Spring 2018

Moire Superlattice Bands in Dirac Materials 

Speaker(s): 
Jeil Jung Woo
Dates: 
Tuesday, May 22, 2018 - 4:00pm to 5:00pm

When atomically thin two-dimensional (2D) materials are layered, they often form incommensurable noncrystalline structures that exhibit long-period moiré patterns when examined by scanning probes. In this presentation we will use graphene and hexagonal boron nitride as examples of gapless and gapped Dirac materials to illustrate how the moire superlattices due to interlayer coupling can alter the materials' intrinsic electronic properties. The derivation of the effective models for these van der Waals materials heterojunctions for arbitrary twist angles can benefit from input obtained from ab initio calculations carried out for commensurate short period crystalline structures. We will discuss how the moire pattern modified electronic structures give rise to a variety of experimentally measurable features including enhanced density of states through van Hove singularities, and flat bands, or to their suppression due to formation of band gaps.

Infrared Radiation for Healthy Living: Disease Diagnostics 

Speaker(s): 
A. G. Unil Perera
Dates: 
Friday, May 18, 2018 - 10:30am to 11:30am

The incidence rates of cancers and other chronic diseases have been increasing in many regions and populations.  There are more than 70,000 new cases of inflammatory bowel diseases (IBD) such as ulcerative colitis, diagnosed every year. Established diagnostic techniques for cancers and ulcerative colitis are invasive, cause discomfort, and are not cost-effective. The compliance rate for the screening of such diseases is very small due to this discomfort, expense, and the risk of complications. Thus, it is important to develop minimally invasive or noninvasive and cost-effective prescreening strategies.   

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy accompanied with different data analysis frameworks can provide an excellent spectroscopic technology to extract biochemical information from bio-fluids which can lead to the identification of diseases. Results show that dried serum samples can be used to detect the biochemical changes induced by cancers and IBDs. This potential technology can be further developed into a noninvasive, personalized diagnostic tool in which patient-to-patient differences in molecular signatures would allow the assessment of disease status and personalized drug management.  

Bradley Slezak Received His Ph.D. Degree 

  • By Burcu Ozden
  • 8 May 2018

Bradley Slezak was a graduate student under the supervision of Wolfgang J. Choyke and Brian D'Urso.

This spring he has successfully passed his Ph.D. defense. On Thursday, April 26, 2018 he attended the commencement ceremony at the John M. and Gertrude E. Petersen Events Center to receive his degree.

His research involved measuring the decoherence rate of non-classical states of the trapped particle.

Congratulations Dr. Bradley Slezak !
 

Walter Klahold Received His PhD Degree

  • By Burcu Ozden
  • 8 May 2018

Walter Klahold was a graduate student under the supervision of Wolfgang J. Choyke and Robert P. Devaty 

This spring he has successfully passed his Ph.D. defense. On Thursday, April 26, 2018, he attended the commencement ceremony  at the John M. and Gertrude E. Petersen Events Center to receive his degree.

His research involved energy level structure of free excitons in 4H SiC from wavelength modulated absorption spectroscopy and low-temperature photoluminescence.

Congratulations Dr. Walter Klahold !

Reeja Jayan was Recognized as an Innovator in 3D Printing by Engineering.com

  • By Burcu Ozden
  • 8 May 2018

B. Reeja Jayan was recognized as an innovator in 3D printing by Engineering.com for her work in creating more efficient ceramic 3D printing techniques. The article, which highlighted Jayan’s recent receipt of a $500,000 NSF CAREER Award, focused on her research in using electromagnetic waves to manipulate ceramic structures. Her method could provide major energy savings in comparison to traditional heat firing, enabling the 3D printing of industrial-grade ceramics and greatly expanding their range of practical applications.

Ultra-Fast Relaxation, Decoherence, and Localization of Photoexcited States in p-Conjugated Polymers

Speaker(s): 
William Barford
Dates: 
Thursday, May 10, 2018 - 4:30pm to 5:30pm

We investigate the energetic relaxation and spatial localization of photoexcited states in conformationally disordered p-conjugated models, choosing poly(para-phenylene vinylene) as a model system. Assuming vertical excitations, the initial photoexcited eigenstates are obtained via the disordered Frenkel model. The subsequent relaxation and localization of the excited statesis determined via the disordered Frenkel-Holstein model coupled to a dissipative environment. In particular, we solve the Lindblad master equation via the time-evolving block decimation (TEBD) and quantum jump trajectory methods.

The values of the model parameters physically relevant to polymer systems naturally lead to a separation of time scales, with the ultra-fast dynamics corresponding to energy transfer from the exciton to the internal phonon modes (i.e., the C-C bond oscillations), while the longer time dynamics correspond to damping of these phonon modes by the external dissipation. Associated with these time scales, we investigate the following processes that are indicative of the system relaxing onto the emissive chromophores of the polymer: 1) Exciton-polaron formation occurs on an ultra-fast time scale, with the associated exciton-phonon correlations present within half a vibrational time period of the C-C bond oscillations. 2) Exciton decoherence is driven by the decay in the vibrational overlaps associated with exciton-polaron formation, occurring on the same time scale. 3) Exciton density localization is driven by the external dissipation, arising from ‘wavefunction collapse’ occurring as a result of the system-environment interactions. Finally, we show how fluorescence anisotropy measurements can be used to investigate the exciton decoherence process during the relaxation dynamics.

Noa Marom Receive the 2018 IUPAP Young Scientist Prize in Computational Physics

  • By Burcu Ozden
  • 1 May 2018

The IUPAP C20 Commission on Computational Physics has selected Noa Marom to receive the 2018 IUPAP Young Scientist Prize in Computational Physics. 

Marom will give a lecture at the upcoming XXX IUPAP International Conference on Computational Physics CCP2018, where she will be presented with the prize, consisting of a medal, a certificate, and a financial award of 1000 Euros, at the University of California, Davis, in July.

Di Xiao Featured Mellon College of Science Website

  • By Burcu Ozden
  • 1 May 2018

Di Xiao gave an interview for the Mellon College of Science website. His interview entitled as "A Quantum Age." 

In this interview, he mentioned how his research is changed and evolved around quantum science over the years.

Also, this article shows how Di Xiao balances his academic career and personal life. 

Furthermore, this article highlights his inspiring academic achievements.
 

Open system approaches for quantum transport through tunneling junctions

Speaker(s): 
François Damanet
Dates: 
Thursday, April 26, 2018 - 4:00pm

Quantum transport is a key area in quantum physics which presents challenges in terms of theoretical description. In this talk, I will present how the non-equilibrium dynamics of tunneling junctions weakly coupled to baths of fermionic or bosonic particles can be investigated using open system approaches, namely input-output formalisms and master equations. As a specific example, I will first present our study of electron transport in a quantum dot tunneling junction connecting two normal or superconducting leads, where both single-particle and Cooper-pair tunneling are considered. In particular, I will show how signatures of Andreev bound states can be obtained in the output currents. Then, I will present our results on spin transport in a quadratic spin system connecting baths modeled as XXZ spin chains. Based on non-Markovian master equations for the system and t-Matrix Product States simulations to compute the bath correlation functions, we showed that the spin current through the system can be enhanced due to the presence of the interaction in the baths as well as exhibit transient rectification (i.e. different current under bias exchange). Finally, I will sketch a more general outlook on how non-Markovian master equations could be used to study the transport properties of a system of unknown spectrum, which is particularly useful for the case of complicated time-dependent or many-body system Hamiltonians.

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