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Stretching and squeezing the Haldane pseudopotentials

7 April 2017

Dr Zlatko Papic and collaborators have recently had a paper published in Physical Review Letter, which was highlighted as Editors’ Suggestion. This short article explains the background to the team’s work and the team’s findings.

 

Stretching and squeezing the Haldane pseudopotentials: a new language for describing the anisotropic fractional quantum Hall effect

In a classic paper from 1983 [1], Duncan Haldane (Nobel Prize in Physics, 2016) formulated what is now known as "the Haldane pseudopotentials" to describe the fractional quantum Hall effect. The latter phenomenon, where the Hall conductance of a two-dimensional electron gas in a magnetic field is curiously quantised in terms of rational numbers like 1/3 or 2/5, had been discovered a year earlier by Tsui, Stormer and Gossard [2]. The effect, however, remained a mystery until the early 1983 when Robert Laughlin explained it as a consequence of subtle correlations between the electrons which make them form exotic kinds of quantum fluids. (Tsui, Stormer and Laughlin shared the 1998 Nobel Prize for their discovery.) One of the crucial steps in the verification and ultimate acceptance of Laughlin's theory came from Haldane’s pseudopotentials, which allowed to write down a rotationally-invariant wave function for the Laughlin fluid and explained why such a state could describe the real system of electrons interacting via Coulomb force.

An underlying assumption of the Haldane pseudopotentials has been that the electron system is rotationally invariant – it looks the same in x and y directions. However, it is known that experimental semiconductor systems, which realise the quantum Hall effect, are not rotationally invariant: for example, semiconductors often have different effective masses along x- and y-directions. A natural question then arises: can Haldane pseudopotentials be defined for quantum Hall systems which are not invariant under x-y rotation?

In a recent paper published in Physical Review Letter and highlighted as Editors’ Suggestion [4], Dr Zlatko Papic and collaborators have generalised the 1983 work of Haldane by formulating the pseudopotentials for anisotropic fractional quantum Hall systems. Their work introduces a new and universal language that allows to describe a broad class of fractional quantum Hall systems without rotational symmetry, such as experiments in tilted magnetic field, or the so-called nematic quantum Hall states which spontaneously break rotational symmetry, similar to liquid crystals. The new language also illuminates a fundamental characteristic of fractional quantum Hall fluids – their geometric degree of freedom. Such degrees of freedom determine the properties of these fluids at low energies and have recently attracted much attention because of connections with models of quantum gravity in two dimensions.

Read the paper in full in Physical Review Letters

References

[1] F. D. M. Haldane, Phys. Rev. Lett. 51, 605 (1983).

[2] D. C. Tsui, H. L. Stormer, and A. C. Gossard, Phys. Rev. Lett. 48, 1559 (1982).

[3] R. B. Laughlin, Phys. Rev. Lett. 50, 1395 (1983).

[4] Bo Yang, Zi-Xiang Hu, Ching-hua Lee, and Z. Papic, Phys. Rev. Lett. 118, 146403 (2017).




Inaugural Professor Ian Ward lecture

3 April 2017

The inaugural Professor Ian Ward lecture, hosted by the Soft Matter Physics Group at Leeds, was held in honour of the outstanding contribution of Professor Ian Ward F.R.S to the group, to the University as a whole, and more widely to the National and International Polymer Physics community.

The picture to the right shows a number of the happy band who attended this annual lecture.

The inaugural speaker was Professor Phil Coates (fourth from the right), Professor of Polymer Engineering at the University of Bradford and the Director of the internationally recognised Polymer Interdisciplinary Research Centre (IRC) (across the Universities of Leeds, Bradford, Durham and Sheffield).

Professor Coates has had a long standing association and collaboration with Professor Ward (who was the first director of the IRC on its inception in 1989), stretching back over 40 years. Professor Coates and his team are leaders in the area of the structure and properties of solid polymers and polymer composites, combining fundamental scientific research with strong industrial links, a theme which was pioneered by Professor Ward.

It was great event, allowing for wonderful reflections of Ian’s contribution from both Professor Coates and our head of School Professor Helen Gleeson (back left). Phil gave a very interesting talk, building up from Ian’s pioneering work and highlighting the new areas that Bradford have taken this forward. Phil also highlighted some of Ian’s inventions, including the single polymer composites work currently exploited by Samsonite in their successful innovative luggage range (Cosmolite etc). The event proved a great opportunity for catching up with friends and colleagues across the sites of the IRC. Thanks to Glenys Bowles (second right) and Ella Gould (off stage right) for help in organising the event and we understand that both Ian, and his wife Margaret (fifth from the right) had a lovely evening. Thanks again to Phil for agreeing to gives this inaugural lecture.




