Physics Home

Condensed Matter Seminars
Fall 2017

Condensed Matter Seminars are in Room NPB 2205
on Mondays @ 4:05 pm to 4:55 pm

Contact: Yasu Takano or Dmitrii Maslov


August 21      

 

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August 28       

 

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September 4 (No seminar - Labor day)      

 

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NA

 

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NA


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NA

 

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September 11 (No seminar – UF will be closed)   

 

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NA

 

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NA

 

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September 18       

 

Speaker

Songci Li (UF)

 

Title

Anomalous transport phenomena in chiral p-wave superconductors

 

Abstract

Spontaneous breaking of time-reversal symmetry in superconductors with the px+ipy symmetry of the order parameter allows for a class of effects which are analogous to the anomalous Hall effect in ferromagnets. These effects exist below the critical temperature, Tc . A kinetic theory of such effects is developed. In particular, anomalous Hall thermal conductivity, the polar Kerr effect, the anomalous Hall effect are considered.

 

Host

Dmitrii Maslov


September 25  

 

Speaker

Jason Haraldsen (University of North Florida)

 

Title

Evolution of Dirac bosons in a honeycomb lattice

 

Abstract

We examine the presence of magnetic Dirac bosons for the Heisenberg honeycomb lattice. Using linear spin-wave theory through exact diagonalization, we evaluate the collinear phase diagram and the evolution of the spin dynamics with increased exchange interactions. We show the creation of bosonic Dirac and Weyl points due to the competition between various superexchange interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to magnetic structure and not the crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations.

 

Host

Mark Meisel


October 2      

 

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October 9    

 

Speaker

Sung-Sik Lee (McMaster University and Perimeter Institute for Theoretical Physics)

 

Title

Low energy field theories for non-Fermi liquids

 

Abstract

In this talk, I will present recent progress on low energy effective field theories for non-Fermi liquid metals which lie beyond the Laudau Fermi liquid paradigm. Based on the dimensional regularization scheme which tunes the co-dimension of Fermi surface, universal properties of non-Fermi liquids can be computed in controlled ways. The systematic expansion provides not only examples of perturbative non-Fermi liquids but also important insight into strongly interacting metals in two dimensions. This allows us to extract the exact critical exponents for the strange metal realized at the antiferromagnetic quantum critical point in two space dimensions.

 

Host

Dmitrii Maslov


October 16    

 

Speaker

Wei Guo (Florida State University, National High Magnetic Field Laboratory)

 

Title

Flow visualization in superfluid helium-4: progresses and future developmentBA

 

Abstract

Helium-4 in the superfluid phase (He II) is a two-fluid system that exhibits fascinating quantum hydrodynamics with important scientific and engineering applications. It supports the most efficient heat-transfer mechanism (i.e. thermal counterflow), and it also allows the generation of flows with extremely high Reynolds numbers for turbulence modeling. However, the lack of high-precision flow measuring tools in He II has impeded progress in understanding and utilizing its hydrodynamics. In recent years, there have been extensive efforts in developing flow visualization techniques applicable to He II. Two types of techniques based on the use of either particle tracers (i.e. micron-sized frozen particles) or molecular tracers (i.e. He2 excimer molecules) have been developed. I will discuss the advantages and issues with these visualization techniques and will highlight some recent results of our visualization study of counterflow and grid turbulence in He II. I will also discuss our on-going work on developing the next generation flow visualization techniques and our effort on imaging quantized vortices in a magnetically levitated He II drop.

 

Host

Yoonseok Lee


October 23    

 

Speaker

Christopher Kay (London Center for Nanotechnology)

 

Title

Pentacene-based room temperature MASER

 

Abstract

The performance of a pulsed, pentacene-based, solid-state, room temperature, zero-field MASER operating at 1.45 GHz has been examined. Nanosecond laser pulses, which are essentially instantaneous on the timescale of the spin dynamics, allow the visible-to-microwave conversion efficiency and temporal response of the MASER to be measured as a function of excitation energy.

The dynamics of the MASER emission may be modelled by a pair of first order, non-linear differential equations, derived from the Lotka-Volterra model (Predator-Prey), whereby the microwave mode of the resonator is the predator and the spin polarization in the triplet state of pentacene is the prey. Simulations allowed the Einstein coefficient of stimulated emission, the spin-lattice relaxation and the number of triplets contributing to the MASER emission to be estimated [1].

