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Condensed Matter Seminars
Fall 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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August 27      

 

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September 3 (No seminar – Labor Day)     

 

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September 10      

 

Speaker

Naween Anand (NHMFL)

 

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Evolution of magnetic phases and emergent magnetic monopoles in the spin ice Ho2Ti2O7

 

Abstract

The presence of geometric and magnetic frustration in spin-ice Ho2Ti2O7 (HTO) leads to a macroscopically degenerate ground state with a magnetic phase exhibiting short-range spin-ice correlation among the Holmium ions. This macroscopic degeneracy gets lifted and the residual entropy is released when external field is applied along certain crystallographic directions, leading to specific long-range ordered phases.

Developing such ordered phase or transition from one to another magnetic phase in HTO leads to a dynamical transient state with a continuous loop of creating and annihilating emergent magnetic monopoles. Torque magnetometry provides a unique technique to study the evolution of such magnetic phases and associated magneto-crystalline anisotropy. The technique has much higher sensitivity and any small change in the order parameter with varying magnetic field or the crystallographic orientation is subsequently reflected as the changed slope and curvature of the data. A phenomenological model for spin flips has been proposed to map out this rich magnetic phase diagram of spin-ice HTO. A direct comparison between single crystals and thin films of varying thicknesses in HTO torque data has helped us in understanding the possible tuning of spin-ice physics in thin films. Other magnetometric techniques, such as tunnel diode oscilloscope (TDO), which provides a scaled measurement of dynamical susceptibility, and standard DC magnetization measurement through MPMS technique strongly support the torque results and model predictions. This thorough study makes a solid stride towards developing another complementary measurement technique for studying a rich magnetic phase diagram, possibly a much more effective tool for thin film studies where neutron scattering technique faces serious limitations.

 

Host

David Tanner


September 17      

 

Speaker

Assel Aitkaliyeva (UF, Materials Science)

 

Title

Establishing defect-property relationship for low dimensional materials

 

Abstract

The radiation response of low dimensional materials (LDMs) deviates dramatically from bulk materials with three-dimensional (3D) bonding networks. In bulk solids, energy deposited by the energetic particles can dissipate in all three-dimensions, unlike in their low dimensional counterparts. The less efficient energy dissipation mechanism in LDMs can lead to increase in local kinetic energy after the impact. This poses important questions such as: how tolerant are LDMs to extreme photon and particle fluxes and what are the mechanisms governing their radiation response? This contribution seeks to gain understanding of the radiation tolerance of various LDMs. We demonstrate that irradiation can be used to manipulate physical properties of LDMs in a controllable manner. The work to be discussed includes previously conducted ion irradiation of carbon nanotubes and graphene and experiments planned on other LDM systems. The PI’s group specializes in: 1) establishing defect formation and evolution mechanisms in LDMs subjected to irradiation, 2) quantifying radiation tolerance of LDMs, and 3) developing the requisite fundamental knowledge base needed to understand defect-property relationship in this unique class of materials.

 

Host

Mark Meisel


September 24      

 

Speaker

Yuxuan Wang (UF)

 

Title

Second-order topological superconductors

 

Abstract

Conventional topological superconductors are fully gapped in the bulk but host gapless Majorana modes on their boundaries. We instead focus on a new class of superconductors, second-order topological superconductors, that have gapped, topological surfaces and gapless Majorana modes instead on lower-dimensional boundaries, i.e., corners of a two-dimensional system or hinges for a three-dimensional system. Here we propose two general scenarios in which second-order topological superconductivity can be realized spontaneously with weak-pairing instabilities. First, we show that px+ipy-wave pairing in a (doped) Dirac semimetal in two dimensions with four mirror symmetric Dirac nodes realizes second-order topological superconductivity. Second, we show that p+id pairing on an ordinary spin-degenerate Fermi surface realizes second-order topological superconductivity as well. In the latter case we find that the topological invariants describing the system can be written using simple formulae involving only the low-energy properties of the Fermi surfaces and superconducting pairing. In both cases we show that these exotic superconducting states can be intrinsically realized in a metallic system with electronic interactions. For the latter case we also show it can be induced by proximity effect in a superconducting heterostructure.

 

Host

Dmitrii Maslov


October 1      

 

Speaker

Andreas Kreisel (Univ. Leipzig)

 

Title

Magnon-phonon interaction in multiferroic h-YMnO3

 

Abstract

The multiferroic material YMnO3 is known to show a large spin lattice coupling such that the spin and lattice degrees of freedom influence various physical properties. Here, we discuss a Heisenberg model describing the low-temperature magnetically ordered phase and the implications of the resulting magnon-phonon interactions from an single-ion magnetostriction mechanism. Especially, an avoided crossing between magnon and phonon modes appears. This can be used to distinguish possible magnetic ground state configurations which otherwise show an identical response in neutron scattering experiments. A comparison to various experimental results from inelastic neutron scattering allows us to exclude several of the earlier proposed models. The combined information from a polarization analysis and the observation of a field-induced magnon splitting points to a magnetic ground state of the P6'3c'm symmetry such that an effective dynamic model relevant for the multiferroic hexagonal manganites is obtained.

 

Host

Peter Hirschfeld


October 8      

 

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Leonid Levitov (MIT)

 

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TBA

 

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Dmitrii Maslov


October 15      

 

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October 22      

 

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Luiz Santos (Emory Univ.)

 

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Yuxuan Wang


October 29      

 

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November 5      

 

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Madhab Neupane (UCF)

 

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TBA

 

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Yoonseok Lee


November 12 (No seminar – Veterans Day)     

 

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November 19 (Monday of Thanksgiving Week)       

 

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Ilya Eremin (Univ. Bochum)

 

Title

Fluctuation-induced magnetic skyrmions at topological insulator surfaces

 

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Host

Peter Hirschfeld


November 26 (Monday after Thanksgiving Holiday)        

 

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December 3      

 

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Physics Home

Condensed Matter Seminars
Spring 2019

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

Contact: Yasu Takano or Dmitrii Maslov

x

January 7      

 

Speaker

Daniel Agterberg (Univ. Wisconsin-Milwaukee)

 

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TBA

 

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Peter Hirschfeld


January 14       

 

Speaker

Stuart Brown (UCLA)

 

Title

Tuning the magnetic fluctuations and superconducting ground state of Sr2RuO4: NMR studies under uniaxial strain

 

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Host

Mark Meisel


January 21 (No seminar - Martin Luther King Jr. Day)      

 

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January 28      

 

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February 4   

 

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February 11      

 

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February 18  

 

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February 25      

 

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March 4 (No Seminar - UF Spring Break Week, APS March Meeting in Boston)

 

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March 11      

 

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March 25       

 

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April 1    

 

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April 8      

 

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April 15      

 

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April 22      

 

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