Condensed Matter
Tuesday, January 17, 2017
11:00 AM
Physics Building, Room 313
Note special date.

Mohammed Ali Rajabpour
[Host: Israel Klich ]
Fluminense Federal University
"Formation probabilities, Postmeasurement entanglement entropy and Casimir effect "

ABSTRACT:
I will first introduce formation probability as a quantity which can determine the universality class of a quantum critical system. In other words, by calculating this quantity one can find the central charge and critical exponents of the quantum system. We will show that calculating this quantity boils down to finding Casimir energy of two needles. Then we will briefly talk about Shannon mutual information as another quantity which can play similar role. Finally, we will introduce postmeasurement entanglement entropy as a tripartite measure of entanglement. We will show that this quantity is related to the Casimir energy of needles on Riemann surfaces and can be calculated exactly for conformal field theories.
Ref:
1: MAR, Europhysics Letters, 112, 66001 (2015), J. Stat. Mech. (2016) 123101 and K. Najafi, MAR, Phys. Rev. B 93, 125139 (2016).
2: F. C. Alcaraz, MAR, Phys. Rev. Lett. 111, 017201(2013), Phys. Rev. B, 90, 075132 (2014).
3: MAR, Phys. Rev. B 92, 075108 (2015) , J. Stat. Mech. (2016) 063109 and MAR,
K. Najafi, MAR, JHEP12(2016)124.


Condensed Matter
Thursday, January 19, 2017
11:00 AM
Physics Building, Room 204
Note special room.

Gabor Halasz
[Host: Marija Vucelja]
KITP
"Resonant inelastic Xray scattering response of the Kitaev spin liquid"

ABSTRACT:
We propose that resonant inelastic Xray scattering (RIXS) is an effective probe to detect spinliquid character in potential material incarnations of the Kitaev spin liquid (such as the honeycomb iridates and ruthenium chloride). Calculating the exact RIXS response of the Kitaev honeycomb model, we find that the fundamental RIXS channels, the spinconserving (SC) and the nonspinconserving (NSC) ones, can probe the fractionalized excitations of the Kitaev spin liquid separately. In particular, SC RIXS picks up the gapless Majorana excitations with a pronounced momentum dispersion, while NSC RIXS creates immobile flux excitations, thereby rendering the response weakly momentum dependent.


Condensed Matter
Thursday, January 26, 2017
11:00 AM
Physics Building, Room 204
Note special room.

RESERVED


Condensed Matter
Thursday, February 2, 2017
3:30 PM
Physics Building, Room 204
Note special time.
Note special room.

Jeffrey Teo
[Host: Eugene Kolomeisky]
UVA  Department of Physics
"Between topological strings and topological phases"

ABSTRACT:
Topological phases in two and three dimensions can be theoretically constructed by coupledwire models whose fundamental constituents are electronic channels along strings. On the other hand the collective topological phases support further fractionalized emergent quasistring excitations or defects such as flux vortices. In this talk I will describe topological superconductors and Dirac (or Weyl) semimetals using coupledwire models, and discuss the fractional behavior of emergent topological strings.


Condensed Matter
Thursday, February 9, 2017
11:00 AM
Physics Building, Room 313

Reserved  Klich


Condensed Matter
Thursday, February 16, 2017
3:30 AM
Physics Building, Room 204
Note special time.
Note special room.

Reserved  Please see the Colloquia schedule


Condensed Matter
Thursday, February 23, 2017
11:00 AM
Physics Building, Room 313

Anjana Samarakoon
[Host: Seunghun Lee]
UVADepartment of Physics
"Dynamics of KitaevHeisenberg model on a Honeycomb lattice in the classical limit"

ABSTRACT:
Quantum spin liquids (QSLs) have achieved great interest in both theoretical and experimental condensed matter physics due to their remarkable topological properties. Among many different candidates, the Kitaev model on the honeycomb lattice is a 2D prototypical QSL which can be experimentally studied in materials based on iridium or ruthenium.. Here we study the spin1/2 Kitaev model using classical MonteCarlo and semiclassical spin dynamics of classical spins on a honeycomb lattice. Both real and reciprocal space pictures highlighting the differences and similarities of the results to the linear spin wave theory will be discussed in terms dispersion relations of the pureKitaev limit and beyond. Interestingly, this technique could capture some of the salient features of the exact quantum solution of the Kitaev model, such as features resembling the Majoranalike mode comparable to the Kitaev energy, which is spectrally narrowed compared to the quantum result, can be explained by magnon excitations on fluctuating onedimensional manifolds (loops). Hence the difference from the classical limit to the quantum limit can be understood by the fractionalization of a magnon to Majorana fermions. The calculations will be directly compared with our neutron scattering data on αRuCl3 which is a prime candidate for experimental realization of Kitaev physics.


