Graeme Luke
Graeme Luke
ABB 260

Research in the Luke group focusses on experimental studies of so-called quantum materials which include exotic superconductors and novel magnetic systems. Systems which combine superconductivity with magnetism are of special interest.

At present, our group is actively studying a number of systems including pnictide and cuprate high temperature superconductors in addition to a variety of so-called heavy fermion systems where electron-electron interactions results in extremely large carrier effective masses. Some of these heavy fermion systems exhibit a number of exotic ordering phenomena ranging from magnetic order and superconductivity to so-called hidden order where a thermodynamic phase transition is apparent in a range of measurements, but the nature of the ordered state is unknown.

We have an ongoing major interest in magnetic systems where geometrical frustration and/or low dimensionality conspire to preclude conventional magnetic order, allowing more exotic magnetic ground states to emerge. An illustration of this type of phenomena is provided by Sr3Cr2O8. This system consists of a loosely connected network of spin dimers. In the presence of large magnetic fields the system undergoes a quantum phase transition from a collective singlet non-magnetic ground state to an ordered state which can be described as a Bose-Einstein condensate of magnetic excitations (magnons).

Muon spin relaxation, Crystal growth, Electronic properties, Magnetism, High pressure, High magnetic fields

Graeme Luke
Department of Physics & Astronomy
McMaster University

Dear Prospective Graduate Student,

Thank you for your interest in condensed matter physics at McMaster. My research is in the area of highly correlated electron systems, especially exotic superconductivity and magnetism. At present I have one graduate student (on the border between MSc and PhD); a second student has just graduated. In the experimental correlated electron physics group as a whole (Gaulin, Luke, Timusk) there are generally 6 students, 2 or 3 postdocs and a few research scientists. Previous students in my group have gone on to work in industry, academia and teaching (in Thailand) and have presented their work at both national (Toronto, Quebec, Vancouver, Victoria) and international (Switzerland, Japan) conferences. I'm an associate in the Canadian Institute for Advanced Study (CIAR) Superconductivity program; each year this program has a summer school for graduate students as well as an annual meeting (for students and faculty).

Much of my research involves the technique of muon spin rotation (µSR), which roughly speaking, is a type of magnetic resonance (like NMR) performed using implanted muons. These experiments are performed mainly at TRIUMF in Vancouver, but also at ISIS (near Oxford, England). Click here for an introduction to the µSR technique.

My present interests include high temperature and other exotic types of superconductivity and low dimensional magnetism. Some of the systems I'm working on are:

  • Sr2RuO4 is a 1.5K superconductor. As a result of the work of our group and others, Sr2RuO4 is thought to be a p-wave superconductor where the electrons forming the Cooper pairs are arranged with parallel spins.
  • La2CuO4+x and La2-xSrxCuO4 are high Tc superconductors which can undergo both superconducting and magnetic/charge ordering (in the form of charge/magnetic stripes). We are using µSR to study the interplay of superconductivity and magnetism in these materials.
  • There a a number of magnetic materials where either the effective dimensionality of the magnetic interactions or the presence of geometrical frustration prevents the formation of an ordered state. Various quantum ground states can subsequently emerge including Anderson's resonating valence bond (RVB) singlet state, a spin Peierls state, a spin plaquette singlet and others. We are using µSR to identify these states and to characterize their excitations.

In addition to my work in µSR, I have a laboratory at McMaster equipped for low temperature magnetic, electrical transport and thermal measurements. The two main systems in my lab are a Quantum Design SQUID magnetometer for measurements from 1.8K to 800K in magnetic fields up to 5.5T and an Oxford Instruments Maglab ExaSystem for ac-susceptibility, specific heat and electrical transport measurements in magnetic fields as high as 9T and temperatures down to 1.5K. Furthermore, we have excellent facilities for materials preparation including two floating zone optical image furnaces which allow us to grow large single crystals of extreme purity.

There are openings in my research group for one or two new graduate students, either at the MSc or PhD level. I have ongoing projects in high Tc and heavy fermion superconductivity as well as low dimensional and frustrated magnetism. Our world-class crystal growth facilities allow us to study virtually any system of interest. New projects of mutual interest are also possible. Please send me an email if you'd like to discuss possibilities for graduate work in my group.

Graeme Luke

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