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Dr. John Adkins 1934-2020

QM members will be saddened to learn that Dr. John Adkins, long-time group member and highly respected colleague, passed away on 17 July. John was an outstanding experimentalist who was a member of the Low Temperature Physics Group from the beginning of his PhD programme in 1956. His contributions included studies of superconductivity, electronic conduction in disordered systems, quantum mechanical tunnelling and the metal-insulator transition. He was appointed a University Lecturer in 1964, and went on to lead the Group from 1982 until his retirement in 1999. A more detailed description of his work and life can be found here. (2/8/20)

Tuning into Novel Quantum Rhythms

Experimentally determined phase diagram of a quantum critical ferroelectric, featuring a new 'Quantum Polar-Acoustic State' emergent from the Quantum Critical Point where ferroelectricity is suppressed to zero temperature.

Can order be caused by quantum zero point fluctuations? A new Proceedings of the National Academy of Sciences paper by Montu's group (Matt Coak, Seb Haines, Cheng Liu) with Stephen Rowley and Gil Lonzarich presents the most comprehensive experimental and theoretical study of order-by-disorder in a solid crystal system to date. Check here for more information. (11/6/2020)

Isaac Sutherland *20/5/20

Warmest congratulations from all QM to Mike Sutherland and partner Monica for the birth of son Isaac a few days ago. This beats everything else we can possibly come up with in a news section! All the very best to the three of you. The first 25 years are the hardest. (24/5/20)

Keiron Murphy PhD

Congratualations to Mike's student Keiron who finished his postgraduate research on quantum oscillations in square-net materials and in the new Fe-based superconductor YFe2Ge2 in the autumn of 2019, just in time to start a postdoctoral position with Radu Coldea's group in Oxford, wrote up his PhD thesis in record time and passed his (online) viva with flying colours mid-May. A big thank you, also, to his distinguished examiners Nigel Hussey and Gil Lonzarich. QM celebrated with a virtual pub outing, but I'm afraid Keiron will have to buy everyone a real drink as soon as this becomes possible again. (20/5/20)

Prof. James Scott 1942-2020

We are very sad to announce that our distinguished colleague and long-time group member Prof. James (Jim) Scott passed away on Monday 6 April. Jim made pioneering contributions to fundamental and applied ferroelectrics research. His developments include ferroelectric memory devices, such as the ferroelectric RAM (FRAM). We shall all miss him greatly. A more detailed description of his work and life can be found here. (7/4/20)

'Spinning Graphene' - a case of magnetic layers!

Lattice structure of FePS3, showing the van der Waals bonded monolayers carrying magnetic moments.

Can less be more? The answer is 'yes', when we compress things and get a result that is beyond our expectations. A new Physical Review Letter on high pressure experiments in FePS3 by Montu's group, with collaborators at Earth Sciences, the Diamond Light Source and the ILL, reports a pressure induced metal insulator transition in a fascinating layered material.

2-Dimensional magnetic materials promise to surpass graphene in a number of ways. We have recently taken a leap towards understanding the dynamic relationship between electronic and structural properties of 'magnetic graphene' that can introduce magnetism to emerging graphene-based technology. For the case of this material, FePS3, an electrical insulator, by applying pressure we were able squash the 2D layers together and switch it into a metal, this is often termed a Mott transition. Magnetism arising from arrangement of electronic spins is exploited in most memory devices and sensors and this is a key constituent for developing technologies like spintronics and spin-caloritronics.

These 2-D materials are characterised by weak mechanical forces between the crystal planes and high pressure (achieved by forcing together two opposed diamonds) hasve the effect of pressing these planes together; gradually and controllably pushing the system from two- to three-dimensionality and simultaneously, from insulator to metal. Our research points to an exciting direction for producing 2-dimensional materials with tunable and conjoined electrical, magnetic and electronic properties. (Montu Saxena, 7/1/19)



How to make a new iron-based superconductor

Superconductivity exerts a particular fascination, when it is caused by an electronic mechanism. Among the transition metal compounds, such unconventional superconductivity is extremely rare and has largely been confined to the copper oxide high temperature superconductors, Sr2RuO4, and to a diverse family of iron-pnictide and chalcogenides. In an earlier manuscript [Chen et al., Physical Review Letters 116, 127001 (2016)], Malte's group had presented compelling evidence that the layered iron system YFe2Ge2 exhibits bulk superconductivity at low temperature.

Low temperature resistivity and heat capacity data in samples of YFe2Ge2 with different levels of impurity scattering, recently published in Physical Review B Rapid Comm.. As sample quality increases and residual resistance values greater than 100 are achieved, the low temperature heat capacity displays an anomaly indicative of bulk superconductivity.

