Group Leader Profiles

The research in our group is focused on the electronic and magnetic properties of few level systems looking for new quantum limits at the atomic scale. We are exploiting the interplay of magnetism, superconductivity, and correlation effects to isolate few level systems and understand their dynamics. Using scanning tunneling microscopy at lowest temperatures (between 10mK and 500mK), we study individual magnetic impurities coupled to superconducting substrates. We are interested in the resulting phenomena, such as Yu-Shiba-Rusinov states, and their suitability for quantum sensing or information processing. In addition, we combine electron spin resonance spectroscopy with scanning tunneling microscopy to understand and manipulate single spin systems isolated from their enviornment.

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

If you are potentially interested in a PhD at the MPGC under my supervision (typically jointly with Prof.Moessner at the MPIPKS), you will also need to apply for a PhD at Cambridge, as acceptance at both is required. You can find instructions, useful links, and further information about the Theory of Condensed Matter group at Cambridge here: http://www.tcm.phy.cam.ac.uk/vacancies/postgrad.html

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.

Research topics:

• Heusler compounds with X2YZ with L21 and XYZ with C1b structure type
• topological insulators, Weyl semimetals, new Fermions
• thermoelectric materials, topological catalysis
• non-centrosymmetric superconductivity

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 research explores the rational synthesis of new functional materials by combining the tools of molecular, solid-state and nanochemistry. Research interests include the design of organic, inorganic and hybrid materials for solar energy conversion and storage, ion conductors for electrochemical energy storage, and “smart” photonic crystals for optical sensing. We aim at creating function from both atomic-scale structure and nanoscale morphology, with a strong emphasis on exploring structure-property relationships based on a variety of diffraction and spectroscopic techniques. Recent activities include the development of molecular frameworks for solar batteries, “dark” photocatalysis, photomemristive sensors, and (photo)electrocatalytic CO2 conversion, the development of quantum materials for (photo)electrocatalysis, as well as the design of lithium and sodium thiophosphate and sulfide solid electrolytes for all-solid-state batteries. 

• Two-dimensional materials and heterostructures

• Spectroscopy

• Quantum transport

• Strong correlation physics

• Topological states of matter

• Exciton condensation

• Magnetism

• Superconductivity 

In the Quantum Many-Body Theory department, electronic properties of solids are analyzed and computed with a main emphasis on systems where electronic correlations play a crucial role, such as high temperature superconductor and other transition metal oxides. Besides bulk properties of one-, two- and three-dimensional systems also surface states of topological phases, as well as problems with a mesoscopic length scale such as quantum dots, quantum wires, and quantum Hall systems are being studied. The correlation problem is treated by various modern numerical and field-theoretical techniques.

Research topics:

• Correlated and topological systems including heavy fermions, high-Tc and Dirac/Weyl/multifold materials
• 3D structural deformation in crystalline structures and its impact on quantum transport
• Size effects and shaping microstructured crystals
• Physical properties in high magnetic fields
• Focused Ion Beam fabrication of quantum materials
• Prototyping of novel materials in applications

What does a single molecule look like? How can we excite it and control its emission? How can we build more complex molecular structures “by hand”? How can we tune the quantum properties of light with atomic precision? In our research team, we answer these questions using the combination of scanning tunneling microscopy (STM) with optics. This way, we bring the best of the two worlds together, the sub-nm resolution of STM, and all the information carried by photons to study optics at the atomic scale. Using this method we learn previously inaccessible details about mechanisms like light-harvesting, photosynthesis, and electron-to-photon conversion.

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/)

Research in the Solid State Nanophysics Group focuses on the study of the many unusual ways in which electrons organize themselves as a result of interactions and correlations among their charge and spin degrees of freedom, when these electrons are confined in one or more dimensions on the nanometer scale. Transport and optical properties are investigated with local probe methods, at low temperatures, in high magnetic fields, under high frequency radiation or any combination thereof. The electrons are confined in strictly two-dimensional crystals such as graphene or other single layers of the large class of layered materials with weak interlayer forces. Also hybrid stacks of these two-dimensional crystals are fabricated and explored in a quest for novel functionalities and interaction physics.

The spectacular physical properties often observed in materials containing transition metal and rare-earth elements challenge our comprehension of solid state physics These properties include superconductivity, unusually large magneto-resistance, metal-insulator transitions, heavy-fermion behaviour, multiferroicity, and phenomena involving topologically protected states. We would like to understand how the electrons in such materials interact with each other as to generate those unusual quantum phenomena.

Superconductivity and Magnetic Correlations

Our group is interested in the way quantum particles, like electrons or atoms, organize themselves while interacting with one another. This way, we aim at understanding how the macroscopic behavior of materials, like various forms of magnetism or superconductivity, emerges. Besides trying to explain existing experimental phenomena in solid-state physics, I investigate under which circumstances entirely new states of matter, like quantum spin liquids, can occur.

To solve these questions, we are developing numerical technology to simulate quantum many-body systems. The quantum many-body problem is considered to be exponentially hard in the number of particles. One approach we are pursuing is to push the limits of exact simulations by developing high-performance computing software and distributed parallel algorithms for quantum many-body systems. Furthermore, we are also embracing tensor network methods to reduce computational complexity by representing data efficiently.