In a set of experiments with a crystal containing a higher concentration of pentacene, we observed oscillations in the MASER output [2]. Fourier transform of the time-domain spectrum reveals a splitting proportional to the square root of the number of spins. In cavity quantum electrodynamics, this is a fingerprint of the strong coupling regime between the collective spin ensemble and the microwave photons in the high Purcell factor resonator. Furthermore, we observe a cavity protection effect which decreases the polariton decay rate as the collective coupling increases.

[1] Enrico Salvadori et al., Scientific Reports 7 (2017) 41836. [2] J.D. Breeze et al. npj Quantum Information 3 (2017) in press.

 

Host

Mark Meisel


October 30    

 

Speaker

Sara Haravifard (Duke University)

 

Title

Mapping the phase diagram of geometrically frustrated magnets

 

Abstract

The interactions that define how spins arrange themselves in a material play a fundamental role in a wide varietyof physical phenomena. Frustrated quantum magnets are systems for which the exchange interactions governing theinteracting spins cannot be simultaneously satisfied, leading to a highly degenerate ground state and new states of matter such as unconventional superconductivity and quantum spin liquid. Quantum spin liquid is a state of matter in which spins are predicted to point simultaneously in different directions while they stay highly entangled even over relatively large distances. In geometrically frustrated spin systems, competition between neighboring spin interactions arises from the geometry of the lattice. In this talk I will discuss how chemical doping, hydrostatic pressure and application of magnetic field regulates the underlying electronic and magnetic interactions in these systems, ultimately driving the ground state across the phase diagram and leading to emergent quantum critical phenomena.

 

Host

Yasu Takano


November 6       

 

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November 13    

 

Speaker

Girsh Blumberg (Rutgers University)

 

Title

Origin of the “hidden order” and antiferromagnetism in URu2Si2

 

Abstract

f-electron heavy fermion (HF) materials hold novel electronic ground states that emerge from hybridization between localized d- or f-orbitals and conduction electrons. The HF compound URu2Si2 hosts two competing staggered phases: a non-magnetic Hidden Order (HO) phase and a Large Moment Antiferromagnetic (LMAF) phase. Both phases are principally due to spacial ordering of the uranium 5f orbitals. The nature of these almost degenerate HO and LMAF phases has been theorized before, but experimental signature of the nature of HO and of the interrelation between HO and LMAF was lacking.

In this talk I will demonstrate that the HO phase is a Chirality Density Wave due to staggering of chiral left- and right-handed 5f orbitals singlet states with an equivalent charge which breaks local chiral symmetry [1]. The LMAF phase is the Orbital Moment Density Wave which breaks local time reversal symmetry [2].

We use polarization resolved Raman spectroscopy to study the interrelation between the HO phase and the LMAF phase. We drive and detect dynamic oscillations between HO and LMAF states by using polarized light, and as such provide direct experimental evidence for a unified order parameter describing the competing HO and LMAF phases.

The experiment is a realization of a similar 1961 proposal by A. Bardasis and J. R. Schrieffer to study unconventional sub-dominant pairing in the superconductors [3].

Research was done in collaboration with H.-H. Kung, R. Baumbach, E. Bauer, K. Haule, J. Mydosh, and M.B. Maple. Research at Rutgers was supported by the DOE, Office of BES through Award No. DE-SC0005463 and by NSF under Grant No. DMR-1709161.

[1] H.H. Kung, R.E. Baumbach, E.D. Bauer, V.K. Thorsmolle, W.L. Zhang, K. Haule, J.A. Mydosh, and G. Blumberg. Chirality density wave of the ’hidden order’ phase in URu2Si2. Science, 347, 1339 (2015). [2] H.-H. Kung, S. Ran, N. Kanchanavatee, V. Krapivin, A. Lee, J.A. Mydosh, K. Haule, M.B. Maple, and G. Blumberg. The analogy between the `hidden order' and the orbital antiferromagnetism in URu2Si2. Phys. Rev. Lett. 117, 227601 (2016). [3] A. Bardasis and J. R. Schrieffer, Phys. Rev. 121, 1050 (1961).


