Dr Sam T. Carr

Institut fur Theorie der Kondensierten Materie
Universitat Karlsruhe

Room: 10-08
Tel: ++49 721 608-7006
Email: carr@tkm.uni-karlsruhe.de

Research Interests

My research interest is broadly in the field of strongly correlated materials - by which I mean materials where the single particle picture breaks down due to interactions.   My current interests can be divided into a few more specific areas:

1. Low dimensional materials

In low dimensions, correlation effects are always more pronounced due to the lack of 'room' for particles to avoid each other.  On the other hand, there are powerful non-perturbative techniques in one dimension such as bosonization, integrability and conformal field theory.  This allows us to make progress in constructing the phase diagram and understanding the exotic correlated phases seen in low dimensional models.

Of particular interest to me has been ladder models, where it is possible to make progress on the old question of what happens when you try to combine orbital effects of magnetic field, a lattice, and interactions all within the same framework.  Another interesting example of a ladder model is the low-energy effective theory of carbon nanotubes, one of natures most perfect examples of a real one-dimensional system

2.Quasi-one-dimensional materials and dimensional crossover

While there is the occasional experimental example of a real one dimensional system, such as carbon nanotubes, most experiments are done on real three dimensional materials.  However, if the material is sufficiently anisotropic, one may consider it as weakly coupled lower dimensional units.  One than can ask the effect of this 'inter-chain coupling' on the phase diagram of the model.

Real materials that can be modelled by such a scheme are Sr14Cu24O41 which has a spin gap, and under calcium doping and pressure has a superconducting transition; and the Bechgaard salts, a large class of organic quasi-one-dimensional crystals.

3. Ultracold atomic systems

The recent advances in atom trap technology and the development of optical lattices (also known as 'crystals of light') have allowed the creation and measurement of quantum systems with an unprecedented level of control.  This allows one to think of them as 'quantum analogue simulations' of models of strongly correlated electrons.  Along with these experiments, there is much theoretical work that can be done: amongst my current interests are exploitation of the dipole-dipole interaction to engineer interesting interaction geometries, and the effect of the harmonic trapping potential on the phases of the system.

4. Transport and non-equilibrium noise through quantum dots

When materials become small enough in some dimensions (which is where interaction effects become strongest), standard scattering experiments become unfeasible due to the lack of scattering cross-section.  For many  true zero-dimensional or one-dimensional systems (as opposed to quasi-one dimensional mentioned above), the only reasonable experiments that can be performed are transport.  While transport measurements themselves will not usually well probe the correlation properties of the system, the current-noise often will.  These non-equilibrium properties however are still not completely understood, even for systems as simple as the Coulomb blockaded quantum dot.