Group Leader Profiles

I am part of the Theory of Condensed Matter group at the Cavendish Laboratory. My interests lie in the area of emergent and out of equilibrium phenomena in strongly correlated many body systems. Current research topics include the effects of hard constraints in classical and quantum systems; freezing and glassiness; response and equilibration properties of systems with fractionalised excitations; frustrated magnetism; topological order, quantum information and quantum computing.

The understanding of fundamental, physical processes in quantum materials and the identification of universal aspects among them constitutes a necessary basis for the design of new quantum materials with desired functionalities. Our group investigates the collective behavior of interacting electrons which gives rise to the many fascinating phases of matter in quantum materials. We seek to explain the underlying mechanisms behind the phase formation and to determine characteristic properties of the different phases.We are particularly interested in situations when excitations of different phases strongly interact so that it is essential to consider their mutual influence on each other. This includes, for example, the study of quantum phase transitions or unconventional superconductivity. To account for the decisive role of interactions and the interplay of different degrees of freedom in these complex situations, we employ modern, field-theoretical tools with an emphasis on renormalization group techniques. We make use of microscopic and effective descriptions inspired by experimental observations to obtain a comprehensive picture of correlated phases in quantum materials.

Davis Group research concentrates upon the fundamental physics of exotic states of electronic, magnetic and atomic quantum matter. A specialty is development of innovative instrumentation to allow direct atomic-scale visualization or perception of the quantum many-body phenomena that are characteristic of these states.

Research Topics:

• electronic liquid crystals
• Cooper-pair density wave states
• monopole and spin liquids
• magnetic topological insulators
• Cu/Fe high-Tc superconductors
• viscous electron fluids
• macroscopic quantum mechanics
• quantum microscope development

Research topics:

• many-body interactions in low-dimensional materials
• optoelectronic excitations at oxides, perovskites, and inorganic/organic interfaces
• ab-intio method and code development
• data-centric approaches to materials science

Research topics:

• epitaxial synthesis of novel materials
• synthesis and properties of free standing and interconnected 1D structures
• nanophotonics for efficient photon harvesting

The department uses neutron and X-ray diffraction and spectroscopy as well as optical spectroscopy and Raman scattering to explore the structure and dynamics of materials with strong electron correlations. We also have a strong effort in the development of new spectroscopic methods. As the close collaboration between experimentalists and theorists is essential for progress in this field, a small theory group operates within the department.

Our interdisciplinary research group explores how to teach crystals tricks of living matter by investigating dynamic features of molecular framework materials such as metal-organic and covalent organic frameworks (MOFs and COFs). By specifically tuning the structural topology of the framework, we create soft porous crystals which exhibit pore contraction and/or expansion as a response to the adsorption of gases and fluids or external triggers such as light irradiation. Such materials can act as responsive cargo-release systems, nanoscopic sensors or feature counterintuitive phenomena such as negative gas adsorption. We furthermore construct frameworks which contain molecular machines such as light-driven molecular motors and switches as responsive and intrinsically dynamic building blocks. We aim towards collective operating molecular machines in the solid state which are able to actively transport molecules in the pore space and facilitate dynamic conversion and storage of energy carriers and other small molecules. Our diverse team uses a wide range of synthetic and experimental tools and collaborates in national and international research projects to push the boundaries of dynamic features in crystalline solids.

Research topics:

• low temperature ordered states
• interacting electron mesoscopics
• thermodynamic and transport measurements on interacting electron systems

Research topics:

• 2D materials and van der Waals heterostructures
• Floquet topological insulators
• ultrafast optoelectronics and opto-spintronics
• on-chip THz spectroscopy
• coherent light-matter interaction

Research topics:

• theory of quantum materials:
• collective phenomena
• new kinds of order
• quantum dynamics

Research topics:

• spintronics
• nano-photonics
• topological materials
• neuromorphic devices

Research topics:

• new exotic states of matter out of equilibrium: Topological materials
• QED-Chemistry and Materials
• fundamental aspects of Time-Dependent Density Functional Theory and Many-Body Perturbation Theory
• strong light-matter interactions and Optimal control Theory
• electronic and Thermal transport
• nanostructures: 2D materials, nanotubes
• code development: development of the first principles open-sorce project octopus (https://octopus-code.org/)

Materials with strong electronic correlations are amongst the most intriguing topics at the forefront of research in condensed matter physics. On the one hand, they exhibit fascinating phenomena like quantum criticality and high-temperature superconductivity, bearing a high potential for applications. On the other hand, they are theoretically very appealing due to their limited understanding, even on the very fundamental level. Within the research group “Theory of Strongly Correlated Quantum Matter”, starting from September 2020, the frontier of this fundamental understanding is pushed by applying cutting-edge numerical quantum field theoretical methods to quantum critical systems, high-temperature superconductors, Mott insulators and magnetically frustrated systems, both in the purely model (Hubbard model, periodic Anderson model) as well as material oriented (heavy fermions, cuprates, organics) context.

Our research group studies electronic and magnetic structures of quantum materials. A special focus is on topological materials, which exhibit unusual properties, such as exotic surface states and anomalous transport phenomena, that are unaffected by continuous deformations, e.g., stretching, compressing, or twisting. Our aim is to develop a theoretical framework to describe these topological properties, and to find new ways how to use them in the laboratory and for device applications. We seek to classify topological materials in terms of symmetries and to discover new remarkable examples. Current research priorities focus on the topological properties of nodal-line semimetals, topological metals with nodal planes, quantum magnets, and unconventional superconductors, which we study using both analytical and numerical techniques.

Research:

• Quantum sensing at the atomic scale beyond 4 K
• Non-invasive magnetic imaging and coherent quantum control of single spin-qubits
• Exploring novel surface-supported spin systems

Entanglement of electrons (electron correlations) in solids, in combination with details of the crystal lattice structure, produce a surprisingly rich variety of electronic phases, that are liquid, liquid-crystal and crystalline states of the charge and spin degrees of freedom. These complex electronic phases and the subtle competition among them very often give rise to novel functionality. The department will be studying these interesting novel phases in transition metal oxides and related compounds where the narrow d-bands, which give rise to strong electron correlations, in combination with the rich chemistry of such materials provides excellent opportunities for new discoveries. The goal of this research will be to hunt for new materials exhibiting exotic electronic states of matter, showing phenomena such as superconductivity or high thermoelectricity, and to explore them with advanced measurement techniques to unveil the physical mechanisms that could be drivers of potentially highly desirable functionality.

The goal of the Quantum Information for Quantum Materials group is to utilize coherent quantum systems as sensors to explore novel materials and collective quantum effects, and utilize quantum materials to create novel hybrid quantum systems. The group mainly specializes in two experimental techniques: quantum scanning magnetometry based on nitrogen-vacancy centers in diamond, and hybrid superconducting circuits integrated with quantum materials.