In the normal state, YFe2Ge2 displays a strongly enhanced heat capacity Sommerfeld coefficient of nearly 100 mJ/(mol K2), an order of magnitude above band structure values, and a distinct non-Fermi liquid temperature dependence of the electrical resistivity at low temperature. Superconductivity is only observed in the purest samples, and the resistive Tc as well as the transition width depend strongly on the electronic mean free path. All of this suggests that superconductivity in YFe2Ge2 is unconventional.

Only high quality samples display bulk superconductivity, however, and it has taken the group another two years to work out how to grow such samples systematically, and what governs sample quality. A new paper in Physical Review B Rapid Comm. reports the main results of this study. By systematically scanning the composition phase diagram of YFe2Ge2, it was possible to determine the dominant source of disorder scattering, and to develop a reliable method for minimizing it. An analysis of the transport and thermodynamic signatures of superconductivity in dozens of samples with varying disorder level has revealed a strong correlation between disorder scattering and the transition temperature. Bulk superconductivity in YFe2Ge2 is suppressed when the scattering rate exceeds 2 kBTc, a strong indication that YFe2Ge2 is indeed that rare breed, an unconventional, transition-metal based superconductor. (4/1/19)



Phasons and superconductivity in a quasiperiodic material

A new Science Advances paper by Malte's group, with collaborators in TCM and at Materials Science, establishes strong-coupling superconductivity in the quasiperiodic structure adopted by high pressure Bi-III as a consequence of exotic vibrational excitations of a quasiperiodic lattice,

Electrical resistivity in aperiodic high-pressure bismuth-IIIElectrical resistivity in aperiodic high-pressure bismuth-III [Strong coupling superconductivity in a quasiperiodic host-guest structure, Science Advances 4, eaao4793 (2018)]

Most condensed matter physics research is based on the periodicity of crystalline lattices. The existence of repeat units enables advanced concepts such as Bloch's theorem, the reciprocal lattice, the Brillouin zone and the Fermi surface, which have become fundamental to our understanding of solids. However, it has long been known that there are many ordered materials that lack discrete translational symmetry and thereby fall outside the standard paradigm of condensed matter physics. Among them are quasicrystals, but also other quasiperiodic structures such as incommensurately modulated lattices or incommensurate host-guest structures. Intensely investigated by crystallographers, these materials tend to linger outside main-stream condensed matter research, and in particular their electronic and vibrational excitations remain largely unexplored. This paper describes the first detailed investigation of the superconducting and normal state properties of bismuth at high pressure, when it assumes the incommensurate host-guest structure Bi-III. The paper reports an unusually high superconducting upper critical field, the highest in any elemental superconductor to date, and an anomalously strong, linear temperature dependence of the electrical resistivity above the superconducting transition temperature. These findings are interpreted in terms of substantial phonon spectral weight at very low energies, attributed to the sliding or phason mode that can arise only in quasiperiodic systems. The sliding motion in Bi-III involves the movement of chains of bismuth atoms with a certain lattice constant inside tubes of bismuth atoms with a different lattice constant. Because the two lattice constants are incommensurate there is an equal energy manifold of spatial arrangements of the two sub-lattices, and their relative sliding motion can occur without energy barriers, pulling this mode down effectively to zero frequency. This is akin to the phenomenon of superlubricity observed, for instance, between slightly misaligned graphite surfaces. Quasiperiodic structures form an intermediate step between conventional crystalline lattices and full disorder. They present fundamentally new challenges to theory, because Bloch's theorem, one of the cornerstones of condensed matter physics, does not apply to them. Very little is known experimentally about their electronic and vibrational excitations, and this work raises further questions: where do we find instances of similar behaviour in compounds, at ambient pressure? Can we turn the structural frustration of quasiperiodic materials into magnetic frustration of an entirely new variety, by including magnetic elements in the structure, producing novel types of quantum magnets and spin liquids? What are the consequences of lacking discrete translational symmetry for the electronic structure? Will it be possible to detect signatures of the Fermi surface of Bi-III, for instance by quantum oscillation measurements? Can the additional low-lying phonon spectral weight inherent to incommensurate host-guest structures be harnessed to produce strong-coupling superconductors with technologically attractive high critical fields or enhanced transition temperatures, and could the peculiarities of electronic and vibrational states be exploited to produce superior thermoelectrics? It looks like there is a lot of work still to do. (20/4/18)



