Dr Dmitry Zmeev

PhD Supervision Interests

1. “Precisely controlled levitating sphere moving in superfluid helium” The student will develop a new type of instrument for studying the properties of cryogenic fluids: a system for controlling the motion of a magnetically levitated superconducting sphere. Several problems remain unresolved in superfluid physics and we will aim to find the solutions. We will concentrate our effort on the following.

Firstly, pinning and nucleation of vortices in superfluid helium-4. Currently, there are two contradictory pictures of how vortices attach (‘pin’) to surfaces and how it affects their motion. The development of quantum turbulence around an object moving in a superfluid has hardly been studied at all. Our instrument promises to be suitable for addressing these issues.

Secondly, the surface-bound states in superfluid helium-3 at microkelvin temperatures represent a largely unexplored physical system with potentially extremely unusual properties. We know how to probe this system by driving it out of equilibrium, and the new instrument promises to enhance our capabilities.

The sphere represents an ideal, numerically tractable geometry, paving the way to direct interpretations of the experiments.

In, principle, the sphere moving in a classical fluid in a circular trajectory at a constant speed is a simpler and more efficient replacement of a hydrodynamic wind tunnel. We will explore the advantages and disadvantages of scale model testing in a cryogenic environment.

We have a track record of successfully secured funding and numerous impactful publications.

2. “The coldest liquid in the Universe” The student working with other members of the Ultralow Temperature Group will attempt to achieve the lowest temperature for any liquid. The project is concentrated around developing and demonstrating a new technique for cooling superfluid Helium-3. By utilising the nuclei of solid Helium-3 adsorbed on the surface of aerogel as a refrigerant in the adiabatic demagnetisation process, we will try and cool the superfluid to well below 100 microkelvins. Measuring such low temperatures is an arduous task. We will develop a method based on creating a Bose-Einstein Condensate of magnons within the superfluid and measure its decay due to the very few thermal excitations remaining in the liquid.

If successful, we will seek to apply the developed technique to cooling other systems, such as electrons in quantum devices and low-dimensional electron systems, where lower temperature means longer coherence times and perhaps new, yet undiscovered phenomena. We have a track record of successfully secured funding and numerous impactful publications.

By joining this project you will design, build and run experiments at the forefront of modern physics. You will become a part of the Lancaster Ultralow Temperature Group led by 6 research-active academics working at the frontiers of experimental Low Temperature Physics. The group is world leading in the field and has an excellent record of high-rank publications and of securing research funding at national and international level.

3. "Superfluid ³He as an instrument for fundamental physics" We are seeking PhD students to join our team in building and implementing experiments at temperatures significantly below one millikelvin. Our current projects include using superfluid ³He as an instrument for fundamental physics: a dark matter detector and a simulator of the early universe.

The detector will use an ultrasensitive superfluid ³He calorimeter and superconducting transition edge sensors for achieving a high resolution in detecting spin-dependent interactions between ³He nuclei and hypothetical dark matter particles.

The simulator will probe the dynamics of phase transitions between two superfluid states in ³He, which is found to be of surprising similarity to the hypothetical phase transitions in the quantum vacuum of the early universe. The results of the experiments will inform the interpretation of the gravitational wave signatures from processes that took place shortly after the Big Bang.