Condensed Matter
Thursday, February 23, 2017
3:30 PM
Physics Building, Room 313
Note special time.

Reserved  Please see the Colloquia schedule


Condensed Matter
Thursday, March 2, 2017
11:00 AM
Physics Building, Room 313

Available


Condensed Matter
Thursday, March 16, 2017
11:00 AM
Physics Building, Room 313

Available


Condensed Matter
Thursday, March 23, 2017
11:00 AM
Physics Building, Room 313

Abhishek Roy
[Host: Jeffrey Teo]
Institute for Theoretical Physics, University of Cologne
"The Haldane phase in spin chains with SU(N) symmetry"

ABSTRACT:
Spin chains with PSU(n) symmetry are known to have symmetry protected topological phases distinguished by boundary states. We determine the parent Hamiltonians of some of these phases at the AKLT point. In the adjoint representation we use a graphical method that produces expressions for arbitrary N. Finally we discuss the fate of the Haldane conjecture.


Condensed Matter
Friday, March 24, 2017
9:00 AM
Physics Building, Room 205
Note special date.
Note special time.
Note special room.

Mulugeta Bekele
[Host: Bellave Shivaram]
Addis Ababa University, Ethiopia
"Energetics of a heat engine: a molecular dynamics simulation study"

ABSTRACT:
I first consider an elevator as a system that lifts a load from a ground floor to a top floor by consuming an input energy. I ask: what amount of load enables the system to perform maximum amount of power? Can I design a mode of operation where I can utilize good enough amount of the input energy better than that of energy utilized at maximum power?
I will then go over to a molecular dynamics simulation study of a heat engine where the working substance is a real gas and try to address similar questions as the elevator system.


Condensed Matter
Thursday, March 30, 2017
11:00 AM
Physics Building, Room 313

Gaurav Giri
[Host: Seunghun Lee]
University of Virginia, Chemical Engineering
"Understanding and Controlling Organic Molecule and Metal Organic Framework Crystallization "

ABSTRACT:
Small organic molecules have had a dramatic impact on our health and daily life over the past century. Small molecule pharmaceuticals have increased human lifespans, and organic pigments have expanded in use in textiles and displays. This impact is set to accelerate in the near future, as small molecules are explored for novel applications such as organic electronics, or metalorganic frameworks for chemical separations, catalysis and sensing. One of the major barriers for using small organic molecules for new applications is the limited understanding we possess on how molecules aggregate together to form different crystal habits and phases. Different crystal structures and morphologies can have wildly varying physical, chemical and physiological properties. Thus, if we do not control the crystallization organic molecules, we cannot predict its behavior for the aforementioned applications. Understanding the crystallization process can also help form metastable phases. These metastable phases can be more useful than the equilibrium phase for many applications. Metastable phases permit tunable optical bandgap for optoelectronics, control over pore size and shape in metal organic frameworks (MOF), and increased bioavailability in pharmaceuticals. General methods used to create metastable phases, like confinement or rapid cooling, require small length scales and extreme rates of heat and mass transfer. Moreover, these processes need precise control to get reliable results. This talk will focus on flow coating and microfluidic methods of controlling organic molecule and MOF crystallization characteristics, and the use of these materials for various applications.