Dr. John Loram 1938-2017

It is with great sorrow that we announce the sad news that our distinguished colleague and valued friend Dr. John Loram passed away suddenly and unexpectedly in hospital in Leeds on Sunday November 5th. John was widely known for his pioneering achievements in ultra-high precision thermodynamic measurements, which have contributed key insights in high temperature superconductivity research. As an active collaborator in ongoing QM projects he was a regular visitor to the Cavendish. We shall all miss him greatly. A more detailed description of his work and life can be found here. (20/11/17)



Feature about QM Professor Gil Lonzarich in Nature magazine

The 28/9/17 issue of Nature magazine contains a comprehensive profile of Gil Lonzarich, long-time member of the Low Temperature Physics group and founding father of its successor, the Quantum Matter group. (1/10/17)



QM students win Physics at Work award

Congratulations to a team of QM students led by senior PhD student Mate Hartstein! They demonstrated and explained superconductivity so engagingly at this week's Physics at Work school outreach activity that they were awarded the shield for the most popular presentation. (21/9/2017)

Sofia Taylor-Coronel with a supremely attentive crowd of what look like Comberton Village College pupils.



Nature Physics paper published on quantum tricritical points in a band magnet

The nature of magnetism in metals is one of the long-standing research topics in the Quantum Matter group. What happens, when a ferromagnetic metal is tuned - by applying pressure or by varying the composition - so that the magnetic ordering temperature is gradually reduced to zero? If the transition is continuous, or second order, then the point in the phase diagram where magnetism just vanishes would be a so-called quantum critical point, but experimentally this appears to be exceedingly rare. Instead, most clean metals escape either into first order, discontinuous phase transitions. Some form another ordered state, such as spin density wave order.

Three dimensional composition-field-temperature phase diagram of NbFe2, showing the ferromagnetic (blue) and spin density wave (red) ordered phases, as well as the newly reported quantum tricritical points.

The band magnet NbFe2 is a nice example of this phenomenon, and in this Nature Physics publication, a team led by QM investigator Malte Grosche, together with colleagues from Bristol (Cavendish alumnus Sven Friedemann), Royal Holloway, Dresden and Munich, was able to show that in NbFe2 the interplay between spin density wave order and ferromagnetism can be nicely modelled in a two-order- parameter Landau theory, that this allows the location of the ferromagnetic quantum critical point to be pinpointed as it is buried inside a spin-density-wave region in the phase diagram, and that moreover all of this causes tricritical points to arise, when the spin density wave order is tuned in a magnetic field. The tricritical points, again, can be suppressed to zero temperature by varying composition or pressure, giving rise to the above-mentioned 'quantum tricritical points', where both the uniform and the staggered magnetic susceptibility diverge down to low temperatures. This phenomenon may be of more general interest, as it could apply, for instance, to certain f-electron systems near the threshold of magnetism, such as the archetypal non-Fermi liquid material YbRh2Si2. More information can be found in press statements by colleagues at MPI-CPfS Dresden and at the Dept. of Physics, Bristol.(20/9/2017)



More Maglab expeditions

Two QM investigator groups, which even included a lucky undergraduate summer student, had the opportunity to carry out measurements at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee/Florida this summer during August and September. One key result was the extension of high pressure Fermi surface studies in the pressure-metallised Mott insulator NiS2 to nearly 120 kbar. See also this recent Maglab Science Highlight. (19/9/2017)

Nature Physics paper published on the 4-spin plaquette singlet state in a in a 2-D quantum material

Phase diagram of SrCu2(BO3)2 as a function of pressure and temperature.

With QM investigator Dr. Montu Saxena, a team of scientists led by colleagues at EPFL and the Paul Scherrer Institut have realized experimentally a new quantum many body state in a material representing a famous theoretical model called the "Shastry-Sutherland" model. The Shastry-Sutherland model is one of the few 2D models that have an exact theoretical solution, which represents the quantum pairwise entanglement of magnetic moments in a square lattice structure. When conceived, the Shastry-Sutherland model seemed an abstract theoretical construct, but remarkably it was discovered that this model is realized experimentally in the material SrCu2(BO3)2. The work is published in Nature Physics. Read more here. (27/9/2017)

A bumper crop of vivas

We celebrate with three QM PhD students - Phil Brown, Hugh Glass, Matt Coak (from left to right in picture) - who have recently or very recently, as in today, successfully defended their theses. Congratulations on the successful completion of some very challenging work in good time, well under four years! Well done! (15/6/2017)



