=1/2$ Heisenberg antiferromagnet on kagome lattice second third neighbor couplings, which allows one...