Condensed Matter Oxford

Condensed Matter Physics Research in Oxford

● Condensed matter physics group ● Research themes ● Graduate study in condensed matter physics

copy of this lecture at www.physics.ox.ac.uk/CM

Condensed Matter Physics at Oxford

(chairman: Prof Roger Davies)

Astrophysics

Atmospheric & Oceanographic Physics

Atomic & Laser Physics

Condensed Matter Physics

Particle & Nuclear Physics

(Head: Dr Andrew Boothroyd)

Theoretical Physics

CMP sub-department

● 17 academics ● 30 research staff/visitors ● 55 graduate students

Dr A Ardavan Dr R M Berry Prof S J Blundell Dr A T Boothroyd Prof R A Cowley Prof A M Glazer Dr J F Gregg Dr L M Herz Dr M B Johnston Prof N F Johnson Mr H Jones Dr A N Kapanidis Prof R J Nicholas Prof J F Ryan Dr R Taylor Prof A J Turberfield Dr R C C Ward

Condensed matter physics in the 20th century Successes: ● one-electron band theory

● simple metals, insulators & semiconductors

● magnetism

● conventional superconductors (BCS theory, 1957)

Developments and challenges in condensed matter physics ● Quantum materials — materials with exotic physical properties arising from quantum effects ● Nanoscale physics — natural and artificial structures for novel electronic devices ● Biological physics — applying physics to understand biology and using biological material to make devices ● Complexity in condensed matter — emergence of large-scale behaviour not pre-existent in the constituents of a system

Quantum Materials Materials with strong electronic correlations can form new states of matter with dramatic physical properties

High temperature superconductivity

Colossal magnetoresistance

Quantum Materials Strong electronic correlations Competition between different electronic degrees of freedom Spin–charge order

1/2-filled band (Mott insulator)

5/8-filled band

3/4-filled band

Charge–orbital order

Quantum Materials Crystal geometry is important

Geometric frustration leads to high degeneracy

Quantum fluctuations important in low dimensions E.g. one-dimensional S=1/2 antiferromagnet

E.g. triangular antiferromagnet

Doubly degenerate ground state

Energy

Spinon dispersion relation

wavevector

Quantum Materials Research groups Ardavan

magnetic molecules, electron-spin resonance, resonance carbon nanomaterials, polarization synchrotron

Blundell

magnetic molecules and oxides, organic superconductors, muon-spin spectroscopy

Boothroyd

magnetic oxides, unconventional superconductors, neutron and X-ray scattering

Cowley

quantum magnetism, magnetic thin films, neutron and X-ray scattering

Glazer

crystallography, phase transitions, polarization microscopy, X-ray diffraction

Jones

applied superconductivity, superconducting materials, magnet development

Ward

Epitaxial growth of magnetic thin films and superlattices, structural characterisation

Muon-spin rotation Prof Steve Blundell’s group Positron decay is asymmetric with respect to the initial muon-spin polarization because of parity violation. Muon-spin precession rate follows local magnetic field

Fundamental studies of molecular magnetism, correlated oxides, and organic superconductivity

MUON

POSITRON

NEUTRINOS

ISIS, Oxfordshire The world’s most intense Source of pulsed muons

PSI, Switzerland - continuous muon beam

Dr Andrew Boothroyd Unravelling electronic order in complex magnetic oxides Current projects: Unconventional superconductors Spin–charge ordered systems Orbital order Multiferroics Mirror furnace in Clarendon Lab

Phase diagram of NaxCoO2 ILL/ESRF site in Grenoble, France MAPS neutron spectrometer at ISIS

Experimental techniques: 1. Neutron and X-ray scattering using international facilities, e.g. Institut Laue-Langevin (France) and ISIS Facility (Rutherford Appleton Lab) Copper oxide superconductor

Magnon dispersion relation

http://xray.physics.ox.ac.uk/Boothroyd

2. Magnetometry, heat capacity, transport, crystal growth, etc, in the Clarendon Lab.

Professor A.M. Glazer (Room 373, tel:272290 [email protected] 1. Study of phase transitions and relationship between crystal structure and physical properties. Uses x-ray and neutron diffraction plus optical microscopy measurements. 2. Design of novel instrumention for the study of crystals e.g. Metripol microscope (see www.metripol.com) The figures below show optical birefringence measurents made with a single crystal of lead magnesium niobate-titanate in which the composition changes linearly from left to right. The whole phase diagram is then traced out automatically when the temperature is changed.

Theme: Characterisation of new materials properties and critical construction methods at cryogenic temperatures for MRI magnets. Industrial CASE project sponsored by Siemens Magnet Technology Ltd. A project which straddles the boundaries of applied physics, materials science and engineering and is highly relevant to both industry and medicine. The theme will encompass many possible experimental and computer modelling techniques. These may include: •Mechanical properties at cryogenic temperatures of metallic, polymeric, superconducting and composite materials. •Electrical properties at cryogenic temperatures and high magnetic fields •Thermal properties at cryogenic temperatures and high magnetic fields •Residual strain using neutron diffraction •Development of superconducting electrical joints and measurement of their critical currents at the pV m-1 level of electric field. The student would play a major role in defining the precise content and direction of the work. A practical, flexible attitude and an interest in technological problem solving is essential. Contact: Harry Jones, [email protected]

Research Projects in the Oxford MBE Group MBE growth and characterisation of nanostructured magnetic materials

Novel uranium multilayers fabrication, characterisation and magnetic properties

(EPSRC collaborative project)

(European research network)

Growth of epitaxial magnetic thin-film devices such as spin-valves and tunnel junctions. Limit to lower dimension (1D and 0D) by lithography/patterning.