Viva(t) Edd Cavanna

QM PhD student Edd Cavanna has taken his viva (at last ...) with external examiner Prof. Andrew Boothroyd, internal Malte Grosche. Congratulations! Edd was supervised by Prof. John Cooper and his dissertation is titled 'New developments in the methods of differential calorimetry'. (16/3/2017)

Tallahassee spring-time expeditions

Numerous QM members have ventured to Florida this winter and spring for high-field measurements at the NHMFL facility in Tallahassee. They return with USB drives/Dropboxes full of data, eager to get on with the analysis. Preliminary results, e.g. observation of quantum oscillations at nearly 100 kbar in a metallised Mott insulator, suggest that this has been a particularly productive season. (14/3/2017)



QM christmas dinner

Quantum Matter has entered the 2015 festive season with a group dinner:





Gil Lonzarich wins the 2015 Kamerlingh Onnes prize

Prof. Gil Lonzarich has been selected for the 2015 Kamerlingh Onnes prize, in recognition of his 'visionary experiments concerning the emergence of superconductivity for strongly renormalized quasiparticles at the edge of magnetic order'. The Kamerlingh Onnes prize is awarded every three years at the M2S Conference, for outstanding experiments which illuminate the nature of superconductivity other than materials. It will be presented on August 24th, 2015 during the 11th International Conference on Materials and Mechanisms of Superconductivity in Geneva, Switzerland. More information can be found on the Departmental website or at the M2S conference website.

QM organises CDQM 2015

The Quantum Matter group is putting together a workshop this year: Concepts and Discovery in Quantum Matter from 12-15 July 2015 in Cambridge. (6/1/2015)

Prof. Jim Scott chosen as Thomson Reuters Citation Laureate

QM member Prof Jim Scott has been selected by Thomson Reuters as a Citation Laureate. More information here and on the Departmental website (1/10/2014)

New PhD students

QM welcomes ten new PhD students this autumn. Corentin Morice, Daniel Molnar and Wenting Guo already know the group well: they completed an MPhil in QM during 2012/13. Hugh Glass, Hajime Shinohara, Phil Brown and Konstantin Semeniuk, carried out research projects in QM during 2012/13. Xiaoye Chen and Matthew Coak join from Oxford (via Korea) and Imperial (via Singapore), and Yu-Te Hsu comes to us from Taiwan. May they have an interesting time here! (1/10/2013)

Landmark paper reaches 1000 citations

The 1998 paper Magnetically mediated superconductivity in heavy fermion compounds has just been referenced more than 1000 times! (30/9/2013)

Suchitra wins the 2012 IUPAP medal

We are pleased to announce that Dr Suchitra E. Sebastian is to be the recipient of the IUPAP Young Scientist Medal 2012. The IUPAP Young Scientist Medals in the field of magnetism are presented every three years, at the International Conference on Magnetism. One medal is awarded for theoretical/computational work and one other for experimental work.

Winton Fellowship to be taken up in QM

We are pleased to welcome new QM group member Dr. Sian Dutton, who is taking up one of the innagural Winton Fellowships at the Cavendish, part of the ambitious Winton Program for the Physics of Sustainability. Sian comes to us from Princeton group of Bob Cava, and plans to work primarily on synthesis and characterisation of novel oxide materials for Li ion batteries.



QM comings and goings

We have had a large turnover of graduate students in the past few months, some familiar faces have moved on, and we've welcomed three new ones. Congratulations to Lara Sibley, Paul Nahai Williamson, Oliver Welzel, Jack Gillet, Seb Haines and Jo Wensley, who have all successfully defended their PhD thesis! Welcome to Luman Qu, Hong'En Tan, Pascal Reiss and Hui Chang who all joined the group in September. Our group secretary, Gerie Lonzarich has retired and our new group administrator is Helen Verrechia, who can be reached at (0)1223 337254.



Patricia Alireza in Oprah Magazine

In QM we are used to seeing our members grace the pages of academic journals such as Physical Review Letters or Nature, but former member and current collaborator Patricia Alireza has pushed the envelope by appearing in an issue of Oprah Magazine. The article highlights Patricia's successful career as a scientist, while balancing the responsibilites of being a mother. While it's not entirely clear what she is doing with that handful of GPIB cables, it definitely makes a nice photo opp. Congratulations Patricia!



SCES 2011 to be held in Cambridge

The international meeting on strongly correlated electron systems will be held this year in Cambridge between August 29 and Septemeber 3. For up to date information on the program, how to register, and travel and accomodation details please see the official website at www.sces2011.org.

Publication of Book by Ross Walker

Congratulations Ross Walker who has just published a book with Cambridge University Press entitled "Reliability in Scientific Research: Improving the Dependability of Measurements, Calculations, Equipment, and Software".

