R. G. Herb Condensed Matter Seminars |
Events During the Week of February 24th through March 3rd, 2013
Monday, February 25th, 2013
- Orthogonal Metals - the simplest non-Fermi liquids
- Time: 4:30 pm
- Place: 5310 Chamberlin
- Speaker: Rahul Nandkishore, Princeton University
- Abstract: I present a fractionalized metallic phase which is indistinguishable from the Fermi liquid in conductivity and thermodynamics, but is sharply distinct in one electron properties, such as the electron spectral function. This phase is dubbed the `Orthogonal Metal.' The Orthogonal Metal and the transition to it from the Fermi liquid are naturally described using a slave particle representation wherein the electron is expressed as a product of a fermion and a slave Ising spin. I emphasize that when the slave spins are disordered the result is not a Mott insulator (as erroneously assumed in the prior literature) but rather the Orthogonal Metal. I present prototypical ground state wavefunctions for the Orthogonal Metal by modifying the Jastrow factor of Slater-Jastrow wave- functions that describe ordinary Fermi liquids. I further demonstrate that the transition from the Fermi liquid to the Orthogonal Metal can, in some circumstances, provide a simple example of a continuous destruction of a Fermi surface with a critical Fermi surface appearing right at the critical point. I present exactly soluble models that realize an Orthogonal Metal phase, and the phase transition to the Fermi liquid. These models thus provide valuable solvable examples for phase transitions associated with the death of a Fermi surface.
Reference: R. Nandkishore, M. Metlitski and T. Senthil, Phys. Rev. B 86, 045128 (2012)
- Host: Chubukov
Tuesday, February 26th, 2013
- Gate control of single electron spin in III-V semiconductor quantum dots: Anisotropy effects
- Time: 10:00 am
- Place: 5280 Chamberlin Hall
- Speaker: Sanjay Prabhakar, Wilfrid Laurier University
- Abstract: Among recent proposals for next-generation non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In the first part of my talk, I present numerical simulations of such spins in single-electron devices for realistic asymmetric confining potentials in two-dimensional electrostatically confined quantum dots. Using both analytical and numerical techniques, I show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g- factor and on the spin-flip rate mediated by phonon with applied gate potentials. In particular, anisotropy either extends the range of the tunability of the g-factor and spin-hot spot to larger quantum dots or viceversa. For example, anisotropy reduces the tunability of the g-factor and spin hot spot to smaller quantum dots radius as well as to smaller magnetic fields if we keep the area of the symmetric and asymmetric quantum dots same. It is well known that the cusp-like structure due to accidental degeneracy in the phonon mediated spin-flip rate can be seen only for the case of pure Rashba spin-orbit coupling in symmetric quantum dots. I present new analytical and numerical results which show that the cusp-like structure can be seen for pure Dresselhaus spin-orbit coupling case in asymmetric quantum dots.
In the second part of my talk, I investigate the geometric phase induced on the spin states during the adiabatic movement of the III-V semiconductor quantum dots in the plane of two-dimensional electron gas under the influence of applied gate potential along the lateral direction. Here, I present the spin-flip probabilities during the adiabatic evolution in the presence of the Rashba and the Dresselhaus linear spin-orbit interactions. I use the Feynman disentanglement technique to determine the non-Abelian Berry phase and find exact analytical expressions for three special cases: (a) the pure Rashba spin-orbit coupling, (b) the pure Dresselhause linear spin-orbit coupling, and (c) the mixture of the Rashba and Dresselhaus spin-orbit couplings with equal strength. For a mixture of the Rashba and the Dresselhaus spin-orbit couplings with unequal strengths, I obtain numerical results by solving the Riccati equation originating from the disentangling procedure. I find that the spin-flip probability in the presence of the mixed spin-orbit couplings is generally larger than those for the pure Rashba case and for the pure Dresselhaus case, and that the complete spin-flip takes place only when the Rashba and the Dresselhaus spin-orbit couplings are mixed symmetrically.
References:
Gate control of a quantum dot single-electron spin in realistic confining potentials: Anisotropy effects; Sanjay Prabhakar and James Raynolds, phys. Rev. B 79, 195307 (2009).
Manipulation of single electron spin in a GaAs quantum dot through the application of geometric phases: The Feynman disentangling technique; Sanjay Prabhakar, James E Raynolds, Akira Inomata and Roderick Melnik, Phys. Rev. B 82, 195306 (2010).
Manipulation of the Lande g-factor in InAs quantum dots through the application of anisotropic gate potentials; Sanjay Prabhakar, James E Raynolds and Roderick Melnik, Phys. Rev. B 84, 155208 (2011).
The influence of anisotropic gate potentials on the phonon induced spin-flip rate in GaAs quantum dots; Sanjay Prabhakar, Roderick Melnik and Luis L Bonilla, Applied Physics Letters 100, 023108 (2012).
- Host: Friesen
Wednesday, February 27th, 2013
- Title to be announced
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Smitha Vishveshwara from the University of Urbana-Champaign.
- Host: Perkins
Thursday, February 28th, 2013
- Engineering Synthetic Quantum Materials from Cold Atoms: Mott Insulators to Emergent Polariton Crystals
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Jonathan Simon, University of Chicago
- Abstract: The tools of atomic physics provide a unique and powerful toolbox for studies of quantum many-body physics. Using such systems it has recently become possible to engineer strongly-correlated materials from the ground up and probe them with single-atom resolution. I will describe experiments in which we have synthesized the first magnetic material composed of ultracold atoms, and watched it undergo a quantum phase transition from a paramagnet to an antiferromagnet. I will then introduce a new algorithmic cooling scheme that we have demonstrated, pointing the way to yet more exotic quantum phases that exist at lower temperatures. Finally, I will describe ongoing efforts to develop materials composed of strongly correlated photons whose long-range anisotropic interactions will open new horizons, permitting studies of quantum soft-matter.
- Host: Vavilov & Saffman
Friday, March 1st, 2013
- No events scheduled