Oct. 2 Club Meeting: Neel Haldolaarachchige

Interesting physical properties hidden inside an uninteresting correlated electron system.

FeGa3 is a non-magnetic semiconducting compound. For a long period it has been considered only for high temperature thermoelectric properties (TE). However, Yin and Picket (1) last year theoretically suggested that possible magnetic ground state hidden inside this compound. Furthermore, they have closely investigated structure of this compound and found that Fe-Fe dimmers in this compound are in non-magnetic spin singlet state. Immediately following Bitter et al. (2) found that small amount Co doping changes the system into a heavy Fermion like with low temperature paramagnetic (PM) behavior and they suggest PM-state is possibly due to Co-Co dimer formation at very low temperature. Followed by that Storchak at al. (3) suggested spin-polaron state formation below 10K and further suggested spin-polaron as a mechanism for possible magnetic state in this compound. We have seen electronic structure of this compound is very sensitive to pressure when we have investigated this compound for TE properties (4). Further investigation gave us  unbelievable results.

References:

(1) Evidence for a spin singlet state in the intermetallic semiconductor FeGa3, PRB, 82, 155202 (2010)

(2) Correlation effects in the small gap semiconductor FeGa3, Journal of Physics: Conference Series, 200, 012014 (2010)

(3) Thermal destruction of spin-polaron bands in the narrow-gap correlated semiconductors FeGa3 and FeSb2, J.Phys.Cond.Matter, 24, 18 (2012)

(4) Effect of chemical doping on the thermoelectric properties of FeGa(3), J.Applied Physics, 109, 103712 (2011)

Time: Oct 2, Tuesday, noon.

Location: Rm. 435, Nicholson Hall.

Foods and drinks will be provided.

Sept. 25 Club Meeting: Dr. Ziyang Meng

Paper to be discussed:

Antiferromagnetism in the Hubbard Model on the Bernal-Stacked Honeycomb Bilayer

Thomas C. Lang, Zi Yang Meng, Michael M. Scherer, Stefan Uebelacker, Fakher F. Assaad, Alejandro Muramatsu, Carsten Honerkamp, and Stefan Wessel.
Phys. Rev. Lett. 109, 126402 (2012)

Abstract:

Using a combination of quantum Monte Carlo simulations, functional renormalization group calculations and mean-field theory, we study the Hubbard model on the Bernal-stacked honeycomb bilayer at half-filling as a model system for bilayer graphene. The free bands consisting of two Fermi points with quadratic dispersions lead to a finite density of states at the Fermi level, which triggers an antiferromagnetic instability that spontaneously breaks sublattice and spin rotational symmetry once local Coulomb repulsions are introduced. Our results reveal an inhomogeneous participation of the spin moments in the ordered ground state, with enhanced moments at the threefold coordinated sites. Furthermore, we find the antiferromagnetic ground state to be robust with respect to enhanced interlayer couplings and extended Coulomb interactions.

Time: Sep 25, Tuesday, noon.

Location: Rm. 435, Nicholson Hall

Foods and drinks will be provided.

Sep 18 Club Meeting: Dr. Ka Ming Tam

Abstract:

Unlike the commonplace electrically charged particles, magnetic monopoles have not been found despite a long time search for them. However, magnetic monopoles among quasi-particles are not unheard of for physicists. In this talk, Ka Ming will introduce the theoretical grounds and the experimental detection of magnetic monopoles in a class of magnets called spin ice.

Time: Sep 18, Tuesday, noon.
Location: Rm. 435, Nicholson Hall
Food and drink will be provided.

Paper to be discussed:

Magnetic Monopoles in Spin Ice
Claudio Castelnovo, Roderich Moessner, Shivaji L. Sondhi
Nature 451, 42-45 (2008)
Download link through arXiv

Welcome to our first meeting! In case anyone doesn't know Room 435, the stairs and the elevator are located at the east half of Nicholson Hall, accessible conveniently from the gate facing the Student Union. Note that we are only permitted to occupy the half of Rm 435 that has tables.