Leeds PhD student strikes Bronze for physics display in Parliament

16 March 2017

Ellen Kendrick, a PhD student here at the University of Leeds, struck Bronze at a competition in the House of Commons for the excellence of her physics research, walking away with a £1,000 prize.

Ellen presented her physics research to dozens of politicians and a panel of expert judges, as part of the poster competition STEM for BRITAIN, on Monday 13 March.

Her research, which focuses on using atomic force microscopy to pull apart protein molecules to investigate their strength and flexibility at a range of temperatures, was judged against 29 other shortlisted researchers' work and she came out as one of the three winners.

Ellen said, 'I am very happy and very surprised. I was not just seeing it as a nice day out but it has been fun and I have spoken to representatives of both my MPs [from her home city Edinburgh and her work in Leeds].'

STEM for BRITAIN aims to help politicians understand more about the UK's thriving science and engineering base and rewards some of the strongest scientific and engineering research being undertaken in the UK.

Stephen Metcalfe MP, Chair of the Parliamentary & Scientific Committee, sponsors of the physics awards said: 'The Parliamentary & Scientific Committee is delighted to sponsor the physics awards. This annual competition is an important date in the parliamentary calendar because it gives MPs an opportunity to speak to a wide range of the country's best young researchers.

'These early career engineers, mathematicians and scientists are the architects of our future and STEM for BRITAIN is politicians' best opportunity to meet them and understand their work.'

Professor Roy Sambles, President of the Institute of Physics said:
'STEM for BRITAIN provides a great opportunity for some of our outstanding young scientists to present aspects of their research in parliament, allowing Members of Parliament to find out first-hand about some of the ground breaking research taking place here in the UK.'

'I wish the best of luck to all the exhibitors, who should feel very pleased with what they have achieved and I hope that they will value sharing the excitement of their research with key politicians and policy makers.'

The Parliamentary and Scientific Committee runs the event in collaboration with the Council for the Mathematical Sciences, the Institute of Physics, The Physiological Society, the Royal Academy of Engineering, the Royal Society of Biology and the Royal Society of Chemistry; with financial support from Research Councils UK, Warwick Manufacturing Group, the Clay Mathematics Institute, the Heilbronn Institute for Mathematical Research, the Institute of Biomedical Science and the Society of Chemical Industry.




University of Leeds to receive multi-million pound share of funding for research into advanced materials.

3 March 2017

Part of a £235 million commitment by Government for the Henry Royce Institute, Leeds will receive £10 million to support its world-leading research.

It follows the decision by the University to invest £96 million to bring together research and teaching across Engineering and Physical Sciences, to inspire new ways of working across disciplines, help tackle industry challenges and support industry collaboration.

Read more...




Innovation award for Leeds Spinout Company

25 January 2017

Creavo Medical Technologies, formerly known as Quantum Imaging Ltd, a spinout company formed in 2014 to develop diagnostic technology for acute medical settings, has won the ‘Best Innovation’ award and the ‘Best Start-Up’ award at the MedilinkWM Medical & Health Business Awards 2016.

Medilink is an industry group that works across all aspects of healthcare to promote industry and work with companies to aid technology adoption and growth. This is the first time in the history of the award that a company has won two awards in the same year.

Creavo Medical Technologies is a start-up focused on the utilisation of advanced quantum principles in the rapid detection of potentially life threatening medical conditions in acute medical settings. Research carried out by students and researchers in the Theory Group in the School of Physics and Astronomy, at the University of Leeds has led to the development of a portable and completely passive medical platform to detect and display the minute bio-magnetic signals associated with various tissues. These signals can be used in a variety of medical applications and for the detection of a range of medical conditions.

This award caps off a great year for the company which has seen its first product, Vitalscan, receive its CE mark (which enables sales), the start of a largescale multi-center clinical at four of the UK’s major A&E departments, namely Bristol, Sheffield, Leicester and Nottingham, followed by a second stage starting at three centres in the United States at Mayo Clinic Rochester, Cincinnati and Baylor Texas. This award follows two awards for Creavo’s CEO, Steve Parker, who has been named as one of the UK’s 100 most inspiring individuals by “The Manufacturer” magazine and CEO of the year by “Finance Monthly” magazine for bringing ground-breaking technology to market.

Early indications from clinical testing indicate that Vitalscan could meet an urgent clinical need for improving the current triage process for patients entering emergency departments with chest pain. The device uses advanced quantum principles to measure, display and store electromagnetic fluctuations caused by heart activity through a simple, non-invasive three to five-minute scan at a patient’s bedside. This scan accurately and quickly rules out significant ischaemic heart disease, such as heart attacks. The device will enable clinical practitioners, who operate in acute medical settings, to ‘rule out’ heart-related problems and prevent healthy patients from having to go through the current lengthy, and costly, chest pain triage process, which includes a variety of diagnostic tests including multiple ECGs and cardiac biomarker blood tests.




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