Covering many techniques widely used in research, this book will help researchers in the physical sciences and engineering solve troublesome, and potentially very time consuming, problems in their work.

The book deals with technical difficulties that often arise unexpectedly during the use of various common experimental methods, as well as with human error. It provides preventive measures and solutions for such problems, thereby saving valuable time for researchers. Some of the topics covered are: sudden leaks in vacuum systems, electromagnetic interference in electronic instruments, vibrations in sensitive equipment, and bugs in computer software. The book also discusses mistakes in mathematical calculations, and pitfalls in designing and carrying out experiments. Each chapter contains a summary of its key points, to give a quick overview of important potential problems and their solutions in a given area.

5 PhD's awarded

Congratulations to a large group of graduating students who successfully defended their PhD theses over the past few months. Stephen Rowley, Chris Ko, David Tompsett, Catherine Zentile and Eoin O'Farrell all passed their vivas.

Gil Lonzarich Awarded the 2010 Rumford Medal

QM is pleased to announce that Prof. Gil Lonzarich, head of the group, has been awarded the 2010 Rumford Medal by the Royal Society.

The Rumford Medal was established in 1800, as is given every alternating year for "an outstandingly important recent discovery in the field of thermal or optical properties of matter made by a scientist working in Europe". Past winners include notable physicists such as Maxwell, Faraday, Bragg, Onnes and Debye.



Honorary Degree for Patricia Alireza

Congratulations to former QM group member and current collaborator who received an honorary degree from Occidental College in California.

This represents a double success for Patricia, whose paper on the pressure phase diagram of the 122 pnictide materials (co-authored with QM members Suchitra Sebastian, Chris Ko, Jack Gillet and Gil Lonzarich) has been named Editor's pick as one of the most highly cited of 2009 by the journal of condensed matter physics!



Prof. Sir Brian Pippard

A memorial page to Prof. Brian Pippard has been set up, with videos and images from his tribute lectures, which took place at the Cavendish laboraory last year..



Gordon Squires

We note with sadness the passing of QM member Dr Gordon Squires, a stalwart member of the Cavendish, who died on April 10th 2010 at the age of 85. Gordon will be remembered both for his research as a pioneer of neutron scattering and as one of our most committed teachers, particularly of experimental physics. He will be sadly missed.

Gordon's family has set up an email address for those who wish to pass along their memories. Please contact the group secretary if you would like to pass along your condolences.



QM comings and goings

Congratulations are in order for several QM students who have successfully defended their theses recently. Mark Dean, Doug Guthrie and Catherine Zentile were awarded Ph.Ds and Paul Syers was awarded an MPhil. QM postdoc (and former PhD student) Tim Benseman has also moved on, taking up a position at Argonne national lab in the US. Best wishes to all!

We have also had several new members join. Welcome to graduate students Sitikantha Das and Beng Tan who will be working with Suchitra. Sven Friedemann has come to the group to work with Malte on a Humbolt Foundation scholarship. Sven was previosuly with Max Planck Institute for Chemical Physics of Solids, where he worked on quantum criticality in YbRh2Si2.



Prof. Jim Scott Joins QM

QM welcomes Prof. James F. Scott, FRS, who is joining the group from the department of Earth Sciences. James is well known for his research on ferroelectric materials. Watch a video of him presenting giving his lecture "Why study Insulators?"



Royal Society URF for Suchitra

Congratulations to QM member Suchitra Sebastian who was awarded a Royal Society University Research Fellowship, which she plans to take up with the group from Oct. 1 2009. Suchitra works on crystal growth and quantum oscillation measurements of correlated electron systems.



One Day Memorial Meeting to Celebrate the Life of Prof. Sir Brian Pippard

The Cavendish Laboratory will be holding a one day memorial meeting to commemorate the life of Sir Brian Pippard. The meeting will be held on May 11 2009 and will consist of talks from physicists who worked with or were influenced by his work. The meeting web site is now up and running and will be updated with the schedule soon. Registration is necessary.



EasyMeeting announcement

We would like to announce the upcoming Cambridge-Leiden EasyMeeting on Quantum Matter which is the second conference in this series, the first having taken place in Cambridge last year. The conference will run on the 6th and 7th of May at the Lorentz Centre in Leiden, The Netherlands. Everyone is welcome to attend and Ph.D. students and post-docs are particularly encouraged to apply. Note that funding has been specially earmarked for junior researchers to help with travel costs and local expenses so please do go ahead and register!

For further information about the meeting see the conference web site.

Old news

To see read about old QM happenings, please visit our news archive.