Growth by UHV sputtering of U/Fe multilayers and other U/TM systems.

Eg. MnFe/FeCo/MgO/Fe TMR structures Superlattices of RE-TM compounds

Exploit 5f electron physics.

Extend to compounds of uranium such as UO2.

Structural and magnetic characterisation X-ray reflectivity and diffraction : laboratory and synchrotron sources ESRF, Grenoble (resonant scattering) with Prof R.Cowley Neutron reflectivity and diffraction : ISIS, Rutherford-Appleton Laboratory, ILL, Grenoble Electron diffraction :

Reflection High Energy Electron Diffraction (in-situ) High Resolution Electron Microscopy (Materials Dept)

SQUID magnetometry : magnetic behaviour of epitaxial device structure

Roger Ward , Dept of Physics

Nano-scale physics The study of atoms, molecules and other objects whose dimensions are on the nanometer scale

● Quantum mechanical phenomena become apparent ● Possibility of making new materials that have different characteristics from bulk materials ● New instrumentation has been developed to fabricate and “see” nanoscale objects (e.g. nanolithography, AFM, STM) ● Applications in novel electronic and spintronic devices STM image of Fe atoms on Cu surface

Nano-scale physics Examples of topical nano-objects

Quantum dots Nano-wires

Quantum dots

Quantum wells FIB patterned nanowires

Carbon nanotubes and fullerenes Thin film structures and devices hν

Single molecules Photonic crystals

molecular nanostructure

Carbon buckyball Carbon nanotubes

Nano-scale physics Research groups

Gregg

magnetic spintronic devices, magneto-optics, magnetic sensors

Herz

organic semiconductors, molecular self-assembly, exciton dynamics, femtosecond spectroscopy

Johnston

Time-domain spectroscopy, semiconductor nanostructures, organic semiconductors

Nicholas

Semiconductor nanostructures, carbon nanotubes, photovoltaic devices, magneto-optical properties

Taylor

Quantum dots and wells, ultrafast spectroscopy, quantum information processing

Turberfield

photonic crystals — fabrication and devices

Spin Electronics Group: Dr. John Gregg

Current Group Interests: • Silicon based spintronic devices • Ultra fast magneto-optics • Novel magnetic sensor designs • Materials and interaction characterisation

Silicon based spin transistor: The integration of magnetic selectivity into conventional semi-conductor technology. Manipulation of spin systems using ultra fast laser pulses. Exploring methods of high speed optical switching and the dynamics of magnetism on femtosecond time scales

Measurement of the electron spin polarisation in metals using new techniques

Magnetic resonance force microscopy, imaging and manipulating magnetism on the nanoscale

Biological Physics and Bionanotechnology Structure of biological molecules

● Dorothy Hodgkin (Oxford): structures of penicillin (1942-49), vitamin B12 (1948-56), insulin (1933-69) by X-ray diffraction ● Double helix structure of DNA (Crick, Watson, Wilkins, Franklin 1953)

Biological Physics and Bionanotechnology Oxford Bio-nanotechnology Interdisciplinary Research Collaboration (IRC) (Director: Prof John Ryan)

● Molecular machines — proteins in which enzymic activity e.g. energy conversion and self-assembly, are integrated to produce linear or rotary motion on a nanometre scale ● Functional membrane proteins — biologically-evolved nano-switches and triggers ● Nano-electronics and photonics — integration of electrically and optically active biomolecules to produce devices, networks and sensors ● State-of-the-art equipment — fabrication, manipulation and detection

Biological Physics and Bio-nanotechnology Research groups

Berry

biological molecular motors, optical tweezers, fluorescence microscopy

Fischer

Mechanisms of viral ion channels, Bio-nanotechnology

Kapanidis

genetic transcription, bio-nanomachines, single molecule fluorecence spectroscopy

Ryan

DNA/RNA motors and machines, bio-nanotechnology, atomic force microscopy

Turberfield

DNA nanostructures, DNA self-assembly, DNA molecular machines

Complexity Complex systems with large numbers of interacting parts can behave in a predictable way

● animal populations ● financial markets ● traffic flows ● interacting electrons ● biological networks

Graduate study in condensed matter physics Some famous Clarendon Lab. graduate students

Henry Gwyn Jeffreys Moseley

Sir Martin Wood (Oxford Instruments plc)

Application Procedure See www.admin.ox.ac.uk/gsp

● studentships (DTA, project, IRC, CASE, DTC, overseas) ● apply through the university ● monthly application deadlines (for UK/EU students) (1 Jan ’06, 1 Feb ’06, etc, 1 June ’06)

● interviews 2–4 weeks after deadline ● decisions

Choosing a project

● Find out about projects — research lecture (today) — projects booklet — group web sites ● ●

Tell us which projects interest you Arrange informal visits to research groups

What will I actually do?

● making samples ● building apparatus ( )

( )

2

intrastripe

inter− stripe

● measurement

i

2 2

i

1.5

Sc/S||

● theory

H = J ∑ Si ⋅ S j + J ′ ∑ Si ⋅ S j′ + Ka ∑ Six + Kc ∑ Siz

1 x = 0.33 Qm = (1.33, 1.33)

0.5

T = 13 K 0

● data analysis ● using international facilities

0

5

10 15 20 Energy (meV)

25

30

Information

● Web sites: www.admin.ox.ac.uk/gsp www.physics.ox.ac.uk/CM ● Research booklet (www.physics.ox.ac.uk/CM/graduateprogramme.htm) ● Director of Graduate Studies: Prof Mike Glazer ([email protected]) ● Consensed Matter secretary: Mrs Janet Andrews ([email protected]) ● Head of Condensed Matter Physics: Dr Andrew Boothroyd ([email protected])