Condensed Matter
Thursday, April 6, 2017
11:00 AM
Physics Building, Room 313

Jon Machta
[Host: Marija Vucelja]
University of Massachusetts
"Understanding glassy systems using population annealing"

ABSTRACT:
Population annealing is a sequential Monte Carlo method for studying the equilibrium properties of glassy systems characterized by rough free energy landscapes. In this talk I will introduce two glassy systems, the Ising spin glass and a glassforming binary mixture of hard spheres. I will describe population annealing and some of its useful features, and then present results from simulations of these glassy systems.
http://people.umass.edu/machta/


Condensed Matter
Thursday, April 13, 2017
11:00 AM
Physics Building, Room 313

Bhanu Mahanti
[Host: Utpal Chatterjee]
Michigan State University
"Unusual magnetic order in some frustrated spin systems: "

ABSTRACT:
Classical and quantum spin systems have played an enormously important role in the study of magnetism. They provide excellent models to understand the ground state magnetic structure and low energy excitations of magnetic systems. In addition, they provide a rich arena for studying the physics of interacting manybody systems. In this talk I will discuss a very specific problem, namely the observation of an unusual ordering of spins, the so called uudd states, in quasi onedimensional Heisenberg spin chains and anisotropic twodimensional Heisenberg spin systems. Theoretical work to understand this and some related issues using both model spin Hamiltonians with competing interactions, exchange anisotropy, biquadratic exchange etc. and ab initio electronic structure calculations, will be discussed.


Condensed Matter
Thursday, April 13, 2017
3:30 PM
Physics Building, Room 204
Note special time.
Note special room.

Syed Raza
[Host: Jeffrey Teo]
UVA Physics Department
"Symmetry preserving gapping of Topological Weyl and Dirac semimetals"

ABSTRACT:
Topological Weyl and Dirac semimetals in three dimensions have gapless (massless) Weyl fermions. These semimetals were predicted theoretically in 2011 (Vishwanath et al, Burkov and Balents) and have been experimentally discovered recently in TaAs, TaP, NbAs, NbP (Weng et al., Huang et al., Shekhar et al., 2015). Although these gapless systems can be gapped (given mass) trivially by symmetry breaking terms, a more interesting problem is if they can be gapped without breaking symmetries? We show that you can indeed do this by introducing many body interactions. We also show that this symmetrypreserving gapping gives pointlike and linelike anyonic excitations in the gapped bulk.


Condensed Matter
Thursday, April 20, 2017
11:00 AM
Physics Building, Room 313

RESERVED


Condensed Matter
Wednesday, April 26, 2017
5:00 PM
Physics Building, Room 313
Note special date.
Note special time.

Alexander Sirota
[Host: Jeffrey Teo]
UVADepartment of Physics
"Surfaces and Slabs of Fractional Topological Insulators"

ABSTRACT:
Fractional topological insulators (FTI) are electronic topological phases in (3 + 1) dimensions enriched by time reversal (TR) and charge U(1) conservation symmetries. We focus on the simplest series of fermionic FTI, whose bulk quasiparticles consist of decon ned partons that carry fractional electric charges in integral units of e = e=(2n + 1) and couple to a discrete Z2n+1 gauge theory. We propose massive symmetry preserving or breaking FTI surface states. Combining the longranged entangled bulk with these topological surface states, we deduce the novel topological order of quasi(2 + 1) dimensional FTI slabs as well as their corresponding edge conformal eld theories. We will also describe some past work on coupled wire constructions of Weyl/Dirac semimetals, and some new work about mechanical topology and conformal field theory.


Condensed Matter
Thursday, April 27, 2017
11:00 AM
Physics Building, Room 313

Boris I. Ivlev
[Host: Genya Kolomeisky]
Landau Institute and Instituto de Fisica, UASLP
"SUBATOMIC STATES IN CONDENSED MATTER AND MAGNETORESISTANCE OF SUPERCONDUCTORS"

ABSTRACT:
In the recent experiments, PRB 94, 054504 (2016), the unusual oscillatory magnetore sistance of superconductors was discovered with a periodicity essentially independent on magnetic ﬁeld direction and even material parameters. The nearly universal period points to a subatomic mechanism of the phenomenon. This mechanism is related to formation inside samples of subatomically thin (10−11cm size) threads in the form of rings of the interatomic radius. Electron states of rings go over into conduction electrons which carry the same spin imbalance in energy as the ring. The imbalance occurs due to the spin interaction with the orbital momentum of the ring. The conductivity neat Tc is determined by ﬂuctuating Cooper pairs consisting of electrons with shifted energies. Due to diﬀerent angular momenta of rings these energies periodically depend on magnetic ﬁeld resulting in the observed oscil latory magnetoresistance. Calculated universal positions of peaks (n + 1)∆H (∆H '"" 0.18T and n = 0, 1, 2, ...) on the R(H) curve are in a good agreement with measurements.