 

Host

Dmitrii Maslov


November 20 (Monday of Thanksgiving Week)       

 

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November 27 (Monday after Thanksgiving Holiday)       

 

Speaker

Vasili Perebeinos (Skolkovo Institute of Science and Technology )

 

Title

Electrical and optical properties of 1D and 2D materials from a microscopic modelling

 

Abstract

In recent years, 1D and 2D materials, such as carbon nanotubes and transition metal dichalcogenides, have attracted much attention due to their excellent transport and optical properties. Using a Bethe-Salpeter equation, we investigate optical and excitonic properties of MoS2 monolayers in an applied in-plane electric field [1]. We predict a quadratic Stark shift and its scaling with the exciton binding energy, determined by the dielectric environment. I will discuss electrical contacts in 1D carbon nanotubes and the role of electronic structure modifications caused by the nanotube deformations due to the metal wetting [2]. Finally, I will discuss our recent results on plasmon scaling in graphene nanoribbon arrays as a function of nanoribbon width, spacing between ribbons, and doping level.

[1] B. Scharf, T. Frank, M. Gmitra, J. Fabian, I. Zutic, and V. Perebeinos, Phys. Rev. B 94, 245434 (2016). [2] R. Hafizi, J. Tersoff, and V. Perebeinos, Phys. Rev. Let. in press.

 

Host

Dmitrii Maslov


December 4      

 

Speaker

Various CM Faculty Speakers

 

Title

Meet the Faculty Shindig

 

Abstract

Various Condensed Matter (CM) Faculty speakers make a pitch about what is hot in their research groups and why
a graduate student should join the fun activity.  Free food and a selection of cold beverages.

 

Host

Takano and Maslov


December 12  (Tuesday – Note the special date)  

 

Speaker

Avadh Saxena (Los Alamos National Laboratory)

 

Title

Skyrmions, merons and monopoles: Topological excitations in chiral magnets

 

Abstract

Stable topological excitations such as domain walls and vortices are ubiquitous in condensed matter as well as high energy physics, and are responsible for many emergent phenomena. In 2009 a new mesoscopic spin texture called skyrmion was discovered experimentally in certain conducting and insulating magnets. It is now believed to exist in Bose-Einstein condensates, 2D electron gases, superconductors, multiferroics, nematic liquid crystals, among other systems. This topological excitation was originally proposed by Tony Skyrme in 1958 in a nonlinear field theory of baryons. In the temperature-magnetic field phase diagram of chiral magnets, skyrmions form a triangular lattice in the low temperature and intermediate magnetic field region (in thin films). In metallic magnets, skyrmions can be driven by a spin polarized current while in insulating magnets by magnons. The threshold current density to depin skyrmions is 4 to 5 orders of magnitude weaker than that for magnetic domain walls. The low depinning current makes skyrmions extremely promising for applications in spintronics. I will first attempt to summarize the experiments and present an overview on skyrmions. Then I will demonstrate how increasing the easy-plane anisotropy results in a transition from a triangular lattice of skyrmions to a square lattice and eventually to merons. The latter are essentially half-skyrmions and with half the topological charge. Finally, I will show that under current driving skyrmions tubes can split or merge at certain points leading to the formation of magnetic monopoles and anti-monopoles connected by a Dirac string.

 

Host

Pradeep Kumar

 

Physics Home

Condensed Matter Seminars
Spring 2018

Condensed Matter Seminars are in Room NPB 2205
on Mondays @ 4:05 pm t0 4:55 pm

Contact: Yasu Takano or Dmitrii Maslov

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January 8      

 

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(Tentatively blocked)

 

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January 15 (No seminar - Martin Luther King Jr. Day)       

 

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January 22        

 

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January 29        

 

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February 5    

 

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February 12       

 

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February 19  

 

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February 26      

 

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March 5 (No Seminar - UF Spring Break Week, APS March Meeting in Los Angeles)

 

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March 12      

 

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March 19       

 

Speaker

Saw Wai Hla (Ohio University and Argonne National Laboratory)

 

Title

TBA

 

Abstract


 

Host

Yasu Takano


March 26       

 

Speaker

Steven May (Drexel University)

 

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TBA

 

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Host

Amlan Biswas


April 2    

 

Speaker

Khandker Quader (Kent State University)

 

Title

Pressure-driven Lifshitz and other transitions in 122 iron pnictides

 

Abstract


 

Host

David Tanner


April 9      

 

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April 16      

 

Speaker

Alexander Chernyshev (UC Irvine)

 

Title

TBA

 

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Host

Yasu Takano


April 23      

 

Speaker

Rena Zieve (UC Davis)

 

Title

TBA

 

Abstract


 

Host

Yoonseok Lee